# LPF or LiFePO4 Top vs Bottom Balancing



## JonasFilipe9 (Jan 9, 2015)

Hello everyone,

Well, I'll open hostilities to a topic that has been discussed by the forum outside and I think that there is not a thread specifically for this.

What is the best way to balance Lithium Iron Phosphate cells: Top or Bottom Balance? (Mid balancing is another story)

And a video I think explains well the 2 processes: http://youtu.be/U7-WHUTLbHY

Facts that everyone agree: These cells need some electronics to control each cell voltage so they do not go over or above the maximum and minimum voltage respectively. If temperature control too, the better.

Here is a guy most of you know but others don´t. Andrea Davide and his 8 reasons why top balancing is better: http://youtu.be/rALhwf9ojZQ

I would like your experience on what you are working with, how long do the cells last with no balancing etc. I would also ask someone who actually uses top balancing to throw his results because I had no answers to this particular case.

All the best


----------



## JonasFilipe9 (Jan 9, 2015)

1st conclusion after the 1st video of Andrea Davide:

Lets try to describe what is top and bottom balance.

Well, *botom balance* is clear to everyone: balance cells at 2.5V.
BUT *top balance* is not balance the cells at 3.5V for example, like he says, is full all the cells. This means all the cells need to reach 3.6V to be fully charged...

How da heck can you do this in a series pack??? The lowest capacity cell in the bank (also known as the weakest) will reach 3.6V before all the others. (Thanks to Sunking) So there is just one cell full. You dont' fully charge all the cells to 3.6V with Vampire boards (that have 1A by pass current max) unless you use a charging current throw the pack of 1A or close. So what he says at 2:15min in the video Part 2 (https://www.youtube.com/watch?v=mNwLeRx1P1Q) just makes sense if we are talking about top balancing before wire the pack.

Does not make sense to vampire boards which balance cells to a voltage at the top usually. (3.41/3.42V for example) This procedure is called what?


----------



## dladd (Jun 1, 2011)

your premise is flawed, I think. There are many here that do not believe that you need active electronics to monitor the cells once they are balanced. 

I'd say the majority of folks here tend to favor bottom balancing if you aren't actively monitoring each cell.

No one advocates mid-balancing, you just can't do it cause the 'plateau' is too large.

Personally I top balance because I have a shunting BMS system, but don't see a real difference between top and bottom if you have an active BMS that will cut charging/power draw when either HVC or LVC is reached. Your pack is limited to the weakest cell either way. I top balanced by charging up each cell individually to 3.6v with a small programmable charger (PL-6).

With no BMS, I'd be inclined to go bottom balance and not fully charge. Seems safer to me.

At the end of the day, it's just a personal decision that you'll have to make and move forward.


----------



## JonasFilipe9 (Jan 9, 2015)

dladd said:


> your premise is flawed, I think. There are many here that do not believe that you need active electronics to monitor the cells once they are balanced.
> 
> I'd say the majority of folks here tend to favor bottom balancing if you aren't actively monitoring each cell.
> 
> ...


Lol I'm starting well then... 
Cell monitoring is the basic control that will shut down you system if anything goes wrong, it's the least you could have...

Do you make this top balancing with the batteries wired in series? Or one by one?

Just want to know what is best in terms of time without drifting to much.. Weakest cell will be there always thats for sure! For me, I'm using this cells in a solar isolated system so I think dissipate power everyday to balance the cells is not very convenient (usually with high currents). I think I'm going bottom balancing although my BMS may do top balancing. Did I waste my money? no, my system should work for more than 5 years and take the cells of the pack is not an option. This way the user may do the balance easily once a year for example.


----------



## dladd (Jun 1, 2011)

JonasFilipe9 said:


> Lol I'm starting well then...
> Cell monitoring is the basic control that will shut down you system if anything goes wrong, it's the least you could have...
> 
> Do you make this top balancing with the batteries wired in series? Or one by one?
> ...


I balanced the cells one by one before they were connected in the car. I can top up individual cells as well when they are connected in series, just put the alligator clips from the charger across one cell. It will charge up without affecting the rest of the series.

However, the more normal scenario is having one cell that needs to be knocked down a little which can be done with a resistor on the batteries terminals while still connected in series.

I don't think any of the balancing methods will affect drift, these Lifep04 cells really don't drift anyway. 

I definitely don't think you want to bottom balance and then use a BMS which actively top balances. That doesn't make sense to me.

i'm no expert, I just happen to be online right now, lol. Davide knows WAY more about this stuff than I do, but I have learned a bit about this stuff over the last few years.


----------



## JonasFilipe9 (Jan 9, 2015)

Here is a post that says whar many of you are saying.

Basically having modules connected to the cells is not good. Idle currents drift the cells apart, although they some say it is < 100 micro Amp...

http://www.myelifenow.com/2012/10/lifepo4-charging-method-dont-ruin-your.html


----------



## JonasFilipe9 (Jan 9, 2015)

dladd said:


> I definitely don't think you want to bottom balance and then use a BMS which actively top balances. That doesn't make sense to me.
> 
> i'm no expert, I just happen to be online right now, lol. Davide knows WAY more about this stuff than I do, but I have learned a bit about this stuff over the last few years.


No wait, I may do bottom balancing but I will not use the BMS to make top balance... I'll use it as a control of the low and high pack voltages. not to balance. basically to shuts the charger and loads off..


----------



## Sunking (Aug 10, 2009)

dladd said:


> I definitely don't think you want to bottom balance and then use a BMS which actively top balances. That doesn't make sense to me.


Hold that thought for a second. 

Let me challenge your analogy with a question, something outside the box.

Who says you have to use the TOP BALANCE capabilities of a BMS? 

Basically a BMS is a PLC aka Programmable Logic Controller. What if we just use the programming logic to operate as a BOTTOM BALANCE CONTROLLER and do not use the TOP BALANCE functions? Instead we use it to monitor cell voltages and do stuff when we reach voltage set points. 

For example we monitor cell voltages that will turn on a Yellow Alarm light when any cell reaches say 3 volts, warning us we are about depleted. We program the unit the send a signal to a LVD if any cell voltage is 2.5 volts or less for more than 15 seconds. Say we program the controller to send a signal to a charger as soon as any cell reaches 3.5 volts that shuts off the charger. 

What I am driving at to my knowledge there is no BMS designed around the Bottom Balance principle. There might be but I am not aware of any. But just about every commercial BMS on the market can be programmed to do exactly what I just described. No one says you have to use the TOP BALANCE feature. The BMS police will not come get you if you do not use the Top Balance function.


----------



## onegreenev (May 18, 2012)

If you are set on a BMS for monitoring you can use the Orion which can be used as a monitoring system and not balance. But if you wanted it could be used to actively balance. Bottom balancing once and monitoring is a good idea. If you use the HPEVS AC motor controller system you can use the Orion and a nice Galaxy to make a nice visual indicator and monitor your cells as you wish. 

Talk to EVMETRO about that. He uses his to balance his cells but it can be used to just monitor.


----------



## EVfun (Mar 14, 2010)

Most of us that are successfully using our LiFeYPO4 pack don't wade into these debates anymore as they tend to just turn into battery gospel holy wars. 

That said, I run my pack of 39 cells top balanced initially to 3.60 volts. That is easy to do by charging them individually with a single cell charger before assembling the pack as good cells have no measurable self discharge. In regular use I charge the cells at 0.2C to 3.50 volts and hold it at that level for 40 minutes. All the cells where still 3.49-3.51 volts at the end of charge on my last check. There is nothing installed on each cell to monitor individual voltages as they introduce their own chances of discharging each cell slightly differently, even 50 microamps will add up over time (about 0.4 amp hour per year.)

Others will disagree with my method, and I don't care. What I'm doing has been protecting my investment, I have yet to loose a cell.


----------



## Sunking (Aug 10, 2009)

Here is how I see the debate. 

Top Balance comes from treating LFP batteries like Lead Acid batteries (Pb). Pb batteries life cycle depends on being kept at 100% SOC for long as a time as possible and hold them forever in FLOAT MODE when not in use. As soon as you start to discharge them, they start degrading by forming Lead Sulfate Crystals. The deeper you discharge them, the process accelerates. Leave then left anything less than 100% SOC and those Lead Sulfate crystals attach to the plates and harden. Once hardened they cannot be dissolved. In just a couple of short years, the internal resistance gets so high from sulfate crystals the battery can no longer accept or deliver a charge. 90% of all lead acid batteries are from sulfation. Pb batteries do not operate or perform well in PSOS (Partial State of Charge). 

Engineers including myself sometimes cannot see the forest because the trees blind us. We always try to get the most out of everything. So on the surface TOP BALANCE makes since to drive the battery to full 100% SOC. It just seems to be the right thing to do because every battery chemistry out there works that way right? Well that is 90% true but does not apply to lithium. Us engineers got caught in a Pb box and did not see the forest because a dang Pb tree blocked our vision. 

Of course the other factor is us engineers work for companies who are in biz to make money, a lot of it and what better way to do that by selling you a complicated expensive electronic gizmo. That puts another dang tree in our way blocking our vision. 

LFP is completely different than every other battery out there. All other batteries are chemical reactions. But not lithium as they are ion exchanges between anode and cathode at the speed of light. We move them back and forth from one electrode to the other. That is why Peukert Law has very little if any effect on LFP batteries. 

OK there are two undesirable characteristics if you Top Balance to 100% that are known facts. 

1. Shorten cycle life.
2. Greatly increases the chances you will have a polarity reversal on weaker cells thus destroying them, and over charging and letting heat cook them. 

Well those two facts got some people thinking outside the Pb Top Balance Box they were trapped in including myself. I have worked with large battery plants and manufactures for 35 years professionally. 

100% SOC is only a REFERENCE POINT and does not tell you anything about the capacity. It is just a voltage that says the battery is full and cannot hold any more like a glass of water. If you buy 100 AH cells, none are equal in capacity ranging from 100 to 115 AH as it is just a characteristic of the manufacturing process. This holds true for all battery types. 

But what if we change the reference point where the capacity is EQUAL across all cells regardless of the full capacity rating. Can you guess what reference point that is? 

If you said 0% SOC or 0 AH you guessed right. The cell voltages and capacity will only be equal at ZERO. Now we got something different to work with. Like a chain a battery pack is only as strong as the weakest link in the serial chain. If we charge until the weakest cell reaches say 90% SOC, and that weakest cell is 100 AH, then all cells have the exact same amount of capacity of 90 AH. Note i said equal capacity, not SOC. The weakest cell will have the highest voltage or SOC, but all the stronger cells wil be at a lessor SOC voltage. No problem.

By using the BOTTOM BALANCE method you just eliminated the two huge disadvantages of Top Balance. It would be highly unlikely to ever over charge or over discharge a cell, and would extend cycle life roughly 50%. 

Not only do you eliminate the problems and complexity of Top Balance you save a lot of COINS to keep in your pocket rather than giving it to a supplier for an elaborate expensive BMS. 

That is my two cents worth. Take what you want, leave the rest.


----------



## dladd (Jun 1, 2011)

Sunking said:


> OK there are two undesirable characteristics if you Top Balance to 100% that are known facts.
> 
> 1. Shorten cycle life.
> 2. Greatly increases the chances you will have a polarity reversal on weaker cells thus destroying them, and over charging and letting heat cook them.


1. nonsense. No one charges to 100%. Top balance at 3.6vpc, charge to 3.5vpc. I think that's pretty commonplace these days. Lately I've been charging to 3.44vpc which is still getting into the steep part of the curve so I don't think I'm giving up any real range.

2. so you drive one cell into reversal instead of your whole pack. Hey, maybe it's a benefit!


----------



## Sunking (Aug 10, 2009)

dladd said:


> 1. nonsense. No one charges to 100%. Top balance at 3.6vpc, charge to 3.5vpc.


Just how are you going to limit current to the value of the bypass board when the first Vampire Board turns on? If you fail to do that you are still charging the cell until the last Vampire Board triggers.


----------



## dladd (Jun 1, 2011)

Sunking said:


> Just how are you going to limit current to the value of the bypass board when the first Vampire Board turns on? If you fail to do that you are still charging the cell until the last Vampire Board triggers.


Haha, I have no idea what a vampire board is. Pretty sure my car doesn't have one. My charger (PFC30) is set to charge to 165v. It goes CC to 165v, then holds CV while the current tapers. Since I'm top balanced, all my cells are more or less equal at 165v/48 cells = 3.44vpc. My MiniBMS does not start shunting off current until it reaches 3.5v, so it never happens in normal use.

Even worse case scenario if I'm out of balance and the MiniBMS shunt cannot keep up with the current the pack is pulling, once any individual cell reaches 3.65v it kills the charger. I'm still safe. And still below 100% even on the most charged cell.


----------



## Hollie Maea (Dec 9, 2009)

Sunking said:


> What I am driving at to my knowledge there is no BMS designed around the Bottom Balance principle.


I think Jack is having one of his disciples design one for him. 

Of course, once it's finished, only morons would go without, or, god forbid, use anything else.


----------



## skooler (Mar 26, 2011)

Bottom balance wotks fine for me. Over 15,000 miles and no issues whatsoever.

Top balance is also acceptable - its about where you place the risk. Bottom balance you are more likely to overcharge a single cell and top balance you are more likely to put a cell into reveraal on discharge.


----------



## Sunking (Aug 10, 2009)

dladd said:


> Even worse case scenario if I'm out of balance and the MiniBMS shunt


That would be your Vampire Board, it can only shunt (bleed) a very small current leaving the rest going through the cell.


----------



## Sunking (Aug 10, 2009)

Hollie Maea said:


> I think Jack is having one of his disciples design one for him.


Who is Jack? I don't know Jack.


----------



## onegreenev (May 18, 2012)

Sunking said:


> Who is Jack? I don't know Jack.


Jack Rickard. The one who loves to step up on his pedestal and tell the story of the Board Watch magazine over and over and over and over and loves to tell how much he's made over the years and that he is a genius and has lots of toys. Once is enough Jack. Time to get over yourself. 

Oh, I forgot, he also does EVTV, sorta.


----------



## skooler (Mar 26, 2011)

onegreenev said:


> Jack Rickard. The one who loves to step up on his pedestal and tell the story of the Board Watch magazine over and over and over and over and loves to tell how much he's made over the years and that he is a genius and has lots of toys. Once is enough Jack. Time to get over yourself.
> 
> Oh, I forgot, he also does EVTV, sorta.


+1

Self proclaimed leader of all things EV conversion related.


----------



## Sunking (Aug 10, 2009)

onegreenev said:


> Jack Rickard. The one who loves to step up on his pedestal and tell the story of the Board Watch magazine over and over and over and over and loves to tell how much he's made over the years and that he is a genius and has lots of toys. Once is enough Jack. Time to get over yourself.
> 
> Oh, I forgot, he also does EVTV, sorta.


Never heard of him until now. I picked up on Bottom Balance when designing off grid solar systems when trying to modify solar charge controllers to work with LFP cells. Using Bottom Balance on solar systems is much easier to implement and a lot less expensive. There is no solar charge controller made to work with LFP batteries and a BMS. It could be done if you know how to modify electronic equipment which invalidates any warranty or support, plus have to buy extra equipment and make it work outside the intended purpose. Joe Homeowner does not buy into that idea. They want KISS (keep it simple stupid) and inexpensive. 

But if you Bottom Balance and an Off-Grid System with LFP you can use any off the shelf charge controller and just set the Bulk = Absorb = Float to around 3.4 vpc and you are off and running. You let the Inverter take care of the LVD set to say 42 volts on a 48 volt system. Doing that you never risk over charge or over discharge, and with no monitors the cells never drift. Only thing you really have to do the first week is tweak the Float Voltage setting so the weakest cell never reaches 3.45 volts. On a 48 volt 16s battery around 55 volts. After that just check periodically no cell goes above 3.4 to 3.45 volts or whatever voltage you are comfortable with under charge.


----------



## dladd (Jun 1, 2011)

Sunking said:


> Never heard of him until now.


here since 2009 with thousands of posts and you've never heard of JR. I don't believe you.

ANyway, obviously top/bottom whatever has been done to death, everyone just needs to do their own research and make up their own mind on how they want to go about managing their pack. The battery pack is the most important and expensive part of the car, and it warrants a bit of time and energy to understand what it means to keep it healthy.

Oh, I got a nice (and free!) bright yellow EVCCON t-shirt from Jack when I ordered a few battery connector straps a few years ago. I wear it on softball weekends, it matches the colors of my daughter's team perfectly!


----------



## Sunking (Aug 10, 2009)

dladd said:


> here since 2009 with thousands of posts and you've never heard of JR. I don't believe you.


Believe what you want. If you looked at a log for me yes I joined in 2009 when I built my first golf cart using Pb batteries. Then I was absent until late last year when I built my second golf cart with LFP. I am not a regular. Ask Major, MetroEv, OneGreenEv and other members who are dealers and quaintness my topics of interest has been HPEV Motors, Controllers, and now lately BMS. I got turned on to Bottom Balance doing professional Solar Off-Grid battery system designs using LFP batteries at remote cell towers in the telecom sector. 

I do not read all threads, very few to be factual. I mostly post questions to get help on motors and controllers. I am an electrical engineer with PE license and have worked with telecom and utility battery plants and battery manufactures for 35 years and all forms of power distribution and generation. 

Take what you like, leave the rest. I did not attack you.

EDIT NOTE:

FWIW I just watched the EVTV video with Jack just to know where you guys are coming from. While I do not agree with him point to point, overall his opinion is based on some pretty good fundamentals and personal experience. He has a very minimalist approach of just Bottom Balance with not much in the way of monitoring or control like flying in the clouds without instrumentation, but it can work if you periodically monitor cell voltages manually. I just prefer a little more control and a different approach using PLC. I got the same toys he has for testing batteries and more as I that is part of what I do for a living. 

I will be the first to admit I originally thought top balance was the way to go. Like many engineers we cannot see the forest because the trees block our vision. In my case I was stuck in the Pb box trying to apply it to LFP and that does not work. That is where the TOP BALANCE mentality came from and carried over. But when i started doing Off Grid Solar applications for cell sites there is no such thing as BMS Solar Charge Controllers for LFP. I am a moderator on the Mike Holt Code forum which is for professionals only comprising of scientist, engineers, technicians, and electricians. I got turned onto Bottom Balance from Solar Contractors there and how to implement using off the shelf solar charge controllers. Difference is changing the reference point of 100% SOC for Pb batteries, to 0% for LFP.

I just took the minimum Bottom Balance concept and ran with it adding my own twist. Might be a market to tap into on the ground floor.


----------



## Hollie Maea (Dec 9, 2009)

Edit: off topic


----------



## Sunking (Aug 10, 2009)

Hollie Maea said:


> How about your own threads?
> 
> http://www.diyelectriccar.com/forums/showthread.php?t=39421


Like i said that was back in 2009 when I first joined and was trapped inside that Pb box I have broken out of since then. 

So what is your point Mr. Sherlock Holmes?

Read my first response post #3 when someone explained BMS to me for the first time. Proves I am being honest and consistant there Dick Tracey. You know what to do with those rolling eyes there right? So you can quit the attacks.


----------



## Hollie Maea (Dec 9, 2009)

Edit: Off topic


----------



## Hollie Maea (Dec 9, 2009)

Edit: Off topic


----------



## Sunking (Aug 10, 2009)

Hollie Maea said:


> I could care less if you know Jack Rickard. But, when someone is actively deceiving us on this board, for any reason, that IS a big deal.
> 
> Your assertion that you had no idea who Jack was was laughable and unbelievable. And sure enough, it ended up being a falsehood:
> 
> ...


No angle here, I just did not make the connection to Jack and EVTV. All that was said was Jack or JR. I just did not connect the dots. 

I first heard of Jack two weeks ago after I goggled EV BMS Bottom Balance, and ran across a Blog where he described his method of Bottom Balance in text format. I had questions so I contacted him. That is all there is too it.

In 2009 I bought a used golf cart, but hated the low speeds and poor acceleration. So I upgraded the DC motor\controller. I also considered using lithium. At the time the cost were too high, and I was not confident using them. So i passed and used Pb.

Then a year or so ago telecoms wanted to start using lithium batteries at remote micro low power cell site on Indian reservations, and isolated sections of I-10, I-20, and I-40 from western OK/TX to CA. There is no such thing as LFP solar charge controllers or BMS made for solar applications. As I said I am a moderator on Mike Holt's Code Forum, have been for more than 12 years. It is a forum for industry professionals only with a membership of around 100K members. In that forum there is a sub forum for Solar, and I know quite a few of the contractors including John Wiles the God Gather of Solar. I met him and worked with him when I was on the NEC Code Panel 9 in 2003 to 2006. John wrote NEC article 690, and has developed most of the engineering principles of solar application. 

Any way I reached out to John and a few other contractors trying to tackle the LFP challenge using the BMS approach. All said it cannot be done, nor should it be done even if it was available. Change your point of reference to the Bottom is what they said. It works with Solar using off the shelf controllers. Nothing else required. 

So here we are today. Last November/December I decided to build another golf cart. One like never built before using AC motor/Controller, and LFP battery. Not many have done it, and none like I was going to do it. At first being an EV BMS first came to my mind forgetting the lesson I learned on solar. So I researched and researched EV BMS. Everything out there is Top Balance. The more I read, the less common sense it made. Then it dawned on me. I googled EV Bottom Bottom Balance and Jacks paper showed up, and it made since as an engineer and I turned 180 degrees on a dime to Bottom Balance.

Where I differ is I want to have cell level control. Jack is a minimalist only operating at pack voltage level. Not me, I am on the cell level. I just reference from the Bottom rather than from the top because it is less complicated, less risk, and less expensive. 

Instead of BMS which has no real definition, I choose PLC because that is what it really is. If you look in the EV world BMS means Top Balance expensive add on equipment. There is another way is all I am saying, and BMS is kind of meaningless because Battery Management can be done from the Top or Bottom. IMHO From the top comes from Pb mentality. LFP is not Pb where you must work from 100% or certain death is near. 

Take what you like, leave the rest. I will not make one dime from you, nor will you make one penny profit from me. Just a third party guy doing it my own way based on 35 years EE experience. I can still learn a new trick.


----------



## Hollie Maea (Dec 9, 2009)

Edit: Off topic


----------



## skooler (Mar 26, 2011)

Please keep on topic.

Suggest you both drop it and keep the conversation to bms / top/ bottom balancing.

As mentioned earlier. I have 15k miles using the below method.

http://www.diyelectriccar.com/forum...cing-85458.html#/forumsite/20977/topics/85458


----------



## PStechPaul (May 1, 2012)

Yet another top/bottom debate? I admit that I was originally sold on the top balance concept, but now, at least for lithium cells in EVs, I agree that bottom balance makes more sense. As for the BMS (or PLC), I still think it is important to "keep an eye" on individual cells, and I think it may still be useful to have a shunting resistor that might be used when the charging current is reduced to 1/20 C, and it also could be used to bottom balance a pack. However, for 100 A-h batteries, 1/20 C is still 5 amps, and that is 15 watts of power and heat on or near each cell. 

If that is not a problem, power resistors, MOSFETs, BJTs, and optos of sufficient rating are pretty cheap, perhaps a couple dollars per cell, and I plan to add them to the BMS I'm working on. Hopefully my plan to use an analog MUX for each group of up to 8 cells will reduce the unbalancing effect of measurement to a negligible amount. With the shunting resistor in the design, it is also possible to automatically perform a bottom balance whenever the pack is almost depleted.


----------



## pdove (Jan 9, 2012)

dladd said:


> 1. nonsense. No one charges to 100%. Top balance at 3.6vpc, charge to 3.5vpc. I think that's pretty commonplace these days. Lately I've been charging to 3.44vpc which is still getting into the steep part of the curve so I don't think I'm giving up any real range.
> 
> 2. so you drive one cell into reversal instead of your whole pack. Hey, maybe it's a benefit!


You have a fundamental misunderstanding of Lithium Battery charging. Voltage set point means nothing. The cell when full is 3.38 volts for Lithium Iron Phosphate. So, if you set your charger to 3.5 and then let the current trickle to C/20 then it charges to full just as if you held the voltage at 3.65v and let the current trickle to C/20 or whatever your set point is.

The only way your scenario is going to work is to eliminate the constant voltage portion of the charge. Manufacturers publish charging procedures that were developed in laboratories to achieve maximum charge. To change these procedure your wim will not get the results you want.

Secondly, reversal happens at the bottom usually although you can short them during charging by holding voltage above 3.4 on them for too long. If, as he said you have two cells one 100 ah and one 110ah and you charge them to 3.5volts CC/CV to c/20.... the next day they will both read 3.38volts. If they read higher then this is just a surface charge and they will go to 3.38V as soon as a load is put on them for a second or two. 3.38 indicates a full cell but only measured open circuit with no load on them and no charger on them. 

Now, if you discharge these cells in series the 100 ah cell will hit 2 volts before the 110ah cell and will go into reversal before the 110 ah cell reaches 2 volts most likely. So top balancing as you call it just creates imbalance at the bottom. It's all about energy in and energy out you can't get there just monitoring voltage.

There are patents out there to do such a thing as you speak of. TI has one. It shuts the charger off periodically and measures open circuit voltage to see SOC of the cells and it can also monitor impedance of the cell. One needs a sophisticated circuit to do what you all are attempting that keeps up with current voltage and impedance if you want maximum charge and cell protection.

You really should read some papers on how Lithium batteries work before designing a BMS.


----------



## JonasFilipe9 (Jan 9, 2015)

Sunking said:


> Who says you have to use the TOP BALANCE capabilities of a BMS? .


That was my initial idea as I told you. I'm going to bottom balance with vampire boards at low by pass programable voltage. 
Just if the bms is not programmable you could not do this but if it's not programmable i think there's no reason to have it, because you could not adjust to your pack along the time. 

I've checked and the boards have an error of +-0.01V. So I'm giving some margin to the low voltage.


----------



## JonasFilipe9 (Jan 9, 2015)

EVfun said:


> In regular use I charge the cells at 0.2C to 3.50 volts and hold it at that level for 40 minutes. All the cells where still 3.49-3.51 volts at the end of charge on my last check. There is nothing installed on each cell to monitor individual voltages as they introduce their own chances of discharging each cell slightly differently, even 50 microamps will add up over time (about 0.4 amp hour per year.)


How do you do it? You set the voltage of the bank you would like to have, so 139.5v?


----------



## JonasFilipe9 (Jan 9, 2015)

dladd said:


> Haha, I have no idea what a vampire board is. Pretty sure my car doesn't have one. My charger (PFC30) is set to charge to 165v. It goes CC to 165v, then holds CV while the current tapers. Since I'm top balanced, all my cells are more or less equal at 165v/48 cells = 3.44vpc. My MiniBMS does not start shunting off current until it reaches 3.5v, so it never happens in normal use.
> 
> 
> 
> Even worse case scenario if I'm out of balance and the MiniBMS shunt cannot keep up with the current the pack is pulling, once any individual cell reaches 3.65v it kills the charger. I'm still safe. And still below 100% even on the most charged cell.



Yes, that's a good way of doing things. You're not doing the balance every cycle, just in case anything goes out of the usual behavior (which is cells don't drift apart).
With a charger with that characteristics you are charging like you do in the initial individual cell charge.


----------



## JonasFilipe9 (Jan 9, 2015)

Thanks a lot for your contributions so far. I've been working with these cells for some months but you guys have years of experience. I've seen both processes have their advantages but want to understand a little more how they work and what results they give in real life. 

15.000miles is pretty good, well they'll have to do a lot more to worth the investment. 
Do you guys have an idea how many cycles you've done so far ?

Do you think that charging a cell for just 1h hour for example and discharge it for 4h is considerate a cycle? Or a cycle is a complete charge and discharge ?


----------



## Sunking (Aug 10, 2009)

PStechPaul said:


> As for the BMS (or PLC), I still think it is important to "keep an eye" on individual cells,


I agree with you on that point, and is where I separate myself from the minimalist crowd. I am doing it with an Orion Jr



PStechPaul said:


> I think it may still be useful to have a shunting resistor that might be used when the charging current is reduced to 1/20 C, and it also could be used to bottom balance a pack. However, for 100 A-h batteries, 1/20 C is still 5 amps, and that is 15 watts of power and heat on or near each cell.


Do you really think that it wise to put such large heat source on or near the batteries. Especially any type of board connected to the battery terminal post with a heat bridge directly inside the battery? 

A 100 AH cell has an Ri of less than 1 milli-ohm. Even at 1C or 100 amps of charge current is 6 to 9 watts depending on SOC and temperature. 

My main issue adding a board like that is a MOSFET has two failure modes. One is open circuit which is no problem. The other failure mode is Shorted which = Dead Fully Discharge Battery. 

IMO one of the main reasons to go to Bottom Balance is to eliminate that possibility, not bring it along from Top Balance methods.

Look when it comes right down to it, I really do not care what method one uses. I got no skin in the game, I am not a dealer or make one single penny from the industry. Makes me no difference if the industry fails or succeeds because I win either way. For me it is a hobby and gives me bragging rights on 4th of July when I win the Golf Cart races where I live. In between once a year contest its a golf cart and NEV to go fishing here on the lake. If the industry dies, I just go back to DC motors and Pb batteries which will always be around.


----------



## Moltenmetal (Mar 20, 2014)

My two cents, probably worth less than one cent:

The notion of balancing is an attempt to maximize the available depth of discharge in a pack. Since cycle life on LiFePO4 cells is known to increase greatly if you keep your depth of discharge from ever going too low, it is important to avoid challenging the bottom end by going too deep on the discharge cycle of your smallest capacity cell due to cell reversal, but I am not clear on the electrochemical damage mechanism associated with taking a cell to a low voltage without actually putting it into reversal. If others know WHY, in electrochemical terms, keeping the cells from going below 70% DOD greatly improves the cycle life versus going to 80% DOD, I'd very much like to know!

The electrochemistry wasn't something I'd studied much, but I learned a lot from a recently posted presentation by a Dalhousie University professor. It's clear that aside from the obvious problems with cell reversal, another primary failure mechanism of lithium ion cells of all chemistry is electrochemical damage to the cell electrolyte and other components of the cell, which lead to fouling coatings forming on the porous electrode surfaces. These surfaces impede ion mobility for obvious reasons, which has an impact on useful available capacity and also should have an effect on effective internal resistance. 

It seems that duration of exposure to high temperature and high voltage are both implicated strongly in the electrolyte damage mechanism, and some chemistries are more sensitive than others and hence last longer. Whereas some people here seem to think that the max voltage given by a cell manufacturer is a threshold below which cell damage doesn't occur at all, it is probably better to think of it as a threshold above which rapid damage is a certainty. The exposure duration to damaging heat and voltage is damaging, independent of cycle life to some degree. 

If this is correct, and in my limited understanding of the chemistry it certainly seems to be, holding cells at a higher voltage any higher than necessary for any longer than necessary, should be avoided.

Given that top balancing gives little meaningful additional capacity to a pack where the cells are close in capacity to begin with, it would seem that the practice of holding the cells at a higher than necessary voltage in order to squeeze an Ah or two more into them (an Ah or two which likely you can't use anyway) is not only a waste of time, it is also potentially damaging to the cells long term.

Given that bottom balancing reduces the risk of cell reversal at the bottom of the pack, it has some merit as an inherently safe protective means against cell reversal. Low voltage itself doesn't seem to be too terribly bad for the cells, whereas cell reversal is deadly for them. Running any pack without a cell level BMS to detect when the first cell goes into low voltage cutoff would also seem to be risky, given the high cost of the cells. However, with a good Ah meter and some discipline in selecting how far you need to drive, and a target of no lower than 70% depth of discharge, bottom balancing is pretty much irrelevant also.

So on the argument of bottom vs top balance, I'd say no to top balancing and "meh" to bottom balancing. I'd say yes to a BMS which can detect either high or low voltage, yes to a good Ah meter, and no to a charger with a complex curve- it just seems unnecessary. That others get away with bottom balancing and without a BMS is just fine- to each their own risk tolerance. They MUST have some means of detecting when the first cell goes above HVC during charging, or else they are ultimately likely to damage their lowest capacity cell at some point. I have no idea what that would be OTHER than a BMS.

As it stands, I'll be wiring my BMS to latch the charger off when the first cell goes into HVC rather than allowing it to cycle back on again to allow the cells a chance to shunt charge which is the way it is currently wired. I'll also probably be dropping my charger's cell count curve by one cell to drop its maximum shut-off voltage, as its total pack voltage for automatic shut-off is too close to the BMS HVC which I cannot adjust.


----------



## dladd (Jun 1, 2011)

Moltenmetal said:


> Given that top balancing gives little meaningful additional capacity to a pack where the cells are close in capacity to begin with, it would seem that the practice of holding the cells at a higher than necessary voltage in order to squeeze an Ah or two more into them (an Ah or two which likely you can't use anyway) is not only a waste of time, it is also potentially damaging to the cells long term.


Top balancing does not mean that you charge to the top every time. It means you bring each cell slightly above the top of your charge level one time, put them in series, and then do as you wish. On a daily basis, I'd suggest that a top balanced pack is less likely to reach a high voltage on any single cell than a bottom balanced pack.

I admit I don't understand all the particulars about how these chemistries work, but based on my reading an my understandings of it all, I've decided that it is best to avoid the top AND the bottom of the cells. As stated, I do this by top balancing, charging to a level relatively low on the 'knee', and never discharging below 75% DOD. It has worked for me!


----------



## EVfun (Mar 14, 2010)

> *Originally Posted by EVfun:*
> In regular use I charge the cells at 0.2C to 3.50 volts and hold it at that level for 40 minutes. All the cells where still 3.49-3.51 volts at the end of charge on my last check. There is nothing installed on each cell to monitor individual voltages as they introduce their own chances of discharging each cell slightly differently, even 50 microamps will add up over time (about 0.4 amp hour per year.)
> 
> 
> ...


The ability to set the charger voltage is needed to top charge the way I do or to charge a bottom balanced pack. I set the peak output voltage based on cell count times target voltage per cell, plus just a tiny bit for wiring resistance. I set my 39 cell pack to reach a peak voltage of 136.6 volts and hold for 40 minutes. The bottom balance guys typically talk about setting the peak voltage based on where the pack is at when the first cell hits some target voltage (perhaps 3.5.) 

I don't test for ending SOC very often because it needs to be done after 24 hours of rest post charge without any (even tiny) loads on the pack for that time. I have to pull a fuse and remove a wire to kill all loads. Last time I checked that my resting voltage was 3.35 volts per cell across the pack. Normally (with the idling DC to DC converter and the Zilla hairball connected) I have 3.33 volts after 24 hours. 

A charger that offers the ability to adjust the output voltage is the only practical way I know to set it for your pack. I use a Manzanita Micro PFC-20 charger myself. It has a recessed pot for adjusting output voltage, a knob for setting charging current (I typically run at about 12 amps) and a little rotary switch for setting charge time after reaching the target voltage.

I do not have any "vampire boards" on my pack.


----------



## EVfun (Mar 14, 2010)

dladd said:


> Top balancing does not mean that you charge to the top every time. It means you bring each cell slightly above the top of your charge level one time, put them in series, and then do as you wish. On a daily basis, I'd suggest that a top balanced pack is less likely to reach a high voltage on any single cell than a bottom balanced pack.
> 
> I admit I don't understand all the particulars about how these chemistries work, but based on my reading an my understandings of it all, I've decided that it is best to avoid the top AND the bottom of the cells. As stated, I do this by top balancing, charging to a level relatively low on the 'knee', and never discharging below 75% DOD. It has worked for me!


Well said. That is the strategy I am following as well.


----------



## major (Apr 4, 2008)

What is LPF?


----------



## Moltenmetal (Mar 20, 2014)

My point was that shunt charging, which is part and parcel of a top balancing BMS, holds cells at a high voltage for longer than necessary at the end of charge. Not just one - on mine, most cells are shunt charging by the end of charge. That gives little useful extra capacity with at least the potential to accumulate electrolyte damage if it happens for a protracted period at the end of each charge. You would be better off to not shunt charge and just stop the charger when the lowest capacity cell hits a conservatively set high voltage cutoff.

Charging to a lower total pack voltage is protective only if you keep checking from time to time that no cell is above HVC at the end of charge. A BMS does that for you, as well as monitoring the bottom end.

We agree that avoiding both top and bottom by a reasonable margin is best.


----------



## Sunking (Aug 10, 2009)

major said:


> What is LPF?


Dyslexia translation for LFP.


----------



## pdove (Jan 9, 2012)

Moltenmetal said:


> My point was that shunt charging, which is part and parcel of a top balancing BMS, holds cells at a high voltage for longer than necessary at the end of charge. Not just one - on mine, most cells are shunt charging by the end of charge. That gives little useful extra capacity with at least the potential to accumulate electrolyte damage if it happens for a protracted period at the end of each charge. You would be better off to not shunt charge and just stop the charger when the lowest capacity cell hits a conservatively set high voltage cutoff.
> 
> Charging to a lower total pack voltage is protective only if you keep checking from time to time that no cell is above HVC at the end of charge. A BMS does that for you, as well as monitoring the bottom end.
> 
> We agree that avoiding both top and bottom by a reasonable margin is best.


The myth is that there is this magic voltage you can hold them at with no damage. There's not. Anything above resting voltage on a full battery is causing damage. The would be 3.4 for a LIFePO4 cell. The voltage is part of a procedure. Energy is what needs to be monitored


----------



## IamIan (Mar 29, 2009)

dladd said:


> At the end of the day, it's just a personal decision that you'll have to make and move forward.


+1

Ideally , also be as honest with yourself (as is reasonable) when you examine the pros and cons of your options... for the specific context of your application ... be it top / bottom / BMS / No-BMS ... etc... try and avoid falling into the mental trap of only seeing your 'chosen' options as 'the only good' option.



dladd said:


> No one advocates mid-balancing, you just can't do it cause the 'plateau' is too large.


I would be the exception 

But .. that's a whole other 'can of worms' .. probably best not to open. ... I'm doing soo well with small (readable) posts


----------



## JonasFilipe9 (Jan 9, 2015)

major said:


> What is LPF?


Ups...  Can't change it now, may be the admin can please...

I Knew I saw a topic about this... The discussion roll since 2011 lol and Davide is also in the forum. This is the world stage!


----------



## PStechPaul (May 1, 2012)

One more thing to consider is the possibility of overcharging a fully charged pack due to regenerative braking. It's probably unlikely unless you have done the charging at the top of a long hill where there may be enough potential energy to cause overcharging. A BMS with shunt resistors might be able to protect the pack if the regen is minimal, but there is the possibility of a high charge current much more than the C/20 that the vampires can handle, especially if you have a hard braking event. A BMS, or even a full pack voltage monitor, could shut down the regen at the controller, or activate a braking resistor. But it may be better to charge the pack only to 90-95%, which is probably what you get if you just terminate charge when a cell reaches the preset maximum during high current charging, and not using the tapered C/20 charging at a float voltage that could cause damage. Those with series wound brushed DC motors need not worry about this.


----------



## JonasFilipe9 (Jan 9, 2015)

dladd said:


> I admit I don't understand all the particulars about how these chemistries work, but based on my reading an my understandings of it all, I've decided that it is best to avoid the top AND the bottom of the cells. As stated, I do this by top balancing, charging to a level relatively low on the 'knee', and never discharging below 75% DOD. It has worked for me!


I agree with you, the cell should work always on the flat side of the curve, this way it will never reach dangerous voltages. 

Another key fact is that these* edges* of the discharge curve don't have much energy. I have a discharge curve and the pack goes from 25 to 23.1V (when one cell reached minimum voltage) in 1h30min. Giving aproximately 7A. This is approximately 250Wh for a cell voltage between 3.12 until 2.8V. This is approximately less than *1/10 of the total energy of the pack*... If you disconnect the pack at 3V voltage on the cells you'll stop the discharging at the middle of the "going down part" of the curve and more energy extract from the pack.


----------



## Sunking (Aug 10, 2009)

PStechPaul said:


> One more thing to consider is the possibility of overcharging a fully charged pack due to regenerative braking. It's probably unlikely


I might be able to shine a bit of light on that.

EZGO makes and AC motor golf cart called the RVX and it does have Regen Braking. In fact there are no mechanical brakes with the exception of a Motor Brake when parked.

Anyway the cart does have a large wire resistor bank under the seat. It is only used when the batteries are full or near full to dump the energy to prevent the batteries from being damaged. After a few minutes of operation all the braking goes into the batteries which are Pb Trojan T-1275's

So me think sit could be a problem for Top Balanced for the first mile or two. That is a lot of heat energy that does not go into a charge. 

I think some commercial designs use Super Caps to absorb the energy, and dump it into acceleration, or back slowly into the batteries.


----------



## Tomdb (Jan 28, 2013)

Regen braking- most controller, the curtis included have a top voltage limit for the pack, after which regen is cut or even throttled back after a set point.

check out the different parameters that are programable even in a "basic" setup like an HEPVS and curtis combo.

http://evwest.com/support/Program%20Instructions%20REV%20A%20VER%205.11%20and%20up.pdf

You could potentially do away with all if periodically check your cells if they run out of wack.

One more thing; a tesla model S is never at 100% soc, same goes for most commercial cars. 
One side is thermal runaway saftey, I have seen tests where a fully charged or fully discharged cell gets punctured and goes in thermal runaway where as a cell between 10-90% SOC does just fine.
Other is cell life and regen braking.


----------



## prensel (Feb 21, 2010)

major said:


> What is LPF?


We used to have a revolutionairy politics party called LPF or 'Lijst Pim Fortuyn' be I doubt he meanted that..


----------



## bwjunkie (Jul 31, 2013)

After running both BMS shunt top balance, and no BMS manual initial balancing then* drive by faith in battery theory*. I'm kind of happy with both options, and they both work easily and nicely IF all your batteries have similar capacity.

Both systems have fundemental issues if the individual cells are not similar capacity. So my focus becomes that of capacity and the balance argument is forever moot.

Bottom balance with a _manual _charge system (simple voltage threshold) could result in over-charging a single weaker battery, it reaches it's max too soon. The "overall voltage cutoff" of my PFC20 charger will never know this and keep pumping electrons.

Top balancing has the problem while your driving, of running a single weak battery below 2.5 resting volts. Fortunately when driving, you are actually there to see problems (if you have instrumentation) whereas while charging nobody is present. 
Regardless, the issue mentioned by EVERYONE's rant is "a healthy battery pack", which solves it all. How to achive this "healthy pack" over many years, is a study in progress.

-josh


----------



## electrodacus (Mar 29, 2014)

There seems to be a lot of confusion here about the way a Lithium battery need to be charged and balanced.
I know my experience is in to OffGrid stationary energy storage but I will try to make a few points about both charging and balancing.
Hope I will keep my answer organised (I'm not that great at that)

First my scope on stationary energy storage is long battery life for good amortisation cost for each unit of energy stored over the life of the battery. For EV maybe energy density is a bit more important it depends.

1) Before installing your cells you should do an individual top balance charge so that all cells are at the same SOC.

2) Charging for long life of any Lithium cells needs to be done with CC (Constant Current) charge only
So when first cell in your pack gets to your set point say 3.5V or 3.6V LiFePO4 the charging is stopped no PWM or any other CV (Constant Voltage) charge method.
Based on battery characteristics and charge rate this will allow about 95% to 99% SOC in a typical LiFePO4 and about 85 to 90% for a LiCoO2 (of course 4.2V set point)


3) Top Balancing (someone should explain how will you do Bottom balancing with a BMS or if you only do that manually how often and how)


I'm not aware of any BMS IC that can be programmed to do bottom balancing and dose not make any sense to me so I hope someone gives me an answer about this.
I use the Intersil ISL94203 in my application and that one can be programmed to do proper cell balancing. I will try to explain the way that works.
ISL94203 measures each individual cell with 14bit ADC and you get the result with 1mV resolution.
Then you program a few parameters for cell balancing 

a) Cell balancing is done during charging only but can be done during discharging or both I prefer during charging only so that no current is wasted from cells and only used in my case from PV panels.
b) I set a minimum and maximum cell balancing level in my case for LiFePO4 I use 3.2V minimum and 3.5V max so if cells are outside this limits the cell balancing is not performed.
c) I set a minimum and maximum delta between cells when cell balance is allowed again in my case 15mV min and 300mV max.
d) I set an amount of time cell balancing is ON then some amount cell balancing is OFF in my case again I use 2 seconds OFF and 8 seconds ON the reason to have those 2s OFF is to be able to precisely measure the cell voltage without the voltage drop on the sense wires.


So this is the proper balancing procedure a bit simplified since there are many other factors that can stop cell balancing like cell temperature or some faults of the BMS or wires.


So even with a very small 100 to 200mA cell balancing current (average can be set lower see point d) ) you can maintain large cells (100Ah to 1000Ah) in balance at least in OffGrid applications where both charge and discharge rate are well under 0.5C
That is because cell balancing can be done based on cell delta and not a fixed voltage independent of other cells and because this is done even at 40 or 50% SOC from what I seen depending on the charge rate so the balance current is there for even a few hours a day.


In OffGrid and probably most other applications cells will be many more times close to 100% SOC than close to 0% SOC so I want to see someone explain how bottom balancing is done. I never discharge any cell below 3V no reason to do that.


I get the fact that with EV you may occasionally run out of battery and for safety reason you can not stop your car immediately you need a few seconds warning and then eventually reduced power to the motor so that you do not permanently damage the batteries. But if that is done enough time in advance and you have precise SOC indication this should almost never happen.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> 1) Before installing your cells you should do an individual top balance charge so that all cells are at the same SOC.


Doesn't have to be top .. Cells can all be at same SoC ... Top .. or .. Bottom .. or other .. Top and bottom are the most common.



electrodacus said:


> 2) Charging for long life of any Lithium cells needs to be done with CC (Constant Current) charge only


Nope ... not unless you have a very good source to back this up claim.

(for all practical purposes) ... 1Ah in is 1Ah in .. weather you got it in from CC or CV the battery doesn't care... if anything .. a stronger arguement can be made in favor of CV for longer battery life.



electrodacus said:


> So when first cell in your pack gets to your set point say 3.5V or 3.6V LiFePO4 the charging is stopped no PWM or any other CV (Constant Voltage) charge method.


It would last longer with shallower / smaller window ... say only to 3.45v ... or longer yet with more shallow window .. say 3.40v ... etc... etc.



electrodacus said:


> Based on battery characteristics and charge rate this will allow about 95% to 99% SOC in a typical LiFePO4


Which will give you fewer life cycles than if you only went to 90% ... or 85% ... etc.



electrodacus said:


> (someone should explain how will you do Bottom balancing with a BMS or if you only do that manually how often and how)


Most use a human BMS to bottom balance once ... not a computer based one.

Computerized BMS bottom balancing is done exactly the same way a human would do it.

Top or Bottom ... they both use the voltage curve at the edges of the battery SoC ... bottom balance puts them all together at the bottom ... top balance puts them all together at the top.



electrodacus said:


> I'm not aware of any BMS IC that can be programmed to do bottom balancing and dose not make any sense to me so I hope someone gives me an answer about this.


There is no electronics , nor computer programming reason why a BMS can not be designed and built to bottom balance ... the ones on the market are supply and demand ... top balancing is more commonly asked for from those who design and sell BMS ... so they make what the majority of their customers ask for.

What about bottom balancing doesn't make sense to you? .. Can you be more specific ?



electrodacus said:


> I want to see someone explain how bottom balancing is done.


Look at the voltage vs SoC curve for cell at bottom SoC ... notice the Voltage changes just as rapidly at the bottom as it does at the top SoC.

Bottom Balancing at the bottom is logically the same mechanism at the top ... in reverse... you go down low enough so that the cell voltages would vary significantly for small changes in SoC ... just like you do on top balance ... than you have a cell by cell method to tweak each individual cell so they are all very very close to the same terminal voltage ... same as is done on top balance.



electrodacus said:


> I get the fact that with EV you may occasionally run out of battery


It can also happen in off grid ... the user wants to run their lights , TV, etc for a few more hours ... they pull it down .. unless you build the electronics to prevent them from using the energy that is there .. same basic thing with an BEV.



electrodacus said:


> this should almost never happen.


The best designs account for unlikely events ... ie ... better safe than sorry... plan for the worst , hope for the best ... etc.


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> Nope ... not unless you have a very good source to back this up claim.
> (for all practical purposes) ... 1Ah in is 1Ah in .. weather you got it in from CC or CV the battery doesn't care... if anything .. a stronger arguement can be made in favor of CV for longer battery life.


The longer a Lithium battery spends at high voltage the sooner degrades.
A LiCoO2 charged at 4.1V instead of 4.2V will last 2x more cycles and about 2x cycle for each additional 100mV lower.
The best value seems to be 3.9V 3.95V that allows almost 8x higher cycle life while the max capacity is just 65% of that at 4.2V
This was used usually in military applications for energy storage.
Those Seiko 5 pin protection IC used in all cheap ebike BMS projects have this 3.95V high voltage limit and are improperly used for LiFePO4 creating bad reputation to both BMS and LiFePO4 battery.

As for CC it dose not necessary mean that current is constant (e.g. Solar PV current is dependent on the amount of solar radiation) but it refers at that part of the battery charge where voltage on battery will increase to the max set point say 3.5V then the charge is immediately terminated. You can continue to use PWM for example to reduce the current slowly in order to keep the voltage at 3.5V until the current is a certain smaller value thus pushing that extra 1 to 5% more energy in a battery.
That part of the charge will be detrimental to Lithium battery life.
That CV part is used in mobile applications like phone ore tablets because that extra 15% capacity in case of LiCoO2 is more important than the life of the battery (you will upgrade your phone or Laptop before the battery will die but you prefer to have a longer run or lighter device)



IamIan said:


> It would last longer with shallower / smaller window ... say only to 3.45v ... or longer yet with more shallow window .. say 3.40v ... etc... etc.


Yes it will but depending on internal impedance of the battery and your charge rate that value may be a bit to small so the battery will be quite far from 100% SOC 
But yes the smaller you can go with that value the better I use 3.5V with my GBS and stop the charge as soon as first cell gets there that gets me close enough to to full charge probably around 95% depending on the charge rate. the smaller the charge rate the closer you are of the full charge. 



IamIan said:


> Which will give you fewer life cycles than if you only went to 90% ... or 85% ... etc.


You can not know precisely the SOC so if you want to charge it at lower capacity just use lower voltage threshold like 3.45V it will depend on the charge rate and battery impedance.



IamIan said:


> Most use a human BMS to bottom balance once ... not a computer based one.
> 
> Computerized BMS bottom balancing is done exactly the same way a human would do it.
> 
> Top or Bottom ... they both use the voltage curve at the edges of the battery SoC ... bottom balance puts them all together at the bottom ... top balance puts them all together at the top.


Human BMS is not a solution in most applications and also not that reliable 

The thing is you are usually never at the bottom in a well designed application EV, OffGrid or anything else.
Yes they will work in a similar way but in Bottom you discharge the cells while on top you do not use any current from the cells since you do that during charging and charge current is usually larger than balance current.




IamIan said:


> There is no electronics , nor computer programming reason why a BMS can not be designed and built to bottom balance ... the ones on the market are supply and demand ... top balancing is more commonly asked for from those who design and sell BMS ... so they make what the majority of their customers ask for.
> 
> What about bottom balancing doesn't make sense to you? .. Can you be more specific ?


yes you can build anything including artificial general intelligence.
Bottom balancing like I mentioned before can never be done in an application where you never want your battery empty.
I only had 2x my battery empty (3V min cell) in two years of OffGrid then I did not had the SOC indication so was hard to guess how much I had left in battery now with SOC indication I know exactly what I have left. 
Is like your car gas tank it is many times full but almost newer unless by accident empty.
So that is why I do not get the bottom balancing.




IamIan said:


> It can also happen in off grid ... the user wants to run their lights , TV, etc for a few more hours ... they pull it down .. unless you build the electronics to prevent them from using the energy that is there .. same basic thing with an BEV.


I mentioned before it only happened two times for me and will probably never happen now that I know quite precisely what I have left.
I will never have my battery under 3V or above 3.5V




IamIan said:


> The best designs account for unlikely events ... ie ... better safe than sorry... plan for the worst , hope for the best ... etc.


With BMS you do not need to do that he can also give you warnings at different SOC levels and eventually disconnect less critical devices at those levels.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> With BMS you do not need to do that he can also give you warnings at different SOC levels and eventually disconnect less critical devices at those levels.


Well I see you are trying to pedal your snake oil here. 

Warning all, this guy is a nut job ran off many forums including mine. He is banned for life on most the solar forums. Mods i suggest you put him out of our misery now.


----------



## electrodacus (Mar 29, 2014)

Sunking said:


> Well I see you are trying to pedal your snake oil here.
> 
> Warning all, this guy is a nut job ran off many forums including mine. He is banned for life on most the solar forums. Mods i suggest you put him out of our misery now.


Good to see you here. I was under the impression you where not interested in LiFePO4.
The snake oil is Open Source so you can build your own or use a different design. Or be a human BMS (I did that and was not that fun but not that hard also).
This is a discussion forum and I do not think this one sells Lead Acid batteries and equipment so there is no conflict.

Edit:
And is to bad to see that the largest Solar forums are not free and have a commercial interest.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> Good to see you here. I was under the impression you where not interested in LiFePO4.
> The snake oil is Open Source so you can build your own or use a different design. Or be a human BMS (I did that and was not that fun but not that hard also).
> This is a discussion forum and I do not think this one sells Lead Acid batteries and equipment so there is no conflict.
> 
> ...


Warning mods this nut job will babble on for weeks until you ban him never ever letting anyone have the last word. You have been warned. He is peddling for your dollars. He does not even understand his terminals on his box cannot handle the deigned current. Mark my words he will now come back and tell you his terminals will work. He has already proven in this thread he does not know much about Lithium batteries.


----------



## electrodacus (Mar 29, 2014)

Sunking said:


> Warning mods this nut job will babble on for weeks until you ban him never ever letting anyone have the last word. You have been warned. He is peddling for your dollars. He does not even understand his terminals on his box cannot handle the deigned current. Mark my words he will now come back and tell you his terminals will work. He has already proven in this thread he does not know much about Lithium batteries.


Works just fine for me and other 100 users. Do you want some photos ? Those terminals where your only good point and I admitted that you can check the forum is still there.
Just did not had a better option for that version.
I do have larger connectors #2 AWG on the new version with no parallel wires needed.
And if there is a question or an argument of course I want to respond to it it dose not mean I want to have the last word.
All that you seen there about the balancing of Lithium batteries is the strategy Intersil uses on their ISL94203 that is the basis of my product.
And I do happen to agree with their method of Lithium cell balancing that is why I chose to use they IC instead of any other.


----------



## dladd (Jun 1, 2011)

in regards to CC and CV charging, here's my data point from my car.

If I charge at 40a (from a 30a 220v line) I give up about 10 ah compared to if I charge at 7a (15a, 110v). That is, if I simply shut off when the first cell hits 3.5v. 

This is with 130ah cells, of which about 100ah is usable, so that's 10%. Small, but hardly negligible.

C/20 is 6.5a, and the cells are 'rated' to be charged to 3.65v, so I don't see how holding them at 3.5v while the current falls from 40a to 7a is doing any harm vs. charging them up to 3.5v at 7a the whole way. Same energy in, no measurable heating of the cells is occurring, and there's a decent 'longevity' factor already built in since I'm only taking them up to 3.5vpc (I actually use 3.44vpc, but same idea).


----------



## electrodacus (Mar 29, 2014)

dladd said:


> in regards to CC and CV charging, here's my data point from my car.
> 
> If I charge at 40a (from a 30a 220v line) I give up about 10 ah compared to if I charge at 7a (15a, 110v). That is, if I simply shut off when the first cell hits 3.5v.
> 
> ...


Yes your numbers are correct and the observation on capacity based on CC only charging and the charge rate.
With solar charging this is not a problem since that 10% will also be done since solar intensity drops at the end of the day do to sun angle on the panel.
Also even if you do not use that top 10 even 15% you increase the life of the battery and that is more important in stationary energy storage. Energy density with EV is a bit different maybe you prefer that 10% extra capacity over battery life.
The LiFePO4 are stressed with anything above about 3.4V so you need to spend as little time as possible above that.
Is better to charge at full 40A up to 3.6V and then stop charging that will only be a few minutes above 3.4V than charge at 3.5V with CC and then stay there with CV for 3 to 4 times longer before the current drops to a much lower value.
There will be some extra capacity with CC then CV at 3.5V but it will degrade a bit more than just CC to 3.6V maybe not much more so can be a small difference not significant.


----------



## Sunking (Aug 10, 2009)

dladd said:


> in regards to CC and CV charging, here's my data point from my car.
> 
> If I charge at 40a (from a 30a 220v line) I give up about 10 ah compared to if I charge at 7a (15a, 110v). That is, if I simply shut off when the first cell hits 3.5v.


You are charging at high rates similar to solar uses. All you have to do is tweak the set point voltages a little higher. 

Had to do that on my NEV so when rested the weakest cell is at 90% SOC and all the others lower. That gives me 90 AH on a 100 AH pack. I just don't have any risk exposure of over discharge on any cell.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> IamIan said:
> 
> 
> > electrodacus said:
> ...


Do you even realize this (blue) comment of yours is refuting your own previous (Red) CC claims ??

A CV charging of 1Ah can be done at a lower battery terminal voltage than the same 1Ah charged from CC ... same 1 Ah charged into the same battery in either case.



electrodacus said:


> electrodacus said:
> 
> 
> > CC (Constant Current)
> ...


Actually constant current does exactly mean the current is constant.

You were correct the first time... incorrect the second time.



electrodacus said:


> electrodacus said:
> 
> 
> > The longer a Lithium battery spends at high voltage the sooner degrades.
> ...


You don't get it both ways.
If you go to a higher voltage with your CC method ... you are doing the very higher voltage damage you already wrote about.

If I put the same __Ah into the battery with a CV to a lower voltage ... I avoid your higher voltage 3.5v damage.



electrodacus said:


> You can not know precisely the SOC


Incorrect.
There are several conditions under which I can know precisely the SoC... if it wasn't possible to precisely know the SoC there would be no possible way to balance a battery pack (top, bottom, or other).



electrodacus said:


> so if you want to charge it at lower capacity just use lower voltage threshold like 3.45V it will depend on the charge rate and battery impedance.


Or I can charge it with just as much Ah capacity input ... thus no lower capacity .. but I can do it without pushing the terminal voltage as high as you did with CC ... because I set a CV point for a lower terminal voltage.



electrodacus said:


> IamIan said:
> 
> 
> > electrodacus said:
> ...


Exactly

I don't see the significance of your "But" you add on after... wh spent balancing are wh spent on balancing (top or bottom)... if anything bottom balancing has the potential to use less balancing wh to achieve a finished balance than top balancing... that's a bottom balance benefit.




electrodacus said:


> Bottom balancing like I mentioned before can never be done in an application where you never want your battery empty.


?? never ?? .. = ... wrong word

The bottom curve starts before reaching 0% or 'empty' ... just like the top curve starts before reaching 100% or 'full'.



electrodacus said:


> Is like your car gas tank it is many times full but almost newer unless by accident empty.
> So that is why I do not get the bottom balancing.


Design , Engineer, and Plans for the worst .. hope for the best.

People almost never deploy the air bags in their cars .. do you also have a hard time understanding why someone would ever want air bags (just in case)?

People almost never have to file a claim for their house burning down ... ... do you also have a hard time understanding why someone would ever want to have insurance (just in case)?

People almost never need to call 911 in a life and death situation .. do you also have a hard time understanding why some people want a 911 emergency option to be there (just in case) ??

etc... etc.



electrodacus said:


> IamIan said:
> 
> 
> > The best designs account for unlikely events ... ie ... better safe than sorry... plan for the worst , hope for the best ... etc.
> ...


Incorrect.

The BMS is an example of that exact same type of designing... ie why you get those warnings at all .. why there is a disconnect of less critical devices .. etc.


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> Do you even realize this (blue) comment of yours is refuting your own previous (Red) CC claims ??
> 
> A CV charging of 1Ah can be done at a lower battery terminal voltage than the same 1Ah charged from CC ... same 1 Ah charged into the same battery in either case.


Not sure you understand exactly what cc and cv is when referring to battery charging stage.

You have a max set point say is 3.5V as long as you are under that at you highest cell terminals you are doing CC when you get there and with a certain method say PWM try to keep the voltage at that set max (in order to do that you reduce the current or average current in case of PWM method).
So if you stop the charging ass soon as you get to your 3.5V limit you spend less at above 3.4V while if you do the second part of the charge cycle called CV you spend more time above 3.4V but you also put some (not much for LiFePO4) additional energy in to battery.
That additional energy is not worth the degradation in OffGrid energy storage in EV I have no idea it depends on what you care most.



IamIan said:


> Actually constant current does exactly mean the current is constant.
> 
> You were correct the first time... incorrect the second time.


I was correct both times. First time I give the definition of CC initials and the second time I explain that CC in battery charging dose not mean constant current it means that you are in the constant current stage of the charging.
e.g. Use a solar PV panels to charge a battery from 40% to 60% the voltage at terminals will be well below the max set point so you are in the constant current phase even if there are clouds and during that part of the charge current has varied from 500mA to 8A (so current was no constant as in fixed value you get usually from an AC to DC charger ) but that charge will still be called constant current since at no point there was any constant voltage regulation used. 




IamIan said:


> You don't get it both ways.
> If you go to a higher voltage with your CC method ... you are doing the very higher voltage damage you already wrote about.
> 
> If I put the same __Ah into the battery with a CV to a lower voltage ... I avoid your higher voltage 3.5v damage.


In my example there I went to 3.6V but at 40A charge rate vs 3.5V with 7A charge rate so it will spend less time to store the same energy with higher charge current (40A) even if it will go to 3.6V (battery DC series equivalent resistance plays also a role).
It will spend more time above 3.4V with just 7A charge current to 3.5V.




IamIan said:


> Incorrect.
> There are several conditions under which I can know precisely the SoC... if it wasn't possible to precisely know the SoC there would be no possible way to balance a battery pack (top, bottom, or other).


Balance is done based on cell voltage and not cell SoC.




IamIan said:


> Or I can charge it with just as much Ah capacity input ... thus no lower capacity .. but I can do it without pushing the terminal voltage as high as you did with CC ... because I set a CV point for a lower terminal voltage.


Like I mentioned before SoC can not be calculated precisely to may variable and measurement errors.
There are the voltage accuracy the battery impedance the current resolution and accuracy the battery temperature, the charge rate just to mention a few of the things influencing SoC calculation.



IamIan said:


> Exactly
> 
> I don't see the significance of your "But" you add on after... wh spent balancing are wh spent on balancing (top or bottom)... if anything bottom balancing has the potential to use less balancing wh to achieve a finished balance than top balancing... that's a bottom balance benefit.




Here with the "but" I'm referring at the fact that energy from solar PV cost less than energy from battery (same with energy from the grid depending on your rate)
This is not such an important point.




IamIan said:


> ?? never ?? .. = ... wrong word
> 
> The bottom curve starts before reaching 0% or 'empty' ... just like the top curve starts before reaching 100% or 'full'.


In most application you will not want to have an empty battery. But you say you have an empty battery and then on top of that apply cell balancing on the cells that are not quite empty that is still stress on those cells and you can not use your battery during that time.
That never happens to me in OffGrid. I can not afford to have no power for my house while waiting for the cell to balance. Never happens so it can not be used here.
And what about EV will you ever have your battery empty ? I know I will not like that ?
It can happen but mostly it dose not so you can not do cell balancing at the bottom. 
I understand what is your reason to do manual bottom cell balancing so that when your battery is empty (should never happen with precise SoC  ) your cells are all quite close to each other and empty and if you only measure the total battery bank voltage is a bit safer but far from perfect.
With a BMS that monitors each individual cell and you do not worry about a cell going under 2.8 or 2.5V since you set and alarm for that and just stop driving your car same way you do if the battery is totally empty because it is.



IamIan said:


> Design , Engineer, and Plans for the worst .. hope for the best.
> 
> People almost never deploy the air bags in their cars .. do you also have a hard time understanding why someone would ever want air bags (just in case)?
> 
> ...


Not sure I see the scope of the analogy if you want insurance use a BMS that is the insurance equivalent of battery protection. 



IamIan said:


> Incorrect.
> 
> The BMS is an example of that exact same type of designing... ie why you get those warnings at all .. why there is a disconnect of less critical devices .. etc.


Again I do not get the pints you are making. Is a BMS and if is a smart one can do those warning so you know your battery is almost empty same as your red light on your gas tank warning you to get to a gas station since you only have little gas left in the tank.


----------



## PStechPaul (May 1, 2012)

I think you may also need to take into account the internal resistance of the cell, so the charge voltage may be higher by the amount of I(chg)*R(int). My 1.25 A-h cells have in internal resistance of about 100 milliohms, so at 1C charge they could be set at 125 mV above the peak resting (stabilized) cell voltage, which seems to be about 3.34 volts. Thus a setting of 3.465 volts would be OK.

Larger cells are probably similar and proportional WRT cell voltage and internal impedance. I think it was mentioned that a 100 A-h cell has internal impedance of about 1 mOhm.

There may also be another effect, perhaps called "surface charge" or parallel capacitance, which may account for a higher cell voltage immediately after charge current has been removed, and then after a few hours this is "absorbed" into the cell and the voltage stabilizes. This may also be an effect of internal temperatures and chemical reactions, but I think it is safe to say that a cell can be safely charged to a higher terminal voltage. It may even be safer to do this at full charging current (1C) where the internal resitance is more predominant. At 1/20 C the additional voltage would be only about 6 mV above nominal, at which point the accuracy of measurement and factors such as temperature add a similar or greater amount of uncertainty.

The "coulomb counting" method may be a valid way to determine SOC, but you must first establish an actual capacity for the cells of a pack. It may be safer to discharge to a minimum where the voltage sag is easily seen, and may represent about 5% SOC. Then you may be able to use the coulomb counting method (I*t) to inject 90 or 95% of capacity while monitoring cell voltage. If all cells meet or exceed their rated capacity, this should not overcharge any cell, and the higher capacity cells will be just a bit undercharged. 

But the problem with coulomb counting in an EV application is that the discharge current can vary widely, and it is difficult to obtain high accuracy over such a wide range. A 100 A-h pack may be subject to 500 amps of discharge so the measurement must be able to accommodate that. It may be unrealistic to expect an accuracy of any better than 0.25% in an automotive environment, so that is an uncertainty of 1.25 amps.


----------



## Sunking (Aug 10, 2009)

Paul you are wasting your time with this idiot. He will not let you have the last word even if it is blatantly obvious he is wrong and has no idea what he is talking about. He has been banned from every Solar Power Forum out there.

If you dance with him, he will go for a thousands of pages as he will never stop disputing you. He is here for one reason, and one reaso only; To push his product at the Forum Owners expense. Go Google these two names he goes by and see what you think as you will get thousands of hits of his countless diatribes and links to his product. He is a Con and Spammer looking to get in your pockets. 

Electrodacus
Dacian Todea

It will lead you to Kickstarter where he hussles you for MONEY.


----------



## electrodacus (Mar 29, 2014)

Sunking said:


> Paul you are wasting your time with this idiot. He will not let you have the last word even if it is blatantly obvious he is wrong and has no idea what he is talking about. He has been banned from every Solar Power Forum out there.
> 
> If you dance with him, he will go for a thousands of pages as he will never stop disputing you. He is here for one reason, and one reaso only; To push his product at the Forum Owners expense. Go Google these two names he goes by and see what you think as you will get thousands of hits of his countless diatribes and links to his product. He is a Con and Spammer looking to get in your pockets.
> 
> ...


Yes I do promote my Solar BMS where I think people may be interested in such a product.
I'm sure it is not the case on this forum since Solar BMS can not power an electric car was never designed for that.
There are some good informations about LiFePO4 here and there are not that many forums about LiFePO4.
From what I remember last time you where of the opinion that Lead Acid is a superior battery for stationary energy storage.
Did you changed your mind?
My comment here was about Lithium cell balancing. I explained how that is done in the Intersil ISL94203 (the same one I use) and I agree with Intersil method of doing cell balancing that is why I chose to use their IC.
People can use any type of cell balancing they want. I was just expressing my opinion about this subject.
I seen some of your other comments an it seem you are the bully of this forums.
I do not feel intimidated by your words and I have more than enough technical and engineering background to know you are more words than understanding of the subjects you are discussing.
So yes please continue to comment on my posts I do not think they have the effect you are hoping for.


----------



## PStechPaul (May 1, 2012)

I have no problem with your comments. In the end, each of us is responsible for our own designs and I can learn from almost anyone, even if they are incorrect. I appreciate challenges and criticism as constructive, and encourages me to make sure I am on the right track. I have sometimes been wrong, and I'm confident enough to accept that and make changes as appropriate and necessary. Most of us on this forum seem to want to help others and the EV community in general, and there is healthy give and take of opinions, knowledge, experience, and new ideas.


----------



## onegreenev (May 18, 2012)

Nope, hes not the bully around here. Not too many here interested in solar or off grid solar. We are about cars and lithium batteries powering them. For now the Lead Acid Large Format Stationary batteries are still king of the solar stationary setup. Its not like a home is being powered heavily by battery power on an off grid setup. Some in the evening but not much. I prefer to use Lithium and think Lithium will be the best for off grid as well. As for balancing LiFePO4 cells, you don't have to do any thing more than bottom balance once and set up a charge algorithm that will charge up to a specified voltage average over the whole pack. So you never go over charge and you will always be balanced when your pack goes low from use. As in a car it is always good to have your cells balanced on the bottom for when you do run your system lower than you should and you know you should stop but don't. A simple setup should be fine but we are waiting for a good charge controller specifically for lithium. It is going to be a slow process and we must wait. I don't see your product as one we can use. It is not promoted well for lithium and the imaging on the box looks old hack dot matrix crap I saw on products from the 80's trying to be computer looking. It just does not say quality and looks more like a toy. This is an honest opinion from someone who has built three electric cars and drives an Nissan Leaf and has a whole house 7.2kW solar array on the house since 05. Nope. the product looks cheesy and looks like it may have some sort of arduino hidden somewhere in there. 

A proper charge controller of sufficient size is required and one that tis configurable to different voltages and AH size. I plan on at least a 24kWh sized pack. Set at 48 volts this should give me plenty of power for off days and evenings. When the time comes I will be going off grid and I won't be buying your product. 

Pete


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> You have a max set point say is 3.5V as long as you are under that at you highest cell terminals you are doing CC when you get there and with a certain method say PWM try to keep the voltage at that set max (in order to do that you reduce the current or average current in case of PWM method).


Red = CV ... As soon as you are trying to 'keep the voltage' ... to any voltage point you are doing CV ... that is what CV means.



electrodacus said:


> I was correct both times. First time I give the definition of CC initials and the second time I explain that CC in battery charging dose not mean constant current it means that you are in the constant current stage of the charging.


Red = Incorrect... again... CC means the current is constant.



electrodacus said:


> e.g. Use a solar PV panels to charge a battery from 40% to 60% the voltage at terminals will be well below the max set point so you are in the constant current phase even if there are clouds and during that part of the charge current has varied from 500mA to 8A (so current was no constant as in fixed value you get usually from an AC to DC charger ) but that charge will still be called constant current since at no point there was any constant voltage regulation used.


Red = incorrect ... Current was not constant .. so it is not constant current charging.



electrodacus said:


> Balance is done based on cell voltage and not cell SoC.


Not necessarily.
Current cell voltage balancing is one option ... but not the only option.



electrodacus said:


> IamIan said:
> 
> 
> > Or I can charge it with just as much Ah capacity input ... thus no lower capacity .. but I can do it without pushing the terminal voltage as high as you did with CC ... because I set a CV point for a lower terminal voltage.
> ...


red = incorrect.

And your comment about SoC .. is an irrelevant comment to reply with to my comment you referenced.

1 Ah charged under CV ... is (for all practical purposes) the same 1 Ah as someone else who charged with CC ... it is the same 1Ah in either case... comments about knowing the precise SoC do not make any difference to them both being the same 1Ah of charge (CV or CC).



electrodacus said:


> IamIan said:
> 
> 
> > The bottom curve starts before reaching 0% or 'empty' ... just like the top curve starts before reaching 100% or 'full'.
> ...


red = incorrect.

Also re-read my comment you posted this reply in reference to ... doesn't have to be empty ... continuous reference to it being empty .. when you are told it doesn't have to be empty .. makes little sense.



electrodacus said:


> That never happens to me in OffGrid. I can not afford to have no power for my house while waiting for the cell to balance. Never happens so it can not be used here.


Multiple errors in this line of thinking.



The initial assumption of not being able to use battery while it is being discharged is incorrect ... the discharge energy (even from balancing) can itself be used.
A PV offgrid system can (and many are) designed to be able to send the PV power directly to the electrical loads (without ever going through the battery) ... thus it is incorrect to equate (can't use batteries) with (can't get electrical power).
If you start with the assumption that your battery is discharged to near empty .. than you get that same starting assumption in either case .. the battery is at the same low SoC in either option ... top balance or bottom balance... now apply the "I need __electrical load" to the battery near the bottom that was top balanced.




electrodacus said:


> electrodacus said:
> 
> 
> > I can not afford to have no power for my house
> ...


Keeping in mind that the top balanced battery pack will be further unbalanced at the bottom ... this (I can't afford to be without __) is why people like to have the bottom balance (just in case) insurance.



electrodacus said:


> electrodacus said:
> 
> 
> > Is like your car gas tank it is many times full but almost newer unless by accident empty.
> ...


You expressed your lack of understanding why people would want to bottom balance.

You sited (as a reason for you lack of understanding them) .. that it is unlikely to be 'empty'.

I explained to you (hoping you would gain the understanding you said you didn't have) .. that .. many people want (just in case) type of insurance and planning .. even for unlikely events .. I listed examples that I thought you would understand this (just in case) thinking .. air bags , 911 , home insurance.

Thus the analogy .. is that ... it being a rare event .. does not stop people from wanting (just in case) types of insurance and planning... thus why your sited reason (it doesn't happen often) , does not hold much traction with people who want to do bottom balancing.



IamIan said:


> The BMS is an example of that exact same type of designing... ie why you get those warnings at all .. why there is a disconnect of less critical devices .. etc.





electrodacus said:


> if you want insurance use a BMS that is the insurance equivalent of battery protection.





electrodacus said:


> Again I do not get the pints you are making. Is a BMS and if is a smart one can do those warning so you know your battery is almost empty same as your red light on your gas tank warning you to get to a gas station since you only have little gas left in the tank.


Exactly as I wrote before ... a BMS is the byproduct .. of that exact same (just in case) kind of desire .. design intent .. it leads some to go with a BMS.

And depending on which you are more concerned about avoiding (over charging) or (over discharging) ... most people go with either top or bottom balanced respectively ... and some others to do both (bottom or top) balance and a BMS combined.


----------



## alvin (Jul 26, 2008)

I don't think electrodacus understands that bottom balance is basically a one time event. It is not done every charge cycle. onegreenev walked me through it about 3years ago and mine are just charged every time to a voltage cut-off point . They are still balanced.


----------



## electrodacus (Mar 29, 2014)

alvin said:


> I don't think electrodacus understands that bottom balance is basically a one time event. It is not done every charge cycle. onegreenev walked me through it about 3years ago and mine are just charged every time to a voltage cut-off point . They are still balanced.



Thanks for confirming that. Yes I was not sure that it was done only once. Cells are not equal so they will drift from that (one time balance) If they are not stressed at high discharge rate then they can stay relatively balanced for quite some times.
I did the same thing before building and installing my Solar BMS. In my case the balance was done manually at the top since I used the battery for OffGrid so the battery was mostly on the top end of the SOC.
It did worked better than expected. I had new batteries purchased at pairs of 4 cells (they are 100Ah GBS) GBS was available in Canada and easy to get but I will not recommend them for high charge discharge rate do to 1.8mohm impedance.
The battery in my application was charged with about 0.25C max and discharged with usually less than 0.5C.
In this conditions I had even more than 3 months with daily use before manual rebalancing was needed. When I did the rebalance the max difference between cells was just a bit less than 1Ah.
But I did checked with a multimeter most of the day during the day to see if any cells will go over 3.5V or so.
So yes is possible in some cases (not sure on EV) to have no BMS and do manual balance either on top or on bottom depending on where you expect to find the battery more (where the risk is higher).
Personally I did not liked to be stressed by the cells going out of balance and ruin my pack.
When you do bottom balancing and have just a high and low voltage cut off for the entire pack the risk is more during charging than during discharging.
One other application that I had was a cordless screw driver that I modified from 12V NiCd to LiFePO4 (small 18650 cells) and that will go out of balance way easier dot to really high charge discharge rates (I had no BMS) and manual balance was done every week usually (that when I used it daily for the house construction).


----------



## electrodacus (Mar 29, 2014)

PStechPaul said:


> I have no problem with your comments. In the end, each of us is responsible for our own designs and I can learn from almost anyone, even if they are incorrect. I appreciate challenges and criticism as constructive, and encourages me to make sure I am on the right track. I have sometimes been wrong, and I'm confident enough to accept that and make changes as appropriate and necessary. Most of us on this forum seem to want to help others and the EV community in general, and there is healthy give and take of opinions, knowledge, experience, and new ideas.


Just wanted to say I like the comment nothing else to say.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> Nope, hes not the bully around here. Not too many here interested in solar or off grid solar. We are about cars and lithium batteries powering them. For now the Lead Acid Large Format Stationary batteries are still king of the solar stationary setup. Its not like a home is being powered heavily by battery power on an off grid setup. Some in the evening but not much. I prefer to use Lithium and think Lithium will be the best for off grid as well. As for balancing LiFePO4 cells, you don't have to do any thing more than bottom balance once and set up a charge algorithm that will charge up to a specified voltage average over the whole pack. So you never go over charge and you will always be balanced when your pack goes low from use. As in a car it is always good to have your cells balanced on the bottom for when you do run your system lower than you should and you know you should stop but don't. A simple setup should be fine but we are waiting for a good charge controller specifically for lithium. It is going to be a slow process and we must wait. I don't see your product as one we can use. It is not promoted well for lithium and the imaging on the box looks old hack dot matrix crap I saw on products from the 80's trying to be computer looking. It just does not say quality and looks more like a toy. This is an honest opinion from someone who has built three electric cars and drives an Nissan Leaf and has a whole house 7.2kW solar array on the house since 05. Nope. the product looks cheesy and looks like it may have some sort of arduino hidden somewhere in there.
> 
> A proper charge controller of sufficient size is required and one that tis configurable to different voltages and AH size. I plan on at least a 24kWh sized pack. Set at 48 volts this should give me plenty of power for off days and evenings. When the time comes I will be going off grid and I won't be buying your product.
> 
> Pete


I disused here about cell balancing (my perspective was a bit from OffGrid perspective since that is where I use LiFePO4) From What I know large EV car manufacturers use top balancing on their usually LiCoO2 cells and of course use a BMS.
Why do you think the DIY EV community dose not like to use a BMS and prefer to do manual balancing ?
My guess is that there are not many car BMS available for DIY they are probably a bit expensive and complicated.
I hope to have also in the future a 7+kWh array but for heating my house not chemical battery for this separate array needed energy is store in thermal form.
At the moment my array is 720W (3x240W) and is appropriate for my usage 60 to 90kWh/month.
I know this is about 10x smaller than a typical grid tie house in North America I'm just more focus on energy efficiency.
The Solar BMS was designed for my use and is capable of just 3KW PV array and same for the max Load (that is on the new version the old one even less 1kW array and 2kW load). 
But it can take any battery size and battery capacity needs to be set inside the BMS so that he can calculate the SOC.
There is no arduino (I never used arduino) the code is written in C and it uses the STM32F072 (an ARM cortex M0 microcontroller) i used AWR more than 12 years ago but I used assembler to program that not the arduino IDE.
The micro is there for programing the parameters and displaying and calculating SOC, energy and other things of that nature all the HW protection is done by the ISL94203 form Intersil that can work independent from the microcontroller and do not depend on my software except for the initial battery and parameter setup.
As for the design that is a matter of personal taste some people will like the design some wont.


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> Red = CV ... As soon as you are trying to 'keep the voltage' ... to any voltage point you are doing CV ... that is what CV means.


Sorry I will not take each line and comment again since I have nothing to add to my original comment.
You just have your own definition about CC and CV when it refers to battery charging.
I will add this using a solar PV panels that has variable current limitation based on the amount of sunlight will still make it constant current charging because the voltage will not stay constant. With a limited resolution voltmeter you may think that is the case but with a high enough resolution you will be able to see that no matter if charge current is 1A or 10A the battery will still continue to increase terminal voltage say from 3.300000002V to 3.300000003V in a few seconds.

Here is a graph charge current is only constant here becose it uses an AC charger with unlimited energy from the grid. If you use a Solar PV panel or other variable current limited source maybe wind turbine the first part where voltage is lower than the set point is called Constant Current (even if current is not or dose not need to be constant) . Is just a naming convention for battery charging and I agree it may sound confusing.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> My guess is that there are not many car BMS available for DIY they are probably a bit expensive and complicated.


 There are 62 BMS systems on the the market for DIY EV's and all of them can be used on Solar. Prices start @ $5 per cell. Complexity varies from very simple passive bleeders to active programming logic control, and everything in between

You call yourself an expert and a manufacture, yet you have no clue what is on the market you are competing against, or any clue how cell balancing works. 

Do yourself a favor and leave now. I will give you this much; You are consistent of making a fool out of yourself on forums peddling your product.


----------



## electrodacus (Mar 29, 2014)

Sunking said:


> There are 62 BMS systems on the the market for DIY EV's and all of them can be used on Solar. Prices start @ $5 per cell. Complexity varies from very simple passive bleeders to active programming logic control, and everything in between
> 
> You call yourself an expert and a manufacture, yet you have no clue what is on the market you are competing against, or any clue how cell balancing works.
> 
> Do yourself a favor and leave now. I will give you this much; You are consistent of making a fool out of yourself on forums peddling your product.


Like I mentioned before cell balancing that I presented is done by Intersil I take no credit on that.
The only reason I did not post on that solar forum was because of my opinions about LiFePO4 where in conflict with the company behind that forum that sells Lead Acid batteries and equipment. It had nothing to do with you.
I have no conflict in here since most of this people use LiFePO4 and my Solar BMS is not designed for EV and can not be used so no conflict of interest.
I wished there was a large free solar power forum not associated with a business maybe that will happen one day.
Yes there are a few BMS for EV but it seems people prefer to use manual cell balancing.
And yes most car BMS can be used for solar also with some small modifications.
Is what I recommend people that ask me about SBMS but need higher battery voltage or larger PV array that what the SBMS is designed for.
Still this thread is about cell balancing so this will be my last replay to you on questions or remarks outside the scope of sixths tread (Top vs Bottom cell balancing).


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> The only reason I did not post on that solar forum was because of my opinions about LiFePO4 where in conflict with the company behind that forum that sells Lead Acid batteries and equipment.


You are also a boldface liar. You posted hundreds of times just on a single thread until you got banned. Not just one Forum, but many of the.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> will still make it constant current charging because the voltage will not stay constant.


100% completely invalid logic ... varying voltage is absolutely no (because) type of reason nor justification that than results to 'make it' Constant Current... this is not a either CC or CV.. as if there were only 2 options.

Battery charging or discharging has 4 different electrical paths:

CC = Current is constant.
CV = Voltage is constant.
CP = Power is constant .. but neither CV nor CC
None of the above = no CC , no CV, no CP .. ie no 'constant' electrical parameter.



electrodacus said:


> is called Constant Current (even if current is not or dose not need to be constant).Is just a naming convention for battery charging and I agree it may sound confusing.


Nope .. it is not called constant current ... when the current is not constant.

It is not confusing ... it's not battery convention ... you are not using it correctly.

None of the publications I've read .. scientific, engineering, battery OEMs .. etc ... NONE share this claim of yours .. As far as I am aware .. it is not convention at all by anyone but you .. AFAIK , it is just you and you alone , trying to incorrectly use the term 'constant'... and CC.


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> 100% completely invalid logic ... varying voltage is absolutely no (because) type of reason nor justification that than results to 'make it' Constant Current... this is not a either CC or CV.. as if there were only 2 options.
> 
> Battery charging or discharging has 4 different electrical paths:
> 
> ...



This is a problem typical to solar or wind charging where current fluctuates based on available recurses light or wind.
You will still call that part of the charge before battery gets close to fully charged say LiFePO4 still under 3.5V (if that is your cut off parameter) constant current charge.
In most other applications current will be constant but it makes no difference for the battery.
Can you came up with a different definition to constant current charging when you use Solar PV for example.
I can call that current limited charging and then second part constant voltage that will make more sens but is not normally used.
Anyway for Lithium where long life is desired more than energy density just one charging method constant current or if you want current limit charging should be applied so that battery spends as little as possible above the normal settling voltage.
If you care more about energy density then you apply the second part constant voltage.
In case of LiFePO4 the gain with constant voltage is usually to small to have any significant gain in stored energy to worth the trouble and battery degradation.
With LiCoO2 gain is a bit more significant and constant voltage is used in most if not all portable electronics where battery life is not an issue do to produce obsolescence.


----------



## Sunking (Aug 10, 2009)

IamIam he does not know the difference between a Current Source and a Voltage Source or any clue how either works in conjunction with a battery Internal Resistance. 

What is amazing to me is the principles of Batteries, Current Sources, and Voltage Sources is very simple basic DC 101 fundamentals any beginner electrical students learns and masters in the first semester. Now he comes here where a significant percentage of the members are educated and actually make a living doing this kind of work and expects us to except he is an Electrical Engineer and battery expert when in reality he has no understanding of basic principles.

I really kind of feel sorry for the guy and he professional needs help. He is either delusional or a pathological liar.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> where current fluctuates based on available recurses light or wind. You will still call that part of the charge before battery gets close to fully charged say LiFePO4 still under 3.5V (if that is your cut off parameter) constant current charge.


Red = Not if you want to use the word 'constant' correctly ... and not if you want to use the terminology CC correctly.

It doesn't matter why the current isn't constant ... PV , Wind , Hydro, etc etc ... if it isn't constant current ... it isn't constant current.



electrodacus said:


> I can call that current limited charging and then second part constant voltage that will make more sens but is not normally used.


Current limited charging would be the correct wording .. as the definition for the words in the English language .. as they are used by scientists ... as they are used by engineers ... as they are used by battery OEMs ... etc.



electrodacus said:


> Anyway for Lithium where long life is desired more than energy density just one charging method constant current or if you want current limit charging should be applied so that battery spends as little as possible above the normal settling voltage.


Progress 

Current limit charging (when it isn't CC) .. is at least using the correct terminology ... but the conclusion itself is still incorrect Red goes too far forces it to be incorrect .. as I described previously when you made this same claim.

Using the same method I described before ... I can put just as many Ah or Wh of charge into the same battery .. and I can do it at a lower peak terminal voltage ... I can put less stress on the battery ... etc.



electrodacus said:


> If you care more about energy density then you apply the second part constant voltage.


Or ... if you care even more about long life .. you can use the CV method I described previously ... The beauty of LiFePO4 .. is that I don't have to be ANY voltage (for all practical purposes) above the final rested and settled voltage... not even for 1 second... thus less damage than the CC method which goes above that rested / settled voltage point for a period of time.



electrodacus said:


> In case of LiFePO4 the gain with constant voltage is usually to small to have any significant gain in stored energy to worth the trouble and battery degradation.


When done incorrectly (as is common for many who use CV at the top of charge) .. yes-ish.

Done correctly .. as I described .. CV prolongs useful life to any chosen SoC usable window .. beyond what CC is capable of.

- - - - - 

@Sunking:
We are making progress ... 'current limited' ... instead of continuing to use CC incorrectly... one tiny tiny step at a time.


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> Red = Not if you want to use the word 'constant' correctly ... and not if you want to use the terminology CC correctly.


Have you ever used a CC / CV lab power supply to charge a battery?

If so you have two indications usually there the power supply is either in CC mode or in CV mode you can not have both at the same time.

Now say you set the voltage at 3.5V and current limit at say 3A. Then take a 20Ah LiFePO4 cell that is fully or almost fully discharged say 10% SOC and connect to that power supply.

What will happen the CC indicator will come on indicating constant current.

Say now you start playing with the Current limit adjusts knob and vary the current from 3A to 1A (the CC indicator will still be ON in all the time you needed to go from 3A down to 1A and after you got there).
At what point here do you go to CV charging ?
Constant Voltage charging will only start when battery voltage gets to 3.5V the CC indicator will go off and the current will not longer be limited and current absorbed by battery will slowly go down.

It is not my fault that people call that first phase CC (constant current) since most of the time with traditional AC to DC chargers current is constant no reason to be other than that since there is almost unlimited energy available from the grid.

So if you want to call that initial charge phase CC as is traditionally done or current limited for battery will make no difference.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> Have you ever used a CC / CV lab power supply to charge a battery?


Almost every day for the last 50 years. Started when I was 8 years old and received my ham operator license. Built more power supplies and solar systems than I can count as a PE, radio operator, RC pilot, and even a couple of EV's under my belt. Have even built solar charge controllers. 





electrodacus said:


> It is not my fault that people call that first phase CC (constant current) since most of the time with traditional AC to DC chargers current is constant no reason to be other than that since there is almost unlimited energy available from the grid.


Hog wash, there is no fundamental or operational difference between a Solar charger or one powered from commercial AC POWER. Any Solar Charge Controller can charge a lithium battery, built several systems for clients. Your controller does nothing special and works like any cheap Chi-Com POS controller on the market you can buy for $20. 

There is no technical difference between a charger made for lead acid batteries or lithium. They both use the exact same algorithms of CC and CV. Does not matter if that charger is a soft source made from unreliable solar power, or a hard source like commercial AC power. The difference is how you terminate the charge, or redirect the charge. 

For lead acid and lithium all that is really being used is a CV power supply with current limiting either fixed or adjustable by the user. Fixed is the most common. If you connect a 10 Amp 3.6 volt power supply to a 100 AH lithium battery with an open circuit voltage of 3 volts and Ri 1 milli-ohm you get 10 amps of current at a voltage of 3.01 volts. As the battery charges will be supplied 10 amps continuously. As the battery voltage gradually increase while being charged at some point it reaches around 3.58 volts, the current will begin to taper. At that point you are now in CV. It happens all by itself.

The operational difference between lead acid and lithium is how battery voltages are monitored. With Lead Acid you measure the pack voltage. Not so with Lithiu. With Lithium you work at the individual cell voltages. Your controller does not do that. It looks at the pack voltage which makes it a Plain Jane Lead Acid battery charger. For your charger to work with lithium wil require a BMS like any other battery charger. Since your charger has no communication port to communicate with a BMS will require one to use a Passive Balance Boards aka Vampire Boards to bleed the cells when they reach 3.5 volts or whatever set point the boards use.

Fortunately several of the higher quality Solar Charge controllers on the market can work with a very simple BMS. Really BMS is the wrong terminology. Just a simple battery cell monitor with simple logic control to send a contact closure to the controller when the first cell reaches to turn it off. Outback, Midnite Solar, and Morningstar all have an auxiliary input (external contact) to turn the controller off and put into sleep mode til the next morning. All you have to do is set the BULK voltage setting higher than the pack voltage to force it into CC mode whenever it is operating.

None of this is news to you electrodacus. You have been told this many times on other forums by myself and others for the last two years and you still do not get it. Acutally I think you do get it. You just will not admit because you are in too deep with a worthless solar charge controller and cannot afford to admit you are dead wrong.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> Have you ever used a CC / CV lab power supply to charge a battery?


Yes ... and CP supplies ... and programmable supplies that have been programmed with an algorithm that is not CV , CC, or CP.



electrodacus said:


> If so you have two indications usually there the power supply is either in CC mode or in CV mode you can not have both at the same time.


True ... but not relevant.

You also can't have a CP supply running in both CV , or CC at the same time it's in CP mode either. 

And

You can't have a 'non-constant' supply running in CC, or CV, or CP at the same time it is in 'non-constant' mode.



electrodacus said:


> Say now you start playing with the Current limit adjusts knob and vary the current from 3A to 1A (the CC indicator will still be ON in all the time you needed to go from 3A down to 1A and after you got there).
> At what point here do you go to CV charging ?


You are repeating the same error I corrected previously... I'll repeat myself again.

It is NOT a two option either / or thing .. there are FOUR electrical charging options / paths ... 

CC = The Current is Constant
CV = The Voltage is Constant
CP = The Power is Constant
Non-Constant = None of the above .. no constant electrical parameter.


At no time was what you described CV .. For the short period of time when you were not moving the Current limit knob setting .. the power supply was in CC mode .. over a wide period of time that includes your changes to the current limit knob setting .. you would be in Option #4 .. Non-Constant charging.



electrodacus said:


> Constant Voltage charging will only start when battery voltage gets to 3.5V the CC indicator will go off and the current will not longer be limited and current absorbed by battery will slowly go down.


Correct.



electrodacus said:


> It is not my fault that people call that first phase CC (constant current)


It is 100% your fault how you use it .. especially when you are notified of your error numerous times... and you resist using it correctly... and even still continue to resist using it correctly... all of that is your fault... Do yourself a favor .. and stop trying to use the terminology incorrectly.

As I said before .. AFAIK you and only you .. are the only one incorrectly using it ... ALL the scientific , engineering , and battery OEM publications I've read disagree with you and use CC as I described.



electrodacus said:


> So if you want to call that initial charge phase CC as is traditionally done or current limited for battery will make no difference.


Incorrect.
It is not traditionally done that way .. AFAIK .. by anyone but you.
It does make a difference.
Do yourself a favor .. and stop trying to use the terminology incorrectly.


----------



## onegreenev (May 18, 2012)

electrodacous,



> Say now you start playing with the Current limit adjusts knob and vary the current from 3A to 1A (the CC indicator will still be ON in all the time you needed to go from 3A down to 1A and after you got there).
> At what point here do you go to CV charging ?


All you have done here is change the CC current setting from 3A to 1A and changed the time it will take the cell to reach its preset 3.5 volts. Nothing more. Until the cell reaches 3.5 volts it will remain in CC mode. 

I have a PowerLab 8 that does both CC/CV and if I change the CC amperage it will still be in CC mode until it reaches 3.5 volts. 

I can however kick it out of CV mode if while in CC mode at lets say 10 amps and I reach my target voltage and the device goes into CV mode and begins to taper the voltage. I could at that time change the amperage to like 3 amps and the cell will drop in voltage because of the lower amperage and will then be back in CC mode until the cell once again rises in voltage to the target voltage then the CV mode kicks in once again until the preset termination amperage is met. 

You see, I do know how it all works. Ive played with my setup to know exactly what it does. 

Set your system to charge at 40 amps and you will reach your target voltage sooner than if you had it at 3 amps. That is all. 

You are talking to folks that DO KNOW what they are talking about. I force a cell to target voltage in less than a minute at 70 amps. At that point it will go into CV mode if your setup is done correct. 

I can do that with a bulk charger and a JLD404 meter and a contactor. Be sure to have your diode in place because you will be arcing the contactor at 70 amps and it can kill the contactor if your not careful.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> electrodacous,
> 
> All you have done here is change the CC current setting from 3A to 1A and changed the time it will take the cell to reach its preset 3.5 volts. Nothing more. Until the cell reaches 3.5 volts it will remain in CC mode.


Yes you are correct power supply stays in CC mode all this time that was my point.
so charging all this time was CC even if you payed with the current limit.



onegreenev said:


> electrodacous,
> I have a PowerLab 8 that does both CC/CV and if I change the CC amperage it will still be in CC mode until it reaches 3.5 volts.


Here is where people are usually wrong a power supply can only be in CC or CV mode not in both at the same time. 



onegreenev said:


> electrodacous,
> I can however kick it out of CV mode if while in CC mode at lets say 10 amps and I reach my target voltage and the device goes into CV mode and begins to taper the voltage. I could at that time change the amperage to like 3 amps and the cell will drop in voltage because of the lower amperage and will then be back in CC mode until the cell once again rises in voltage to the target voltage then the CV mode kicks in once again until the preset termination amperage is met.


As above mentioned and as for your correct example the power supply will be either in CC mode or in CV mode.



onegreenev said:


> electrodacous,
> You see, I do know how it all works. Ive played with my setup to know exactly what it does.


Yes you know what the setup does. 



onegreenev said:


> electrodacous,
> Set your system to charge at 40 amps and you will reach your target voltage sooner than if you had it at 3 amps. That is all.
> 
> You are talking to folks that DO KNOW what they are talking about. I force a cell to target voltage in less than a minute at 70 amps. At that point it will go into CV mode if your setup is done correct.


Yes because energy is power and time.




onegreenev said:


> electrodacous,
> I can do that with a bulk charger and a JLD404 meter and a contactor. Be sure to have your diode in place because you will be arcing the contactor at 70 amps and it can kill the contactor if your not careful.


?


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> Yes ... and CP supplies ... and programmable supplies that have been programmed with an algorithm that is not CV , CC, or CP.


Any power supply will allow a voltage and a current limit setting. All others like constant power is done by playing with this two. 




IamIan said:


> True ... but not relevant.


I will say is extremely relevant most do not seems to understand this point.



IamIan said:


> You also can't have a CP supply running in both CV , or CC at the same time it's in CP mode either.
> And
> You can't have a 'non-constant' supply running in CC, or CV, or CP at the same time it is in 'non-constant' mode.


Is hard to understand what you want to say here but a CP power supply will be in one of the two modes at any time CC or CV depending on the Load attached.




IamIan said:


> You are repeating the same error I corrected previously... I'll repeat myself again.
> 
> It is NOT a two option either / or thing .. there are FOUR electrical charging options / paths ...
> 
> ...


There are only one of the two possible at any one time CV or CC.



IamIan said:


> Correct.
> It is 100% your fault how you use it .. especially when you are notified of your error numerous times... and you resist using it correctly... and even still continue to resist using it correctly... all of that is your fault... Do yourself a favor .. and stop trying to use the terminology incorrectly.
> As I said before .. AFAIK you and only you .. are the only one incorrectly using it ... ALL the scientific , engineering , and battery OEM publications I've read disagree with you and use CC as I described.
> Incorrect.
> ...


Is all that we debating here about calling the bulk part of the charge constant current or current limited ?
Both therms can be correct when you use an AC charger that has a fixed value current limit and second is more correct when charging with PV or similar source where current is limited but the value depends on external factors can can have different values over time. 

This thread is about cell balancing so I think we are a bit off topic.

What is your opinion about cell balancing? do you prefer top or bottom ? will you use a BMS or do manual balancing at some interval of time ? What is the advantage of the one you prefer over the other?


----------



## onegreenev (May 18, 2012)

electrodacus said:


> ?


I have a bulk charger. When I connect a cell or pack it will automatically know the voltage and you can read that on the gauge. All Analog. I can change the current with a combination of two switches. One is a course setting and the other is a fine setting. I can go up to 20 amps and a maximum of 150 volts. Even when the battery has filled to max the charger will continue to pump in power at the amperage set. It does not change. It is constant to what I tell it. I can blow a lithium battery pretty easy with this charger. So this is what I call my bulk charger. No real control except amperage. 

I can use this charger with a JLD404 device. It is a volt meter and amp meter and amp counter all in one. It has two relays to trigger contactors or lights or what ever you want at specified levels. It can be used to stop a charge or it can be set to stop a charge at a specific voltage then when the cell voltage drops because the charge is no longer on and drops to a set voltage the contactor is turned on again to continue the charge until the voltage comes back to your specified voltage then off again until the voltage drops to your set voltage the on again until the voltage reaches the set voltage. It will cycle like this until the battery can no longer drop in voltage to your set low voltage. Let that go and eventually it will never cycle and you will have a full battery. It is a sudo way to do CV if you have nothing more than a bulk charger and a JLD404 and contactor. Because the contactor is being shut off under load it will spike the voltage so you really need to prevent that with a diode so the spikes don't kill the contacts on the contactor. 

It works fine. Ive used it for my Leaf Modules and it works great. 

JLD404 : 










http://www.lightobject.com/Programm...ed-led-Ideal-for-battery-monitoring-P870.aspx


http://www.lightobject.info/download/file.php?id=926


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> Any power supply will allow a voltage and a current limit setting. All others like constant power is done by playing with this two.


Incorrect.

Say I build a power supply that is always in CP mode .. that power supply doesn't have a CV mode .. nor does it have a CC mode.

Say I a programmable power supplies .. and I program a Non-Constant algorithm .. in that case there is also No-CV .. and No-CC , and No-CP. 



electrodacus said:


> IamIan said:
> 
> 
> > electrodacus said:
> ...


I don't know who the 'most' you refer to are ... but it isn't me , and it isn't the context of this discussion .. thus , not relevant here.



electrodacus said:


> Is hard to understand what you want to say here but a CP power supply will be in one of the two modes at any time CC or CV depending on the Load attached.


 It is not only CC or CV .. this assumption you keep making is incorrect .. this is not a choice between only two options. There are four electrical mode options .. CV, CC, CP , Non-Constant.

Welcome to EE:101 

Power = Volt x Amps

I can vary both Volts and Amps at the exact same time .. and thus not be in either CV or CC modes ... and simultaneously maintain the same watts of power... thus being in CP mode.

100 Watts = 20V * 5A
100 Watts = 5V * 20A
100 Watts = 10V * 10A
100 Watts = 100V * 1A
etc... etc.



electrodacus said:


> There are only one of the two possible at any one time CV or CC.


Incorrect .. no matter how many times you repeat it .. see above.



electrodacus said:


> Is all that we debating here about calling the bulk part of the charge constant current or current limited ?


No .. not 'all'... that was one part.. there have been other errors I've been trying to explain / educate you about as well.



electrodacus said:


> What is your opinion about cell balancing?


It has finite benefit .. and comes with costs ... A good design with weigh the cost benefits of various options for the specific conditions being designed for... sometimes that analysis leads to various cell balancing designs .. other times it doesn't.

I've had designs that sometimes include cell balancing ... and other times have not... over all ... baring some specific contextual reason not to .. I generally prefer some type of cell balancing.



electrodacus said:


> do you prefer top or bottom ?


Depends on the specifics of the conditions being designed to use it for.
Top , bottom , or other .. balancing points have different pros and cons .. there is no ... one is always better than the other in every possible situation.

For example .. in the PHEV pack I'm building .. I'll be going with Middle Balance .. neither top nor bottom... that is due to the specifics of that context... and would not necessarily be a good idea in all other possible contexts.



electrodacus said:


> will you use a BMS or do manual balancing at some interval of time ?


Same as above .. Depends on the specifics of the contexts being used for.

BMSs be they manual or computerized .. are not cost free .. so a good design honestly weighs the pros and cons to find the best for that specific context.

I will be using a limited BMS in my PHEV pack combined with time interval manual maintenance checks .. but it will not be a individual cell level BMS ... the cons outweigh the pros .. for that specific context.



electrodacus said:


> What is the advantage of the one you prefer over the other?


Sorry .. I'm not going to write a couple hundred page book here .. that would be needed to cover every possible advantage .. of every possible method .. for every possible specific context.

In the more narrow context of my current PHEV build (and not other contexts) :


I have a very good chance to reach both high SoC near the top .. and low SoC near the bottom ... both on a nearly daily basis .. both just about equally as likely to happen ... so I am designing to account for both directions reasonably safely.
By avoiding per cell monitors I greatly improve the MTBF of the overall BMS itself.
By avoiding per cell monitors I greatly reduce the total cost of the system itself.
A fully computerized BMS for every cell to do all the things that I would want to do .. with as high of a MTBF that I want .. would cost more than the benefit such a system would offer.
Ockham's Razor KISS devices trump Rube Goldberg devices.. The vast majority of the time.


----------



## Sunking (Aug 10, 2009)

IamIan said:


> Sorry .. I'm not going to write a couple hundred page book here .. that would be needed to cover every possible advantage .. of every possible method .. for every possible specific context.


You will if you keep replying to this moron. That is his mode of operation, and he will not allow you to have the last word. 

All of you have been warned, This guy is delusional. Don't believe it. He is trying to sell you his controller. He has been at for two years I know of on other forums, and will continue to do the same here until the MOD's decide to NUKE HIM. It is the only way to get rid of him.


----------



## onegreenev (May 18, 2012)

I see. I understand. I'll discontinue conversing. Its pretty obvious already. Ignore and he should slip into the ether eventually.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> I have a bulk charger. When I connect a cell or pack it will automatically know the voltage and you can read that on the gauge. All Analog. I can change the current with a combination of two switches. One is a course setting and the other is a fine setting. I can go up to 20 amps and a maximum of 150 volts. Even when the battery has filled to max the charger will continue to pump in power at the amperage set. It does not change. It is constant to what I tell it. I can blow a lithium battery pretty easy with this charger. So this is what I call my bulk charger. No real control except amperage.
> 
> I can use this charger with a JLD404 device. It is a volt meter and amp meter and amp counter all in one. It has two relays to trigger contactors or lights or what ever you want at specified levels. It can be used to stop a charge or it can be set to stop a charge at a specific voltage then when the cell voltage drops because the charge is no longer on and drops to a set voltage the contactor is turned on again to continue the charge until the voltage comes back to your specified voltage then off again until the voltage drops to your set voltage the on again until the voltage reaches the set voltage. It will cycle like this until the battery can no longer drop in voltage to your set low voltage. Let that go and eventually it will never cycle and you will have a full battery. It is a sudo way to do CV if you have nothing more than a bulk charger and a JLD404 and contactor. Because the contactor is being shut off under load it will spike the voltage so you really need to prevent that with a diode so the spikes don't kill the contacts on the contactor.
> 
> ...


That Ammeter looks similar to my re-flow oven temperature controller 
So on your bulk charger have no settings for voltage ? is fixed at 150V and has just current limiting settings.
Power supply will not automatically know the pack voltage but since is current limited it will indicate the voltage of the pack.
It is fine to do this type of charging with manual monitoring if you only need to do that a few times but if you need this everyday it is better and safer to invest in a proper BMS.

You will need a proper DC contactor do not use an AC one especially above 24V a DC contactor will have a proper mechanism to extinguish the arc. Same is valid for circuit breakers.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> I see. I understand. I'll discontinue conversing. Its pretty obvious already. Ignore and he should slip into the ether eventually.


I did not try to sell you or anyone anything. I can not even do that since you need a totally different BMS for EV not Solar. 
Not to mention I have no BMS for sale is a Kickstarter project so no product exist without the contribution of those that needed and want to support the development of this product. Kickstarter is not a website for product sales as stated clearly on their website.
The Solar BMS that I designed and build was because nothing like this existed and I needed for my OffGrid House.
That King of the Sun is a big fan of Lead Acid and we are really good friends  from some time ago when I challenged the cost of Lead Acid vs LiFePO4 in solar energy storage.

Anyway topic is about LiFePO4 Top vs Bottom you can not do any of that without a BMS or manually charging or discharging each individual cell.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> Anyway topic is about LiFePO4 Top vs Bottom you can not do any of that without a BMS or manually charging or discharging each individual cell.


BS Bottom Balance requires no BMS. Just a one time Bottom Balance and your done. You can use any kind of charger with Bottom Balance, even off the self solar charge controllers. 

You can also do Top Balance with any of the shelf charge controller plus Balance Boards aka Vampire Boards that are cheaper and much higher quality than your controller. 

Bottom line for whatever reason you are stuck in fantasy land in with make believe theory. What you ran into here on this forum is very much unlike DIY Solar Forums full of clueless people and will believe any BS. Here a significant portion of the membership are well educated in things electrical especially LFP batteries and you are not baffling anyone with your BS. You dang sure lost any chance to dazzle anyone with your brilliance. 

Your done here.


----------



## onegreenev (May 18, 2012)

Hey king. Follow your own words. Just ignore. This is not the site for solar on or off grid stuff anyway. Its about EV. We know what it takes for the bottom balance and he does not. I chose to ignore since he chooses to not listen to those that do know.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> . I chose to ignore since he chooses to not listen to those that do know.


 Everyone has the right to an opinion. Do you have a credible document that says bottom balance is useful?
I can admit if I'm wrong about something it dose not seems to me to be the case this time.
Any of the new EV cars do bottom balancing or are not using a BMS?
I'm not referring to DIY cars made as a hobby by a few people.


----------



## onegreenev (May 18, 2012)

Crap, bottom balance does not require a BMS but no one is saying not to monitor your cells. No, the OEMS do neither top or bottom balancing. They don't need to so they only monitor and have safe guards in place to prevent over charge and over discharge. I have a similar system on my DIY vehicle. My monitoring system consists of a charger and controller. Both do what they are designed to do. I also have volt meter and AH meter to keep track of things. 

If you know how lithium cells operate you will know you don't need an active balance system. 

It is not just an opinion It is a proven way to do your setup. It will work with solar or electric cars. 

Enough of this crap. Go learn something.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> No, the OEMS do neither top or bottom balancing.


Pleas provide a document in support to your claim.

I will not like other people reading your comment and taking that as the truth that is how religion works not science.


----------



## onegreenev (May 18, 2012)

I can do better. I'll give you a graph of the leaf modules at full charge. If balanced they would all be the same. No OEM has freely given any documentation but it is easy enough to get the information from the car to show.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> I can do better. I'll give you a graph of the leaf modules at full charge. If balanced they would all be the same. No OEM has freely given any documentation but it is easy enough to get the information from the car to show.


Balance do not mean all cells will be the same.
There will be a 20 to 30mV difference or less depending on the cell voltage monitoring accuracy and how they set the cell balance.


----------



## onegreenev (May 18, 2012)

If balanced they would be the same voltage. If they are not the same they are not balanced. I did not say they wont be close. In fact they are close. Its close because the modules are close when they come out of the factory. Like most all cells you buy.


Here is my Leaf Pack after this Leaf had over 36,000 miles. If the BMS balanced the cells then they would be closer in balance than what this shows. But they are close. Bottom balancing ONCE will ensure that your DIY pack is balanced when they need to be balanced. They don't need to be balanced on the top because the current during charging is so low it won't be an issue. During fast charging the Leaf limits the charge to 80%. That is 80% of what they allow for the top voltage limits. Capacity is not balance. Voltage is balanced. All cells have different capacities and you will always be limited to your lowest capacity cell no matter if you bottom, top or not balance at all. There is a KNEE of charge or discharge that you need to stay away from and the OEMS do just that. 



This is a graph of a fully charged pack with a 24% loss in capacity. But the car is fully charged. This program reveals the true values and not what Nissan allows you the driver to see. 

The SOC is less than 100%. I will give you another graph as soon as I connect my NEW LEAF to my Leaf Spy program designed for digging out the truth.


----------



## onegreenev (May 18, 2012)

A link to the source of that diagram would be in order.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> If balanced they would be the same voltage. If they are not the same they are not balanced. I did not say they wont be close. In fact they are close. Its close because the modules are close when they come out of the factory. Like most all cells you buy.
> 
> 
> Here is my Leaf Pack after this Leaf had over 36,000 miles. If the BMS balanced the cells then they would be closer in balance than what this shows. But they are close. Bottom balancing ONCE will ensure that your DIY pack is balanced when they need to be balanced. They don't need to be balanced on the top because the current during charging is so low it won't be an issue. During fast charging the Leaf limits the charge to 80%. That is 80% of what they allow for the top voltage limits. Capacity is not balance. Voltage is balanced. All cells have different capacities and you will always be limited to your lowest capacity cell no matter if you bottom, top or not balance at all. There is a KNEE of charge or discharge that you need to stay away from and the OEMS do just that.
> ...



Those look like ultra balanced cells at just 23mV delta. In my BMS I usually set a 15 to 20mV min delta so it means that if cells have a delta equal or smaller than this 20mV I set as minimum then no cell balancing will be performed.
And I have mV resolution reading not 10mV like it seems to be the case on the Leaf so that 23mV is excellent and you will not have that after 36k miles.

Are you saying that capacity loss is 24% compared to the new pack? It seems a bit high but heard something about bad thermal management on Leaf and premature degradation in hot climate.
Are you living in a hot climate ?
Also not sure what they do about charging in below freezing do they have some heat pads for the cells?

That schematic is form the leaf forum let me find the link again.
Here it is hope it works http://www.mynissanleaf.com/viewtopic.php?f=8&t=17470
It seems like some sort of active cell balancing with those inductors and zener diodes is like moving energy from one cell that is higher to the neighbouring cell.
They went to quite a bit of trouble for the cell balancing but at the volume they sell this and price is not a problem.


----------



## PStechPaul (May 1, 2012)

I found an article on active cell balancing with a schematic similar to that shown in the Leaf thread:

http://cache.freescale.com/files/32bit/doc/app_note/AN4428.pdf

I would think there would not be enough difference in energy or good enough efficiency to make this worthwhile. It would probably be better to select all the cells for a pack to be within a few percent of each other.


----------



## electrodacus (Mar 29, 2014)

PStechPaul said:


> I found an article on active cell balancing with a schematic similar to that shown in the Leaf thread:
> 
> http://cache.freescale.com/files/32bit/doc/app_note/AN4428.pdf
> 
> I would think there would not be enough difference in energy or good enough efficiency to make this worthwhile. It would probably be better to select all the cells for a pack to be within a few percent of each other.


Yes it looks quite similar thanks for the document.


----------



## onegreenev (May 18, 2012)

Yes they are rather well balanced but if you really look at the data but that is more due to the quality of manufacture than the use of an active balancing BMS. We can and do get similar results on cells we purchase for our DIY projects and so many just whine and bitch about how far out your top would be if you bottom balanced. With bottom balancing you do get a little more ragged on the top but not enough to worry about. If you have worry then your cells are poorly matched from the beginning.

The issue with the heat was the chemicals used in the Leaf Modules. They were unable to handle the heat and the electrolyte broke down prematurely and degraded the modules. Excess heat from outside and from within. One of the issues was a person would go out and drive and that would heat up the cells. Then they would come home and just plug in and charge away. If it was scorching hot out it would exasperate the issue. They figured it out and changed the chemicals in the electrolyte so the battery would not degrade in the heat that the cells would be subject to in daily use. My new Leaf has the new chemistry. We shall see. I'll give it three years of daily driving. There is no method to only charge to 80% any longer either in the Leaf except when you charge with the fast charger. That will limit so you don't over charge the battery.


----------



## onegreenev (May 18, 2012)

Thanks for the link to the Nissan Site. That guy that posted these is the very guy that build the Leaf Spy program. So it does look like there is an active balancing. I have two removed leaf packs at home and I did checks on the modules and found them to all be very much in sync and all the cells within the module have been in perfect balance. Each module is made of two cells in parallel and two sets in series for 4 cells in each module. The balance between them has been dead on regardless of when I charge them full then drain the and check again. The cells are so well matched from manufacturer I can't see any reason for any need to have an active balance setup. 

Pete


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> Yes they are rather well balanced but if you really look at the data but that is more due to the quality of manufacture than the use of an active balancing BMS. We can and do get similar results on cells we purchase for our DIY projects and so many just whine and bitch about how far out your top would be if you bottom balanced. With bottom balancing you do get a little more ragged on the top but not enough to worry about. If you have worry then your cells are poorly matched from the beginning.


Is not a problem if you have a way to monitor each cell and stop charging when the highest cell gets to your preferred limit.
In solar offgrid I think I mentioned without cell balancing after 3 to 4 months the imbalance was less than 1Ah with 100Ah cells so 1% loss in capacity do to imbalance over 3 months but that is a relatively low charge discharge rate under 0.5C for discharge. With higher discharge rate the imbalance can be quite a bit more than that depending on cells quality and discharge rate.





onegreenev said:


> The issue with the heat was the chemicals used in the Leaf Modules. They were unable to handle the heat and the electrolyte broke down prematurely and degraded the modules. Excess heat from outside and from within. One of the issues was a person would go out and drive and that would heat up the cells. Then they would come home and just plug in and charge away. If it was scorching hot out it would exasperate the issue. They figured it out and changed the chemicals in the electrolyte so the battery would not degrade in the heat that the cells would be subject to in daily use. My new Leaf has the new chemistry. We shall see. I'll give it three years of daily driving. There is no method to only charge to 80% any longer either in the Leaf except when you charge with the fast charger. That will limit so you don't over charge the battery.


Extreme heat and cold are always a problem with batteries of any type.


----------



## electrodacus (Mar 29, 2014)

onegreenev said:


> Thanks for the link to the Nissan Site. That guy that posted these is the very guy that build the Leaf Spy program. So it does look like there is an active balancing. I have two removed leaf packs at home and I did checks on the modules and found them to all be very much in sync and all the cells within the module have been in perfect balance. Each module is made of two cells in parallel and two sets in series for 4 cells in each module. The balance between them has been dead on regardless of when I charge them full then drain the and check again. The cells are so well matched from manufacturer I can't see any reason for any need to have an active balance setup.
> 
> Pete


It seems to know what it was doing that is why I posted that reverse engineering schematic.
The probably use a really small current to do cell balancing it may even be done after the charging has ended maybe just 50mA or 100mA that will be more than enough to keep them in balance.
I seen the Leaf modules on eBay some time ago I was tempted to get a few to play with. I still prefer LiFePO4 much safer to have inside the house.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> Do you have a credible document that says bottom balance is useful?


Do you have one that shows it is not useful ?

credible as in .. peer reviewed scientific or engineering publication.



electrodacus said:


> I can admit if I'm wrong about something


Haven't seen that once yet .. despite you being wrong numerous times... So far .. I've only seen demonstration of the opposite .. you not being able to admit you were wrong.


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> Do you have one that shows it is not useful ?
> 
> credible as in .. peer reviewed scientific or engineering publication.


Not sure anyone has bothered to write a paper on something that is usually not useful. Maybe there is a special case where bottom balancing makes sense but I'm not aware of such thing at the moment.
There are plenty of monitoring and balancing IC from large manufacturers I have not seen one that will do bottom balancing.
You may argue that bottom balancing is an one time deal that you perform manually but no matter how good the cells are those small differences between the cells will increase the SOC delta between cells with each charge discharge cycle especially with the high discharge rate unusually needed in EV applications.





IamIan said:


> Haven't seen that once yet .. despite you being wrong numerous times... So far .. I've only seen demonstration of the opposite .. you not being able to admit you were wrong.


Well it was my opinion that I was not wrong on the things you probably consider I was wrong about.
I was wrong numerous times as anyone else and this is how you learn.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> Not sure anyone has bothered to write a paper on something that is usually not useful.


You don't read many science papers do you ?

Well .. I prefer science myself ... you see in science .. you're claim of 'not useful' ... needs proof to support it.

If you don't like reading it from me .. how about reading it from yourself?



electrodacus said:


> Pleas provide a document in support to your claim.
> 
> I will not like other people reading your comment and taking that as the truth that is how religion works not science.


- - - - - - - - - - 



electrodacus said:


> Well it was my opinion that I was not wrong on the things you probably consider I was wrong about.


Exactly .. another demonstration of you not being willing to admit when you were wrong ... even after it was pointed out to you and explained to you.

Here's some reminders of you being wrong ... in no particular order .. but by all means .. give another demonstration of you NOT being willing to admit it , when you were wrong.



electrodacus said:


> a CP power supply will be in one of the two modes at any time CC or CV


Wrong and it was explained to you.



electrodacus said:


> There are only one of the two possible at any one time CV or CC.


Wrong and it was explained to you.



electrodacus said:


> As for CC it dose not necessary mean that current is constant


Wrong and it was explained to you several times , as you repeatedly resisted the correct use of the word 'constant'.



electrodacus said:


> you can not use your battery during that time


Wrong and it was explained to you.


----------



## electrodacus (Mar 29, 2014)

IamIan said:


> You don't read many science papers do you ?


I stand to all my statements I was not wrong on any of them.

You need to understand that CV and CC is not possible at the same time you only have one or the other. Do you agree with this or not?. If not then that is why we have a conflict in our understanding of each other.

As for a CP limit on a power supply did you ever used one? If so what was your setting and what you connected to output. If you have looked at all the indicators you will have seen that the power supply was in CV or CC mode never both at the same time and that all the CP does is try to maintain a limit on the power used by either have the power supply in CV or CC mode.
If power required by the load is smaller the power supply will be in CV mode if it is higher it will be in CC mode.

If you think that is not true it should be easy for you to demonstrate with a simple example.

I can give you one to start with and correct me if I'm wrong here.
You have a 30V 5A (150W) CC/CV lab power supply with CP functionality.
Say you set the power limit at 50W and leave the CC and CV settings at max 30V and 5A 
Now you connect a 30 ohm resistor on the output of this power supply. What you will get is that power supply will be in CV mode as it was since it was powered ON with no load so 30V and current will not be limited since is 1A and power limit is set at 50W that is higher than 30W (30Vx1A)
Now say I add another 30 ohm resistor in parallel with the one already there so 15ohm equivalent resistor is now on the output of this power supply.
What will happen now? The power is limited at 50W so this 15ohm resistor can not get more. How will the power supply limit the power ?
It will limit the current to what is needed to keep the power at 50W so 50W/30V = 1.6666A so it will enter in CC mode.
So as I mentioned the power supply can only be in CC or CV mode.

Connecting a battery to this power supply will be no different. Say you want to connect a 3.2V (1mohm DC internal resistance) LiFePO4 to the output of the same power supply with the exact same settings as before.
What will happen is that current will go to the 5A limit and the voltage will drop to the battery terminal voltage say 3.2V + the voltage drop on the internal 1mohm so around 3.205V but the battery will absorb this energy and slowly increase the voltage at the terminals and the power supply is in CC mode and will remain in CC mode even if you play with the Constant limit knob as a good DJ will do with vinyl disk. 

Pleas let me know where I'm wrong or give an example that sow a power supply can be in a different mode that either CC or CV at any point.


----------



## samwichse (Jan 28, 2012)

http://www.politicsforum.org/images/flame_warriors/flame_20.php


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> I can give you one to start with and correct me if I'm wrong here.
> You have a 30V 5A (150W) CC/CV lab power supply with CP functionality.
> Say you set the power limit at 50W and leave the CC and CV settings at max 30V and 5A


You hung yourself with your own rope. Good Job. 

An Ideal Constant Power Source is a a device that supplies power that NEVER varies? No matter the nature of what it is connected to, its voltage and amperage would be adjusted automatically to provide constant power. 

Just like a Current Source there is no IDEAL Constant Current Source. A current source can only supply Constant Current into a resistance of 0 Ohms up to I x R of the voltage source pushing the current. Example a 10 amp Current Source using a 10 volt battery can only push 10 amps from 0 to 1 Ohm. If the voltage source is 100 volts then 0 to 100 Ohms. 

A Constant Power Source can only operate over a given resistance range which is determined by the voltage of the source. Anything above or below resistance range would be a Constant Current Source below the operation resistance, and a Voltage source above the operational Resistance range. 

So your example is invalid because your source has a voltage Limit of 30 volts, and a range of 5 amps. If limited to 50 watts the range is on the 50 watts / 5^2 amps = *2 Ohms* on the low side, and 30^2 volts / 50 watts = *18 Ohms*. Below 2 Ohm's and it is a 5 amp Constant Current source. Anything above 18 Ohms it is a 30 volt Constant Voltage source.

Here is where you just hung yourself by the family jewels you cannot talk your way out of. A Constant Power Source is a Switch Mode Boost Converter. Care to guess what is a Switch Mode Boost Converter is? 







Wait For It







Any MPPT Charge Controller stupid. Don't bother trying to talk around it. Any beginning electrical student knows the principles and anyone can look it up. I will give you a hint, something you have never heard of:



*OHM's* fricken *LAW*


----------



## electrodacus (Mar 29, 2014)

I want that magic power supply data sheet  All real (not imaginary) power supply have limits for both voltage and current.


----------



## major (Apr 4, 2008)

electrodacus said:


> ...........
> 
> The power is limited at 50W so this 15ohm resistor can not get more. How will the power supply limit the power ?
> It will limit the current to what is needed to keep the power at 50W so 50W/30V = 1.6666A so it will enter in CC mode.
> ...


Obviously wrong with those numbers. 15Ω, 30V, 1.6666A and 50W do NOT satisfy Ohm's Law. Try V = I * R. Doesn't work, does it? Try P = I²R. Nope, doesn't work.


----------



## electrodacus (Mar 29, 2014)

> Obviously wrong with those numbers. 15Ω, 30V, 1.6666A and 50W do NOT satisfy Ohm's Law. Try V = I * R. Doesn't work, does it? Try P = I²R. Nope, doesn't work.


It is a power limit set on that power supply that is why it looks to you as it dose not make sense.
Power supply current limit is set at 5A and a power limit set at 50W.
50W / 30V = 1.6666A that is what will power supply limit the current to so that the power will not go over the 50W limit.


----------



## major (Apr 4, 2008)

electrodacus said:


> It is a power limit set on that power supply that is why it looks to you as it dose not make sense.
> Power supply current limit is set at 5A and a power limit set at 50W.
> 50W / 30V = 1.6666A that is what will power supply limit the current to so that the power will not go over the 50W limit.


So you insist that the 15Ω resistor will draw 1.6666A with 30V across it. Even though that clearly violates Ohm's Law.


----------



## Sunking (Aug 10, 2009)

major said:


> So you insist that the 15Ω resistor will draw 1.6666A with 30V across it. Even though that clearly violates Ohm's Law.


He does not even know what Ohm's Law is?


----------



## electrodacus (Mar 29, 2014)

major said:


> So you insist that the 15Ω resistor will draw 1.6666A with 30V across it. Even though that clearly violates Ohm's Law.



I think you did not noticed we are talking about a power limited power supply.
It is limited at 50W.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> It is a power limit set on that power supply that is why it looks to you as it dose not make sense.
> Power supply current limit is set at 5A and a power limit set at 50W.
> 50W / 30V = 1.6666A that is what will power supply limit the current to so that the power will not go over the 50W limit.


The *Voltage and Current * of the source are the limits not the Power. Power is the product of Voltage and Current. Any first year electrical student knows that day 1.


----------



## electrodacus (Mar 29, 2014)

I think you guys are just trolls 
Just wasting my time.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> IJust wasting my time.


You finally you said something TRUE that everyone agrees with and backed up by scientific facts.

FWIW 30 volts across 15 Oms is 2 amps @ 60 watts. YOU are so BUSTED


----------



## major (Apr 4, 2008)

electrodacus said:


> I think you did not noticed we are talking about a power limited power supply.
> It is limited at 50W.


So I understand that you imply that for that reason, Ohm's Law can be violated. You are wrong again. Or still. Ohm's Law always applies. Your numbers are wrong. You asked for someone to point out what was wrong with your post, I did that.



electrodacus said:


> .... Pleas let me know where I'm wrong .....


----------



## electrodacus (Mar 29, 2014)

major said:


> So I understand that you imply that for that reason, Ohm's Law can be violated. You are wrong again. Or still. Ohm's Law always applies. Your numbers are wrong. You asked for someone to point out what was wrong with your post, I did that.


Hey you are right. Thanks for getting back to me with this. With 15 ohm voltage will also need to drop on the 15ohm resistor in order to maintain the 50W limit.
The correct answer is square root of 50W/15ohm so 1.828A then voltage will been at 27.35V in this example still in constant current mode.
But I must apologise for the earlier troll comment.


----------



## PStechPaul (May 1, 2012)

This has become an immature sniping session over semantics, definitions, and perhaps a few errors. The 15 ohms and 50 watts dictates the current must be 1.826 amps, at which point the voltage will be 27.4 volts. Thus the power limit trumps the voltage and current limits. The design of the power supply may dictate whether it regulates the voltage or the current.

An MPPT system is generally used to extract the maximum power from a source such as a solar array where there is a "sweet spot" for the load where the power is higher than at higher current or voltage. In this case the load is usually a switching power supply that changes its effective input impedance according to the load, and if the load is a battery bank, it will adjust the charging current until maximum power is obtained. Of course there are also limits to the output current and voltage depending on SOC.

Hopefully my explanation will help others who may be reading, to understand the principles involved. None of this discussion has anything to do with the top/bottom balance debate, and that is a matter for design preferences which may be different for stationary solar installations versus EVs.


----------



## Sunking (Aug 10, 2009)

electrodacus said:


> The correct answer is square root of 50W/15ohm so 1.828A then voltage will been at 27.35V in this example still in c*onstant current mode*.


Wrong again. In constant power voltage and current ere not fixed they are variables. Under you example of a 30 volt 5 amp power supply with a 50 watt limit:

Voltage range is 10 volts to 30 volts
Current range is from 1.67 amps to 5 amps
Resistance of the load range is 2 to 18 Ohm's


----------



## electrodacus (Mar 29, 2014)

PStechPaul said:


> This has become an immature sniping session over semantics, definitions, and perhaps a few errors. The 15 ohms and 50 watts dictates the current must be 1.826 amps, at which point the voltage will be 27.4 volts. Thus the power limit trumps the voltage and current limits. The design of the power supply may dictate whether it regulates the voltage or the current.


in this case it is in current limit mode in order to maintain constant power in the earlier example with 30ohm it was in constant voltage mode since it was under the power limit.
So conclusion will be constant power will do either constant voltage or current limitation in order to maintain a power limit so there is nothing else other than CC or CV on a power supply. 




PStechPaul said:


> Hopefully my explanation will help others who may be reading, to understand the principles involved. None of this discussion has anything to do with the top/bottom balance debate, and that is a matter for design preferences which may be different for stationary solar installations versus EVs.


Thanks for pointing that we are deviating from the subject of the thread.


----------



## Sunking (Aug 10, 2009)

PStechPaul said:


> This has become an immature sniping session over semantics, definitions, and perhaps a few errors.


Paul the issue is Electrcuda claims to be an engineer and an expert. He clearly has no idea of very basic fundamentals like Ohm's Law. Engineers do not make those kind if errors of semantics and definitions. Only Frauds make those mistakes, and then tells us we are wrong. I warned the Mods as soon as this guy showed up this would happen and will continue until he is NUKED. It is the only way to make him quit. He is here only to get free PR and advertisement to his business. He has a Link embedded in his Signature. It is not that hard to figure out what he is up too. He does this on ALL FORUMS HE JOINS. He came here because he has been banned on all Solar Forums.

So Paul only thing one can conclude is the site administrations approve by allowing it to continue. Electrocudas will not allow anyone to have the last word, including yourself.


----------



## pdove (Jan 9, 2012)

http://www.google.com/patents/US20090096419?dq=20090096419&ei=7DMUTrOcNKaNmQWknti2BQ

The present disclosure relates to battery charging, and more particularly to bottom based balancing in lithium ion batteries.


----------



## IamIan (Mar 29, 2009)

electrodacus said:


> I stand to all my statements I was not wrong on any of them.


 


electrodacus said:


> You need to understand that CV and CC is not possible at the same time you only have one or the other. Do you agree with this or not?


Already answered previously .. repeating .. yes... in the context of charging a battery ... there are other contexts I can think of that actually could be both CV and CC at the same time.


electrodacus said:


> As for a CP limit on a power supply did you ever used one? If so what was your setting and what you connected to output.


Already answered previously .. repeating ... yes.

I've used several different kinds.

A simple example would be 100W charging or a LiFePO4 battery .. It did NOT have CV or CC the entire charge ... the entire charge the voltage was increasing and the current was decreasing.

100W @ 2.9v = ~34.5A Start
100W @ 3.6v = ~27.7A End

Or how about taking a look at this charging output. For a sinusoidal Charging algorithm ... It's not CV ... It's not CC ... It's not even CP.

Link


electrodacus said:


> If you have looked at all the indicators you will have seen that the power supply was in CV or CC mode


 Incorrect .. it was not in CV the entire time .. it was not in CC the entire time .. It was in CP mode ... for the simple 100W CP example above.

The sinusoidal charge was not in CV .. it was not in CC ... it was not in CP either.


electrodacus said:


> If you think that is not true it should be easy for you to demonstrate with a simple example.


I gave you two above.. yes .. it is easy to demonstrate... this is very easy EE 101 stuff.


electrodacus said:


> Pleas let me know where I'm wrong or give an example that sow a power supply can be in a different mode that either CC or CV at any point.


Other have already pointed out errors in your example ... So I won't bother ... and examples you asked for are listed above.


----------

