# Charger Algorithm



## Guest (Dec 21, 2010)

What would be the proper charger algorithm for Hi-Power LiFePO 100 AH batteries? They said I need to let them know what the BMS requirements will be. I am not using one. I want the charger but am afraid to say I am not using one for fear of them not selling me the charger due to no BMS. 

Pete 

120 volts 
two strings of 38 100AH Hi-Power Batteries.


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## frodus (Apr 12, 2008)

are you monitoring the batteries at least? Not manually, but with a monitor of some sort that can control LVC and HVC?


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## Guest (Dec 21, 2010)

Manually monitoring them and have no thermal cut off or HV cutoff or LV cutoff. The controller will be my LV cut back cut off controller. My charger will be my HV shut off and I will get a thermal switch that will shut down the charger if any batteries in the pack overheat. No electronic battery monitor system will be used.


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## frodus (Apr 12, 2008)

bad idea. Hipower doesn't really like high current discharges, and if you're putting this in a car and ONE cell hits LVC, you'll never know because the rest of the pack "apears" fine to the controller.

Not sure why people don't just get a bunch of those cell-log 8's and wire them together. its the cheapest LVC alarm, and it'l save you from making expensive mistakes.

Manually monitoring depends on a process that includes a Human being as a potentially problematic factor. You can't manually check while driving.

The charger being the HVC is a bad idea too, because many batteries charge at different rates in series. You'd need a thermal switch for every battery. Temperature is NOT a measure of SOC.


Good luck, but you'll probably have more problems than you think. Monitoring pack voltage for charge/discharge is dangerous. I'm not saying you need a full balancing BMS (Although I would use one), but you absolutely need LVC and HVC at the very least.


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## Guest (Dec 21, 2010)

and if one BMS goes out for what ever reason I am in the same boat as without one.


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## Guest (Dec 21, 2010)

I do not want to get into a debate over BMS or no BMS as this has been hashed over and over and over and over. I just want to know what the chargers use as an algorithm and what temp a thermal shut off should be. I need a charger and need to have a proper algorithm built for the Hi-Power Batteries. I am fully aware of the Hi-Power batteries and I am not building a race car. It is a street cruiser. It is going in an old VW Bus. So 0 to 60 will be old man speeds. I am in no huge hurry. Looking more for distance than quickness. 

Pete


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## EVfun (Mar 14, 2010)

I'm having a hard time finding a good spec sheet for the newer HiP cells but I did find some data posted at EV Equipment Supply. Scrolling down the page it looks like they charged their cells at about 3.85 volts peak. 

Since you are not using a BMS I would recommend staying a bit below that point. If you do not top balance the pack you will have to determine the voltage where the first one begins flying up and limit to stay below that point. This might also be an application to consider using one of the amp hour counting meters to limit discharge by amp hours (after all, if top balanced you can trash one on discharge if you go slightly to far down.)

I found a link to a data sheet for the 200 amp hour cell here.


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## frodus (Apr 12, 2008)

gottdi said:


> I do not want to get into a debate over BMS or no BMS as this has been hashed over and over and over and over. I just want to know what the chargers use as an algorithm and what temp a thermal shut off should be. I need a charger and need to have a proper algorithm built for the Hi-Power Batteries. I am fully aware of the Hi-Power batteries and I am not building a race car. It is a street cruiser. It is going in an old VW Bus. So 0 to 60 will be old man speeds. I am in no huge hurry. Looking more for distance than quickness.
> 
> Pete


Yes, it has been hashed out over and over.... and people still think they can get away with no monitoring. Go ask a certain someone at EVTV and ask what happened to his pack of thundersky's..... he didn't have anything on them and overcharged them. I'm saying you need to have LVC. and HVC at the very least. I don't care about balancing, which was the actual topic of the discussion if you paid attention. It was almost always agreed that monitoring is bare minimum. 

Electronic components have a failure rate in the millions. All it takes is one over-charge or over-discharge without a monitoring device and your cell is toast. 


anyway, CC/CV until current drops to 0. Not sure why you need to know what algorithm you need.... just tell them you need an algorithm set up for Hi-Power cells.


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## Guest (Dec 21, 2010)

The TS batteries that were overcharged were also test cells and connected to a charger that was a dumb charger and he forgot to check. They were not connected to a smart charger. So far all his batteries have been just fine while connected to the cars and are charging to the set voltages and then terminates. The chargers are dead on. Monitoring is at minimum a good thing but so far I MUST monitor manually and I must be diligent but I will have a charger and closely balanced pack of cells. I will be undercharging and under discharging to keep within the safe limits of the batteries. We will have an amp meter that will count and record amps in and out and a volt gauge to help as well. We will be monitoring the batteries closely at first to determine the limits that we need to control with the charger and controller both of which are smart and accurate. So you see we will be monitoring the system but not at a cell level except to check voltages for a few charge discharge cycles to better see what is happening. I will also be getting a thermal switch to check temp of the pack and if too high will cut off the charger. 

We will be using an Elcon 3000 charger. Should be picking it up in the next day or two from the Elcon Folks Directly in Sacramento. 

Pete 

If I were to leave it to Elcon or any other company they would look at the site and just do what the manufacturer states and that is at the limits. I want below the limits. 

I am also asking to learn about how the algorithm works and what is required and how it's done. Since I am just starting lithium I am in need of some more learning. I am understanding of a whole bunch of stuff but some things still need clarifying. Like the ins and outs of charge algorithms for lithium. Since it has never really been addressed at that kind of level in an educational standpoint I decided to ask. 

So why do you take it down to 0 amps and and not like stop at 2 amps? 
So why charge to the limits of the batteries rather than stop a bit before? 

Hi-Power says 3.8 volts per cell. I want 3.6 to 3.7 volts per cell. Discharge is for the older ones 2 volts per cell so I will keep mine at 2.4 volts per cell or 2.6 volts per cell. 

These are the areas I plan on keeping my batteries. Never over and never under.


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## Overlander23 (Jun 15, 2009)

If you go with an Elcon you really just have to tell them the number of cells, what the capacity of the cells are, what you want the absolute cut-off voltage to be, and what you want the "knee" voltage to be. The algorithm is made up of several charge points based around those four pieces of data... and is handled by Elcon/Zivan.

I'm using an Elcon with TS cells. My PFC-5000 is setup for 3.8v absolute cutoff (on 64 cells, that's 243.2v), and a knee of 3.65v (233.6v). The charger will output full current to the knee, and then switch to a lower current mode that tails off as it gets to 3.8v average per cell. Apparently you have control of that last bit of the charge curve, being able to ramp up or down that "finishing" current. So, for example, you would plug the charger in, it would charge full output to 3.65v average cell voltage, and then switch to the much lower charge rate which (from looking at the algorithm curve) looks like a current limited CV mode. By default I think mine is set to a C/50 rate for this last bit. At least, that's what I've been able to glean from Elcon/Zivan's responses when I purchased the charger, and my interpretation of the charge-profile graphs they supply.

If you want to go more conservative, you could tell them to set the cutoff voltage to something like 3.65v average, and set the knee a bit earlier, like 3.55v or even 3.6v. But it all depends on the charge characteristics of those Hi-Power cells, namely where the knee occurs. 

In the case of the TS cells, they're essentially full after 3.6v, but nothing untold occurs until you hit over 4.0v. I've top balanced to keep the variances down at the top end... and have designed the system with 50-70% average consumption use driving conditions. That should be well safe enough on the LVC side, short of a cell going bad on its own.

No idea about the Hi Power cells... 

The next thing I'll install are voltmeters to monitor the traction pack split symmetrically (split two or four times, not sure yet). This technique might inform me of some imbalances, and be safer (less wiring to be fused) and cheaper than individual monitoring. If I notice something awry, I can then drop a box and manually check stuff out.


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## Guest (Dec 21, 2010)

From what I get you CC to the absolute Charge Voltage limit you want then switch to CV then allow the amperage or current to drop to about 2 amps then cut off the charge. This leaves fudge room if your cells are not absolutely perfect which none are. But you need to have a good set of batteries within specs to have a good balanced pack both top and bottom. You will never see a group of batteries all be 3.85 then discharge to 2.45 and all be exactly the same. Fudge on the safe side and don't charge to the absolute limits. Hi Power cells are charged a bit lower than TS or CALB. They all are saying 3.8 and I am sure they are all correct that it is the safe limit and not the upper most that was originally published for TS cells. HiPower always said 3.8 for the safe top voltage. I say 3.6 to 3.7 for HiPower. 

Pete


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## Overlander23 (Jun 15, 2009)

Elcon/Zivan would obviously know better here, but I'm pretty sure the Elcon chargers do CC to the "knee" voltage (whatever you specify). Then it switches to a current limited CV mode to the absolute voltage limit. It's why I can set the knee (or CC) side to 3.65v but get away with a 3.8v (current-limited CV) finish.


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## Guest (Dec 21, 2010)

I would not say they'd know better about the Type of Battery requirements unless they have done an algorithm that was successful for the cell. They did not mention anything about charge to a knee voltage then to an absolute voltage. CV means constant Voltage not changing voltage. So Charge with Constant Current (CC) to 3.8 and hold until the current reaches 2 amps or less. Then terminate. 

They gave no indication of any algorithm or that they knew about HiPower. They suggested to 3.8 as the others are set to. They asked what my BMS was configured to produce. Well, nothing since I won't be using one.


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## frodus (Apr 12, 2008)

BTW it was not a dumb charger, it was a charger that wasn't set up by the user correctly.



> So why do you take it down to 0 amps and and not like stop at 2 amps?


Because that charges the batteries completely. I was telling you, for a normal pack, if you hold at the recommended peak voltage of the battery and charge until you see no current flowing, you charge them completely. It doesn't overcharge. Overcharge is overvoltage of a single battery, which I think you'll find very difficult to monitor. Just because you're setting a little lower than that peak voltage, doesn't mean that another battery won't come up quickly.

I've seen quite a few lifepo4 batteries being charged, and in a pack, even if matched, some come up a little quicker than others. As the pack ages, this will be more and more pronounced.



> So why charge to the limits of the batteries rather than stop a bit before?


 Because you'd never completely charge the pack. You asked what the algorithm is. I assumed you meant what a normal algorithm is, not an algorithm for someone that wants to charge differently at a lower voltage and with a higher cutoff current. Why didn't you just say "this is what I want to do, is this ok" rather than "what is the charge algorithm for lithium". You left yourself open.

Charge to 2.0A at a lower voltage and then stop. That should be just fine, just keep an eye on voltages of the cells.



> Hi-Power says 3.8 volts per cell. I want 3.6 to 3.7 volts per cell. Discharge is for the older ones 2 volts per cell so I will keep mine at 2.4 volts per cell or 2.6 volts per cell.


Not sure how you're going to monitor that while you're driving. Under accel, those batteries are going to drop their voltage, so just be careful. 

I think you should just get some cell-log 8's. They're cheap, they log, they monitor and they have an output that can control a dash light for LVC and HVC.

I don't care if you balance, thats now what I'm saying, I just don't see you with your multimeter for the 8 hours it takes to charge your batteries, every night, watching the battery voltages. They can come up in a matter of minutes if you're not watching.

Maybe at least bring some "tap" wires out so you can easily check voltages and in the future, easily measure the voltages of the cells. Keep the wire length the same to ensure voltage drop along the wire is the same for each cell. 

Then you can always add the cell logs. They do like 8 cells each and they're like $20 or so. That'd be what, 5 of those? So for around $100, you protect yourself. Sounds like they'd pay for themselves quite quickly and give you the ability to log data, which would tell you how well they're staying in balance.


And not sure if you plan on it or not, but parallel the 100Ah cells first, and then put them in series. You'll have a more reliable and balanced pack.


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## Overlander23 (Jun 15, 2009)

gottdi said:


> I would not say they'd know better about the Type of Battery requirements unless they have done an algorithm that was successful for the cell.


I meant, Elcon/Zivan would know better regarding what *their* algorithm does. I can't be sure, you'd have to ask them, but I don't think they build a custom algorithm for each brand of LiFePO4 cell except to change where certain charge point trigger values sit; the values I mentioned. After all, LiFePO4 really only requires a simple CCCV curve. And I'm just relaying what my Elcon charge algorithm looks like, not what you may think an "ideal" charge curve to be.

They need to know BMS info, if you use one, so that they can do their best to integrate the charger with the requirements of the BMS. For instance, there's no point in setting a low charger cut-off voltage if it means never getting to the BMS' cut-off/shunting stage, provided that's what you want the BMS to do (I'm not necessarily agreeing with this technique, just using it as an example).


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## Guest (Dec 22, 2010)

I did ask about a normal algorithm. Is the normal algorithm just as simple as CC to the charge limit you choose then switch to the CV and hold that voltage until the current drops to 2 amps or 0 amps or what ever you choose? 

If so then it is a pretty simple thing. But one thing I'd need to ask then for my own knowledge is how the heck does a charger hold a voltage or current. What is the mechanism that does this? Are these just standard transformer chargers with computer controls? Or what? I am needing to fill my brain while I wait for my charger. 

As for taking time to check batteries during charging, I have no troubles doing that because it is for my knowledge to do so. I need to know. I trust my work. If I see I need a BMS then one will go in. No one here needs to sell me. No one needs to explain the merits of their decisions. I am basing my stuff on my work and the work of others. Hard core solid proof is what I am after and not words. I only know of one who is doing this level of work and showing the results no matter what you may or may not think. 

So if you'd like and could explain the algorithm more in depth or explain in depth how a charger works or better how a charger controls and holds CC and or CV and how it monitors the system to shut down when asked. These are the types of things that need taught and we do not need to be getting into debates or set up some committee to decide if this is this or that. 

Real education is needed with back up proof. Real proof. Hard core proof. Do it and show it and teach it. 

Pete


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## frodus (Apr 12, 2008)

How about you take the initiative. You're the one asking, not me. Pick up a book on power systems and power conversion.

I got a BSEE in electrical engineering and I don't feel like regurgitating the ins and outs of power conversion. Lots of PWM, current sensing, switching frequencies, transformers, caps, FET's....etc.


It's a switching power supply, google it. They are not the large heavy transformer chargers you're thinking, but they do have a transformer in them.


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## Guest (Dec 28, 2010)

Gladly, Just needed to know the direction to go. I will go do a bunch of reading. Thank you. Never expected you to be the teacher but to help point the direction. Since I do not know I need to ask a few things to get me going. 

Thanks a bunch.

Pete 

Love learning and reading about new things. Gives a better understanding even though I will never be an EE.


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## ElectriCar (Jun 15, 2008)

Pete, is your existing charger capable of charging to the first voltage? IE mine will charge to 186 or so. I am getting a pack of Calb and will run 50 cells. At 3.5V that is 175V. What I'm going to do is do the swap, then charge them with my Zivan NG5, watching like a hawk of course as it approaches the top. 

Here's my plan, BMS FREE of course. I'll watch it closely as it approaches 175V to see if I have any rogue cells. 


Starting around 170V I'll check each battery and note the voltage and time.
Then I'll note if any are higher than the norm
Continue to monitor any high cells periodically until probably 174V if all is well.
At that point I'll check and log each again to see if any other cells are high.
If I make it to 175V ok, monitoring high cells closely like a hawk, I'll march on toward 180V or 3.6V/cell, checking the entire pack at every voltage for surprises.
When I see one start to spike I'll know that's the limit, for now anyway.
Then I'll drive and repeat after a 70+% discharge & repeat, maybe 5 times or so.
If the data is stable I may repeat more. If it changes and moves higher I will evaluate and at some point determine a save voltage to charge to in the CC mode.
At that point I'll notify Zivan of what I want for the CC mode and tell them to switch to CV mode at the same voltage then stop charging at 1 or 2 amps, or whatever amperage I determine is best based on my notes.
Sound reasonable? I've mulled this over in my mind, specifically what you are thinking about how to set this thing up. Each time I send it to them for reprogramming I'm without an EV until it returns so I want it right the first time.

And I am considering the cell log 8's but I'm not going to if I don't need it. *However I'd advise and I'm going to install an AH counter of some type and hope to drive an idiot light at around 20% remaining. *A BMS isn't going to know a SOC based on the terminal voltage and you and I both know that isn't meaningful data.

In case you were wondering, a charger doesn't do anything magical regardless of the technology of the battery. What matters is the finishing parameters.


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## Overlander23 (Jun 15, 2009)

Are you going to wire the new cells in series and assume that they're all at the same state of charge?

Just curious.


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