# With <$350/Kwh LiFePO4s is lead-acid dead?



## speculawyer (Feb 10, 2009)

Dave Kois has done a wonderful job of establishing a good pipeline to Chinese-made LiFePO4 batteries. See here:
http://www.evcomponents.com/SearchResults.asp?Cat=28

With LiFePO4s now costing less than $350/KWH, is there really any point to getting lead-acid batteries anymore? Granted, the LiFePO4s are still more expensive than lead-acid, but the fact that they are supposed to be good for some 2000 cycles means that they should easily last more than twice as long as a lead-acid set.

I think the only advantages of lead-acid at this point are:
1) Upfront price . . . they are less up front, but in the long run they will cost more.
2) Durability - Lead acid batteries can be abused and over-charged and they'll still work fine. LiFePO4s are much more sensitive. If you over-charge them or over-discharge them, they may die.

But (2) can be addressed with a good Battery management system. And this is the only area where I see real weakness in lithium-ion batteries. The available battery management systems are crappy, expensive, flaky, and/or not easy to use. If someone produces a good *inexpensive *mass-produced easy-to-use Battery management system, I really think lead-acid is on its last legs.


This idea came to me when I was looking at helping someone deal with an NEV having battery issues. To replace a full set of 6 12-Volt lead acid batteries for an NEV can be pretty expensive. If you get good deep cycle marine batteries, they can cost close to $200 a piece. And since they are so damn heavy, you know the shipping will push them to that $200 price such that a full set of six batteries for a 72Volt based NEV is $1200.

Well, if one picks up 24 of these 60 Amp-hour lithium iron phophate batteries, the total price is just $1584:
http://www.evcomponents.com/ProductDetails.asp?ProductCode=TS-LFP60AHA
$1584 is just a little more expensive than the $1200 price for a full new set of lead-acids. But that is more than made up for by the longevity, lighter weight, and improved performance of the LiFePO4s. 

But the problem is that you really should have a BMS system. You can probably get away without one for a while (Just hook up the 24 cells in series and charge them up . . . maybe even with the existing charger.). But if you do that, you are taking a risk. If one cell shorts out, you may end up over-charging the others thus destroying the whole pack. 

If someone made an inexpensive BMS, I think lead-acid would start going away.


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## JRP3 (Mar 7, 2008)

Actually I'm seeing pretty good evidence that a cell level BMS is not necessary if you keep well within the discharge/charge parameters. Jack Rickard has made a pretty good argument to split your pack in half and monitor each half. As long as they are equal you know they are in balance, and as long as you don't pull high C rates they should stay in balance.


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## jorhyne (Aug 20, 2008)

Another trick I have heard of is occasionally (or at least initially) is to equalize all of your batteries by connecting them in parallel and charging them as one big 3.2 volt battery. Once they are fully charged rearrange them back into your series alignment and supposedly they will stay close to balanced for a good while.


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## speculawyer (Feb 10, 2009)

> Actually I'm seeing pretty good evidence that a cell level BMS is not necessary if you keep well within the discharge/charge parameters. Jack Rickard has made a pretty good argument to split your pack in half and monitor each half. As long as they are equal you know they are in balance, and as long as you don't pull high C rates they should stay in balance.


I figure that an NEV that ran on lead-acid batteries won't really stress a LiFePO4 cells. And if I periodically test the cells and manually balance them somehow, I would think it would work fine. 



jorhyne said:


> Another trick I have heard of is occasionally (or at least initially) is to equalize all of your batteries by connecting them in parallel and charging them as one big 3.2 volt battery. Once they are fully charged rearrange them back into your series alignment and supposedly they will stay close to balanced for a good while.


Is there some kind of special charger for this?


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## JRP3 (Mar 7, 2008)

An adjustable 5 volt power supply should work, though it might take a loooong time to get it done unless it's a high current unit. I suppose you could charge the pack in series to maybe 3.5V per cell or so then finish off in parallel for the final charge to 3.6. You would need to monitor closely during the series charge because if one or more cells is at a significantly higher SOC they could start overcharging before the others are done.


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## sunworksco (Sep 8, 2008)

A BMS system is so easy to install on your individual batteries.Why is everyone here getting their shorts in a bunch?


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## dimitri (May 16, 2008)

sunworksco said:


> A BMS system is so easy to install on your individual batteries.Why is everyone here getting their shorts in a bunch?


I think its the fact that with LiFePo4 prices being lower nowdays, the cost of BMS becomes significant part of overall cost, so naturally people are looking for cheaper alternatives, nothing wrong with that.

And what do you mean by "easy to install" ? This is too general of a statement. Does that include charger and controller integration with BMS? Because there is nothing easy about it these days since chargers and controllers are all different. If you are referring to a simple shunting / balancing BMS, then yes, its easy enough, but many people want more safety / protection than that.

There are many opinions on BMS, ranging from complete ignorance to ridiculous overkill, so until there is a standard off the shelf system that is widely accepted by most users, these discussions will live on


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## Bowser330 (Jun 15, 2008)

I hope they continue to drop, the prices of LIfepo4s that is...

Also whatever happened to those optimized lead-acid batteries e.g. firefly?

BMS, 

Say I wanted to install a small genset (240V & 20A 5kw) can a BMS balance the charge and discharge profile of cells at the sametime...say I wanted to charge my pack (via the Nivan charger) while I was driving...


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## sunworksco (Sep 8, 2008)

People on this forum need to study and play with RC planes,rock crawlers,boats.These are small versions of ac motor drivetrains with lipo batteries,balancers,contollers and chargers.Learn inexpensively before you take the expensive plunge.No one ever said evs are cheap except the no fear blissfull ignorant ones. This is not to say that skills are not required but they can be obtained if you research the subject.You need a smart pc sensored contoller/charging system and balancer harnesses installed on individual batteries connected to a battery balancer to keep minimum/maximum voltage levels.This is needed for charge/discharge and brake regeneration.A pc tablet to anaylise the controller/motor/BMS system is required as well and can be used for your gauge cluster.This is not a black art and anyone with electrical skills can obtain.


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## dimitri (May 16, 2008)

Bowser330 said:


> Say I wanted to install a small genset (240V & 20A 5kw) can a BMS balance the charge and discharge profile of cells at the sametime...say I wanted to charge my pack (via the Nivan charger) while I was driving...


If you use genset AC output and connect it to the charger AC input, then everything after charger looks and works the same as if it was plugged into the garage outlet, i.e. charger will slow down at the end and your genset will pretty much waste fuel running idle.

However, in real life you will never get to the balancing stage via genset during driving because you will spend energy 5-10 times faster than genset puts it back, so it will always be below balancing voltage levels.


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## sunworksco (Sep 8, 2008)

Not true.Regen can be working to maximum levels with ev traveling downhill with battery levels already near full charge and the balancer will keep batteries going to higher than recommended voltage levels.If you talk to RC hobbyists about lipo battery balancers,they will tell you it is mandatory or batteries will self-destruct.Go to www.rcgroups.com and read all you can about lipo batteries and balancers and misuse of batteries/chargers.This is the small world of evs and mirrors the full scale evs.Look at Novak brushless motors/ESC controllers.these are dc but on the power graph are really miniature ac motors with sensored controllers and brake regeneration.


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## dimitri (May 16, 2008)

sunworksco said:


> Not true.Regen can be working to maximum levels with ev traveling downhill with battery levels already near full charge and the balancer will keep batteries going to higher than recommended voltage levels.If you talk to RC hobbyists about lipo battery balancers,they will tell you it is mandatory or batteries will self-destruct.Go to www.rcgroups.com and read all you can about lipo batteries and balancers and misuse of batteries/chargers.This is the small world of evs and mirrors the full scale evs.Look at Novak brushless motors/ESC controllers.these are dc but on the power graph are really miniature ac motors with sensored controllers and brake regeneration.


Dude, we weren't talking about regen, we were talking about gas powered genset. And enough with RC advertisment already, it has similar technologies but specific applications and power levels involved in real EV is way too different compared to RC world. Sure the knowledge helps, but there aren't any EV controllers or chargers or BMS that have standard connectors and signals like in RC world, so it doesn't really apply here. Maybe one day in a distant future EV market will standardize on connections like RC market, but those days aren't here yet. It doesn't help to tell people not to get their shorts in a bunch when they spent 10K on battery and naturally want to protect it.

And even with regen as you said, overcharge is virtually impossible. Only if you charge to full at the top of the mountain and then start rolling down, then you maybe able to overcharge, but in any other situation you will always spend more energy to get up to speed than you will ever hope to recover during regen.


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## sunworksco (Sep 8, 2008)

dimitri said:


> Dude, we weren't talking about regen, we were talking about gas powered genset. And enough with RC advertisment already, it has similar technologies but specific applications and power levels involved in real EV is way too different compared to RC world. Sure the knowledge helps, but there aren't any EV controllers or chargers or BMS that have standard connectors and signals like in RC world, so it doesn't really apply here. Maybe one day in a distant future EV market will standardize on connections like RC market, but those days aren't here yet. It doesn't help to tell people not to get their shorts in a bunch when they spent 10K on battery and naturally want to protect it.
> 
> And even with regen as you said, overcharge is virtually impossible. Only if you charge to full at the top of the mountain and then start rolling down, then you maybe able to overcharge, but in any other situation you will always spend more energy to get up to speed than you will ever hope to recover during regen.


I am merely providing the link to offer to forum members here to do some research.Go visit an rc forum and there is more science there about motors and lipo batteries than here.I have been nothing except helpful in every way of design and building evs. How dare you say that I am advertising. I am in a completely different business. I have never directed anyone here to my solar industry business? I have never done business with any forum member here and find it very irritating how closed minded this forum can be at times.I take your comment as disrespectful and your comments sounding as if this is your own personal membership club and can be sensored at will by you!


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## sunworksco (Sep 8, 2008)

P.S.
I see you do have weblinks on your forum comment page!


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## sunworksco (Sep 8, 2008)

"Shorts in a bunch" was intended as a light-hearted joke and pun but I can see that I was laboring on a misapprehension the this forum membership possesed any humorous attributes.


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## sunworksco (Sep 8, 2008)

sunworksco said:


> I am merely providing the link to offer to forum members here to do some research.Go visit an rc forum and there is more science there about motors and lipo batteries than here.I have been nothing except helpful in every way of design and building evs. How dare you say that I am advertising. I am in a completely different business. I have never directed anyone here to my solar industry business? I have never done business with any forum member here and find it very irritating how closed minded this forum can be at times.I take your comment as disrespectful and your comments sounding as if this is your own personal membership club and can be sensored at will by you!


Although BLDC motors are practically identical to permanent magnet AC motors, the controller implementation is what makes them DC. While AC motors feed sinusoidal current simultaneously to each of the legs (with an equal phase distribution), DC controllers only approximate this by feeding full positive and negative current to two of the legs at a time. The major advantage of this is that both the logic controllers and battery power sources operate on DC, such as in computers and electric cars. In addition, the approximated sine wave leaves one leg undriven at all times, allowing for back-EMF-based sensorless feedback.
Vector drives are DC controllers that take the extra step of converting back to AC for the motor. The DC-to-AC conversion circuitry is usually expensive and less efficient, but they have the advantage of being able to run smoothly at very low speeds or completely stop in a position not directly aligned with a pole. Motors used with a vector drive are typically called AC motors


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## JRP3 (Mar 7, 2008)

I'm not sure if RC sized cells are comparable to EV sized cells. It's simply going to take a lot more to get a 100ah or larger cell to over volt, and as mentioned unless you are starting fully charged at the top of a long hill it will not be an issue. If you are routinely starting off at the top of a large hill with a full charge the smart thing to do would be to turn down the charger a little bit to allow room in the cells to take the recharge.
People have been running successfully without a BMS on the newer cells. Time will tell if there is a long term difference, but to say a sophisticated cell level BMS is a necessity seems to be a stretch. If you charge a TS type cell to 3.6 volts and never go below 2.7 volts I doubt you'll ever come close to damaging a cell. Monitor two halves of the pack to check for imbalances, if one shows up check that out. This is what Jack Rickard has been doing and he's had no cell failures yet, I think he has about 5000 miles on his pack.
As to the sense of humor on the forum, I've found plenty of funny people here


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## bblocher (Jul 30, 2008)

From my personal experience, the monitoring the two halves of the pack idea will definately not work.

I've done some experiments by manually bypassing my BMS to see how quickly one cell could rise on a balanced pack before the charger will cutback as the other cells caught up.

There are two ways to test this, one way makes it look like it works and that's if the pack is already charged but has had been sitting for awhile. The voltages increase close to each other and the charger ramps down amps until it finishes.

If I do this test after a drive it will fail every time. As soon as a cell reaches 3.8v, it will continue to climb to >4.2v in seconds if not controlled. There simply isn't enough delay as the voltage curve ramps up too quickly towards the end of charge cycle. I've seen my charger still outputing 30amps until the first cell hits high voltage forcing it to ramp down.

I know there is a lot of talk out there about not needing a BMS, and I disagree completely. Please do some closely monitored tests on your side and you'll see what I mean (again make sure you're discharging the pack significantly between tests, 50% SOC or so).


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## sunworksco (Sep 8, 2008)

JRP3 said:


> I'm not sure if RC sized cells are comparable to EV sized cells. It's simply going to take a lot more to get a 100ah or larger cell to over volt, and as mentioned unless you are starting fully charged at the top of a long hill it will not be an issue. If you are routinely starting off at the top of a large hill with a full charge the smart thing to do would be to turn down the charger a little bit to allow room in the cells to take the recharge.
> People have been running successfully without a BMS on the newer cells. Time will tell if there is a long term difference, but to say a sophisticated cell level BMS is a necessity seems to be a stretch. If you charge a TS type cell to 3.6 volts and never go below 2.7 volts I doubt you'll ever come close to damaging a cell. Monitor two halves of the pack to check for imbalances, if one shows up check that out. This is what Jack Rickard has been doing and he's had no cell failures yet, I think he has about 5000 miles on his pack.
> As to the sense of humor on the forum, I've found plenty of funny people here


 Lithium iron phosphate batteries are used in rc rock crawlers,submarines and other various models.It is not recommended to use these or any other lipo batteries without balancers.


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## JRP3 (Mar 7, 2008)

bblocher said:


> If I do this test after a drive it will fail every time. As soon as a cell reaches 3.8v, it will continue to climb to >4.2v in seconds if not controlled. There simply isn't enough delay as the voltage curve ramps up too quickly towards the end of charge cycle. I've seen my charger still outputing 30amps until the first cell hits high voltage forcing it to ramp down.


The difference may be how the charger works. What charger are you using? Jack is using a Brusa which as I understand it can be set up to have one charge stage up to a certain point, then stop charging for a period of time, then come back on with a low amp charge, and do this a number of times. He claims to have not overvolted a single cell. Along with not charging above 3.6 volts this may be the key to doing a pack without BMS.


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## sunworksco (Sep 8, 2008)

Sounds like Russian roulette.
I use a battery balancer that measures each battery and stops charging the batteries when they are within a certain average voltage.


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## dimitri (May 16, 2008)

JRP3 said:


> Jack is using a Brusa


Jack's Brusa costs more than Zivan + BMS + lots and lots of beer 

I think you can get away without BMS if you stop charging at 3.6V and do manual initial balancing and checking each cell every week or so, but you will give up maybe 5% of capacity to minimize the risk of SOC drift on some cells and you will gain a headache of weekly cell checking for next 10 years. IMHO, this is not a fair trade off compared to a simple resonably priced BMS and a peace of mind that comes with it.


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## dimitri (May 16, 2008)

sunworksco said:


> "Shorts in a bunch" was intended as a light-hearted joke and pun but I can see that I was laboring on a misapprehension the this forum membership possesed any humorous attributes.


Lets refrain from personal attacks here, I have a very good sense of humor and its not "shorts in a bunch" that got me, but a fact that your first post was utterly useless without giving any insight of what you meant by BMS being very simple to do in EV. When I challenged you to give more details, you posted a picture of a toy motor and a toy controller, which is completely unrelated to this thread and entire section of the forum, so what could that possibly mean?

Then later you go quoting yourself with more motor info which was possibly meant for another thread 

I provided several specific bits of info that shows how far RC stuff is from EV, yet the only thing that caught your eye was 2 of my words taken out of context.

You quote RC info in several threads here, but you fail to prove how these toys can help anyone build an EV on real world budget. Everyone knows that AC and BLDC motor/controllers are better, doh, but show me where I can buy it in US for comparable cost with same size/weight/power DC motor/controller combo? Nowhere..... So what is the point of playing with toys that don't scale up? How does that help?

As for forum etiquette, I read dozens of forums and this one is one of the best with almost no moderation and wealth of real world info, not some useless theoretical crap that is fun to read, but not very helpful in day to day life. If you like those other forums better, please, no one is twisting your arm here....

Sorry everyone for getting a bit off subject, mods feel free to delete this if you want.


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## JRP3 (Mar 7, 2008)

dimitri said:


> Jack's Brusa costs more than Zivan + BMS + lots and lots of beer


Yes there is that problem. I'm still on the fence as to how I'm going to spend my beer money 
Zivan + BMS
Manzanita + BMS
Brusa + ?


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## sunworksco (Sep 8, 2008)

I'm withdrawing my forum membership since none of my posts have any bearing or intellect on the subjects here.So go sell your ev business and I will not bother your authority on the subject of ev technology.


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## JRP3 (Mar 7, 2008)

That's a bit over the top dude. I don't think your RC stuff was really applicable to the situation but no need for you to bail out on us. Your choice of course.


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## rbgrn (Jul 24, 2007)

sunworksco said:


> I'm withdrawing my forum membership since none of my posts have any bearing or intellect on the subjects here.So go sell your ev business and I will not bother your authority on the subject of ev technology.


I'd like to thank dimitri for stating that this is a good forum. I'm proud of how well everyone gets along and manages themselves and I'm super happy that the goal of information accumulation and sharing really is working.

Sunworksco, I'm sorry you feel that way. You know, it's very difficult to truly understand the tone and intent of what people say in a text-only world. Everyone appreciates your expertise and input of knowledge. I know most everyone has good intentions when posting so I hope you can understand and try to take things with a grain of salt.

If you really don't want to stick around, I understand and thank you for being a part of the community.


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## dimitri (May 16, 2008)

sunworksco said:


> I'm withdrawing my forum membership since none of my posts have any bearing or intellect on the subjects here.So go sell your ev business and I will not bother your authority on the subject of ev technology.


I am very sorry that we failed to engage you in meaningful logical discussion. I am also sorry that you confuse experience and logic with authority. My only intend is to help people avoid pitfalls that I have seen in my own EV experience and I never post on subjects in which I have no first hand experience or ability to defend my position and learn from others in a logical and meaningful way.


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## speculawyer (Feb 10, 2009)

sunworksco said:


> A BMS system is so easy to install on your individual batteries.Why is everyone here getting their shorts in a bunch?


Well, when I looked several months ago, there was not much out there. There is a bit more now, but most are kinda pricey. The ones at bmsbattery.com are reasonably priced . . . but there is no documentation about them. Anyone know anything about those BMS systems? Is there any documentation?


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## Guest (Aug 10, 2009)

The BMS thing is a problem. I don't agree that the solution is easy. I do recognize that my views are a little controversial. But they seem to be working. Yes, I do advocate a more advanced charger than is quite available at an affordable price.

First the RC thing. Actually I have BOXES of eBay purchased RV balancers and chargers. And actually, they are the closest thing to a workable and affordable device even for large cell work. They typically only "balance" at the rate of 250 ma or so, although a few do a half amp. In this way, you could very SLOWLY balance your pack over time. And they SEEM to pose little fire danger.

The problem is they mostly work as least common denominator - they bleed connected cells to equal the lowest cell by voltage. This causes them to step down your pack over time if you leave one sitting.

They are useless while charging because you are charging at much higher currents than RC guys. They may even be dangerous and so you are faced with some way to connect/disconnect while charging.

But I've played with a lot of them and actually like them. The cute little aluminum cases are part of it probably. 

The cell bleeder shunt concept I just have a problem with. Yes, I played with Blochers as well. I hooked four of them up to 4 cells and left it for 3 days. One of them bled a cell to zero volts and it never recovered.

They started conducting at 3.6 volts, which I didn't like, and it was not adjustable.

I devised a number of circuits that were actually quite similar, typically LM431 designs with a FET or darlington and a 50 watt resistor. Actually, they worked pretty well at the design voltage. If I turned up the voltage to say 1.5 or 1.6 of the 4.0 preset, they went into thermal runaway and terminated when the copper heat sink melted and broke the connection. Remember, you are talking about connecting these across the cells of a battery than CAN put out 1000 amps briefly.

I've tracked down three or four cases of cars burning to the ground. In every case, there was at least a probability, and to my way of thinking, more than a probability that the current shunts actually caused the fire. I think the batteries are "basically" safe. They don't start fires. But they are great fuel if you melt one and short it. And you can do that with a current shunt.

I'm working on the same concept right now. But the shunts aren't mounted on the batteries. They're mounted on a foot square heat sink. And the thing will roll around on a cart. And I'll hook it up to the car, use a special charging algorithm to bring them up to a 4.00 volts and do this as a maintenance procedure. The shunts, if they fail can't burn the car to the ground because:

1. They aren't in the car at all.
2. I'm standing there watching them.

And after it is done, I'll disconnect them.

But in practice, my cells have been REMARKABLY well "balanced" most of the time. The comparator works quite well at detecting anomalies. It's basically built into the EVision. Lee Hart orginally described it. And it's not only simple, but simple enough to use while driving.

It certainly can detect imbalance, all vendors views to the contrary. It can't detect them or do much about them if you are charging your cells to max voltage.

And that brings me to another little thing I'm coming to feel strongly about. We just don't charge them to max voltage. On the thundersky's we're charging to 3.6-3.75 volts. We'll do the Blue Skys' sprobably to 3.45. 

I have been testing the Blue Sky batteries quite a bit the last couple of days. We just received our shipment for EVcomponents last Friday.

And I love them. A couple of things. The dimensions we got from the specs are NOT accurate. They are EXACTLY the same size and shape as the THundersky 90Ah cells. The ribbing is the same. The color is blue instead of yellow.

They come with threaded rod and brackets for the ends. Not good. They take up much more room than the flat straps and plates of the Thunderskies. We are just going to have devise our own clamp system using the battery boxes themselves in the Mini Cooper.

Their voltage is lower. They describe 3.6v down to 2.0. Which APPEARS different from the THundersky. I'm not sure how different they are. I'm starting to think they are just reading my mail. 

In any event, if anything it has a FLATTER charge discharge curve. There really isn't anything above about 3.45 volts on the high side. On the low side, I'm a little unclear about the 2.0 volts. They take the dive right about at 3.0 volts just like the Thundersky's. Perhaps they are more tolerant of the lower voltage, but it doesn't matter. From 3.0v down to 2.0volts, there isn't anything in the way of stored energy anyway.

In fact, the ends seem a little sharper on the Blue Sky's and the 3.3 to 3.0 volts a little wider and flatter as a result.

I got 111.83 Ah out of one of these 100 Ah cells picked at random.

So again, my belief is the strategy should be to avoid the ends and stay in the middle. Balance really only comes into play when you fall off the lower end. The problem is that one cell always reaches the 3.0 volts first. And it starts to plunge. The others are still at 3.05 and just digging it - hoping for another massive acceleration so they can show their stuff. By the time they reach 2.5 volts. The one that hit 3.0 volts first is shorted - completely dead and irrecoverably so.

Actually JRP, I HAVE cratered some batteries. But I'm in a little bit different situation from you guys. You're trying to preserve your batteries. I'm trying to learn how to kill them. This is a good deal for you. I buy the battery, and you get the info.

Overcharging doesn't precisely kill the batteries, within reason. It causes lithium plating on the cathode and will reduce the life of the cell. But over discharging is death. Some you can bring back. Some you can't. The ones you can't, feel free to bandsaw and take a look inside. 

So I view the 3.0 volts, basically the knee of the discharge curve where it turns downward, as the end of range. The little you have from 3.0 to 2.0 on the Blue Skys is your "pad" and really it is precious little.

I'm coming to admire Victors EVISION more all the time. It lets me see how many AMP HOURS I've taken out of the battery. Voltage is actually a pretty good indication, but if know your batteries after awhile, you pretty much know how many amp hours you can take out and live. It does have the balance indication, and actually a quite nice battery charge fuel gage that probably works fine, I've just never trusted it. It monitors amp hours going out, and indeed it will monitor amp hours going back in when you are charging.

So when I say I don't like BMS, I'm talking about most of the systems out there and all of the current shunt balancers. I guess the EVISION is a kind of "monitoring system." 

Having a smart charger is an advantage. But many of the chargers now can do basic constant current/constant voltage stuff and let you set the voltage. Really MOST of the problems go away if you just charge to a lower voltage and the range you sacrifice is typically between 1 and two miles.

The other end is just making sure you don't run them too far out - a key component to battery cycle life. Remember that 3000 cycles is at 70% discharge. At 80% you're looking at 2000 cycles. And I would guess at about 3.0 volts per cell, you are pretty much at 92-93% discharge on these Blue Sky cells

And I am actually amazed at how well they stay in balance. But when marrying a new battery into a pack, I do have to do some manual balancing. Basically a 12 v charger and a big 5000watt 1/4 ohm load I made makes even that pretty easy. But for drill, I'm kind of playing with this cart level shunt thing that will do about 5 amps per cell and allow me to "top em all off" as a once every month or so maintenance procedure. If I charge them normally to 3.6 volts, I can hook this up, run a charge cycle up to 4.00 volts which should hardly take 20 minutes. There is NOTHING in the land from 4.00 to 4.25 volts. It' sjust wasted effort.

I do have a video showing the insides of a Thundersky if anyone is curious. http://evtv.me/videos.html. 

If you want a full Linux Ubuntu server in your car monitoring your batteries and current shunts wired over the top of your cells everywhere it's all good with me. I'm not trying to kill the BMS industry, and indeed if I could find a good one, I'd buy it obviously. I've bought most of the bad ones so I'm not opposed to investing in a good one. I just havent' found one.

But ff you do have a fire, please send photos.

Jack Rickard
http://evtv.me


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## JRP3 (Mar 7, 2008)

I too am a bit concerned with the potential problems with cell mounted shunt balancers and have been considering a remote mounting location where a failure would be less likely to cause problems, but never considered doing it outside of the vehicle for temporary connection.
I'm disappointed in your description of the threaded rods and brackets that come with the SE cells, for just the reasons you mentioned. The pics I've seen made them look bulkier than the TS plates and straps and I had been hoping they would actually ship with the TS system or something similar. Since battery space is almost always a concern in an EV the SE system seems like a very poor design.
Thanks for all your work and information, keep trashing batteries so we don't have to


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## Guest (Aug 11, 2009)

JRP3 said:


> I too am a bit concerned with the potential problems with cell mounted shunt balancers and have been considering a remote mounting location where a failure would be less likely to cause problems, but never considered doing it outside of the vehicle for temporary connection.
> I'm disappointed in your description of the threaded rods and brackets that come with the SE cells, for just the reasons you mentioned. The pics I've seen made them look bulkier than the TS plates and straps and I had been hoping they would actually ship with the TS system or something similar. Since battery space is almost always a concern in an EV the SE system seems like a very poor design.


I like the Thundersky hardware much better. It was important in the Speedster. 

We have a series of "boxes" that are quickly growing into modules on the Mini Cooper. One of them holds 55 cells. We aren't going to use the hardware there anyway. The box is 30x29 and 10 inches deep and the cells will be more or less packed in there.

One thing I forgot to mention was that is quite important. We were seeing 40C case temperatures at 99 Amp discharge rate. This is quite a bit higher than the Thunderskys. 

In the Porsche, almost all the boxes were narrow and hung under the car in the air stream. So we did nothing about cell cooling.

With 55 cells in the main box, and basically a square design, cooling is probably required. What we're doing is a little different from BMW's approach. We're going to drill holes in the bottom of the box along the vent lines under the cells. We're going to mount a fan on the aft end of the box with a thermostat that has a probe, which we'll put in the middle of the pack.

When the temp rises to a set value on the thermostat, the fan will come on and blow air INTO the box. It will then have to pass between the batteries and out the holes in the bottom. We can put the holes closer together in the center of the box, and wider apart near the edges. This should increase the flow around the middle batteries at the expense of those on the edge. 

Understand this box is entirely contained inside the car. It doesn't get any passing air. We can blow out the bottom onto two boxes where the fuel tanks were, but this area is pretty much open, just out of the air stream.

In this way, we don't bring heat into the passenger compartment, it is blown to the car exterior. If we have air conditioning on, this will also aid the cell cooling.

But note that heat is more of an issue with the Blue Sky's than it was with the THunderkys.

Jack Rickard
http://evtv.me


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## Bowser330 (Jun 15, 2008)

Jack, Sir, Ive seen your website/videos and really enjoy the in depth analysis. Thank you for those. Your Porsche gets an amazing efficiency (i'm guessing primarily due to the lightweight)..245whr/mile...exactly what I am looking for...

Question for you...The 90AH TS cells are now stating 20C Impulse discharge current.. .However I am more interested in your personal experience with the cells..Do you have any stats on the "C" rating of the TS or SE cells?

Your p-car has a 1200A controller, and you have a 180AH pack...what has been your strongest amperage draw you've experienced, and how did affect our packs overall balance?


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## JRP3 (Mar 7, 2008)

The 40C operating temperature you describe sounds rather close to their 55C max operating temperature. With the claimed higher C rates for the SE cells I would expect less internal resistance than the TS cells, not more. What were your ambient temperatures? This could complicate things if I have to provide active cooling for the cells.


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## CroDriver (Jan 8, 2009)

Bowser330 said:


> Jack, Sir, Ive seen your website/videos and really enjoy the in depth analysis. Thank you for those. Your Porsche gets an amazing efficiency (i'm guessing primarily due to the lightweight)..245whr/mile...exactly what I am looking for...
> 
> Question for you...The 90AH TS cells are now stating 20C Impulse discharge current.. .However I am more interested in your personal experience with the cells..Do you have any stats on the "C" rating of the TS or SE cells?


This is the holly grail of the TS cells.  It seems like no one knows that


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## Guest (Aug 12, 2009)

The max battery current draw I see is about 540 amps. I don't think it ever goes very much above that. 

The 15C pad between 40C and 55C is quite a bit. And it's true the ambient at the time was 34C and this was a ONE HOUR continuous draw at 99Amps. 

Still, I've never seen that with the TS cells. And it is of concern to me since in the Mini Cooper, I have one 30x29 inch box that will hold 55 cells, and it is NOT in the airstream beneath the car, but rather in the passenger compartment.

That probably leads to an inevitable heat buildup in the center of that box. And so we' ve had to add a fan and thermostat to it, and drill some holes in the bottom of the box. It's a 235CFM fan, and quite quiet, so I think it will work very well. By venting out the bottom of the box into the area below the rear seats, it will vent outside the car instead of into the passenger compartment, where we are trying to cool it with an air conditioner for example. So I think it will work very well. We'll cluster more ventilation holes in the center of the box bottom than at the edges.

The problem of course is that if you have a big temperature differential between your cells, you exacerbate the cell balance issues.

Jack RIckard
http://evtv.me


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## Bowser330 (Jun 15, 2008)

jrickard said:


> The max battery current draw I see is about 540 amps. I don't think it ever goes very much above that.


 
So 540A on a 180AH pack is 3C...Is this because you set your controller to limit battery current to 3C? Can the Kelly 1200A do that?

Curious...why did you purchase the 1200A model for a max draw of 540A? To keep a safety margin?


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## Russco (Dec 23, 2008)

Back to the original question: Lithium Iron Phosphate vs. Lead Acid. 

The gold standard of LA EV batteries is the 6 volt golf cart battery rated at 220 AH. The Wh/# = 6 volts x the one hour rate of 50%, which is 110 AH = 660 watts for one hour. The weight per battery is about 62 pounds = 10.5 Wh/#.

A yellow Thunder Sky one hour rated 100 AH battery = 100 AH x 3.2 volts = 320 watts for one hour. The weight is 7.15 pounds = 44.7 Wh/#.

The lithium battery has over _four_ times the energy density.

For a cost $ comparison, the golf cart battery cost about $110. Two 100 AH LiFePo4 cells from EV Components will equal 6.4 volts in series and cost about $250. That's about 2 1/2 times the lead acid battery cost. 

One golf cart battery will weigh 62 pounds; two Thunder Sky cells will weigh 14.3 pounds. That's less than 1/4 the weight of lead acid!

Lithium is safe, higher density, much lower weight and cost per mile comparable to lead acid.

Lithium is the present. Lead acid is the past.


Russ Kaufmann

RUSSCO Engineering


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## dimitri (May 16, 2008)

Russco said:


> For a cost $ comparison, the golf cart battery cost about $110. Two 100 AH LiFePo4 cells from EV Components will equal 6.4 volts in series and cost about $250. That's about 2 1/2 times the lead acid battery cost.


You forgot one of most important factors, lifecycle. Generally speaking LiFePo4 should last 4-5 times longer than LA, so cost comparison over lifetime makes LiFePo4 half the price of LA.


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## Russco (Dec 23, 2008)

dimitri said:


> You forgot one of most important factors, lifecycle. Generally speaking LiFePo4 should last 4-5 times longer than LA, so cost comparison over lifetime makes LiFePo4 half the price of LA.


Yep, but no ones gone there yet. The LiFePo4 are too new. The only bummer is the initial one time higher cost.


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## Guest (Aug 13, 2009)

Bowser330 said:


> So 540A on a 180AH pack is 3C...Is this because you set your controller to limit battery current to 3C? Can the Kelly 1200A do that?
> 
> Curious...why did you purchase the 1200A model for a max draw of 540A? To keep a safety margin?


Overkill is always appropriate. But controller amps and battery amps are not precisely the same thing. It is a PULSE in pulse width modulated. The controller may well provide a higher current to the motor than the battery will ever quite see.

Yes, it looks suspiciously like 3C. But of course, that is what the batteries will do continously. And basically, I see this when accelerating at already highway speeds. It is quite possible to do more at the low end while accelerating and the problem is noting it. You typically only accelerate for a few seconds.

Jack Rickard
http://evtv.me


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## Bowser330 (Jun 15, 2008)

jrickard said:


> Overkill is always appropriate. But controller amps and battery amps are not precisely the same thing. It is a PULSE in pulse width modulated. The controller may well provide a higher current to the motor than the battery will ever quite see.
> 
> Yes, it looks suspiciously like 3C. But of course, that is what the batteries will do continously. And basically, I see this when accelerating at already highway speeds. It is quite possible to do more at the low end while accelerating and the problem is noting it. You typically only accelerate for a few seconds.
> 
> ...


You're right...so the battery amps may be 540A but the motor amps could be 1080A if the PWM was at 50%...is that right?

so at highway speeds i would think you would need 100% pwm to get the full voltage to the motor, that would mean that even at full 120V you were pulling 540A...is that right? what motor rpm is "highway speeds" in your setup? 4000?


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## Guest (Aug 14, 2009)

Bowser330 said:


> You're right...so the battery amps may be 540A but the motor amps could be 1080A if the PWM was at 50%...is that right?
> 
> so at highway speeds i would think you would need 100% pwm to get the full voltage to the motor, that would mean that even at full 120V you were pulling 540A...is that right? what motor rpm is "highway speeds" in your setup? 4000?


Yes, a little over 4000 rpm.

Jack Rickard
http://evtv.me


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## Bowser330 (Jun 15, 2008)

jrickard said:


> Yes, a little over 4000 rpm.
> 
> Jack Rickard
> http://evtv.me


Wow, thats great!

4000Rpm pulling 540A with 120V....

Theoretically would you be able to pull 1080A @ 4000rpm if you had a 240V system?


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