CALB CA series cell performances

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mattcarr
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Re: CALB CA series cell performances

Postby mattcarr » Tue Jul 17, 2012 7:23 am

I have got a Zivan NG3 in my car and I know that the BMS does throttle the charger back as the battery come to the end of it's charge. I believe that my BMS actively tries to balance my pack during charge. It does this by switching on a load to the cells with the highest voltage. This allows the lower voltage cells to catch up. As all of the cell voltages come up the BMS reduces the output of the charger and it keeps doing this to keep all cells below 4.08 volts. When the pack voltage hits 102 volts ( I have 25 cells in the pack ) it stops the charge completly and resets the SOC meter to 100%. My pack voltage never drops after this so I can safetly assume that no more loads are placed on any of the cells.

mikethebike3
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Location: NE Norfolk, UK

Re: CALB CA series cell performances

Postby mikethebike3 » Tue Jul 17, 2012 10:50 am

The thing that concerns me is that IIUC, to honour the warranty, CALB insist on a BMS which (amongst other things) top balances individual cells, even though many believe that this shouldn't be necessary if the battery is monitored and not abused in any way.

The MiniBMS (is that what you have too Matt?) is a great product in that it top balances and switches off the charger automatically, and gives warnings and limits discharge when the pack voltage gets too low. This is ideal for a generally hands-off user, but it doesn't actually tell you the individual cell voltages which is what I would really like, and even at a mere $500 + carriage and import taxes it's a little expensive just as a pro-tem. I remember looking at Peter and Greg's BMS project a while back and thinking what a cool system it is, and as a retired electronics engineer I think it's something I could implement myself, with help from forum members of course. Then once the CALB warranty runs out I can review the situation and do what I think best! :twisted:

My NG3 was originally set up for 120V LA, but Gareth at Electrofit kindly explained how to reduce the output voltage to my present 72V LA system, albeit at lower current (I guess) than a native 72V version. Reinstating to 120V is easy, and from what Greg says, maybe I won't need the Lithium charge profile, although my old LA's are flooded.

Mike

Beemer
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Re: CALB CA series cell performances

Postby Beemer » Tue Jul 17, 2012 4:09 pm

I keep on referring to Jack Rickard of EVTV. He has half a dozen vehicles and none have a BMS at all. He's had no nasty surprises.
Top balanced packs suffer from the BMS cutting the power because the whole pack shows a low voltage condition under load as if its going empty.... This happens while accelerating and it still has plenty of charge in it. What good is that?

There is no way over this unless its bottom balanced (Do once, good for ever) so no cell can be forced into reverse... That means bottom balancing and only warning when voltages drop.

When bottom balanced you need nothing more "intelligent" than a Lee Hart Batt Bridge.
Image

mattcarr
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Location: Hampshire

Re: CALB CA series cell performances

Postby mattcarr » Tue Jul 17, 2012 7:36 pm

Mike, I have got a custom BMS that was designed and built by the company that converted the Citroen C1's. It does quite a few things. It constantly monitors every cell voltage in the pack and when driving if any one cell drops below a certain threshold it reduces the power draw from the batteries. The controller also has the 820 spyglass display - which shows pack voltage, battery current and state of charge. As soon as the state of charge gets to 25% the car ir limited to 30 mph top speed - this again helps to keep the current draw lower while the pack is in a lower state of charge. When on charge the BMS monitors each cell voltage and it a call starts to climb above the others the BMS will place a 1 amp load on the cell to help stop the voltage getting to far out from the others. When the pack voltage starts climbing near the end of a charge the BMS then tells the charger to slow down it's charging rate until the cells hit there maximum voltage, then it finishes the charge and resets the state of charge back to 100%. I believe that the BMS can manage up to 50 cells in total.

Take a look at my ealrier posts as I have posted pictures of the electrical innards of my car.

Beemer
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Re: CALB CA series cell performances

Postby Beemer » Tue Jul 17, 2012 7:47 pm

A real BMS would GIVE power to the low(er) cell(s) to bottom balance so give more effective range. A charger should knock off at a sensible Voltage. Not have another circuit dump energy into a potential fire hazard :shock:

See this video from our John Hardy about the fabled "cell drift" 00:52:50 in:
http://youtu.be/jiBunCL_ywI

ATM he's only 300 or so cycles into his test and so far, no creep.

GregsGarage
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Re: CALB CA series cell performances

Postby GregsGarage » Tue Jul 17, 2012 8:17 pm

Beemer wrote:Top balanced packs suffer from the BMS cutting the power because the whole pack shows a low voltage condition under load as if its going empty....

Rubbish!
It is only an insurmountable problem if you choose to make it one. :shock: I won't claim it never happens, it is quite possible with the wrong choice of bms and battery pack that you could suffer from false warnings under acceleration. One person that did have this problem was Chip Yates when he was setting electric bike speed records at Bonneville last year. Pushing the bike above 190 mph and cell discharge rates of around 20C meant that indeed the bms would of cut power so it was disconnected for the runs only, but used before and after to check the pack. For the rest of us who aren't trying to break speed records a properly configured bms will not interfere with normal driving and will only warn you when a cell is getting low. When I fitted my HiPower cells (made in 2009) I took Jack's advice at the time which was do nothing, don't top or bottom balance, just fit them and keep them within limits. It turns out that the HiPower cells from 2009 didn't have the consistency of the CALB cells (shortly after I purchased mine HiPower introduced a new range of cells which are supposed to be better). The upshot is my pack has never been balanced, top or bottom. My bms tells me which cells are the weakest and so I have been able to top up individual weak cells bringing the pack more into balance. It also warned me on a problem after the first few runs that turned out to be a poor cell connection, embarrassing on my part, but with 144 cells that is 288 connections, I suppose I was bound to miss one. :wink:

I said probably at least 2 years ago that I wouldn't be surprised if Jack can run his vehicles with no bms, problem free. I am still not surprised. Jack can do this because he is his own bms. He has hundreds of hours of testing and really understands how to kill a cell. Problem is someone else may not fully understand why he does things the way he does and push his pack to destruction.

Regarding the warranty requirements of a top balancing bms, I have to wonder if this is a response to Jack's bottom balancing. It could be they are concerned about the risk of someone trying to bottom balance a pack and accidentally going too far with a cell and over discharging it. To the best of my knowledge, there are no automated bottom balancers or bottom balancing bms's on the market, so this has to be done manually. By specifying a top balancing bms they won't have to warantee any cells that have been bottom balancing.

But the fact is that balancing will not improve cell life one bit. With a proper bms to keep an eye on cell voltages the only effect of pack imbalance is reduced range. In an adequately balanced pack your weakest cell determines your range. Balancing is only required when the weakest cell is not the one that triggers both the high cell cut off on charge and low cell cut off on discharge. Even then if this reduced range is still more than the range you require of the vehicle, you may decide to put off balancing.
Greg Fordyce

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http://www.evalbum.com/4191

GregsGarage
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Re: CALB CA series cell performances

Postby GregsGarage » Tue Jul 17, 2012 8:20 pm

Beemer wrote:A real BMS would GIVE power to the low(er) cell(s) to bottom balance so give more effective range.


The Lee Hart Battery Balancer does exactly this.
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

Beemer
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Re: CALB CA series cell performances

Postby Beemer » Tue Jul 17, 2012 8:30 pm

"Rubbish"....and then you say.. "I won't claim it never happens," .... That, is what I call hung with ones own petard. :shock:

It happens! You load a pack and the voltage sags. No BMS can see the difference.

JR needs no BMS. He has an indicator to say his pack is low by counting the AH.
His charger simply does not overcharge.

If he needs to get off the highway AFTER his indicator has cut the controller; all he has to do is press two buttons together and he can still drive it until there is no power left to drive the car... They simmer down as one. No busted cells!

What's he have to be a human BMS for?

Beemer
Posts: 294
Joined: Sat Jun 04, 2011 12:10 pm

Re: CALB CA series cell performances

Postby Beemer » Tue Jul 17, 2012 8:33 pm

GregsGarage wrote:
Beemer wrote:A real BMS would GIVE power to the low(er) cell(s) to bottom balance so give more effective range.


The Lee Hart Battery Balancer does exactly this.


He's not the first nor will he be the last but lets be fair, Lee is a lead acid guy, they go awry after a short time.

GregsGarage
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Re: CALB CA series cell performances

Postby GregsGarage » Tue Jul 17, 2012 9:06 pm

Beemer wrote:"Rubbish"....and then you say.. "I won't claim it never happens," .... That, is what I call hung with ones own petard. :shock:

It happens! You load a pack and the voltage sags. No BMS can see the difference.


Not at all. It would be absurd for me to claim it isn't a potential problem, but bms that is monitoring current draw can tell if the voltage sag is a problem or not. But even a simple bms can work fine. Jack has been saying this for quite a while. I'm sorry, but just because he keeps saying it doesn't make it true. Back when Cedric Lynche's team won the very first TTXGP on the isle of mann, Jack was saying bms's would restrict power under acceleration. Guess what, Cedrics team won with a bike he designed fitted with his simple but effective cell protectors. So I still say... Rubbish. :twisted:
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191


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