Gary12345
Posts: 34
Joined: Tue Feb 12, 2019 4:15 am
Location: Essex, UK

Re: Single LEV50-cell wanted for our Citroen C-Zero

Thu Jul 25, 2019 3:39 am

me68 wrote:Hello,
again: one cell does not reach end of charge cell voltage anymore.


Hi,

I notice your screenshot is at 85% charge - does it have the same voltage as other cells when the battery is fully charged, or is that as far as it will charge up?

Looks like the cell is faulty, these cells are hard to get hold of, your only option is usually salvaging them from a dead car, but then they can be low capacity as they are used.

I may have some cells in the next few weeks but I don't know if they are any good, will need to test them once they arrive.

Cheers.

DBMandrake
Posts: 156
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Single LEV50-cell wanted for our Citroen C-Zero

Thu Jul 25, 2019 8:32 am

Low voltage of one cell at or near full charge that the balancing system can’t eliminate even across multiple charge cycles could be a fault in the cell balancer for that cell such as a shorted transistor for the balancing resistor.

Unless it’s so bad that the car can barely drive any distance a weak cell would not normally cause a voltage imbalance at full charge - instead it would cause an imbalance at a low state of charge as the weak cell discharged and reached minimum voltage before the others.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

JoeS
Site Moderator
Posts: 3736
Joined: Thu Dec 15, 2011 5:47 am
Location: Silicon Valley, California

Re: Single LEV50-cell wanted for our Citroen C-Zero

Fri Jul 26, 2019 11:35 am

I'd like to point out to those new to this forum is that Martin (me68) is the developer who created the CaniOn app and was the first (on this forum) to successfully replace a battery cell, which he documented for us earlier in this thread.

Can anyone suggest a specific test to perform when the pack is opened up on the bench to verify the cell balancer is operational?

Hope someone can provide Martin with a good usable cell. His free CaniOn app has been such a great contribution to our i-MiEV community and I would hope that we can help him out.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

DBMandrake
Posts: 156
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Single LEV50-cell wanted for our Citroen C-Zero

Sun Jul 28, 2019 10:46 am

JoeS wrote:Can anyone suggest a specific test to perform when the pack is opened up on the bench to verify the cell balancer is operational?

Before even opening the pack I would try running the "cell smoothing" diagnostic operation to attempt to force the cells back into balance.

This can be done with Diagbox (which I suspect Martin has access to) or it can also apparently be activated by recent beta versions of Hobdrive.

Although I have not used this diagnostic mode before (my cells balance perfectly during a charge) I believe what it does is attempt to balance the cells without charging. Normally balancing occurs towards the end of the charging cycle however if the imbalance is too large it could take multiple cycles to balance.

The smoothing operation will work at any SoC and activate the balancers on all high cells to bleed them down to the lowest cell's voltage without charging, and as a result should be able to correct even a large imbalance. As the bleeders are small this could take many many hours but in theory should bleed the high cells down until they match the low cell and then a charge could be performed to charge all cells back up again.

Assuming this succeeded I would then watch to see whether the cells get out of balance again.

A persistent cell voltage imbalance at a low SoC indicates a difference in Ah capacity between cells, however at a high SoC it indicates either a problem with the balancing circuitry, or a parasitic load that is discharging one cell more than others. (Such as a fault on the CMU board) In theory a cell with high internal leakage could also cause this but it is unlikely.

We've seen a failure of quite a few LTC chips on the CMU boards now - a faulty LTC chip could easily cause the balancer for a cell to remain on all the time, or the LTC chip itself could present a parasitic load since it is individually connected to each cell.

If one cell is subject to a parasitic load/discharge path which exceeds the discharge rate of the cell balancers, then the balancing system will not be able to maintain balance of the cells. There has been a reported case of this happening on a Leaf over on Speakev.com.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

JoeS
Site Moderator
Posts: 3736
Joined: Thu Dec 15, 2011 5:47 am
Location: Silicon Valley, California

Re: Single LEV50-cell wanted for our Citroen C-Zero

Mon Jul 29, 2019 9:16 pm

Not that it will do much good in this case, but here's an eBay ad for a single cell out of a 2015 i-MiEV (I didn't know there was such a model year in USA) so it must be LEV50N and they're asking $40USD with free shipping from Texas.

https://www.ebay.com/itm/2015-imiev-battery-3-7v-50AH-RV-Golf-Cart-Off-Grid-Solar-EV-i-miev/173781412444
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

DBMandrake
Posts: 156
Joined: Mon Mar 20, 2017 4:57 am
Location: Scotland

Re: Single LEV50-cell wanted for our Citroen C-Zero

Tue Jul 30, 2019 5:08 am

JoeS wrote:Not that it will do much good in this case, but here's an eBay ad for a single cell out of a 2015 i-MiEV (I didn't know there was such a model year in USA) so it must be LEV50N and they're asking $40USD with free shipping from Texas.

https://www.ebay.com/itm/2015-imiev-battery-3-7v-50AH-RV-Golf-Cart-Off-Grid-Solar-EV-i-miev/173781412444

For someone in the UK or EU you could also try this UK based company:

https://www.secondlife-evbatteries.com/

I've just ordered 4 cells for my car yesterday and expect delivery tomorrow. I can't vouch for the quality (eg remaining capacity) of their cells yet however I've been assured that the cells they supply should have a capacity of 40Ah or higher and that they are happy to fully refund the purchase if my testing proves otherwise. My weak cells are now at about 33Ah and the best cells in my pack are around 40Ah so this should be fine.

I will of course be doing my own Ah capacity measurement when I get the cells. Unfortunately the discharge rate on my tester is quite low as it's designed for radio controlled cars and quadcopters, so it will take approximately 2 days per cell to do a discharge capacity test, so I should know how good the cells are in a week or two... :lol:

One question I haven't decided on yet is how low in voltage to do the discharge test. From memory the lowest my tester will let you discharge a Lithium Ion cell is 3.0 volts, and the highest is 3.3 volts. Depending on what end voltage you choose you will of course get a slightly different result. In the car the cells are only ever used down to approximately 3.6 volts before the car shuts down to avoid a low voltage situation under load, so I'm inclined to test them only down to about 3.2/3.3 volts even though that will give a lower Ah figure.

I should add that the account signup process on their website seems to be broken (I've let them know) however I was able to place an order without creating an account.
- Simon

EV: 2011 Peugeot Ion
ICE: 1997 Citroen Xantia V6

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