Fuel gauge vs tortoise

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I obtained my 4 second hand cells from the following UK company:

https://www.secondlife-evbatteries.com/ev-batteries/yuasa-lev50.html

All of them were about 43Ah when discharge tested from 4.1 volts down to 3.0 volts, so better than even the best cells in my pack.

I see they are currently out of stock however I think they get stock in regularly (from scrapped cars) so it may be worth contacting them. Not sure where you are located but I suspect they may also ship to Europe.

There is also a guy in the Netherlands who strips and sells LEV50 cells (and other types) I can find his contact details if needed.
 
Car is in Bahamas .. still don't get why one weak cell will suddenly prevent pack from charging more than 25% though.
 
vh2q said:
Car is in Bahamas .. still don't get why one weak cell will suddenly prevent pack from charging more than 25% though.
Because all the cells are in series, so the usable capacity of the pack as a whole is limited to that of the weakest cell.

Weakest link in the chain. It only takes one faulty cell to decimate the usable capacity and range of the pack.
 
So the problem is the weak cell gets down to 3V pretty quick and the computer then shuts down the car to protect it? Can one short out the bad cell?
 
vh2q said:
So the problem is the weak cell gets down to 3V pretty quick and the computer then shuts down the car to protect it?
Essentially yes. Although it won't let it go down as low as 3.0 volts. It will only go down to about 3.6 volts before turtle mode will come on.
Can one short out the bad cell?
Definitely not. (I presume you mean remove and bypass, not literally short it out. :shock: )

The Battery management system monitors every cell individually if there is a problem with any cell the car will not work properly.

A cell swap with a good cell would be the only option.
 
I didn't mention it earlier but I got these two errors when I first scanned car:
P1AE6 EEPROM error
P1A51 EEPROM abnormal
I cleared them and they did not come back. The other two errors cannot be cleared
P1A4B cell voltage abnormal
P1A2F cell error

And this all happened after aux battery was out of car for some months
 
It's unfortunate that you had a cell go bad,

the first two DTC about the eeprom are likely due to the lack of a 12V aux battery for a time, and the ECU was confused at first when coming back up with power.

The last two are due to the failed cell.
 
For what it's worth, I ran battery down to 0 bars and when the turtle came on the bad cell was down to 3.48V, the rest were still at 4.0V. So it seems that the bmu software sets the charge gauge based on the weakest cell, but controls the charger based on the strongest cell.

After two charging cycles, weakest cell still does not get above 3.9V when the rest are at 4.1

Hobdrive was useful in diagnosing this situation, but there are an awful lot of meaningless screens and data. A lot of the fields come up as zero and you can't even get a current draw off the aux or the dc to dc converter. You can get a draw off the MCU. Many of the temps default to 32F. You can turn off the trouble codes but the car will regenerate them so the serious ones just pop up again. The cell smoothing function does not work. There are a bunch of screens that display CMU voltage. These appear to be clusters of 8 battery cells. This data is pretty useless.

And finally, a battery pack that is only as good as its weakest cell is an abomination. Especially when, all too often it seems, one cell goes bad.
 
vh2q said:
For what it's worth, I ran battery down to 0 bars and when the turtle came on the bad cell was down to 3.48V, the rest were still at 4.0V. So it seems that the bmu software sets the charge gauge based on the weakest cell, but controls the charger based on the strongest cell.
This is essentially correct. The BMU will not allow any cell to charge above 4.1 volts or below a minimum limit which seems to be a bit more flexible - typically between 3.3 volts and 3.6 volts.

When there is a weak cell these limits will be reached much sooner and the effective usable capacity is reduced.
After two charging cycles, weakest cell still does not get above 3.9V when the rest are at 4.1
Two charging cycles is not enough to do anything of significance. It took nearly 40 cycles to correct a 50mV error on my car.
Hobdrive was useful in diagnosing this situation, but there are an awful lot of meaningless screens and data. A lot of the fields come up as zero and you can't even get a current draw off the aux or the dc to dc converter. You can get a draw off the MCU. Many of the temps default to 32F. You can turn off the trouble codes but the car will regenerate them so the serious ones just pop up again. The cell smoothing function does not work. There are a bunch of screens that display CMU voltage. These appear to be clusters of 8 battery cells. This data is pretty useless.
The user interface of Hobdrive is pretty poor, I agree. However it can only provide information that the ECU's in the car make available. Under many conditions some of those fields are not applicable.

Resetting a fault code is not a magic cure - if the fault returns its because the fault is still there! Not the problem of the diagnostic tool.

The cell smoothing process is just a diagnostic process that can be initiated in the BMU ECU - I have an official Lexia 3 diagnostic tool for my Ion (the same tool used by dealers) and the cell smoothing function in that also did not work for me.

For reading cell voltages the best tool to use by far is Canion. If you have an STN11xx based adaptor like an OBDLink LX you can use Canion. Canion is read only and cannot reset codes or make any changes but I found it the best tool to diagnose weak cells on my car.
And finally, a battery pack that is only as good as its weakest cell is an abomination. Especially when, all too often it seems, one cell goes bad.
Unfortunately that's just the way it is - with nearly all EV's! Most EV's use either a single series string or more commonly a xxs2p configuration where cells are connected in parallel in pairs then the pairs are connected in series. The Leaf uses this paired approach.

However even in a pared approach there will be a large drop in capacity of the pair of cells if one cells go bad and the same issue will occur. Plenty of Leaf's have had cell failures as well.

About the only cars not affected by individual cell failures are Tesla's, which use massively parallel groups of small cells which are independently fused. If one cell in a parallel cluster of >20 cells goes faulty the capacity loss is minimal and the usable capacity of the pack will only be affected a small amount. However with a large number of cells the likelyhood of failure of a given cell is higher of course.

At least in the i-Miev a faulty cell can be replaced somewhat easily - I've done it on mine. The hardest part is getting the pack out of the car and back in again. Once the pack is down on a trolley the cell swap is relatively easy if you are an experienced DIY'er and have some electrical knowledge. Cells and modules in a Tesla pack are not DIY serviceable.
 
That is helpful thanks.

What tools do I need to pull the pack? Am on the proverbial desert island here. Instructions?
 
Hi,

You can check my blog over on frenchcarforum.co.uk, starting at this post:

https://www.frenchcarforum.co.uk/forum/viewtopic.php?p=624171#p624171

You'll need to register on the forum to read threads in the blog section.

One mistake I made during my cell swap was to attempt the swap when the pack was at 20% SoC. I would recommend that you do the cell swap with all the (good) cells fully charged to 4.1 volts, and also charge the replacement cell to 4.1 volts before fitting using a Lithium Ion cell charger.

Please be extremely careful when jacking the car up to make sure it is stable and also working with the high voltages. Even with the link plug removed from the battery pack once the cover is off there is still a risk of electrocution if you touch between different parts of the pack that have have a potential difference of more than about 50 volts.
 
I recall a post by ikiev, may be in the OBC trouble-shooting thread, with a reference to a user-manual page, saying that it's not recommended to disconnect the aux for over a month. If so, the computer has to be re-learn, something about the pack status.
 
found the page:

http://mmc-manuals.ru/manuals/i-miev/online/Service_Manual/2012/54/html/M154100230004500ENG.HTM
 
Thanks for that. I may have more than one problem. No way to modify bmu variables as I don't have Mut, only hobdrive. BMU may be confused in addition to bad cell
 
Have not really driven the car any distance since the surgery as this is a vacation home car. Right after the single cell swap was getting 13 bars. Then 14. 9 months later, put the accy batt back in car and ran it through a few partial cycles. The replacement cell is still about 0.1V higher voltage than the original cells but pack is charging up to 15 bars , it gets higher with each charge. I finally took it for longish gentle drive, under 40, and was surprised to get circa 5 miles per bar. Upon my return, had 4 bars left, started getting intermittent turtle. Got home, hooked up hobdrive, noted all cells around 3.7 except for the replaced cell at 3.8. no error codes. Checked coolant level it was full. So why the turtle? It just flashes on briefly, goes away when i back off the "gas".
 
16 bars today! Have not seen that since 2018. Wife's birthday. Taking her out for lunch in the Purple Peril!
 
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