About to drop the battery to replace a bad cell. It is one of the cells in a 4 cell pack so i plan to replace the entire module. Could not buy just one cell. Question: is the replacement 4 pack plug and play or am i going to get into an eprom nightmare?
Replacing 4 cell pack
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coulomb
Well-known member
You will encounter problems unless
* You are lucky and the replacement block of 4 cells has the right CMU id. Since there are only two 4-cell blocks in the pack, I figure that your chances are about 50%, or
* You have a scanner that can emulate a MUT-III and issue the magic command to renumber the CMU ids.
* You are lucky and the replacement block of 4 cells has the right CMU id. Since there are only two 4-cell blocks in the pack, I figure that your chances are about 50%, or
* You have a scanner that can emulate a MUT-III and issue the magic command to renumber the CMU ids.
The replacement pack is at 16v. The rest of the traction battery is fully charged. So they are all circa 4V. The balancing function will level it all out, I hope. The bad pack I have one cell that is about 3.6V and another about 4v when the rest of them are at full 4.1V. The BMU shows only 4 bars at full charge due to these two weak cells .. it shuts the car down to protect the weakest cell.
coulomb
Well-known member
My guess (and it's only a guess, I have no direct experience with this) is that the battery will refuse to work (can't go to ready), and you'll get a DTC about non-responding CMU or the like.vh2q said:
Edit: but you could swap the CMU boards in that case. A lot of work once the battery is reassembled.
Well that is the plan, to just switch out the cells. unless there is some way (not requiring sophisticated diagnostic equipment) to confirm that the 4 cell replacement pack is a plug and play for the bad pack that's causing the problem. Last thing I want to do is to pull the battery twice. Since two of the cells in the 4 pack are the laggards, I am somewhat concerned that the other two might be dubious, or that the electronics themselves are at fault (eg the balancing function) and not the cells.
Planning to get on it in a couple of weeks.
Planning to get on it in a couple of weeks.
I made a bottom balance.
https://www.youtube.com/watch?v=UJx7qL6Eo08
https://www.youtube.com/watch?v=o-9LMiZdoNc
DbMandrake and others after replace cells observe a no relevance gain. I´m not an expert but an electric mechanic in Spain "80% electricos" has a lot of experience special with Smart and Citroën C-zero (i-miev) from carsharing companies. Following his information is important reset BMS and BMS history. Are two steps.
Don't believe the display of charge and the new autonomy!!!!!!! . And drive only with the old autonomy. You can drive with the Obd plug in and reading the voltage for more security.
After this, I charged and finally discharged finding the minimum voltage diference between cells. Wait two hours. Drive a few Kms. Wait two hours. Charge maybe only 15-20 min. Wait. Drive. Etc.....Charge a few minutes and you can see with Hobdrive how up the voltage but the "Ah BMS remaining state" up very slow. You can go down the voltage and finally discharge the car with balanced cells. With no charge in display of the car, I started charge. Then, before inject intensitivy , the voltage go very fast to 3.8v. When the display marks 3 steps all change. Out of reserve, start the intensivity. After this is very dificult to balance charge for the BMS.
I use Hobdrive watching BMS state. Min Max voltage Ah remaining etc....
The voltage and charge has a correlation but are not the same. 4.1v maybe is not a full charge for some cells.
The goal is a battery pack balanced not only with full charge, with bottom charge too.
Car Scanner App "can" make a "smoothing voltage" free. But I dind´t use yet.
This is my experience not a recomendation.
https://www.youtube.com/watch?v=UJx7qL6Eo08
https://www.youtube.com/watch?v=o-9LMiZdoNc
DbMandrake and others after replace cells observe a no relevance gain. I´m not an expert but an electric mechanic in Spain "80% electricos" has a lot of experience special with Smart and Citroën C-zero (i-miev) from carsharing companies. Following his information is important reset BMS and BMS history. Are two steps.
Don't believe the display of charge and the new autonomy!!!!!!! . And drive only with the old autonomy. You can drive with the Obd plug in and reading the voltage for more security.
After this, I charged and finally discharged finding the minimum voltage diference between cells. Wait two hours. Drive a few Kms. Wait two hours. Charge maybe only 15-20 min. Wait. Drive. Etc.....Charge a few minutes and you can see with Hobdrive how up the voltage but the "Ah BMS remaining state" up very slow. You can go down the voltage and finally discharge the car with balanced cells. With no charge in display of the car, I started charge. Then, before inject intensitivy , the voltage go very fast to 3.8v. When the display marks 3 steps all change. Out of reserve, start the intensivity. After this is very dificult to balance charge for the BMS.
I use Hobdrive watching BMS state. Min Max voltage Ah remaining etc....
The voltage and charge has a correlation but are not the same. 4.1v maybe is not a full charge for some cells.
The goal is a battery pack balanced not only with full charge, with bottom charge too.
Car Scanner App "can" make a "smoothing voltage" free. But I dind´t use yet.
This is my experience not a recomendation.
OK interesting .. the BMU in the car does try to balance the cells but only at the top? (And this balancing function is rather limited requiring LOTS of cycles to achieve a balance).
To clarify my situation .. I have two cells (both in the same 4 pack) that lag behind the remaining cells when the charging cycle ends. They don't get to the same voltage as the rest. Thus, the fuel gauge shows only 4 bars when the car is fully charged. And if you drive the car, the laggard cells reach the lower limit quite fast thus limiting the range before the "turtle" comes on.
Are you saying you can force a bottom balance by following the steps you have described? ie drive, wait, small charge, drive, wait ...
If so perhaps I don't have to replace my cells, perhaps they are just out of whack with the rest. (I am in a location where I cannot take the car to the dealer for an external balance?) And if I do replace my cells, it sounds like unless I am v careful, I will just end up where I started with 2 cells out of line with the remainder?
To clarify my situation .. I have two cells (both in the same 4 pack) that lag behind the remaining cells when the charging cycle ends. They don't get to the same voltage as the rest. Thus, the fuel gauge shows only 4 bars when the car is fully charged. And if you drive the car, the laggard cells reach the lower limit quite fast thus limiting the range before the "turtle" comes on.
Are you saying you can force a bottom balance by following the steps you have described? ie drive, wait, small charge, drive, wait ...
If so perhaps I don't have to replace my cells, perhaps they are just out of whack with the rest. (I am in a location where I cannot take the car to the dealer for an external balance?) And if I do replace my cells, it sounds like unless I am v careful, I will just end up where I started with 2 cells out of line with the remainder?
Balancing sounds like a good idea and is best done at some known reference level, either at the top or the bottom end of the cell voltage range.
The question here is what has caused the imbalance situation with the two cells--Were they drained from providing power to the BMS board, or do they have an internal defect? Are the two cells neighbors or is there good cell(s) between them?
The balancing in the miev is only a bleeder function at a very low current, so it would take a very long time to correct even a small imbalance voltage.
It somewhat depends upon how much work you want to do, e.g. pull and open the pack several times vs one time, open the pack after fully charging or fully discharging, etc.
Some scenarios,
Open pack and use lab power supply to charge just the 2 low cells up to match the rest, then assemble and test.
Open pack and replace the 2 cells after bench charging the new ones up to match the rest, assemble and test.
Open pack after being discharged, use lab supply to charge 2 low cells up to the rest, then discharge entire pack toward the bottom while making adjustments to the 2 bad cells to prevent going too low, etc. with goal to bottom balance the entire pack (with the laggard cells). Once balanced, assemble and test, this might work if the cells were just drained from the BMS, but not if they were defective.
Same as above but done at top voltage, top balancing.
Open pack, remove the 4-cell module and swap the CMU board between the old and new module, charge the new module using bench supply to match the rest of the pack cell voltage, assemble and test.
Same as above but fiddle around trying to remove and swap eeprom chips, or reprogram eeprom chip.
etc...i'm sure there are other options too.
The question here is what has caused the imbalance situation with the two cells--Were they drained from providing power to the BMS board, or do they have an internal defect? Are the two cells neighbors or is there good cell(s) between them?
The balancing in the miev is only a bleeder function at a very low current, so it would take a very long time to correct even a small imbalance voltage.
It somewhat depends upon how much work you want to do, e.g. pull and open the pack several times vs one time, open the pack after fully charging or fully discharging, etc.
Some scenarios,
Open pack and use lab power supply to charge just the 2 low cells up to match the rest, then assemble and test.
Open pack and replace the 2 cells after bench charging the new ones up to match the rest, assemble and test.
Open pack after being discharged, use lab supply to charge 2 low cells up to the rest, then discharge entire pack toward the bottom while making adjustments to the 2 bad cells to prevent going too low, etc. with goal to bottom balance the entire pack (with the laggard cells). Once balanced, assemble and test, this might work if the cells were just drained from the BMS, but not if they were defective.
Same as above but done at top voltage, top balancing.
Open pack, remove the 4-cell module and swap the CMU board between the old and new module, charge the new module using bench supply to match the rest of the pack cell voltage, assemble and test.
Same as above but fiddle around trying to remove and swap eeprom chips, or reprogram eeprom chip.
etc...i'm sure there are other options too.
Rather hard to balance at the bottom since you can't get all the good cells to the lower limit in the car, you can however get them to the upper limit quite easily. Then worry about the two bad cells. The problem surfaced after the car stood for a very long time (I was going through cancer surgery and then chemo at the time). It does not appear to have gotten worse. The two cells are 41 and 43 .. 41 is the worse of the two, gets to 3.71 when the rest of the pack is at 4.09 or 4.1. 43 gets to 4.07
Cell 43 might be okay, just somehow got out of balance. Cell 41 is way out of family, probably a bad cell.
i had a cell that was way off such as that and tried all manner of charging and discharging to try to top balance to bring up a low cell, but it was hopeless. If the cell is bad then it can not be balanced back up.
i assume your pack is not under warranty.
i had a cell that was way off such as that and tried all manner of charging and discharging to try to top balance to bring up a low cell, but it was hopeless. If the cell is bad then it can not be balanced back up.
i assume your pack is not under warranty.
Thanks for your perspective Kiev, I am going to yank both of the cells and see if that fixes things. I will precharge them to match the rest of the pack before I swap them out. Once you go to the trouble of dropping the battery, may as well replace any suspect cells. Hope to finally get this vehicle back on the road. I think I will send the bad cells to Mits USA when I am done.
Where are you located--if in US then your pack is still under warranty.
vh2q said:
The BMS depends of his software and always are not the best. BMS try to protect the cells between 2.7v-4.1v. Real capacity 2.5v-4.2v.The cells needs maintance . Desbalancing appers when you don´t go to display reserve. With MUT you can make a better balance.
With no bars or less than 2, the cells they go quickly to 3.8v. Maybe in 20 minutes. If the desbalancing are to big and you continue charging the BMS can´t fix the problem. Go down and start again.
Now your desbalancing are enormous. Maybe it´s not possible to fix but you don't loose nothing to try.
How many kms can you drive? can´t you go to no bars? with no bars, which are the voltage cells?.
I did try to drive the car to zero bars a couple of times. I could get about 8kms. The second and third time it improved a bit. After each trip I recharge but it only gave me 3 bars then it shuts down.
I don't recall the cell voltages when the car was at zero bars, but I think (from memory) the bad cell was at the lower limit and the rest were nearly full.
No MTU unfortunately. I have hobdrive and that's it. And even that is now not working, I can't pull up the cell voltages. I am going to try a different plug-in module.
I don't recall the cell voltages when the car was at zero bars, but I think (from memory) the bad cell was at the lower limit and the rest were nearly full.
No MTU unfortunately. I have hobdrive and that's it. And even that is now not working, I can't pull up the cell voltages. I am going to try a different plug-in module.
There are 2 brackets each secured by 3 10mm bolts just north of the trailing arms. Not clear what they do but they have to come out w a 12mm socket. There is also an electrical connector left rear that's hard to see.
17" clearance to bottom of battery, covers off, is absolute min to slide battery out. Rear more critical than front.
Threaded rods have to come out as well, at the end, unless they are v short, which would create other problems.
The lowering calls for a person on either side, or a lot of cussing.
Cell swap next
17" clearance to bottom of battery, covers off, is absolute min to slide battery out. Rear more critical than front.
Threaded rods have to come out as well, at the end, unless they are v short, which would create other problems.
The lowering calls for a person on either side, or a lot of cussing.
Cell swap next
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