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LiFePO4 DIY batterie not charging !

walex

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Joined
Feb 21, 2020
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7
Hello !
I build this exact battery (same BMS and cells) as in :
I have issue to charge it to the top with an all in one MPTT chargeur-bosster able to charge from solar panel and also a car alternator.

The batterie is at 13.0 V SoC and thus not accepting any Amp when charging (well 0.1 to 0.4 A so very little compare to its 105Qh capacity).
When the engine runs, the eng-battery and alternator voltage is 13.8 and the aux battery goes up to 13.4... though it's not accepting much amp.
Seems like it comes from the charger as with an epever MPTT solar charger I can charge up to 5 A with a small solar panel.

I don't know where to see now. But from the booster LED I can see it tries few times to absorption-stage charge the battery:
the voltage go up for a short time and it accept like 5 A for few second (like 3s) but then stop.
After 1 second, the booster try again charging and the same happen.
After like 5-10 try, the charge goes in mode bulk charge and I have no more than 0.3 A going into the batterie.

It seems to me that the BMS open the circuit when the booster try the boost charge. But the BMS is set to allow up to 3.65/cell and 14.6 V total pack (I setup this via bluethooth).
Also this does not happen with the solar charger.

Any idea why ??
Thanks a lot for your help !!
 
What make / model DC-DC charger are you using to charge your lifepo4 battery from your vehicle's 12V system?
 
Do you have a multimeter with a peak hold feature that you can check the voltage from the charger when operating from the vehicle's 12V system instead of solar? From the spec sheet the charger only goes up to 14.2V when configured for lithium batteries. That should be low enough to not cause your BMS to trip on over voltage.

Another explanation might be that when you are charging from solar the charge current is lower than when charging from 12V and that increased current may be allowing cells in the battery to rise in voltage faster than the battery's BMS can cope with so it trips on cell over voltage rather than battery over voltage.

I tried to find a manual, preferably in English, but couldn't even find a French one. Do you have a link for the manual?
 
Thanks for your answer :) !
I don't have a multimeter with peak hold.
Here is the manual https://www.h2r-equipements.com/index.php?controller=attachment&id_attachment=1599
Unfortunately in french! From the doc quality it seems we are already lucky to have one in french lol !
Let me know if you need me to translate a part of it. I'll be glad to help you help me ;-) !

I set the BMS cell overcharge to 3.65 and the package overcharge to 14.6.
Charging with solar the pack does not go over this. Maybe with the booster, as it takes more amp (at least 4 probably more but we can not see, BMS open the circuit before - however no more than 25A as the fuse did not burn) and thus the voltage goes higher ?

The BMS default setting where much higher value for cell and package overvoltage (I can't remember nor restore those value).
Maybe I should set higher values ? Like 4.2V and 16V ? but it looks like a bad idea right ?...
 
According to the manual the lifepo4 absorption voltage is 14.8. That may well be why your BMS is disconnecting. The the battery is near fully charged it will quickly rise up to 14.8V. 14.8V is 3.7V / cell. The charger looks like it turns off once that voltage is reached so it would only pull the cells up to that momentarily, hopefully.

As a test only raise your BMS cell over-charge voltage to 3.7 and battery over-charge voltage to 14.8 and see if the BMS holds on. It may even be necessary to set the cell voltage to 3.75 and battery to 14.9. If the BMS does not trip off under these circumstances confirm that the charger turns off its output as you don't want to hold the cells at those voltages.
 
Ok. I think I got the issue. Updating the BMS app helped a lot on understanding what was happening. Indeed the new version is much better (graph and translated event counter...).
In short some cells are going to high as soon as charging start and the BMS trip off, then on again and a loop start. I guess it make mess also for the booster that seems to lower progressively the intensity until very low charging intensity but no more loop.

At rest, the every cell are having more or less the same voltage of 2.29 V with a max diff of 0.07V.
But under charging or discharging 2 cell are going either too high :
up to 4.0 V when charging (vs 3.45 V for the 2 others)
down to 2.3 V when under a 4A load (vs 2.9 V for the 2 others).

I wonder if those cell are damaged or just not matching the other 2 in term of internal resistance....
Indeed I received it brand new and I am pretty sure I didn't do much mistake as I never could overcharge it (because the BMS always trip off, then the booster lower the power to almost nothing). I did not under charge it either (I could the BMS trip off also under my fridge load).
Also their well balanced in term of voltage at delivery.

How can I know why these 2 cell over-react on charging/discharging compare to the 2 others ?
Can internal resistance be responsible for such behaviour ?
How can I measure the internal resistance ?

I hope the vendor can change those 2 cells, but i got it for 3-4 month now even if I did not use it at all the first 2 month while waiting for the BMS (covid delivery issue) and then very few uses.

Thanks for your reply.
 
No I didn't. I understand and know why I should have with this great video :) !

Allthough I wonder if this explains my problem :
If those 2 cells were more charged than the 2 others, it is normal they go higher while charging and the BMS cut off.
But then while discharging these cells should be equal or higher than the 2 others, not lower right ? there are much lower.
that is why I think of damaged cells or another problem..

that said, once this problem solved for sure it ALSO need a top balance.

What do you think ?
 
That could be a bad cell or maybe not the same capacity.
But I think your cell are less charge and it is why you see them lower on the discharge cycle and on the charging cycle the two oder are the one that trip the BMS. Try to number your cell to keep record of your voltage reading and do a top balance to start!
 
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Top balance first and retest. Which cells are showing high? I'm curious about this as I'm wondering if the order of the cells in the battery pack matters.
 
Your choice look limited on amazon.fr , do you consider this one for more precision !



note : Spécifications: Tension d'entrée: Tension d'entrée: 220V ± 10% / 60Hz (commutateur de réglage à l'arrière), Tension de sortie: 0-30V, Courant de sortie: 0-10A ( je ne sais pas si ca veux dire que le commutateur est 50/60 hz)
 
Hello there !!
Thanks for your answer! I could perform the top balance and get each cells charged up to 3.65 V with exact same voltage when IDLE.
Then I packed the cells in series and applied some load on it for a few hour, getting to around 50% SoC I guess. Voltage of each cell remains very close (max delta is 0,05 under load).
However when charging again after this (cell in series in the pack), I still have one cell getting a higher voltage than the others under charging (up to 3.9). This trip the BMS and a charge/no charge loop starts. If I stop the charge, the suspicious cell get back to the same level as the other ones...

I will perform a second top balance to 3.65 with all cells in parallel and try a second time.... but I am pretty sure this specific cell is dammaged and have to be changed for another one.

What do you think ??
Thx !
 
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