Lifepo4 Battery not charging

[dogman dan]

Once you do have all the simpler possiblities eliminated, such as broken or misaligned connectors, broken wires, broken chargers, etc, that pretty much leaves the bms is not working a the last possibility.

Not unheard of for sure, but you do want to look for the eaiser to fix and more common faults first.

 

[leonardo]

My BMS, looks normal to me.

 

[leonardo]

Now I have eliminated all simple errors: no cells broken, no connector problem, no broken wires, I have ordered a new BMS from China. Hopefully it will arrive soon.
I also ordered a book on BMS from amazon: Battery Management Systems for Large Lithium Ion Battery Packs by Davide Andrea to learn some more about the subject.

For charging only: I have a balanced charger which can handle 12 cells LiFePo4 batteries (Thunder 1220 Pro charger). For charging without BMS this is a perfect solution. This charger will do all the balancing.
This does not not solve the problem of over-discharging when using the batteries! So still some simple protection is needed here to prevent from over-discharging.

 

[leonardo]

I have received the new BMS! Type: AE-LMD17 REV A1. In spite of a lot of bad comments in this forum I have ordered this BMS in China, making sure to have the right schedule to connect it to the 12 cell 36 volt 7Ah battery. First I have mesured the current power of the battery (40.1 volts). The output from the BMS was exactly the same. Time to connect it to my skateboard again. It worked perfectly!
Secondly I have connected the BMS to the charger (43.8 volts, 2Ah).
At the end of the charge the battery was 43.4 volts. I do have to check if all cells are nicely balanced, but I think it's gonna be okay.

 

[dnmun]

refresh what your problem was with that other BMS. were you using a bulk charger with that original BMS to charge or were you using the octopus charger to charge and balance it?

it did not look dead, no burned up mosfets so it may have been a bad connection in the sense wire bundles. it looks like there are two sets of plugs on the sense wire cables. you could check continuity on the sense wires through those plugs. does the charging current flow through the sense wires to the cells or is there a second set of wires that connect to the cells?

my original point was that it is not safe to remove the BMS and charge the pack up without the BMS when the BMS is actively trying to prevent more charge from entering the high cells. this would appear just to be a charger not cutting in to charge when the pack voltage seemed low enuff that it should take charge.

if you feel a need to charge it without the BMS under that circumstance, then first check all the cell voltages to make sure that one of the cells is not already full, at 3.9V already, before using the bulk charger without a BMS, and then you would have to monitor all the cells with a voltmeter during the charge to make sure you stop before any cell goes above 3.9V.

 

[leonardo]

Thank you for your comments, Dnmun.

I used the bulk charger. It just switches of when 43.8 volts is reached. No sense wires to the charger.
I agree on you that the old BMS did not look dead at all. Nothing burnt. The voltage output was significant lower though.
So I checked the cells separately, all of them were alive. All wiring was fine too. I have used the original wiring on the battery to connect to the new BMS as well. There is no second set of sense wires.
Next time (if any) I will use the sensed charger (Thunder 1220 pro)

I agree on you that it is not wise to charge the pack without BMS using a bulk charger. Luckily all cells were healthy after charging without BMS. I did check the voltage of every cell every five minutes. Doing so showed me that the battery was fine and the problem had to be in the wiring, the connectors or the BMS.
I guess the old BMS (dissipative) allowed one ore more cells to get discharged to far to charge again using the same BMS. Normally dissipative BMS should 'bleed' the lower cells to normal voltage again. This did not happen and I ended up with an unusable battery pack. After charging the pack again, the old BMS did not open up anymore where the new BMS (capacitive) did using the same wires.

Finally, I am happy having the pack usable again. The new BMS costs 18 dollars plus shipping at http://www.freegopower.com (via alibaba). I decided to buy an inline Turnigy Power Analyzer Watt-Meter Ampere-Meter to attach to my skateboard as well.