headway 38120, fully discharged, are they dead?

[Pablo_1985]

A friend of mine left a 16 cells battery pack for months with a bad BMS (some cables where not getting the reading from some cells), so the BMS discharged all the batteries a point in whci the complete pack give 2 volts... He tried to charge it with its charger, but it doesn't charge it ( i guess it is too low voltage), he ask me and i don't know if there is any chance to get them back to life, maybe with a constant current source or charging them by voltage step progressively... But i am just brainstorming because i don't have any idea.

I guess this is the kind of topic that should starts with a "HEEEELLLLPP"

Cheers and thanks in advance.

Ps: sorry, there is a lot of gramatical misrakes but writting with my phone here is a pain kn the ass.

 

[SamTexas]

A friend of mine left a 16 cells battery pack for months with a bad BMS ...

"bad" is redundant! Most BMSs are bad.

Anyway, there's hope for your friend pack. Most Battery Murdering Systems only bleed a few consecutive cells. Usually the first or last 3 or 4 cells. So the rest of the cells should be ok. Voltage can be measured through the balance wires if accessible from the outside. Most of the time, the shrink wrap needs to be removed for access. Once opened, the low cells can be charged (if they are not yet dead) individually using a low amp cell phone chargers.

Whatever your friend will be doing, tell him not to listen to some fool who will be coming around soon and telling your friend to modify the charger.

 

[Ypedal]

I've taken my PSI pack ( 24 cell 10ah ) to 0v , twice, and got them back....

first, remove the BMS, duh.

Then, using slowly bring the voltage up ( limit to a few amps max.. 1amp is plenty ) until all cells read 2.x volts or more .. then remove the charger/power supply.. wait a few minutes and check the cells again.. if they drop to 0v quickly.. the pack is toast.. if the voltage stays... proceed with carefull charging while monitoring for hot cells etc.. checking voltage along the way..

a single cell charger is almost a must here... you will want to fully charge each cell to bring the pack back in ballance.. IF it takes a charge .

 

[dnmun]

you don't have to remove the BMS to charge it from zero.

you can jumper from the charger negative lead on the BMS to the B- spot on the BMS then it will charge. you can use a power resistor in series to limit the charging current.

use a jumper with alligator clips and when the pack gets charged up enuff to turn on the mosfets you can charge it normally through the BMS and you can remove the jumper.

you may have the BMS that uses the output mosfets so if you can post up a picture of the BMS we can give you accurate info.

 

[Pablo_1985]

Thanks gus!! I already told him to remove the cables from the BMS, but not the power ones. Apparently he has a regulated power source from 0 to 50, i can check the current during the process, but at least i have the materials to do the job . I will not disconnect the power cables from the BMS after all the BMS is in series with thebattery pack, y can connect directly to the pack and not passing by the BMS.
Battery Murdering System... That's killing me ha! I cannot understand why don't they have some diodes in series with the discharge resistor so they will not overdischarge over a specific value (0,7 x number of diodes)....ALL the problems i had with batteries have been related with a malfunction of the BMS... Nonsense!!

Thank you very much guys, you are the best!

Ps: hopefully i will change my e-bike for a toyota auris hsd... I am already thinking about plugin conversions

 

[SamTexas]

ALL the problems i had with batteries have been related with a malfunction of the BMS... Nonsense!!

Amen to that. "malfunction" is redundant though, because most BMSs are not functioning. Damn, why is it so hard to find one that actually works?

 

[dogman dan]

Love the way the bms gets blamed when the problem was apparently the wiring that goes from the battery cell to the bms.

Sticking it on a shelf and ignoring it for 6 months had nothing to do with it either. 100% the bms's fault.

It is a shame though, that these batteries don't come with some simple care instructions, like unplug the bms for long term storage.

Definitely worth a try to revive them since they aren't lico, and the discharge was a very slow one.

 

[dnmun]

yep, no evidence that the BMS is broken at all.

 

[melodious]

I've said this in another thread before and I'll say it again. These batteries are a LOT of $$$ going in. If you aren't going to use them on a daily/weekly basis then it's relegated to "toy status". A very expensive toy. And we all know how we used to deal with toys during childhood: throw them under the bed and forget about them when we get bored of it. If you don't use them, time will take it's toll. :|

 

[etriker]

Love the way the bms gets blamed when the problem was apparently the wiring that goes from the battery cell to the bms.

Sticking it on a shelf and ignoring it for 6 months had nothing to do with it either. 100% the bms's fault.

It is a shame though, that these batteries don't come with some simple care instructions, like unplug the bms for long term storage.

Definitely worth a try to revive them since they aren't lico, and the discharge was a very slow one.

Sticking it on a shelf and ignoring it for 6 months was a master bms failure.

The slave bms was lost without a master bms all that time and did not know what to do so it killed the pack ?

 

[Pablo_1985]

Wow! That sclated quickly! Was the BMS Some familiar of yours? You took it personal! Hahaha, well at the end you are right it wasn't BMS Failure but the BMS shouldn't discharge the cells completely! But I Agree, the biggest mistake has been ignoring the pack for months. But I think the BMS design is far from perfect, remember that this things should be done for dummies, or at least that's the point if we want this technology to expand.

Cheers!

 

[dnmun]

the BMS is there for dummies because nobody is smart enuff to be able to tweak each cell to just the same voltage as a BMS does and protect the battery from accidental shorting which would damage it or cause a fire or shut off the charging when one cell goes too high or shut off the BMS when a cell goes too low. the headway cells can go outa balance without the BMS to balance them. a BMS does not consume very much current. it take effort to deliberately ignore it and drain it down to nothing.

try 15mA, 24 hours a day = .36Ah/day so it only takes a month to discharge the 10Ah cell if the cell was full when the battery was put up. at 5mA it would take 3 months.

you can put a switch in the circuit current to turn off the BMS when not used so it consumes essentially no current while sitting around unused.