johnnyz383
100 W
Ypedal said:
Ok im going to have to get a charger...but ill do it and see if they come back..alternately i can put my voltmeter on the balance leads that go to that group and see if they are putting out the required voltage
John
48 volt lifepo4 battery cutting out prematurely
- Thread starter johnnyz383
- Start date
Ok im going to have to get a charger...but ill do it and see if they come back..alternately i can put my voltmeter on the balance leads that go to that group and see if they are putting out the required voltage
John
dnmun
1 PW
can you say who was the manufacturer of battery and BMS?
you can test the BMS by measuring the voltage across the shunt resistor for that channel while it is charging. if the shunt transistor is ok then the problem is in the parallel string.
you can test the BMS by measuring the voltage across the shunt resistor for that channel while it is charging. if the shunt transistor is ok then the problem is in the parallel string.
johnnyz383
100 W
I took the pack apart and one of the 16 cells looks like it had a short..i measured the 16 and they began falling in voltage doing nothing...so i disconnected the cell that looked bad and it quickly felll from 2.3 volts through less than a volt...looks like its shorted...the other cells of the remaining 15 seem to be holding 2 volts but when i go to charge the pack, it says full charge...but the 15 cells are slowly going up in charge....we'll see.....
John
John
dnmun
1 PW
since you can't say which BMS we will just have to assume 40mA for the balancing current, so the 20Ah will take 500 hours to fill. so leave it charging for 20 days minimum.
izeman
1 GW
it would be easier to charge through the balance leads. use a 2pin male header and plug this into the disconnected female balance plug (at the right place of course *ggg*). then charge with a rc charger or if you don't have one with a 5v 1a (or 2a) small power supply while monitoring the voltage (eg every 10-30min or so). the string should be charged up to 4.1 volt and then reconnected to the bms. then do the finale balance charging with the supplied charger.dnmun said:
johnnyz383
100 W
I had originally bought the battery on ebay (duct tape). Supplied with the battery was the BMS...however the BMS failed and caused a string of batteries to also be depleted to zero volts. Through much wrangling i got them ( china) to give me 16 new cells and a bms.I had to take the battery apart and solder the new cells in place.
So over night the string went from 2.1 volts to 2.7. So if i under stand correctly simply disconnect 1 of the 2 balance leads from the BMS, hook a charger to the 2 wires going to the string affected and charge to 4 volts and then reconnect to BMS?. Seems easier. Hopefully the cells are still ok,
John
So over night the string went from 2.1 volts to 2.7. So if i under stand correctly simply disconnect 1 of the 2 balance leads from the BMS, hook a charger to the 2 wires going to the string affected and charge to 4 volts and then reconnect to BMS?. Seems easier. Hopefully the cells are still ok,
John
izeman
1 GW
johnnyz383 said:
correct. this is how i would do it. if you unplug the balance connector, use a voltmeter to measure voltage between pins. you should easily find the low cell string. then connect the charger to these pins. please DOUBLE CHECK polarity and insolation before connecting the charger.
going from 2.1 to 2.7 should be a matter of minutes doing this procedure. "real" charge is between 3 and 3.4v if i remember correctly (this is chemistry dependant). for lifepo4 eg it will stay at 3.3v for ages, then go up to 3.6v quite fast, only to jump to 3.8v within minutes.
dnmun
1 PW
you don't have to disconnect anything.
just clip the alligator clips from the single cell charger onto the ends of the battery cell that is dead and charge it up.
you should be able to charge it up in a few hours with a 10A single cell lifepo4 charger but it is totally discharged if it is still under 2.7V now.
just clip the alligator clips from the single cell charger onto the ends of the battery cell that is dead and charge it up.
you should be able to charge it up in a few hours with a 10A single cell lifepo4 charger but it is totally discharged if it is still under 2.7V now.
Ypedal
100 TW
i disagree, keep it up 2 amps max when dealing with potential bad cells in a group, if a BAD cell starts to heat up, it will happen much slower at 2 amps. giving you time to disconnect the charger..
if you tap into the balance leads ( to save yourself a pack teardown for the moment ) those tiny wires only handle up to 2 amps safely.
if you tap into the balance leads ( to save yourself a pack teardown for the moment ) those tiny wires only handle up to 2 amps safely.
izeman
1 GW
+1. if you're unsure about cell health slower is better. i would not let the pack charge left alone. check, check, double check. better to be safe then sorry.Ypedal said:
i made a little charge plug: banana plug 4mm at one end that goes into the icharger, and a little 2pin header on the other side. both pins covered by heat shrink, and all together in another heat shrink. super safe. just plug into the balance connector and charge. no need to clamp those crocodiles and fear that those could fall off. and if you got some cheap ones they will NEVER EVER handle 10a anyway
dnmun
1 PW
i was under the impression he had removed the shorted cell.
i did not feel he should take the sense wire plug apart since he had access to the cells already so he could hook the alligator clips directly to the cell.
i did not feel he should take the sense wire plug apart since he had access to the cells already so he could hook the alligator clips directly to the cell.
izeman
1 GW
i guess he DID remove the bad cell. but still it's imho easier to just unplug a connector and plug in a little pinhead then try to squeeze a crocodile between tightly packed cells. if those cells are lying on your desk it's a totally different story of course.
anyway: i wish you all the best charging this pack.
anyway: i wish you all the best charging this pack.
johnnyz383
100 W
I appreciate all the feedback wow!!...anyway i went and got a 5 volt 1.5 amp charger and went to charge up the string, and its fallen from 2.5 volts to 1.6 in about 7 hours...so i dont know if i have another cell that still has a short or the cells have been damaged...but i am going to charge them up tomorrow and see what happens
Yes i removed the cell that had a short...
John
Yes i removed the cell that had a short...
John
dnmun
1 PW
is it connected to the BMS as it drops in voltage or does the group drop by itself? if they got dragged to 0V they will show it too but below 2V means something is draining it imo.
johnnyz383
100 W
dnmun said:
Yes they were all connected to the BMS...im charging the whole battery up over night because i dont want the affected cells to drop any further...and then tomorrow ill charge the affected cells by themselves to 4 volts and see what happens.
John
DAND214
10 MW
Not 4v! It's not a lipo it's a lifepo, which doesn't like over 3.7v. IMO
Dan
Dan
izeman
1 GW
DAND214 said:
ooops. sorry. i over read that. don't know why, but i had 18650 cells in mind. of course you are right: lifepo4 should not be charged over 3.7v under regular conditions (though they still should not take any serious harm going to 4.0v)
Ypedal
100 TW
NEVER plug something like this to charge and then go to bed... never.... :|
izeman
1 GW
i guess he want to use the charger connected to the bms to charge the battery. that should be ok, but as you, i don't like having a charger connected to the battery and not being nearby. no matter what the battery looks like, and how fast i charge. ok. my nimh charger is connected all the time, and my laptop battery as well - but those were not built by MEYpedal said:
johnnyz383
100 W
I plugged in the WHOLE battery over night and the affected cells only came up to 2.8 volts all the others were around 3.6-3.8 volts, so i guess this method of charging when the cells are so out of balance would probably take a week. I hooked up my 5 volt 1.5 amp charger to the string going to the affected cells, as you can see in the picture...took about 3 mins to go from 2.8 to 3.0 volts..now slowing down....and yes ill charge to 3.8 voltsView attachment 1
izeman
1 GW
looks fine. your bms most certainly stops the charge when the other strings have reached their final voltage, so this is why we proposed to do it directly. just watch the voltage closely and check cell's temp during charge.
johnnyz383
100 W
Im closely monitoring the cells....no temp increase at all...my only worry is that since the cells were depleted down way past 2 volts that they are not permanently damaged.
I want to thank everyone who submitted to this post...really awesome..
I want to thank everyone who submitted to this post...really awesome..
999zip999
100 TW
Yo Bro never or may I say Never walk away thinking you will come back. ???? Never...
O.k. just because close to full and maybe full are milli sec's All batteries behave with there own reson's. So don't walk.
O.k. just because close to full and maybe full are milli sec's All batteries behave with there own reson's. So don't walk.
johnnyz383
100 W
Ok...the affected string (minus one cell) holding at 3.5 volts. Im going to button everything up and take the trike out for a test drive. Seems like the cells are fine....we'll see after the test.
John
John
dnmun
1 PW
you should charge it until it reaches full charge. you need to be able to get it up to 3.65V on the cell that was discharged and then monitor how rapidly it drops in voltage while disconnected from the BMS.
