48 volt lifepo4 pack at 35 volts

pauldo said:
It looks like that is the only way to charge individual cells,pull the pack apart
Click to expand...
no, you do not have to take the pack apart. plug in the charger. measure the current going into the charging wire with and ammeter, then connect the negative charging wire to the B- terminal of the battery and measure the current flowing into the battery. use wire to connect the B- terminal to the C- terminal on the BMS. just bend it into a loop with the two ends exposed so you can push each end into that spot on the BMS. measure the current flowing into the battery.
 
dnmun said:
..... then connect the negative charging wire to the B- terminal of the battery and measure the current flowing into the battery. use wire to connect the B- terminal to the C- terminal on the BMS. ....
Click to expand...

Bulk charging? :?:

:D
 
we have to figure out why his charger does not charge his pack. it may have a bad connection somewhere so he needs to bypass the BMS to charge it to rule out the other factors first. very simple and elemental systematic analysis of his failure and symptoms.
 
I agree, no need to disassemble yet.

Try charging bypassing the bms. But that may overcharge the better cells fast, so keep a close eye on it.

Best if you use a 3-5v power supply or single cell charger to try to perk up the really low cells first. See if they will take and keep a charge with the bms sensor wires disconnected.

You can stuff a wire into the female slots on the plug, to charge just one cell at a time. Maybe put a tiny bit of solder on the wire to stiffen it, make it into a male prong. The wire on the 4v cell phone power supply I mean.

If you can get the cells to look ok, then on to finding out if the bms is not working, and causing this.
 
dnmun said:
pauldo said:
It looks like that is the only way to charge individual cells,pull the pack apart
Click to expand...
no, you do not have to take the pack apart. plug in the charger. measure the current going into the charging wire with and ammeter, then connect the negative charging wire to the B- terminal of the battery and measure the current flowing into the battery. use wire to connect the B- terminal to the C- terminal on the BMS. just bend it into a loop with the two ends exposed so you can push each end into that spot on the BMS. measure the current flowing into the battery.
Click to expand...
What do you call the c- terminal
 
pauldo said:
What do you call the c- terminal
Click to expand...

The negative wire on you battery charger is the C- wire.
The wire that connects the negative side of you battery to the bms is the B- wire.

:D
 
I bypassed the bms,voltage went up to 48v in a couple of minutes,disconnected and hooked up to bms,started charging again.
Has been on the charger for 1 1/2 hours,is up to 52v,will let you know what happens.
 
Your pack is badly out of balance, so it probably won't have full capacity when it finishes charging. To balance, finish charging, then discharge the pack just enough to get the charger to come back on and repeat the charge cycle many times to improve balance.

It would be a good idea to measure the individual cell voltages when it finishes charging the first time so you can get an idea about the balance condition.
 
you can make it balance faster if you use a power resistor of about 5 ohms and 5 watts and when the high cells get up to the 3.9V level and shut off the charging, you can use some alligator clips on the ends of the wire to the power resistor and clip the resistor on to each end of the high cell to drain it down faster, while continuing to charge the others up.
 
I have charged the battery once.let the charger cycle on and off for 2 hours.
!5 cells are around the 3.46 mark,one is 0.8.
Have left the battery for 18 hours.
15 cells are on around 3.26,one is completely dead.
I thought the good cells would be less,because they would be trying to top up the dead cell,i guess not.
I do not think it would be much good like this because the bms would cutout with lvc early.
Suppose i will have to try and replace the dead cell.
I was thinking of splitting the pack anyway.
What are your thoughts on why one cell is completely dead.
Thankyou for all the advice i have received so far.
 
did you try charging up the cell at .8V with the single cell charger? the other cells are not charged up either. can you put an ammeter or wattmeter in the charging current path so you can monitor the charging current?

you will need to measure the current in the sense wire for the low cell to determine if it has a shorted shunt transistor. you can measure the voltage across the shunt resistor to determine if it has current flowing through it.
 
dnmun said:
did you try charging up the cell at .8V with the single cell charger? the other cells are not charged up either. can you put an ammeter or wattmeter in the charging current path so you can monitor the charging current?

you will need to measure the current in the sense wire for the low cell to determine if it has a shorted shunt transistor. you can measure the voltage across the shunt resistor to determine if it has current flowing through it.
Click to expand...
What should they be charged at
This is new to me,i do not know what you are talking about with shunt resistor.
When the charger turns off the bad cell no12 is only .8 it drops back to maybe .3 then charger turns back on goes back to .8
How do i charge individual cells.no12 already has 36 odd volts,if you know what i mean,1-3.2 2-6.4 3-9.6 then up to 16-52v.
Were do i put the negative and the positive to charge cell 12
 
You have a dead set of parelle cells as one. Don't put it on the charger.
It might over a different cell as it is pushing to 54 volts as final charge.
Charging a dead cause fire.
 
Well it was worth a try. Your dead cell is likely caused by one cell in that cell group getting an internal short, then it self discharges the remaining good cells in that group as well, killing them too.

So what I mean is, out of all the cells in the pack, just one was not the best possible quality, and died early. Once that cell is a gonner, it takes the cells that are paralleled to it with it.
 
if you want to determine if the cell with the low voltage is itself a bad cell, or if it is low because the balancing shunt transistor is shorted, then you have to determine if the BMS balancing shunt transistor is shorted out and is now draining the cell to low voltage. you do that by measuring the current in the sense wire to that cell.

you can test the transistor with the diode tester on the DVM or just measure the voltage drop across the shunt resistor for that channel. there will be a voltage across the balancing shunt resistor when there is current flowing through it.
 
you would only need to expose the BMS so you can measure the voltage on the balancing shunt resistors of the channel that has the low cell in order to know if the problem is the shunt transistor. it will be the same as the voltage you measure on the cell. so low.
 
How does one identify the shunt transistor?

:D
 
I have pulled the pack apart,looks easy to split in two,that is what i wanted to do anyway
Nothing looks unusual to me.
It is in 16 rows of 7.
batteries are unmarked,so i assume they are 3.2v 3000ma each=48volt 20ah.
Now to find some.
 
pauldo said:
I have pulled the pack apart,looks easy to split in two,that is what i wanted to do anyway
Nothing looks unusual to me.
It is in 16 rows of 7.
batteries are unmarked,so i assume they are 3.2v 3000ma each=48volt 20ah.
Now to find some.
Click to expand...

It being a VPOWER battery, I would bet that they are not 3000mah calls. They have never built a battery that is what was speced.

I would guess that they are 2500 to 2800 tops.
You need to know what they really are if you are going to replace them.

I would contact them and ask for replacements, since they should know what they are.

Dan
 
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