Reviving a 36V Li-ionDead Battery

[Lawman]

Hi all I have a 36V 20 Cell Li-ion battery, it wouldn't take a charge when connected to the original charger via the charging socket so I removed the battery and managed to get it charging again with the charger connected directly to the BMS. I wrongly assumed it was permanently fixed and left it for a few days but it drained and now the battery no longer accepts a charge no matter what I do.

The battery is now at 26V and im guessing some or all of the cells are very low on voltage? Is there any hope for this battery, can it be fixed? It looks brand new and seems such a waste!

 

[WheezyRider]

Hi all I have a 36V 20 Cell Li-ion battery, it wouldn't take a charge when connected to the original charger via the charging socket so I removed the battery and managed to get it charging again with the charger connected directly to the BMS. I wrongly assumed it was permanently fixed and left it for a few days but it drained and now the battery no longer accepts a charge no matter what I do.

The battery is now at 26V and im guessing some or all of the cells are very low on voltage? Is there any hope for this battery, can it be fixed? It looks brand new and seems such a waste!

When you look at the individual banks, what voltages do you get? Are they all the same, or is one bank significantly different?

The pack is only 4Ah...what are you running on them?

 

[Lawman]

When you look at the individual banks, what voltages do you get? Are they all the same, or is one bank significantly different?

The pack is only 4Ah...what are you running on them?

I cant get my head round how to measure the banks individually. I watched a load of videos and researched on a lot of forums over the past few weeks but if i'm honest im a bit scared in case the thing goes bang if I measure the wrong terminals and create a short? Had an Iphone battery blow up and it wasn't good fun at all.

Its a Nilox Doc skateboard. Sorry its not a bike. They do bikes too though. I can try find another forum if I shouldn't be posting in here. Cheers

 

[Nealh]

Pull/disconnect the BMS connector, using your meter probes put the Black on B- 7 red probe on b1+ write down the voltage. Move the Red probe along the connector till you have all 10 readings. Then you will see if one or all are problematic.

 

[WheezyRider]

I cant get my head round how to measure the banks individually. I watched a load of videos and researched on a lot of forums over the past few weeks but if i'm honest im a bit scared in case the thing goes bang if I measure the wrong terminals and create a short? Had an Iphone battery blow up and it wasn't good fun at all.

Its a Nilox Doc skateboard. Sorry its not a bike. They do bikes too though. I can try find another forum if I shouldn't be posting in here. Cheers

The pack looks like it is made of banks of 2 cells in parallel and 10 of these in series. Just think of a string of folded sausages, where the connecting string alternates on the bottom and the top...in this case the connecting string is the conducting metal strip...hope that makes sense!

You can do what Nealh says, but be careful not to short the mutimeter probes between the pins on the connector, they are often quite close together.

The alternative is to measure the voltage from sets of cells by putting the multimeter on the top and bottom electrodes of the cells, and just go along the pack, one bank at a time (think of the folded string of sausages ).

Make sure the multimeter is in volts mode, not amps!

If you are worried about shorts, get some thin wire and attach it to the ends of the multimeter tips, so if you do get a short, it will burn out and not draw enough current for long enough to do any harm.

And if you are really worried, do it in the garden, so if there is a fire you don't burn the house down

 

[vfr400]

Here's what I'd do. Charge it up, then pull the multi-pin connector on the BMS. That will switch off the BMS, so you'll have to measure the voltage of the pack directly on the cells. If it goes down like that, you've got self-discharging cells, though that's not very likely. If it stays up, you have a faulty BMS, which is much more likely. In that case, you can replace the BMS, which won't cost much.

 

[Lawman]

Pull/disconnect the BMS connector, using your meter probes put the Black on B- 7 red probe on b1+ write down the voltage. Move the Red probe along the connector till you have all four readings. Then you will see if one or all are problematic.

Ive disconnected the BMS and removed all the ESD tape, and put some ESD tape back under the BMS so it doesnt short on the cells if it moves.

I dont understand sorry, where is Black on B- 7 red probe on b1+ on the battery? battery negative 7, red on battery one positive? Honestly I'll get there, but just now its like trying to teach an old dog new tricks. Did electronic engineering a long long time ago....

Bare with me, got it, its on the underside of the BMS.

B+, B9, B8, B7, B6, B5, B4, B3, B2 and B1 are all positive? and B- is negative? So I can put the black meter probe on B-, then take positive readings for all B+, B9, B8, B7, B6, B5, B4, B3, B2 and B1 including B+ is that correct? Cheers

 

[Lawman]

The pack looks like it is made of banks of 2 cells in parallel and 10 of these in series. Just think of a string of folded sausages, where the connecting string alternates on the bottom and the top...in this case the connecting string is the conducting metal strip...hope that makes sense!

You can do what Nealh says, but be careful not to short the mutimeter probes between the pins on the connector, they are often quite close together.

The alternative is to measure the voltage from sets of cells by putting the multimeter on the top and bottom electrodes of the cells, and just go along the pack, one bank at a time (think of the folded string of sausages ).

Make sure the multimeter is in volts mode, not amps!

If you are worried about shorts, get some thin wire and attach it to the ends of the multimeter tips, so if you do get a short, it will burn out and not draw enough current for long enough to do any harm.

And if you are really worried, do it in the garden, so if there is a fire you don't burn the house down

Yeah that makes sense, thank you and yes I am in the back garden.

 

[WheezyRider]

Yeah that makes sense, thank you and yes I am in the back garden.

So if you think about them as a pack of folded sausages, each one of those red wires goes to the bit of connecting "string" between each sausage.

You can put one multimeter electrode on B- and then look at how the voltage increases as you move the other multimeter electrode from B1 to B2 etc and then look for an even increase each time, or you can measure across B-:B1, then B1:B2 and so on, to get individual bank voltages, but it is more tricky as you are more likely to accidentally short that way.

 

[Nealh]

Ive disconnected the BMS and removed all the ESD tape, and put some ESD tape back under the BMS so it doesnt short on the cells if it moves.

I dont understand sorry, where is Black on B- 7 red probe on b1+ on the battery? battery negative 7, red on battery one positive? Honestly I'll get there, but just now its like trying to teach an old dog new tricks. Did electronic engineering a long long time ago....

Bare with me, got it, its on the underside of the BMS.

B+, B9, B8, B7, B6, B5, B4, B3, B2 and B1 are all positive? and B- is negative? So I can put the black meter probe on B-, then take positive readings for all B+, B9, B8, B7, B6, B5, B4, B3, B2 and B1 including B+ is that correct? Cheers

Yes, correct.

I amended my post as I said take four readings of course you have 36v/10s so 10 readings.
Write them all down as you go along and post the results so we can see them.

 

[Lawman]

And we have some readings!

B1: 0 ohms
B2: 0 ohms
B3: 4.0 volts
B4: 7.9 volts
B5: 11.8 volts
B6: 15.5 volts
B7: 19.4 volts
B8: 23.3 volts
B9: 22.8 volts
B+: 26.3 volts

 

[Lawman]

Here's what I'd do. Charge it up, then pull the multi-pin connector on the BMS. That will switch off the BMS, so you'll have to measure the voltage of the pack directly on the cells. If it goes down like that, you've got self-discharging cells, though that's not very likely. If it stays up, you have a faulty BMS, which is much more likely. In that case, you can replace the BMS, which won't cost much.

Just had a better look at the BMS. There is corrosion between pins B1 and B2 and light corrosion over most of the circuit boards. Possibly been taken out in the rain at some point.

One R005 resistor is missing.

 

[vfr400]

R005 are the shunts. They use different arrangements for different currents. There never was one where you can can see the gap, neither was there meant to be.

 

[mike killay]

R005 are the shunts. They use different arrangements for different currents. There never was one where you can can see the gap, neither was there meant to be.

I take it that there is no hope of soldering those shunts?

 

[Nealh]

And we have some readings!

B1: 0 ohms
B2: 0 ohms
B3: 4.0 volts
B4: 7.9 volts
B5: 11.8 volts
B6: 15.5 volts
B7: 19.4 volts
B8: 23.3 volts
B9: 22.8 volts
B+: 26.3 volts

B1/B2 0 ohms ? typo error, cell groups 1 & 2 dead.
Something a miss with B8 reading.
Looks like a new battery is needed anyhow.

 

[Lawman]

B1/B2 0 ohms ? typo error, cell groups 1 & 2 dead.
Something a miss with B8 reading.
Looks like a new battery is needed anyhow.

My multi meter was set to auto detect, B1/B2 immediately went to 0 ohms while the rest gave a voltage reading. Those readings where taken from the BMS, when it was still connected to the battery.

Tomorrow morning I will pull the multi-pin connector on the BMS to switch off the BMS, and measure the voltage of the pack directly on the cells. Cheers

 

[Nealh]

Ok, thanks for clarifying the strange readings.

 

[vfr400]

I take it that there is no hope of soldering those shunts?

He's got two 005s in parallel, which makes .0025. If you added an 010 to the empty space, you'd have .002, so you'd get a 25% increase in current. By choosing appropriate values, you can get whatever current you want.

 

[Lawman]

Morning,

Can I simply measure the voltage by putting the multimeter electrode directly on each cells positive and negative ends or will that create a short due to the way they are attached to each other?

 

[WheezyRider]

Morning,

Can I simply measure the voltage by putting the multimeter electrode directly on each cells positive and negative ends or will that create a short due to the way they are attached to each other?

Yes that is fine. You will get a short if you put the electrode across a gap between two cells in series, but otherwise you will be fine. Look at where the red wires go on the cells and put the electrodes on the part of the cells where they are, They should alternate from one side to the other.

If you can, try and force the multimeter to read volts. I don't like these auto detect modes.