Is my charger broken? 4.2A@84.3V for 20s li-ion battery

[HEAD]

My battery used to get charged up to 84v, but recently the charger only does up to about 82.5v, so I connected to the charger this ammeter:

started charging and monitoring the status:

79.9V@4.42A
81.7V@4.28A
84.2V@4.28A

it looked too dangerous, so I disconnected the charger, then the battery dropped to 83v(verified with 3 meters: ammter/voltage(in pic), standard multimeter and the controller display

What do you think?

 

[amberwolf]

My battery used to get charged up to 84v, but recently the charger only does up to about 82.5v, so I connected to the charger this ammeter:

and started charging, and monitored the status:

79.9V@4.42A
81.7V@4.28A
84.2V@4.28A

it looked too dangerous, so I disconnected the charger, then the battery dropped to 83v(verified with 3 meters: ammter/voltage(in pic), standard multimeter and the controller display

What do you think?

What specifically looked dangerous?

If it was voltage, you might want to also monitor the voltage itself at the same point with all three during charge, to ensure the multi-function meter is reading the same while current is flowing, as the other two, and not reading over or under.


If by "recently the charger only does up to about 82.5v" you mean that the battery's final charge is only 82.5v, that usually means that one or more cell groups is unbalanced, for one reason or another. Sometimes this can be fixed by leaving on the charger a while; for a balance problem bad enough to cause almost two volts difference, that could be days to weeks.

Before doing that I would check the voltages of all cell groups inside the battery, at the BMS connector, to make sure one of them isn't so low that it would be dangerous to recharge.

 

[HEAD]

My battery used to get charged up to 84v, but recently the charger only does up to about 82.5v, so I connected to the charger this ammeter:

and started charging, and monitored the status:

79.9V@4.42A
81.7V@4.28A
84.2V@4.28A

it looked too dangerous, so I disconnected the charger, then the battery dropped to 83v(verified with 3 meters: ammter/voltage(in pic), standard multimeter and the controller display

What do you think?

What specifically looked dangerous?
1.the voltage was above 84v 2. the charging current should drop drastically near the end, am I wrong?
If it was voltage, you might want to also monitor the voltage itself at the same point with all three during charge, to ensure the multi-function meter is reading the same while current is flowing, as the other two, and not reading over or under.
I monitored it during charge with the controller's display, it's about the same as the ammeter - over 84V during charge

If by "recently the charger only does up to about 82.5v" you mean that the battery's final charge is only 82.5v,YES that usually means that one or more cell groups is unbalanced, for one reason or another. Sometimes this can be fixed by leaving on the charger a while; for a balance problem bad enough to cause almost two volts difference, that could be days to weeks.
I think that the battery may start to balance itself, last time it only did 82v, now 83v and probably more had I not stopped it, thanks for the advice, is it considered safe to leave it connected to a charger for such a long period of time, or maybe you mean extra few hours after each charge accumulated in the long run to many hours?

Before doing that I would check the voltages of all cell groups inside the battery, at the BMS connector, to make sure one of them isn't so low that it would be dangerous to recharge.
I wish my BMS had bluetooth, right now the pack is sealed and I prefer not to open it without being able to seal it back

Replied in color
Thank you so much!

 

[amberwolf]

1.the voltage was above 84v 2. the charging current should drop drastically near the end,

Generally, yes...but if the battery has a problem, where internal resistance is high on some cells, their voltage will increase more than normal under the high current, and cause the pack voltage to appear higher than it actually is. Depending on charger design, and unloaded charger voltage (what voltage does it reach when not plugged into a battery?), it may be able to keep going up in voltage to maintain "full" current under those conditions.

Keep in mind that 84.3v over 20 cells is only 4.215v per cell, if they are balanced. Unlikley to be dangerous for 4.2v cells, even if it's not healthy for their lifespan to stay there. The BMS, if working, would reduce that in reasonable amount of time, to whatever it's max balancer voltage is.

If they are *not* balanced, then some cells may be much higher than that, if the BMS is not doing what it is supposed to and shutting off as needed to prevent overcharge.

No way to know without opening up the battery to check voltages both static (just sitting there) and during charge.

I think that the battery may start to balance itself, last time it only did 82v, now 83v and probably more had I not stopped it, thanks for the advice, is it considered safe to leave it connected to a charger for such a long period of time, or maybe you mean extra few hours after each charge accumulated in the long run to many hours?

That depends on what is wrong with the battery that's causing the issue. If it's a bunch of groups with small voltage differences causing the imbalance, it's generally safe to just leave it on the charger until it is fixed. (assuming the BMS is working correclty and shutting off charge as needed to prevent overcharge of cells).

If something is seriously wrong in there (like groups at 2v and groups at 5v, etc) and the BMS is not doing the job it should, then even charging the battery at all, or discharging it, could result in a fire (you wouldn't even need to leave it on for balancing).

Most likely there is nothing wrong other than many groups just being different by a small amount (typical unbalanced pack), but there is no way to know without opening up the battery to check voltages both static (just sitting there) and during charge.

I wish my BMS had bluetooth, right now the pack is sealed and I prefer not to open it without being able to seal it back

It's your call. There's no way to know what's going on or for us to give any calls about safety without knowing what is happening inside the pack.

 

[john61ct]

Yes it is mandatory to be able to see voltages per cell/group

or else only charge to 4.1Vpc average and sacrifice some capacity

 

[HEAD]

So I decided to continue charging from the last stop (83v),during charge it climbed up to 84.5v and down to 1.6A just before turning to green, the final voltage after disconnecting is 83.6V... I'll get a better BMS and check the cells soon

thank you :thumb:

 

[999zip999]

The only way to know is to know what the voltage is in each cell group. State of charge. Easiest to do is write it down on a piece of paper. Like.

1. 4.15v
2. 4.20v
3. 4.09v

20. Xxx volt
voltage of battery
Voltage of charger.

 

[amberwolf]

So I decided to continue charging from the last stop (83v),during charge it climbed up to 84.5v and down to 1.6A just before turning to green, the final voltage after disconnecting is 83.6V... I'll get a better BMS and check the cells soon

thank you :thumb:

The BMS might be perfectly fine (probably is fine, just doing it's job), so dont' get parts until you test things--it's much more likely that the problem is in the cells themselves.

Keep in mind that once you have already balanced the pack, then to test it you would need to either wait until it is unbalanced again, or perform tests that cause it to become unbalanced, to show you which cells are problematic.

 

[HEAD]

The only way to know is to know what the voltage is in each cell group. State of charge. Easiest to do is write it down on a piece of paper. Like.

1. 4.15v
2. 4.20v
3. 4.09v

20. Xxx volt
voltage of battery
Voltage of charger.

:thumb:

So I decided to continue charging from the last stop (83v),during charge it climbed up to 84.5v and down to 1.6A just before turning to green, the final voltage after disconnecting is 83.6V... I'll get a better BMS and check the cells soon

thank you :thumb:

The BMS might be perfectly fine (probably is fine, just doing it's job), so dont' get parts until you test things--it's much more likely that the problem is in the cells themselves.

Keep in mind that once you have already balanced the pack, then to test it you would need to either wait until it is unbalanced again, or perform tests that cause it to become unbalanced, to show you which cells are problematic.

I planned to get a better BMS regardless of the recent partial charge issue, so I'll do both checking and replacement once the BMS (with bluetooth) arrives :wink:

 

[999zip999]

I have one pack 20s 6p 21700 Samsung 40t cells with Bluetooth BMS the one with the elephant. Been trying to get it to turn on for a week it only does it when it wants to. Elephants are very stubborn. I have three other packs with just balance wire no bms soon to have one more pack no bms. plus I charged my no bms packs to 84 volts and I take them off the charger and try level off at 83.2v or something.
okay try it again I'm down in the park and all my sales are perfectly balanced. but only get 17 ah out by of a 24 ah pack. that guy won't take my emails but I do have a phone number which I'm probably going to have to call, but I don't know if I'll get anywhere with this thousand-dollar battery.
Where'd you get the pack what cells are in there ?
How do you use it before at How many amps is your controller

 

[HEAD]

i got my battery from a local builder, cells are samsung 25r

 

[dogman dan]

Ideally, you'd have 20 voltmeters on that pack, watching all 20 cell groups as they charge.

There are devices that watch 6 or 8 cells voltage at a time, from the RC lipo world. You'd have to install the plugs to match the devices, splicing them into the balance wires leading to the bms.

Then you can watch each cell fill, watch the bms stop the charge on that cell, and start discharging it. You can confirm that the bms works or not. Or that the bms is doing its best with a weak, or just out of balance cell group.

With one voltmeter, you can look at each cell in turn one at a time as it charges, find the highest charged one, then watch what the bms does to that one cell. More difficult, time consuming, but you can find your weaker cell groups and keep an eye on them as it charges.

As for dangerous,,, if its inside your house,,,,. My idea of dangerous changed after my bike caught fire. Now I charge everything, drill batteries, mower batteries, all that "safe" stuff out in a shed in the backyard.

 

[HEAD]

Ideally, you'd have 20 voltmeters on that pack, watching all 20 cell groups as they charge.

There are devices that watch 6 or 8 cells voltage at a time, from the RC lipo world. You'd have to install the plugs to match the devices, splicing them into the balance wires leading to the bms.

Then you can watch each cell fill, watch the bms stop the charge on that cell, and start discharging it. You can confirm that the bms works or not. Or that the bms is doing its best with a weak, or just out of balance cell group.

With one voltmeter, you can look at each cell in turn one at a time as it charges, find the highest charged one, then watch what the bms does to that one cell. More difficult, time consuming, but you can find your weaker cell groups and keep an eye on them as it charges.

As for dangerous,,, if its inside your house,,,,. My idea of dangerous changed after my bike caught fire. Now I charge everything, drill batteries, mower batteries, all that "safe" stuff out in a shed in the backyard.

I appreciate your advices
I also never charge the battery in my house

 

[999zip999]

I sure love to have balance wires. And a r/c balance charger Plus I bulk charge at 15 amps with meanwells.
Samsung 25r cells can charged at high rate depending on your bms and how many in parallel.

 

[dogman dan]

Without balance wires you can get to, as is the case with many bike batteries, the next thing you can do is charge it full, let sit a half hour for the bms to discharge any high cells, then put back on the charger. If the charger won't restart then, ride around the block, then put back on the charger.

This allows the bms multiple chances to re balance a pack that is ok, but just out of balance. If this does not work, and your pack still lost 20% or more capacity, then you have bad cells in there for sure. Then its REALLY important to charge in a safe place. Gradual loss of capacity, and increase in sag under load is normal as a pack ages. But sudden loss of capacity is not normal.

When I say lost 20%, I mean 20% of what you had, not 20% of what spec said capacity should have been. Capacity varies by discharge rate.

 

[kaning]

What is an accepted voltage delta when fully charged?
This is my max delta
4,168 lowest voltage
4,182 highest voltage

Delta - 0,016v

 

[Steven Sheng]

Your charger is not broken.

My battery used to get charged up to 84v, but recently the charger only does up to about 82.5v.
This is a normal loss process.

Before the power outage, the charger encounters 84.2V, after disconnecting the charger, the battery drops to 83v.
This is normal, current will only go into your battery when the charger voltage is higher. The actual battery of the battery must be lower than the voltage of the charger.
It also stops charging automatically if you don't disconnect the charger. It is not dangerous.

 

[john61ct]

I'm OK with 50mV deltas

even more if it's a pack scheduled for a balance in coming months

I don't bother going closer than 20mV unless it's quick and easy

Sitting at high SoC for long actually does damage

imbalances only temporarily reduce pack capacity a little, no actual harm

so long as LVC/HVC is based off per-cell voltages

if pack level then just get more conservative about your cutoffs, accept lower cap utilisatiin