Too late to top balance with BMS?

[kolek]

I've been trying to top balance a 16 cell battery in sets of 4 (in parallel, using a charger), but it's taken 1 week and I've made little progress on the first set of 4.
Here are the voltages of the 4 cells I have tried to charge:
3.343V
3.340V
3.333V
3.332V
(They didn't charge evenly because for the first 5 days of charging, I had the both the positive and negative charging wires on the terminals of the first cell, rather than splitting it between the 1st and 4th cell).

All the other cells are about 3.292V.

The charger is a 60A charger but it's charging at about 4.5A, I'm using 18AWG wire. LF280 batteries.

Is there too big a difference between these cells to just use my JK-BMS to charge all 16 cells together?

At this stage what's the best course of action? Charging in sets of 4 is going to take a month or more at this rate.

 

[squowse]

Jk bms can probably manage a 12S battery, depends on model. Depends if you have a charger that will do 36V. Victron smartsolar will for example.

 

[kolek]

Jk bms can probably manage a 12S battery, depends on model. Depends if you have a charger that will do 36V. Victron smartsolar will for example.

My charger is the Kikusui PAK6-60A, it does 0-6V at up to 60 amps. I thought I was a freakin' genius buying a low voltage high amperage charger because I thought that would enable me to charge real fast at low voltage. Apparently I was an idiot.

 

[kolek]

My JK-BMS is the JK-B2A24S20P

 

[squowse]

My charger is the Kikusui PAK6-60A, it does 0-6V at up to 60 amps. I thought I was a freakin' genius buying a low voltage high amperage charger because I thought that would enable me to charge real fast at low voltage. Apparently I was an idiot.

But its only done about 7A average? Sounds like fraudulent specs. It might benefit from better cables.

 

[kolek]

Way less than 7A, it's doing like 4.5A, I guess because the differential between 3.65V and 3.3V is so small?
Either that or the power supply is bad, or the wires are too thin.

 

[squowse]

Way less than 7A, it's doing like 4.5A, I guess because the differential between 3.65V and 3.3V is so small?
Either that or the power supply is bad, or the wires are too thin.

I just converted 18awg to mm2. Yes thats way too small. 60A would want 10mm2 cables. The voltage drop on the cables is throttling the current.
I would still use the bms to charge the cells first though,

 

[kolek]

I just converted 18awg to mm2. Yes thats way too small. 60A would want 10mm2 cables. The voltage drop on the cables is throttling the current.
I would still use the bms to charge the cells first though,

Wouldn't the wires be getting warm if they were throttling the current?

 

[squowse]

The current is low - so no. It finds it’s equilibrium. Even at 4.5A you will be getting 0.2V drop on 1metre cables. 60A requires 10mm2 even at a very short length. Thicker is obviously better.

 

[MattiFin]

Wouldn't the wires be getting warm if they were throttling the current?

Not really, as the voltage drop is so small.

Your power supply seem to have possibility to use external voltage sensing that connects another set of (thinner) wires to the load and senses the voltage drop in the cables.

https://manuals.repeater-builder.com/te-files/KIKUSUI/KIKUSUI%20PAK-A,AM%20Series%20Instruction.pdf

With external voltage sense you can use even long wires and voltage drop doesn't matter as long as the wires are enough to handle the current without overheating. For 60A I'd use minimum of 6AWG or 10mm2. Sense wires can be any thin wire (ie 14 to 22AWG) you happen to have.

 

[kolek]

Guys, this was really helpful.

I just converted 18awg to mm2. Yes thats way too small. 60A would want 10mm2 cables. The voltage drop on the cables is throttling the current.
I would still use the bms to charge the cells first though,

@squowse Thanks a lot for your help!
So I can learn from this blunder, what online calculator are you using to get this info?

 

[kolek]

Not really, as the voltage drop is so small.

Your power supply seem to have possibility to use external voltage sensing that connects another set of (thinner) wires to the load and senses the voltage drop in the cables.

https://manuals.repeater-builder.com/te-files/KIKUSUI/KIKUSUI%20PAK-A,AM%20Series%20Instruction.pdf

With external voltage sense you can use even long wires and voltage drop doesn't matter as long as the wires are enough to handle the current without overheating. For 60A I'd use minimum of 6AWG or 10mm2. Sense wires can be any thin wire (ie 14 to 22AWG) you happen to have.

@MattiFin Amazing you actually found an English user manual for my power supply. Looks like it was typed using an old IBM Selectric typewriter and looks like the date on the manual is 1989. When I searched I couldn't find one. I think this model was mainly sold in Japan.

 

[TimE]

I just connect the JK BMS and charge the battery. Monitor the cell voltages when you get up near fully charged and see how the balancer gets on. If there are any cells lagging badly behind, connect your charger to that cell. Let the balancer cut off the high cell voltages.

 

[hwy17]

If you build all 16 then the 4 will be way more out of balance than they would have been from scratch, but it will be possible.

I would parallel all them for a couple days first at least.

 

[ZEUS-FL]

Way less than 7A, it's doing like 4.5A, I guess because the differential between 3.65V and 3.3V is so small?
Either that or the power supply is bad, or the wires are too thin.

Do not expect a LiFePo4 cell to sit on 3.65V. You will never seen that. They are fully charge sitting on 3.35-3.38V after few hours of been charge. In fact. Do not charge to 3.65V. There is no benefit anything over 3.45V.

 

[MisterSandals]

Wouldn't the wires be getting warm if they were throttling the current?

Are you using little alligator clips to connect your charger to your 4 cells in parallel? This is a known problem that its solved with ring terminals.

Happen to have a pic of your charging setup?

 

[squowse]

Guys, this was really helpful.

@squowse Thanks a lot for your help!
So I can learn from this blunder, what online calculator are you using to get this info?

For cable sizes? I use BS7671 tables. And experience.

 

[Checkthisout]

I've been trying to top balance a 16 cell battery in sets of 4 (in parallel, using a charger), but it's taken 1 week and I've made little progress on the first set of 4.
Here are the voltages of the 4 cells I have tried to charge:
3.343V
3.340V
3.333V
3.332V
(They didn't charge evenly because for the first 5 days of charging, I had the both the positive and negative charging wires on the terminals of the first cell, rather than splitting it between the 1st and 4th cell).

All the other cells are about 3.292V.

The charger is a 60A charger but it's charging at about 4.5A, I'm using 18AWG wire. LF280 batteries.

Is there too big a difference between these cells to just use my JK-BMS to charge all 16 cells together?

At this stage what's the best course of action? Charging in sets of 4 is going to take a month or more at this rate.

Why don't you just have all 16 connected in parallel?

 

[Checkthisout]

Do not expect a LiFePo4 cell to sit on 3.65V. You will never seen that. They are fully charge sitting on 3.35-3.38V after few hours of been charge. In fact. Do not charge to 3.65V. There is no benefit anything over 3.45V.

That won't achieve a top balance

 

[kolek]

Are you using little alligator clips to connect your charger to your 4 cells in parallel? This is a known problem that its solved with ring terminals.

Happen to have a pic of your charging setup?

Not using alligator clips was the only thing I did right. I am using ring terminals, too bad the wire I chose was too thin.

 

[kolek]

Why don't you just have all 16 connected in parallel?

I think you can only parallel cells if they are within a certain number of volts to each other. If someone else who knows can chime in....

 

[alcook62]

I think you can only parallel cells if they are within a certain number of volts to each other. If someone else who knows can chime in....

To achieve a good top balance you should have all 16 cells in parallel while doing the top balance. You may be confusing this with paralleling multiple batteries. If you parallel two or more batteries they should be as close to the same state of charge as possible to avoid a large inrush of current (big scary spark!) as the batteries seek to enter a state of balance.

 

[Ampster]

That won't achieve a top balance

If you define a top balance as balanced at 3.65 volts I suppose that would be correct. However 3.45 volts is far enough up on the steep part of the charge curve that it will be sufficient for most purposes. There is very little capacity to gain from charging to 3.65 versus 3.45. They are going to settle at 3.33 anyway.

 

[Checkthisout]

If you define a top balance as balanced at 3.65 volts I suppose that would be correct. However 3.45 volts is far enough up on the steep part of the charge curve that it will be sufficient for most purposes. There is very little capacity to gain from charging to 3.65 versus 3.45. They are going to settle at 3.33 anyway.

You want to top balance to 3.65 volts.

After putting into service, you can daily cycle to 3.45.

 

[S Davis]

I've been trying to top balance a 16 cell battery in sets of 4 (in parallel, using a charger), but it's taken 1 week and I've made little progress on the first set of 4.
Here are the voltages of the 4 cells I have tried to charge:
3.343V
3.340V
3.333V
3.332V
(They didn't charge evenly because for the first 5 days of charging, I had the both the positive and negative charging wires on the terminals of the first cell, rather than splitting it between the 1st and 4th cell).

All the other cells are about 3.292V.

The charger is a 60A charger but it's charging at about 4.5A, I'm using 18AWG wire. LF280 batteries.

Is there too big a difference between these cells to just use my JK-BMS to charge all 16 cells together?

At this stage what's the best course of action? Charging in sets of 4 is going to take a month or more at this rate.have put together 8-4s

If these are 280ah each set of 4 cells will take between 68-72 hours, I have put together eight with a 30volt 10amp supply charging at 10 amps.

So around 280 hours.