Top Balance Confusion

[Squeezer04]

I just purchased a 30 volt 30 amp variable power supply to use in top balancing a 4S 12 volt 200AH LIPO pack. It is my understanding that I should set the power supply to 3.6 volts and when amps go to zero (or close), I’m balanced. With the batteries not connected I set the output of the ps to 3.6 volts. I connect the batteries and the output of the ps drops to about 3.4 volts. If I then slowly increase the volts output adjustment the lights on my ps switch from constant voltage to constant current. Is it OK to be in constant current?

I’m obviously new to this. Be kind.

Thanks

 

[Whinny]

Do not adjust the power supply when connected to a load (the cells)-you will toast the cells....
Set the supply when disconnected and leave it-the voltage drops because of the load. Do not increase the voltage...

turn it all off until you understand it.....
You may be better of setting the voltage to 3.4 when disconnected and keep an eye on it, when the current drops disconnect again and set to 3.6.
Only set the voltage when disconnected-it is very important.

 

[Dzl]

I just purchased a 30 volt 30 amp variable power supply to use in top balancing a 4S 12 volt 200AH LIPO pack. It is my understanding that I should set the power supply to 3.6 volts and when amps go to zero (or close), I’m balanced. With the batteries not connected I set the output of the ps to 3.6 volts. I connect the batteries and the output of the ps drops to about 3.4 volts. If I then slowly increase the volts output adjustment the lights on my ps switch from constant voltage to constant current. Is it OK to be in constant current?

I’m obviously new to this. Be kind.

Thanks

Be careful, I'm not 100% sure I follow what you are saying, BUT you want to set the voltage first. If you adjust it once its connected and powered on you risk overcharging the cells if you do not closely monitor them.

Here is a beginners guide to top balancing please read it or another guide before continuing. Screwing up during top balancing is one of the most common screwups/causes of damaged cells that we see here. Its not difficult but you want to be clear on what you are doing before you do it.

 

[Squeezer04]

The cells were about 3.2 volts each when I got them new. Any idea how long it should take to bring them up to 3.4 volts with my setup? I waited about six hours with no apparent change. Thanks again.

 

[Dzl]

The cells were about 3.2 volts each when I got them new. Any idea how long it should take to bring them up to 3.4 volts with my setup? I waited about six hours with no apparent change. Thanks again.

It takes a long time.
I suggest reading the resource I linked to earlier.

Here is a typical lifepo4 charge curve. As you can see, the voltage is very flat for the majority of the SOC range, its only towards the extremes that it will change rapidly.

 

[Squeezer04]

Thanks DzL. I review the resource. I disconnected all the bus bars and read 3.13 volts on each cell. I should re-parallel the cells, set 3.4 volts on the ps with no load, connect the batteries and wait for 0 amps no matter how long it takes, right? Then repeat at 3.6 volts (?).

 

[Sback]

The cells were about 3.2 volts each when I got them new. Any idea how long it should take to bring them up to 3.4 volts with my setup? I waited about six hours with no apparent change. Thanks again.

Most batteries are shipped at about 30% state of charge. That means you need to put 560 amps back in the batteries when they are hooked up in parallel. If your power box is a 10 amp it will take about 56 hours to top ballance. Probably more like 60 hours...
Disconnect your bench power box from the battery, set the voltage to 3.65 using a volt meter.
Hook up to battery once hooked up you will see the voltage drop. This is normal. DO NOT ADJUST VOLTAGE voltage will rise on its own as the battery charge. As the battery charges you will see the amps start to go down. And you will see the voltage go up. This is also normal. Once the amps get to near 0 amps and the voltage at the batteries are at 3.65 your batteries are top ballanced.
Good luck. There is also lots of videos on you tube.

 

[Squeezer04]

After reading the resource I think I’ve got it. I’ll pre charge the assembled full battery through the BMS to 14.6 volts then top balance the batteries in parallel to 3.65 volts. I wont touch the voltage knob during the top balance procedure. Thanks everyone.

 

[Dzl]

After reading the resource I think I’ve got it. I’ll pre charge the assembled full battery through the BMS to 14.6 volts then top balance the batteries in parallel to 3.65 volts. I wont touch the voltage knob during the top balance procedure. Thanks everyone.

Yeah that would be the quicker way to go about it, if you've got the BMS and a 12V charger

 

[time2roll]

Are you getting 30 amps into the cells? Most of the OEM connection leads are very poor about getting the full rating. #8 wire and ring terminals would help.

 

[Squeezer04]

Yes I am because I’m using the leads that came with my inverter. I think they are 6 maybe 4 AWG.

 

[Johnson]

Some good advise already, thought I would give you some of my thoughts. I did top balance my first set of 8 cells and that took a week, when I got my second batch of 8 cells, I brought all 16 at the same and connected them in parallel overnight. After putting them in their final configuration, 2p8s, I just started using them and allow the BMS to do the last bit of balancing.

Top balancing is a must if you want to do capacity testing, optional if you are not. Although I imagine people might have different opinions on that.

 

[Squeezer04]

Yes Johnson I’m probably overdoing this. The battery is just going into my new camping trailer which sits unused for weeks at a time. The BMS would probably do the job but for me it’s fun to learn this stuff. Thanks for the inputs.

 

[Squeezer04]

OK did the full pack charge. Set the amps to 24, set the volts to 16 and connected the power supply. The BMS disconnected after a couple of hours. I disconnected the ps and measured the battery pack volts. It read 13.6. The high voltage cutoff was set to 14.6 volts. Shouldn’t the battery read 14.6 volts?

 

[Sback]

OK did the full pack charge. Set the amps to 24, set the volts to 16 and connected the power supply. The BMS disconnected after a couple of hours. I disconnected the ps and measured the battery pack volts. It read 13.6. The high voltage cutoff was set to 14.6 volts. Shouldn’t the battery read 14.6 volts?

Why did you set the volts to 16? If you are charging a12v pack you should set the voltage to 14.6v let the bms shut it off. Hook up in parallel and do the top ballance at 3.65.
What brand cells do you have. If they are not a quality battery you will have cells that will drift apart from each other.

 

[time2roll]

OK did the full pack charge. Set the amps to 24, set the volts to 16 and connected the power supply. The BMS disconnected after a couple of hours. I disconnected the ps and measured the battery pack volts. It read 13.6. The high voltage cutoff was set to 14.6 volts. Shouldn’t the battery read 14.6 volts?

The cells fully charged will normally settle to about 3.4 or lower depending on the balance. Now that they are mostly charged the top balance in parallel should go pretty fast.

 

[Dzl]

Shouldn’t the battery read 14.6 volts?

Cells won't remain at that voltage for long once the charger is switched off. Natural resting voltage is closer to </= 3.4ish Vpc

 

[Squeezer04]

OK thanks. On to the cel balancing.

 

[Rogermija]

I posted a similar thread elsewhere but in reading this thread, it seems spot on to my question. Single prismatic cell with 3.295v before connecting to Longwei ps. Set ps to 3.40v, shut it off, connect cell, turn on and display shows a voltage of 3.41 but random current of 1.75 to 1.98. Is this normal? The ps internal fan cycles....it this normal? BTW...currently I'm using the supplied banana plug and clips and will fabricate leads to suggested specs prior to top balancing the 13 cells. Thank you.

 

[John Frum]

I posted a similar thread elsewhere but in reading this thread, it seems spot on to my question. Single prismatic cell with 3.295v before connecting to Longwei ps. Set ps to 3.40v, shut it off, connect cell, turn on and display shows a voltage of 3.41 but random current of 1.75 to 1.98. Is this normal? The ps internal fan cycles....it this normal? BTW...currently I'm using the supplied banana plug and clips and will fabricate leads to suggested specs prior to top balancing the 13 cells. Thank you.

Not normal.
Assuming the cell is LFP you should set the psu to 3.65 volts.
The current should be pretty steady until the cell gets into the high knee.
Suspect a defective power supply or bad joinery.
This is a what charge curve should look like.

100Ah Cell - Test 1

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