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Top balancing power supply question

TimC

WI/UP Border
Joined
Apr 17, 2020
Messages
139
I'm wondering about top balancing duration.

I've paralleled 16 lifepo4 75ahr batteries and have been attempting to top balance them. They seem to be stuck at 3.34v. They are currently at 3.34v after sitting off the charger for 12 hours (wasn't around to monitor the charger today).

The power supply is a longwei 10a 30v variable like Will shows in some of his top balancing videos.

If I set the PS at 3.6v and max amps the display always drops to read 3.4v and doesn't move below 10.1 to 10.3a. It has been like this for each daily charge session for two days straight.

I see on some voltage charts for lifepo4 that 3.33 is somewhere around 90% charged.

The cells have been charging for five days almost non stop. Now that they are above 3.33v I shut it down at night when I can't monitor them.

Does this seem like a normal amount of time to get these top balanced? Though this is a small battery it is larger than anything I've ever top balanced. My only experience is with paralleled 32650 cylindrical banks. Is this a "just be patient" situation?


20220724_202826.jpg

If I set the PS at 3.3
 
Dozens of stories like this. The vast majority of the charging occurs below 3.4V. Once you hit 3.4V, it will finish quickly (relative to the days you've spent charging)

16 cells * 75Ah * 0.7 = 840Ah input needed (typically shipped 30-50% charged).

840Ah / 10A = 84 hours

Voltage settling after charge removed is normal.

Drop from 3.6 on display to 3.4V is normal. Power supply and battery can't be at different voltages, so the power supply lowers to the battery level.

Everything sounds like it's progressing exactly as it should.

You're very fortunate that you followed the guide and made new leads, or your post would be about how you're only getting 3A when the power supply reads 3.6V immediately after you start charging.
 
It will stay at that number for lot of time and then in the last moments of the charging it will move to 3.65, remember the AMPS will go down with the time, and 16 cells take more than a week.

There is a error with the calculations, all ppl i read say 5 amp x 16 cells, etc, the charge begin at 5 amp but with the time go to 4 then 3 then 2, soo that calculation is wrong, the AMPS are not 5 amp all the time, soo no is not 84 hours, is lot more time.

I recommend to charge 4 cells first and soo on.
 
If you have BMS and higher voltage power supply you can speed-up the process of top balancing. I was top balancing 16 LiFePO4 280Ah cells and it took 2 days only. It is two phase procedure. In the first phase, you connected them the same way as in your final battery setup. Thus, 16 in the series with BMS. Make sure you have correct BMS configuration. Then you apply power supply with at least 58.4V (16x 3.65V) but you can use slightly higher voltage to overcome voltage drops on the connection cables. You wait till BMS does its job and stop charging due to one of the cell reaches 3.65V first. In the second phase, you connect them in parallel and apply 3.65V. This will end up top balancing process much quickly. While in parallel, you need charge just differences between cells at their top and not the majority of their capacity.
 
Thanks everyone. Good to know I am following a good procedure. Patience!
 
Also, make sure you set the voltage of the power supply while it's disconnected from the cells. I have no reason to think that you didn't, but with some power supplies, if you set the voltage while it's charging, it can get all out of whack and overcharge the cells.
 
Thanks again. I'm going to rewire it now to opposing ends and see what happens.

Do you top balance to 3.65 and call it good? On my last build, using 32650 cylindrical cells, after getting to 3.6 I'd let it rest and then another short charge until the PS went to <1 amp. I did that two or three times.. Am I just wasting time doing that?
 
Charge to 3.65 and call it good. The batteries will rest to a voltage closer to 3.4 volts. Totally normal.

Charging in steps is acceptable, but there is no need to rest between steps. Disconnect the leads, change the power supply setting, turn off power supply, connect leads, turn supply back on.
 
Thanks. Battery bank #1 is fully top balanced. I don't intend to do a capacity test. I'll just build the battery and let it sit until I get # 2 top balanced and built into a 48v battery.

I did charge the 2nd battery as four individual 4S 12v packs and they are now sitting parallel at 3.33v. The second stage of that should go fairly quick. A couple days maybe.
 
I've seen many instances where a recently top balanced battery went out of balance after sitting a couple weeks. In one case, when we measured what it took to get them all back to 100%, they were only out of balance by 0.1%, but that was enough to cause a runner when trying to get fully charged.

Probably worth spending a few hours re-topping off all cells before you actually deploy batteries.
 
Dozens of stories like this. The vast majority of the charging occurs below 3.4V. Once you hit 3.4V, it will finish quickly (relative to the days you've spent charging)

16 cells * 75Ah * 0.7 = 840Ah input needed (typically shipped 30-50% charged).

840Ah / 10A = 84 hours

Voltage settling after charge removed is normal.

Drop from 3.6 on display to 3.4V is normal. Power supply and battery can't be at different voltages, so the power supply lowers to the battery level.

Everything sounds like it's progressing exactly as it should.

You're very fortunate that you followed the guide and made new leads, or your post would be about how you're only getting 3A when the power supply reads 3.6V immediately after you start charging.
This should be a sticky some place . Simple, math worked out .. Bam! done :) . It's been mentioned before but I would HIGHLY recommend making leads for the top balancing and not use clamps of any sort. I attached mine alligator clips while making leads up, once I added my larger power supply leads, the current difference was more then I would have guessed, . For the Original poster : My pack stayed at 3.34 volts for several days. My total time for a 200ah 24 volt pack was 5+ days. But once it hit 3.36 it climbed to 3.65 within 24 hours.
 
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Another option is to get them all to something around 3.38V-3.4V so they are mostly full and then build the banks and let an active balancer(s) hooked to your system do the final top balancing in their finial configuration. At least this way they aren't sitting around fully charged and potentially discharging while finishing the remaining cells, plus they are all topped off and balanced at the same time. Something to consider anyway if you're using a JK or other active BMS.
 
I'm wondering about top balancing duration.

I've paralleled 16 lifepo4 75ahr batteries and have been attempting to top balance them. They seem to be stuck at 3.34v. They are currently at 3.34v after sitting off the charger for 12 hours (wasn't around to monitor the charger today).

The power supply is a longwei 10a 30v variable like Will shows in some of his top balancing videos.

If I set the PS at 3.6v and max amps the display always drops to read 3.4v and doesn't move below 10.1 to 10.3a. It has been like this for each daily charge session for two days straight.

I see on some voltage charts for lifepo4 that 3.33 is somewhere around 90% charged.

The cells have been charging for five days almost non stop. Now that they are above 3.33v I shut it down at night when I can't monitor them.

Does this seem like a normal amount of time to get these top balanced? Though this is a small battery it is larger than anything I've ever top balanced. My only experience is with paralleled 32650 cylindrical banks. Is this a "just be patient" situation?


View attachment 103992

If I set the PS at 3.3
The original post concerned the PSU charging voltage dropping lower than the no load set point. You are taking 10.3 Amps from a 10 Amp supply. It is hardly surprising the PSU is in current limit and the voltage has dropped. That is how CC charging works. You are getting more than you paid for !
Charging time is calculated in Amp Hours. Do the math to see if it is excessive.
 
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Hope it's ok to borrow the thread a little.

I'm about to top balance my 280AH cells each individually using a 30V 10A PS. The problem is it doesn't turn green and start charging. I tried it on another battery (50AH) and it works no problem. Voltage is set 3.65 and A on max. Anyone got an idea why this is?
 
Hope it's ok to borrow the thread a little.

I'm about to top balance my 280AH cells each individually using a 30V 10A PS. The problem is it doesn't turn green and start charging. I tried it on another battery (50AH) and it works no problem. Voltage is set 3.65 and A on max. Anyone got an idea why this is?
I would start a new thread and ask your question there. The only people who are going to see this are people who are part of the previous discussion a few months ago.

Some pictures, as well as the make and model of the power supply would be very helpful.
 
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