Top Balancing Voltage Variation Between the Charger and the Cells

MrM1

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I know when top balancing multiple cells in parallel the rule of thumb is to
- 1st set the bench top power supply to 3.65v
- Then connect the power supply to the battery posts , preferably with hi quality leads

But when I do this and the paralleled group of cells is at a low state of charge, the voltage at the cells is much lower than the voltage at the charger

Actually, the charger reads 3.65v, but at the lead connection at the charger it will be less and at the battery postsoof the group it will be even less. Like if I start the charge with the group at 3.29v, the voltage at the cells might read 3.295v or whatever.

As the charge cycle continues (for days with a 10 amp supply) batteries might be at 3.35v for a long time. But the charge amps really start to drop off

Question. Other than it being risky because you may walk away and forget, only to return to a room full of ballooned cells, why is it bad to increase the voltage on the charger to say 3.7v or 3.8v to get the amps up to 10 amps AS LONG AS the volts at the cell posts are not over 3.5 or 3.6v. I know when it hits the knee it will run like crazy, so it risky, but does it hurt the cells early on to increase the volts at the charger display so that you are getting max amps as long as your not exceeding 3.5-3.6v at the cell's posts.

Just wondering.
 

Bob B

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You already answered your own question.

If the power supply is adjusted after connecting it .... there is no way of really knowing what the setting is ..... Is impatience worth risking damaging the cells?

I would turn the current as high as it will go .... adjust the voltage setting .... connect to cells .... wait.
 

MrM1

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Thx I do understand and do that, but one can turn the power supply voltage up.

I'm wondering what is the battery is actually seeing at the post.? If a good quality meter connected to the post says the charge voltage is 3.5v but the display on the supply reads 3.9 or 4v is that damaging the battery at that moment, so long as one never let's the voltage at the battery terminal exceed 3.65vdc?

I thought I saw Will do this in a video once to "speed things up, but don't try this at home" but I can't find the video. I'm trying to remember if I saw Will do this.
 

time2roll

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No. No harm to the cells to go right to the top at 10 amps. Over voltage at the cell terminal is the issue. This why some, including myself, assemble the battery including BMS and let it charge to the high cell cut off by the BMS. My last battery all cells were above 3.400 so it was placed in service immediately. The active balancer will eventually finish the balance.
 

MrM1

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No. No harm to the cells to go right to the top at 10 amps. Over voltage at the cell terminal is the issue. This why some, including myself, assemble the battery including BMS and let it charge to the high cell cut off by the BMS. My last battery all cells were above 3.400 so it was placed in service immediately. The active balancer will eventually finish the balance.
Yeah I did that with my 8s pack until I got a runner and the BMS stopped charging at the runners 3.63 setting. I then paralleled the group and top balancing only took about 7 hours (using proper techniques)
 

Bob B

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Thx I do understand and do that, but one can turn the power supply voltage up.

I'm wondering what is the battery is actually seeing at the post.? If a good quality meter connected to the post says the charge voltage is 3.5v but the display on the supply reads 3.9 or 4v is that damaging the battery at that moment, so long as one never let's the voltage at the battery terminal exceed 3.65vdc?

I thought I saw Will do this in a video once to "speed things up, but don't try this at home" but I can't find the video. I'm trying to remember if I saw Will do this.

Will went back and edited that out of the video due to the number of people who were overcharging and damaging their cells. There's a thread about on here somewhere.

I think you understand the risk.
 

740GLE

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I think the biggest thing to do is check for voltage drop at either end of the charging lead, verify you don’t have a voltage drop as well as quality ring terminals on the battery posts.

I’ve also see staggered leads at opposite ends of the parallel string, or multiple leads for long strings at various points.
 
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