Question about top balancing???

ericfx1984

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So initially when I built these battery packs I decided I was going to allow my RC car charger to balance them in series as it has the ability to do active balancing

However it became obvious that the RC car charger really wasn't the best option for something like this..

So I purchased a 10 amp variable regulated power supply from Amazon think it cost about $50

I pulled all the bus bars off and wired all eight cells in parallel it looks pretty damn Goofy

Then I powered up the power supply and connected it to my Amprobe multimeter and adjusted it to 3.65 volts.. which interestingly enough according to the display on the power supply is only 3.6 volts.. but I feel like my multimeter is probably more trustworthy

From there I took a voltage reading of the entire Bank and I don't recall exactly what it was but it was something in the 3.5 range nearly 3.6

Anyway when I first hooked it up the amperage was somewhere around 3:00 to 4 amps going in if I recall correctly.. it is now at 0.092a and approximately 0.327w

Have I reached the point now where I can consider this to be properly top balanced or should I continue to allow it to do its thing or.. should I disconnect it let it rest for a little while and hook it back up and go at it again?
 

sunshine_eggo

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So initially when I built these battery packs I decided I was going to allow my RC car charger to balance them in series as it has the ability to do active balancing

However it became obvious that the RC car charger really wasn't the best option for something like this..

Please share why.

So I purchased a 10 amp variable regulated power supply from Amazon think it cost about $50

I pulled all the bus bars off and wired all eight cells in parallel it looks pretty damn Goofy

Then I powered up the power supply and connected it to my Amprobe multimeter and adjusted it to 3.65 volts.. which interestingly enough according to the display on the power supply is only 3.6 volts.. but I feel like my multimeter is probably more trustworthy

Both are accurate-ish. It's likely that you're using the leads that came with it, and you have excessive voltage drop. There are instructions on how to fabricate your own leads in the top balancing guide.

From there I took a voltage reading of the entire Bank and I don't recall exactly what it was but it was something in the 3.5 range nearly 3.6

Anyway when I first hooked it up the amperage was somewhere around 3:00 to 4 amps going in if I recall correctly.. it is now at 0.092a and approximately 0.327w

Have I reached the point now where I can consider this to be properly top balanced or should I continue to allow it to do its thing or.. should I disconnect it let it rest for a little while and hook it back up and go at it again?

If the bank measures 3.65V w/the multimeter, and the current is as you describe, yes.
 

ericfx1984

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Please share why.
Happy to.. so it seems that the remote control car charger, which is capable of handling many different types of battery chemistries, and is capable of charging at 10a per channel(2 channels) becomes painfully slow once it gets to the final part of the charge.. and effectively it functions as an act of balancer at that point except it only seems to balance at around a quarter of an amp and that can take quite a while if one cell is a tenth of a volt or even slightly more out of balance from the others

Both are accurate-ish. It's likely that you're using the leads that came with it, and you have excessive voltage drop. There are instructions on how to fabricate your own leads in the top balancing guide.

In short close enough... Not too worried about the drop... I can just take a reading on the bank

If the bank measures 3.65V w/the multimeter, and the current is as you describe, yes.

Awesome thank you
 

sunshine_eggo

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Happy to.. so it seems that the remote control car charger, which is capable of handling many different types of battery chemistries, and is capable of charging at 10a per channel(2 channels) becomes painfully slow once it gets to the final part of the charge.. and effectively it functions as an act of balancer at that point except it only seems to balance at around a quarter of an amp and that can take quite a while if one cell is a tenth of a volt or even slightly more out of balance from the others

Thanks. Good to know. I've proposed this as a solution, but with a charger that has a 1A balance capability, so it might not be much better. If the cells come in only 5-10Ah apart, then no big deal, but I've seen worse than that. The only advantage in that case is the touch-free aspect.

In short close enough... Not too worried about the drop... I can just take a reading on the bank

The concern is that the voltage drop also causes reduced current. If the cells are at 3.5, and the charger sees 3.6 due to the drop, then the charger will reduce the current in response to the drop, thus slowing down your charge.
 

sunshine_eggo

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Thanks. Good to know. I've proposed this as a solution, but with a charger that has a 1A balance capability, so it might not be much better. If the cells come in only 5-10Ah apart, then no big deal, but I've seen worse than that. The only advantage in that case is the touch-free aspect.

Thinking about this again...

While it's suboptimal, as the peak cell fills, and the others are creeping along, one could just remove the high cell from the circuit and drop one on the cell count.
 

mikefitz

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as the peak cell fills, and the others are creeping along, one could just remove the high cell from the circuit and drop one on the cell count.
This would be difficult to carry out. With all the cells in parallel how do you check the 'fullest'?

The concept of carrying out a top balance with multiple cells connected in parallel with inexperienced newcomers to electrics often ends in cell damage.

A safer method is to charge the cells in series arranged in the final format as a battery ( ideally with compression or restraint) with the BMS operational. Add or remove charge from the appropriate cell as required, whilst the battery is nearing full charge.
The BMS will act as a 'safety valve'.

Mike
 

sunshine_eggo

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This would be difficult to carry out. With all the cells in parallel how do you check the 'fullest'?

They're not. They're in series connected to a RC balance charger. The issue was when the first cell hit peak, the balance current was a pitiful 0.25A.
 

ericfx1984

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Thinking about this again...

While it's suboptimal, as the peak cell fills, and the others are creeping along, one could just remove the high cell from the circuit and drop one on the cell count.
Infact I did just that hehehe
 

ericfx1984

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They're not. They're in series connected to a RC balance charger. The issue was when the first cell hit peak, the balance current was a pitiful 0.25A.
That's very similar to what I experienced.. but as mentioned above the fix for this would be to remove the cell that had already fully charged and to go on about your business from there
 

ericfx1984

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Glad to hear it. It eliminates the benefit of "set it and forget it," but it's an option for expediting the charge.
Even then.. the charge was never really completed I finally wired all eight of them in parallel and charged it with my shiny new variable charger bench power supply
 
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