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Do I need a bench DC power supply to top balance cells?

filippomasoni

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Jul 26, 2021
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Tuscany, Italy
Do I need a variable bench DC power supply or I can get by with one of these: https://shop.gwl.eu/Chargers-6V-to-36V/Charger-3-6V-20A-for-LiFePO4-cells-1-cell.html?cur=1
I'd like to have a small power supply, that works all over the world (AC 100-240V 50-60Hz) that I could keep in the camper in case of need and I don't like those bulky variable bench chargers. I'd also get this: https://shop.gwl.eu/Chargers-6V-to-...attery-charger-27-6V-21A-600W.html?cur=1#tab1 as my shore power charger, that also works worldwide.

Will this be able to top balance my cells in parallel? What's the difference with a variable power supply that I see everyone using?

I guess the upside of the variable one is that I can choose the voltage and charge for example at a more conservative 3.6V or maybe 3.25 if I need to store the cells for a few months, which I will have to actually.
 
Should be fine. Count on this at the bottom of that page:

"Note
The imperfect connection of the clamps to the battery terminals, causes the transient resistance and current loss which result in max. current charging of 10A. It is recommended to change the original clamps for eyelets which perfectly match to used battery terminals (screws)."


I would also consider thicker gauge wire and making them as short as practical.

Both of which you would need to do on a benchtop power supply.

Storage is easy. Just discharge the battery a known-ish amount. Hit anywhere in 40-70% SoC, and you're good. BMS should also be disconnected as they pull a tiny current from the battery.
 
Should be fine. Count on this at the bottom of that page:

"Note
The imperfect connection of the clamps to the battery terminals, causes the transient resistance and current loss which result in max. current charging of 10A. It is recommended to change the original clamps for eyelets which perfectly match to used battery terminals (screws)."


I would also consider thicker gauge wire and making them as short as practical.

Both of which you would need to do on a benchtop power supply.

Storage is easy. Just discharge the battery a known-ish amount. Hit anywhere in 40-70% SoC, and you're good. BMS should also be disconnected as they pull a tiny current from the battery.
Yes, I was planning on adding my own proper wires and lugs anyway. Thanks for the tip.
Any experience with GWL products? In Europe, they seem to be the only "quality" option other than China (Aliexpress Alibaba).
 
I bought good quality cells and did not need to top balance.

Ditto on the storage.
 
Mine are in service and top balancing with an active balancer as I type this. Never did a parallel top balance. Daily charge to 13.8 volts and equalize at 14.2 every three weeks.
 
I would top balance them. I did that for my two 24 volt 25 ah packs, and I did that for my two 280 ah 24 volt batteries.

Maybe it would be fine. Maybe not. If you go back a couple years people would bottom balance a pack. Drain each cell to 2.5 volts, assemble the pack, and then charge. I don't think the saying is "you need to top balance unless its inconvenient or you don't want to."

I had to wait four months to receive them, so I did not want to take a short cut, so I took an extra week and a half to top balance the large batteries. Charged in 8S to 3.45 volts per cell, and took apart, and topped off 4P on a bench top charger to 3.65.

If you're not, perhaps they're being balanced somehow. If they are, check to see how those batteries are balanced and what the triggers are. My Overkill is configurable to and the standard is above 3.4 volts and charging. So, basically my battery will balance only when receiving current and only when volts are above 3.4.

Even when it is top balancing, it only does 1 amp. In a 280 ah cell, that's not a lot. It could take weeks for my BMS to top balance.

I believe an active balancer could help out, especially if it moves more amps, but I'd still not want to balance below a certain level.
 
I would top balance them. I did that for my two 24 volt 25 ah packs, and I did that for my two 280 ah 24 volt batteries.

Maybe it would be fine. Maybe not. If you go back a couple years people would bottom balance a pack. Drain each cell to 2.5 volts, assemble the pack, and then charge. I don't think the saying is "you need to top balance unless its inconvenient or you don't want to."

I had to wait four months to receive them, so I did not want to take a short cut, so I took an extra week and a half to top balance the large batteries. Charged in 8S to 3.45 volts per cell, and took apart, and topped off 4P on a bench top charger to 3.65.

If you're not, perhaps they're being balanced somehow. If they are, check to see how those batteries are balanced and what the triggers are. My Overkill is configurable to and the standard is above 3.4 volts and charging. So, basically my battery will balance only when receiving current and only when volts are above 3.4.

Even when it is top balancing, it only does 1 amp. In a 280 ah cell, that's not a lot. It could take weeks for my BMS to top balance.

I believe an active balancer could help out, especially if it moves more amps, but I'd still not want to balance below a certain level.
I do want to top balance and I'd like to capacity test as well even if my cells are supposed to be grade A from Amy of Shenzhen Luyuan.
I'm supposed to receive them (8 cells) in the next couple of weeks and I won't start the build at least until next May (vehicle delivery and preparation will take much more than I previously anticipated).
I have all the time to do the slow top balancing and discharge, even if it will be tedious. I currently don't have a BMS yet, as I still haven't decided if going 12V or 24V and I also don't have any 12V load or an inverter yet, so I need a way of charging and discharging the single cells to test them and then leave it at a storage voltage.

Do you think it's worth getting a classic Chinese bench power supply 30V 10A over a simpler single voltage 3.65V like the one linked above?
 
I bought good quality cells and did not need to top balance.

Ditto on the storage.
What brought you to the conclusion?

A first charge in series config got you to roughly equal voltages I assume. Or at least that they all entered the full charge knee roughly simultaneously.

If they're all in the knee together then they're probably not off by more than a few ah tops and passive balance will sort it without any significant loss in usable capacity in the interim.

It's important to explain what conditions to look for to someone to determine whether a balance is needed or not so they can spot it too.

Unfortunately a lot of folks don't have high quality cells due to some sketchy sellers still being recommended here and there. The one I'm currently slapping together was nowhere near close on the first series charge, and despite only having 80-84ah available capacity per cell still took almost 6 hours to finish up in parallel after the first in the pack (of 4) hit 3.65 cutoff in series with my cheapo 10a power supply, so some 50+ ah went into the last 3. Quite the discrepancy.

They're objectively garbage cells but 80ah is still over 48 hours of use for my needs out of it so whatever.
 
What brought you to the conclusion?

A first charge in series config got you to roughly equal voltages I assume. Or at least that they all entered the full charge knee roughly simultaneously.

If they're all in the knee together then they're probably not off by more than a few ah tops and passive balance will sort it without any significant loss in usable capacity in the interim.

It's important to explain what conditions to look for to someone to determine whether a balance is needed or not so they can spot it too.

Unfortunately a lot of folks don't have high quality cells due to some sketchy sellers still being recommended here and there. The one I'm currently slapping together was nowhere near close on the first series charge, and despite only having 80-84ah available capacity per cell still took almost 6 hours to finish up in parallel after the first in the pack (of 4) hit 3.65 cutoff in series with my cheapo 10a power supply, so some 50+ ah went into the last 3. Quite the discrepancy.

They're objectively garbage cells but 80ah is still over 48 hours of use for my needs out of it so whatever.
Pretty much the same deal if it takes a couple of months to balance.
 
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