Charge one half of the battery pack, then the other half?

[Longlight]

So I have a theoretical question. If I made, say a 10S battery pack that used two separate 5S balancing modules (not in the drawing) could I charge half the pack first with a 5S charger, and then just charge the other half when the first one was done? I assume this will work perfectly fine as long you remember to charge both halves up to the same voltage before discharge, but I figured it would be best to ask in case I missed something obvious here.

 

[john61ct]

Yes, but of course no loads fed while charging as you can do normally.

If doing multiple packs concurrently, common grounds from non-isolated supplies may mean have to physically break the string while charging then re-wire once done,

And yes, getting out of balance can be dangerous, certainly hurts longevity.

Best is very precise chargers with exact same termination setpoints, tested & verified both halves at same finish SoC.

Balance chargers in this case 2S versions, designed to do exactly this.

 

[fechter]

I've run packs like that before. Just be sure both halves are charged to the same level before discharging.

If you get a second charger so you can do both at the same time, that's where you can run into problems. Each charger needs to be isolated from the other or it will short something out. You can't run two chargers off a single supply.

 

[john61ct]

I believe you can, as long as either the upstream PSU or both downstream DC-DC converter / controllers are of the (more expensive) fully isolated type.

Or separate galvanic isolators put to use.

The principal being no connection between the input AC common reference ("ground" wire) and the DC output common reference (negative return).

I believe if the AC PSU is Floating - only Neutral and Load wires connected - then that also makes it fully isolated.

Of course if the two packs are still wired in series - positive to negative - to each other while charging, that can cause its own problems, I guess depends on the DC-DC unit used.

I welcome correction if any of the above is not accurate.

 

[Longlight]

Thanks guys! I will probably not run two chargers, but If I ever did, I will make sure I run them, or atleast one(?) through an galvanic isolator.

As for checking voltages, I guess the only potential issue with using only one charger, is that you need to wait a while before you measure the other half of the pack, because the first one has rested a few hours.

 

[999zip999]

I run two setups of a meanwell at 29vols and a hp550 power supply 12.6v for 41volts on one power strip. This for for my 24s charge as two 12s. I have left the battery connected ro controller and C.A. I don't do this often. I usually disconnect red power to controller.

 

[neptronix]

If you have 10s, well.. there's tons of 10S chargers out there.

See my post stickied in this section about RC Lipo management. It talks about 2x 5S charging extensively.

 

[999zip999]

I don't use a bms but monitor always and I have balance charge a dozen times over 5yrs or as needed. Not much..

 

[VietJr]

I've run packs like that before. Just be sure both halves are charged to the same level before discharging.

If you get a second charger so you can do both at the same time, that's where you can run into problems. Each charger needs to be isolated from the other or it will short something out. You can't run two chargers off a single supply.

If the chargers are isolated, would there still be any problem connecting them to a single supply? Also, if you had two chargers, is there any benefit from connecting each of them to half a battery pack versus connecting the chargers in series and charging the whole pack? Seems like you would need more connection points with treating the battery as two halves, making it more inconvenient to use and possibly adding room for user error?

 

[fechter]

If the chargers are isolated, would there still be any problem connecting them to a single supply? Also, if you had two chargers, is there any benefit from connecting each of them to half a battery pack versus connecting the chargers in series and charging the whole pack? Seems like you would need more connection points with treating the battery as two halves, making it more inconvenient to use and possibly adding room for user error?

I have never seen isolated RC battery chargers. If they exist, then you could use a single supply.

There is no reason you couldn't combine the chargers and run them at the same time on the whole pack. The OP intended to use the balancing feature of the charger so would need balance wire connections.

 

[Longlight]

The OP intended to use the balancing feature of the charger so would need balance wire connections.

I have to clarify that I didn't intend to use a charger with balance function. Each half would be connected to it's own balance board Also I have to add that the idea of the 10S pack was just the principle (and easier to draw :lol: ). I was thinking more of making a 36-40S pack, where the problem is that chargers and balance boards are rare and expensive, compared to anything below 36S.

 

[fechter]

OK, I stand corrected.
It should work fine with multiple chargers in tandem.

 

[999zip999]

My HP power supplies are isolated. I guess my meanwells are too ?

 

[Voltron]

The main drawback is going to be suddenly wanting to use it, and having to wait until both halves are charged. It's annoying, where if both halves or the whole thing are charging, you can grab it and use it without being all the way full, as long as your chargers are matched.

 

[Jez]

I do exactly this. I have two 7s packs that together form a 14s battery and each battery is joined in series when in use. To charge I use an iCharger duo balance charger which has two channels. Each 7s pack (the charger can only charge up to 8s) will charge each "7s" battery simultaneously and balance them. Then when I need to use them I just wire them back up in series and all is well.

Note there are no BMSs in my batteries.

In this approach it just makes sense to charge both batteries at the same time. The iCharger duo makes that easy so nothing gets out of balance and both batteries are used equally.