Adjustable voltage and current chargers

[Elias lector]

Hello people who are much smarter I am. I need some help with finding a charger/power supply capable of up to 120v atleast. That part is rather easy but where my problem lies is in the amp output, everything I've found has a max of only 30amps. With a 21s 2p battery made with (sorry I can't remember exact numbers) 84ah cells that can be charged at up to 75amps. It would take like a week to charge. I'm not sure if, and I would rather not do this, but could I use multiple power supplies? I just forsee to many possible problems with that. So what are you folks using for higher voltage and capacity batteries?

 

[dominik h]

You can use two telecom rectifiers in series.
Most of them only go to 58,5V , but there exist others that can do up to 72V
Eltek Flatpack 2 HE 48-60
Or use two Flatpacl 110-120 in paralell.

Or you can buy a modified Huawei 4kw they can be bought with up to 120V and can do 4kW charging power on 230V mains.

I use two Huawei R4875G5 to charge my 21S battery up to 88V.

With this setup you can charge up to 28S or to max 117V up to 82A and up to 8kw. A friend charges his Zero with the same setup.

 

[scianiac]

Wait how are you doing your math, at 30A and 168Ah that would only take 5.6hr (technically a little longer once you are voltage limited).

Also of course keep in mind how much power you can pull out of the wall factoring in where you will be plugging it in. But yes power supplies in series or parallel are possible although you have to be aware of what you are doing.

If in series you generally have to take them apart and isolate the ground on all but 1 so all the cases are grounded and the negative rails of all but 1 are floating.

And finally remember that unless your battery is actively cooled you don't want to go pumping in max rated charging current as you'll heat them up and reduce their lifespan. If you really need super fast charging and have the wall power to do it multiple power supplies in parallel so you can charge it at a slower rate when you don't need to rush would be a good option.

 

[dominik h]

Don't mess around with 12V server supplies.
The Delta, the Huawei, the Eltek and the Vertiv telecom rectifiers are all isolated to the housing.
I never opend one of them to use the im series.
Here are a few 2S Setups i have used and a 4S setup. They were use for charging 84-88V and for 220VDC

I also use a 1.8kw 24V in series with a 48V 4kw , that gives me 5,4kw charging power in the range of 70-88VDC

 

[Elias lector]

Wait how are you doing your math, at 30A and 168Ah that would only take 5.6hr (technically a little longer once you are voltage limited).

Also of course keep in mind how much power you can pull out of the wall factoring in where you will be plugging it in. But yes power supplies in series or parallel are possible although you have to be aware of what you are doing.

If in series you generally have to take them apart and isolate the ground on all but 1 so all the cases are grounded and the negative rails of all but 1 are floating.

And finally remember that unless your battery is actively cooled you don't want to go pumping in max rated charging current as you'll heat them up and reduce their lifespan. If you really need super fast charging and have the wall power to do it multiple power supplies in parallel so you can charge it at a slower rate when you don't need to rush would be a good option.

So technically speaking I could charge my bikes battery at 2500 amps max. I would never do that but it is able to take it. That's a 240amp max in a 21s 2p configuration. I normally stay around 10-15 amps. But I don't let it go below 70v if I can help it But I'm planning to build an much beefier battery for a golf cart as well as one for the bike I'm currently building. I may go crazy with a 30s4p but I have to see what 24s does first.

 

[Elias lector]

So with multiple power supplies, let's just say two, do you set each to half the voltage? Or each to full voltage? And what happens if you have more resistance from one or the other? Or do you run them both through a regulator of sorts before they contact with the battery/ bms?

 

[dominik h]

I have set them for my 21S Li-NMC batterie to 44V each.
As long as you do not get under a low voltage protection limit, they work perfectly in series.

The Huawei R4875G5 setup has a low voltage current limiting function. If one of them drops under 35V then it limits its output current from 82A to 55A.
The Vertiv R48-2000e3 Duo has only a slight current drop with lower output voltages. They always charge with 35A or more.

They work best at their highest voltage settings. To run them at there lowest voltage setting does not work with all of them.

But it was asked for a 120V charger, all of them charge perfectly from 80-117VDC

 

[dominik h]

The Eltek Flatpack 110-125 can be set from 89,2V to 170Vdc