How to automate high voltage pack charging with low voltage charger

[Simonas0]

Hello everyone,
Soon I will be building a 96V battery pack of 18650 LiIo batteries (27S 5P).
I think, the cheapest good way to charge batteries would be to build the pack of three 9S 5P modules in series, then charge each of them with 36V power supply (I'm thinking of getting Mean Well HLG-240H-36A).
Is there any BMS-like device, which could charge those three 32V modules one by one without my interruption?

 

[john61ct]

RC Hobby chargers, at the high end very precise and robust.

10S units are getting rarer

consider 4 strings of 7S if 28S total is doable?

Junsi iCharger, FMA Cellpro, Graupner, maybe ISDT or Hyperion

These do the cell (top) balancing as well, but if not needed every cycle, look for a "fast charge" option to skip when you're in a hurry.

Discharge to a spec'd storage voltage as well.'

Good ones are not directly mains-powered, need a 20-40V PSU to feed them.

Otherwise, adjustable bulk-level like a pair of Satiator would work well, isolated outputs so no need to separate the two halves at the midpoint tap.

But then separate balancing gear is required.

 

[amberwolf]

There isn't any BMS system designed to do what you want.

You would either have to manually disconnect and reconnect each of the packs with the charger, or design and build a system that would do that (which would have to guarantee disconnection of one before connection of the next, with no possibility of arcing, failed disconnects, etc., or else you'll short across an entire pack and probably have a fire).

It's a lot simpler to charge it all as one pack.

The meanwells are isolated, so you can use multiple units in series to charge the pack.

I have a set of four HLG-600H-54A units taht were used by the previous owner in series-parallel, for charging a 28s pack; they worked fine for that.

I expect you'd get similar results from three lower voltage units in series.



You're still left with the need for a BMS (or other monitoring system) that could do the whole pack, if you want to monitor discharge and shut off when empty (to prevent overdischarging any cells), and if you want to monitor charging with all the chargers in series.


You can use three separate BMS units to monitor the packs separately, and wire them so they don't use the FETs to control anything, but only use the signals from the FET drivers to enable/disable teh Meanwells (the HLG series has an enable line, IIRC, so you could make a fairly simple circuit to do this).

 

[john61ct]

BMS just means a collection of functionality.

Balancing can be taken care of separately, and can be very important with older / sub-par / mismatched cells.

HVC / stop-charge should ideally be based on the cell-level, unless you are conservative with a lower stop-charge voltage, and feel very secure about your top-balancing system.

No need to disconnect serial'd sub-pack modules with well isolated chargers like Satiator or Mean Well HLG series.

@amberwolf Are you saying **all** the MW are product lines isolated?

LV alarms / lights and/or cutoff cell-level as well, when top balancing you really should not rely on pack voltage at the bottom.

Conservative stop-discharge based on a calibrated Ah-counting / SoC meter is best, with lowest-cell LVC as a failsafe.

 

[billvon]

I think, the cheapest good way to charge batteries would be to build the pack of three 9S 5P modules in series, then charge each of them with 36V power supply (I'm thinking of getting Mean Well HLG-240H-36A). Is there any BMS-like device, which could charge those three 32V modules one by one without my interruption?

You're not looking for a BMS. You are looking for a charger. (The battery pack still needs a BMS.) Your options:

Get three 36V isolated chargers. They are cheap. Meanwells will work.

Get one 36V charger and two DPDT relays. Build a little digital counter that will sequence the relays to charge battery bank 1, 2 and 3 over and over again. Set the clock speed to something like 30 minutes.

 

[john61ct]

Need a stop-charge circuit to fulfill the "automated charging" part.

And "something like a BMS", IOW cell-level voltage sensing HVC is safest.

That way the worst consequence of growing imbalances, is reduced capacity at the pack level.

 

[Simonas0]

Thank you all for suggestions, I decided to build myself such charging system with arduino and relays, will post info when I'm done (most probably sometime in january).