Current limiting of regular PSU for battery charging

I have two large battery packs which I need a charger for. They are 36V nominal and 42V maximum. They each have a 10S4P config and have an onboard BMS that does protection and balancing. All I need is a power supply for it but the PSU needs current limiting so it doesn’t trip. Each pack wants 3.8A max current (So 7.68A total) but the BMS will allow you to put way more than that into it, beyond the rated charge current of the cells (3.84A based on 4P config). I don’t want to buy an expensive charger and just want to use an ERPF-400-48 with a step down converter to 42V. I am stuck on how to limit the current without wasting heaps of power.

Welcome to the Technical Forum. I have sent this to the group for additional help. I wanted you to know we are working on this for you.

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If anyone has a better solution that isn’t expensive I’m open to ideas

Buying a purpose-built battery charger of appropriate specification is likely your best option, as the effort & expense of trying to cobble together something around a conventional fixed-output supply is likely to eat up the difference. GC330A36-C4P may be a good option assuming that your two packs are to be charged in parallel.

From what little I understand about Li-Ion battery charging, if you can charge them slower, they tend to last longer.

Not a100% guarantee, but using an LED Driver that has Constant Current control, could do the trick.

This one will deliver 1.4A, as high as 42V LPC-60-1400

NPF-120D-42 will deliver 2.9A (appears to be out of stock, right now).

There are a number of others that max out at 42V…

Just a thought.

remember it is a 42V pack so it needs to be 42V. There is the FSP168-10S4AC8 which does 4A @ 42V so I guess I could use that even though I would like more charge current

That is a fair idea except I’m not sure how much the driver would drop the voltage to maintain the current because those cells can pass a lot of current so it may not hold 42V