BMS or active battery balancer for 20s pack

[litespeed]

Hi all,

So I find in an odd spot. Been around for a long, long time yet need some advice…….So for years I ran a Adapto MaxE controller with built in BMS and charging. It was wonderful……just charging and riding without a care in the world with a 24s15p 30q pack. So then I upgrade to the Nuc 24F which is a better more powerful controller but no BMS yet. I can charge in the same way the MaxE did with a 24v power supply at any amperage I want…….but no BMS. So one time my cells got out of balance bulk charging so I have been using my hobby balance charger to charge my packs which I built as two 8s15p and one 4s15p. I absolutely hate charging like this. So this my question. Should I get a BMS with a 20s charger and go that route (example JBDBT 6S-21S LFP 200A Smart Bluetooth Dongle BMS ) or do I charge the way I have been through the Nuc 24F and get an active balancer like this, Heltec 21s 5A Li-ion LiFepo4 Battery Active Equalizer BMS ?

I’m not sure which way is better? I’m thinking the active balancer is easiest since I done need to buy another charger and the ESC controls the amp draw/charge current but not sure if this is the best route? Talk me into one way or the other please?

Thanks in advance!

Tom

 

[amberwolf]

If the Nuc charging function does everything a BMS does except balance, including monitor the individual cells for HVC and LVC, then you are best off just using a balancer if you have to do that.

But if it does not monitor the cells, you would be safer to use a separate BMS that has a common charge/discharge port (not separate C- / P- pads), perhaps with it's own built in balancer.

Note that if your pack is made of well-matched cells it won't need balancing until it ages enough for the cells to no longer be matched; if it's already reached that age, then you're just stuck with a balancer.


But: How does the Nuc deal with a battery's own BMS shutting off charge current? Does it do this gracefully, or could it cause problems?

Does it restart charging current automatically when the bms reconnects it's input, after the bms has turned that input off for hvc on imbalanced cells?

 

[litespeed]

Hey Amberwolf,

I’m not sure how it would act with just an active balancer. I assume it just constantly charges and drops current as it gets to the programmed voltage. I charge to 82 volts if memory serves me. If I lean toward the BMS but then have to buy another charger but if I go with a balancer I can use my computer power supply. This is kinda temporary since Nuc is developing a BMS…..it’s just on the back table right now. Active all in one balancing will be the bomb.

thanks

 

[amberwolf]

An active balancer shouldn't do anything to interfere with the Nuc operations, since it doesn't connect to anything but the cells, and doesn't go between the pack and charger, etc. All an active balancer does is transfer charge from one cell to another, constantly, all the time it is connected, so that all cells are equal voltage. Some of them have limits below which they do nothing, some old crappy ones would keep going until all cells are dead if there's a "leak" in a cell that keeps dropping it's voltage relative to others.

A passive balancer is identical in connection, but all it does is drain any voltage on a cell that is over it's built in or programmed limit, so if no cells are over that limit, it does nothing.

Only an actual BMS that is wired up with FETs (or contactor) between pack and charger (or discharger) would interfere with the Nuc / charging, and that's something you'd have to check with Nuc to see how it responds to shutoffs.

If the Nuc charging works like an actual charger and just resumes charging after interruptions, wihtout manual intervention, then a BMS on the battery will work just like it would wtih any other charger.