Max controller amps for a 50A bms battery?

[Just Give'r]

Hi All,

After a loooong time planning, this will be my first build and is budget minded. I've researched the above and seems about 40a is the max recommended controller amps for a 50A bms.

Could I go with a 45a controller? I would probably only use short/medium bursts of full throttle, and live in a desert climate. Is the main consequence the battery triggering an off condition if overused/overheated? I am ok with a 1% chance of frying my motor. Can I get by with just monitoring temps? Any insight and experience is welcomed.

Thanks in advance.

EXTRA INFO BELOW

Parts list so far: voilamart 1000w 9C style, upp 60V, existing donor bike.

Goals: get the most out of my 60v battery. Reach 30 mph on flat, no pedaling with 60lb bike and 190lb rider. Yes I have used the grin simulator.

 

[E-HP]

Hi All,

After a loooong time planning, this will be my first build and is budget minded. I've researched the above and seems about 40a is the max recommended controller amps for a 50A bms.

Could I go with a 45a controller? I would probably only use short/medium bursts of full throttle, and live in a desert climate. Is the main consequence the battery triggering an off condition if overused/overheated? I am ok with a 1% chance of frying my motor. Can I get by with just monitoring temps? Any insight and experience is welcomed.

Thanks in advance.

EXTRA INFO BELOW

Parts list so far: voilamart 1000w 9C style, upp 60V, existing donor bike.

Goals: get the most out of my 60v battery. Reach 30 mph on flat, no pedaling with 60lb bike and 190lb rider. Yes I have used the grin simulator.

The BMS doesn’t provide any insight into the capability of the cells used in the pack, which is what you want to know. With that info, you would want to use a controller that has a 10%-20% lower max current than that value to account for degradation as the pack ages, so at no point are you are drawing more than the pack capability during its lifetime. Doing so you would accelerate the degradation. Do you have more info on the pack (link, photo of any labels, etc.)?

 

[Just Give'r]

thanks for the response, cells are LG5200mAH

Amazon.com

can you open the link?

It's $350. I'm open to better battery suggestions in a similar price range.

 

[E-HP]

thanks for the response, cells are LG5200mAH

Amazon.com

can you open the link?

It's $350. I'm open to better battery suggestions in a similar price range.

You said you live in a desert climate. The cells are good for 15A, per the data sheet, with ambient temps between 10C-25C (50F-77F) and drops to 7.5A above that. It’s a 4P pack, so that’s 60A and 30A respectively. Not so great if it’s warm out, since they are high energy storage cells rather than high output cells (storage and output are trade offs). If you’re mostly riding with temps higher than 77F, I’d look for cells better suited for that, if you need 45A.

 

[Nix Liou]

I'm not sure what cell is actually being referred to by LG 5200mAh. The only 5200mAh cell I am aware of from LG is the M52VT, which I wouldn't trust past 10A CDR in a battery pack, but I haven't tested it myself. That indicates that the battery would only be capable of 40A from the cells, or less in warm weather.

Besides the somewhat mediocre cell choice, UPP is not a very trusted battery builder, and are known to cut corners on everything they can including:
Waterproofing
Steel strips over nickel
Balancing (Some models had no balancing)
Overvoltage protection
Weld quality (punctured cells, bad welds)
B grade cells or mystery cells

There's a reason they're cheap, and they have a pretty high failure rate within just a few months. They had a single model with 13 reported battery fires from it (U004) last year.

Alternatives I can recommend include Em3ev, affordableebikes.ca, and while I hesitate to to rec them, Amorge seems to have okay build quality at a cheaper price point.

TL;DR: I wouldn't do more than 30a from that pack myself, and it has a solid chance to be dangerous especially if pushed hard.