Battery Pack Mods (External BMS)

[SubRider]

Are there advantageous modifications to battery packs
(such as pulling out the BMS board for air cooling) ?

 

[Nobuo]

BMS's works usually at ~99% efficiency charging and discharging. Unless you are using a wrong AWG wiring on the BMS, or the BMS itself has a wrong BUS conductors capability for the amps required, they don't heat up noticeably more than slightly warm while charging or discharging.

The heat should be only common during the last charging stage (when the cells are near fully charged) when balancing section starts to discharge higher charged cells through their BMS's resistors

The most real advantageous mods, unless you have a wrong built battery pack (not enough/thick nickel conductors, wrong nickel thickness on main battery poles (too much common), wrong AWG wiring, wrong BMS amps limiting factor for cells capability) so you must add or change some materials, is really related to the treatment received.

- Avoid harming SOC (state of charge) levels (less than 10%, more than 90%) the most time you could with a reliable use of your battery.

- Avoid heat in the cells. Direct sun, hot storage places. Use the pack with the right BMS current limiting, or with the right controller power output.

- At least one out of ten full cycles, let the battery plugged on the charger for a couple extra hours since 100% being sure the balancing is completely done (BMS stop heating) so the cells equilibrate maximizing capacity and avoiding dangerous paralleled groups reaching bad SOC levels

 

[SubRider]

Thanks Nobuo.

What about battery fire bags?
Are they worth it?
Are there any negatives (such as overheating the battery)?
Where can they be purchased?

 

[Wheazel]

Depends entirely on how and where you charge your batteries and what type of battery it is. If dealing with rc lipos, where quality generally is inconsistent, a batterybag would make more sense compared to when charging your laptop.

 

[SubRider]

Thanks Wheazel.

I'm favoring LiFePO batteries, about 20-25 Ah. This is for an e-bike

 

[dnmun]

there is no risk of fire. not sure why everybody has to keep saying this even though they know nothing.

it does help the mosfets to stay cool if you have them exposed to the air and not wrapped up inside a plastic shrink wrap sleeve against the battery pack so if you can expose it then do that. keep the rain off of it because it may shut off if the signal lines get wet and send a false LVC signal. and you don't want high voltage bleeding into lower voltage parts of the MS through the water on the BMS.

 

[dcuste]

I have a new 48v 17.5ah battery with an internal BMS. As far as I can tell everything is working as it should except the BMS is warmer than I would expect from a device that is supposed to be 99% efficient. It stsys cool during charging and very light discharge, but if I'm pulling 1000w for more than a few minutes it gets up around 130°F. I've pulled the cover off and can't pinpoint the heat source. Just the whole metal case is warm. I don't see any bad connections. I did have a controller problem that cause a direct short and blew a 35amp fuse. After that, the battery power switch will turn off, but there is still power at the battery terminals. I'm assuming that the short somehow damaged something in the BMS.

Does anybody have any thoughts on what else I should check for?