Battery for regen

[erikstunes]

Does anyone here have experience with which batteries work better with regenerative braking? My bike is capable of regen of over 10 amps as read off the cycle analyst, and I want to buy a bigger battery, but I don't know if the charge rate capacity during regen is an issue. I have some long steep descents

 

[E-HP]

Technically, most lithium 18650 cells can handle between a 0.25C to 0.5C charge rate, so if you are charging through the discharge port, then for a 20Ah battery, you could charge at 10A. However, even though you have seen 10A of regen via the CA, you won't see that continuously, even on a steep descent. Some of this depends on whether you are primarily using regen for recovery or for braking? For recovery, you have to set the regen current lower, since you need to bike to be moving in order to recover energy and too high a setting just brakes the bike to a speed where you get no recovery. It sort of all works out on it's own, whether you set the regen current higher or lower, when it comes to your battery, unless you start the long descent when your battery is fully charged, so one simple rule to remember.

The bigger concern on long descents is not to start the long descent right after a long ascent. The motor will create heat during regen almost as much it will on the ascent of the same hill. So, if your motor hits 100C on the way up, and you immediately start your descent, you can cook your motor before you get to the bottom, so a second rule to remember.

 

[erikstunes]

The question is more about the battery and bms. Just wondering if anyone had similar glitches with different batteries.

The regen on descent works fine (if of course the battery is not full) until the hill gets too steep and then the CA cuts out power and braking although the direct is still lit. I'm not sure why, temp is not too high, goes higher on subsequent ascent. I'm still experimenting to figure out why

 

[erikstunes]

... although the display is still lit. I meant to write

 

[amberwolf]

If the battery uses a common-port BMS it should be able to prevent overcharge if it was already full, which will protect the battery. But...if it turns off the input during regen the controller-side voltage can spike high enough to damage things depending on the system and conditions at the time (see the discussions I linked in your other thread(s)). So....

Which battery is actually better depends on your needs and the conditions it will see--if you never fully charge the battery during braking it shouldn't shut off...you can calculate out how to size the battery for your actual capacity needs vs how much you might have to discharge before the dowhhills, or leave uncharged during normal charging, to have room for all the regen Wh you'll create on the downhill, knowing about how much current you get on average and how long a time it flows.

The battery needs to be able to charge continuously at the worst-case current rate you see, both the BMS and the cells have to handle it. (the interconnects/etc can because they can already handle mroe than that for discharge).