V11: Why can't we charge at 8amps?

[Tryptych]

Can someone remind me why I can't use my 3A charger and my 5A charger at the same time?

 

 

[madbikes]

Hardware of the wheel does not support charging more than 5A. You can use your 5A fast charger, but not both together.

[Zopper]

Well… you can. But you are exceeding the limits it was made for and you risk that something will die. There is no fuse that would stop you after getting over 5A. 

According to Samsung 50g cell datasheet, standard charging current is 0.3C - 1.6A. And V11 is a 20s4p pack, meaning 4 cells in parallel and 20 in series. For current, it’s only the 4p that intrigues us. Because the current splits equally, so each parallel cell means another 1.6A faster charging. That gives us that the battery cells can easily handle about 6.4A charging. So the 5A charging is almost as high as the recommended value for the cells. And the charging electronics inside of the wheel is made for this current as well.

Fast charging (where the cells begin to suffer and their lifetime is degraded) is generally placed at about 0.5C, which in this case is about 2.6A/cell -> 10A for the whole wheel.

To sum it: If you want to be safe, use 5A max. If you feel more adventurous (and I’m not responsible for your burned home), 8A should be still relatively safe, especially if you use it only occasionally and ensure that the wheel can cool well (no direct sun, etc). But don’t go over that (unless you really know what you are doing and if it’s safe and if you did, you wouldn’t ask this question).

Edited August 15, 2021 by Zopper

[Chriull]

3 hours ago, Zopper said:

According to Samsung 50g cell datasheet

These cells seem to have an a bit untypical recommendation/specification:

5%C cutoff current for charging for specified cycle life! For the 20s4p config of the V11 this leads to 4*245mA~1A!

That's by far the highest value as charge current threshold i've seen so far - after all the 50-66mA per cell...