Pack voltage vs. Charging voltage. How close with BMS?

[__Tango]

Hi folks.

I'm trying to figure out how close the specified charge voltage needs to be compared to the pack voltage when using a BMS. Specifically the Fechter/Goodrum BMS.

Let me explain a little...

I'm building an e-motorcycle that i'm hoping to get 36 Thundersky LiFePO4 batteries into. If i can't fit all 36, i'm pretty sure i can get 32 or 30.

I've sized most of the system (controller, motor) so that it can handle the max amount of batteries, and i'm using a Fechter Goodrum BMS, so making that handle 30/32/36 batteries is easy enough.

The charger however, is where i'm confused. Can i just get a charger that does more than 133.2V (36 * 3.7V) and let the BMS take care of the rest? What if i use this same charge voltage (133.2V+) but on the 32 cell pack (118.4V at 32 * 3.7V), again using the Fechter/Goodrum BMS for 32 cells. Will that still work?

Does it matter if the charger is a CC/CV charger that cuts over from CC to CV at 80%?

Thanks for helping me clear up from this confusion...

...tango...

 

[fechter]

In theory, as long as the charger voltage is higher than 3.7v per cell, the BMS should take care of the rest. I've run a charger that's over 12v more than the pack voltage with no issues. It is important that the charger has a CC mode. Changeover from CC to CV at 80% would be fine.

At 133v, it will be pushing the limits of the parts, but the main charge control FET really only sees the voltage difference between the charger and the pack, so a 100v rated FET should be OK.