View Single Post
      08-16-2018, 03:04 PM   #13
The Wind Breezes
Lieutenant Colonel
The Wind Breezes's Avatar
852
Rep
1,856
Posts

Drives: 135i N55 DCT
Join Date: Apr 2015
Location: USA

iTrader: (0)

Quote:
Originally Posted by CO_Steve View Post
So a completely unrelated question. When I first started looking into ebikes I saw models claiming 250-1kW power levels. Given the common use of 18650 cells that made sense to me. You claim 4-16kW of power. Could you fill me in on the details? An 18650 cell can deliver about 6W so that would be 2666 cells for 16kW. You must be doing something different.
Easy, you are confusing energy density (the number quoted is for a real shitty cell anyway) for power density.

18650s have capacities around 9-11 WATT-HOURS for a 2.5-3Ah cell. That's the energy density. Power density will be around 10x higher--good cheap cells like the Samsung 25R can discharge 25 amps, slightly more for very short periods. That's a discharge rating of about 10C or about 90 watts per battery with a nominal voltage of 3.6 volts. You would deplete the battery in about 6 minutes and it will be very hot, but real world use is considerably more tolerant. A ~1KWh nominal capacity pack with good cells can output about 10KW for short periods on a fresh charge. You can lookup a datasheet for any given battery and it should have discharge curves at different power levels.

Also I don't screw with 18650 anymore, I use high discharge RC LiPo and drain them to about 20% of capacity. Much higher average discharge voltage, and way easier to configure a pack (no laborious spot welding needed).


Quote:
Originally Posted by yearningirish View Post
love to bike... and yours are quite a companion to flaunt
Thanks

Last edited by The Wind Breezes; 08-16-2018 at 03:10 PM..