DC Battery step down 80V to 48V

Thread Starter

YMHP95B

Joined Sep 1, 2020
5
Hi. I have an e-bike with 48V 30A motor.
I also have 5 li-Ion batteries Kobalt/Greenworks 80V. I'd like to step down their voltage from 80V to 50V or so for the e-bike motor. I'm thinking making a bracket to parallel connect the Kobalt 80V batteries. It'll need to be 20A at 80V or 30A at 50V side. What's the best way to step down? Need some sort of resistor for this, not sure what to use/do. I can build something if I have the electronic diagram with the parts. Didn't find anything over the counter.
Thanks!
 

MasterG

Joined Jan 18, 2022
9
Well, you are looking to reduce 32V in DC, so, Zener and a Resistance? No, the efficiency is BAD(likely 5-15% efficient if the motor is on stand by) , a Linear Voltage regulator like the LM338K may work, but the efficiency will still suck, (around 50%), the best bet for efficiency is a switching Voltage regulator, a custom one maybe
 

crutschow

Joined Mar 14, 2008
29,792
Can't use a resistor to drop the voltage for the high current the motor uses as it gives poor regulation and will dissipate a large amount of power.

What you need is a high-power DC-DC buck converter.
Building one with little electronic experience is problematic.
 

Ian0

Joined Aug 7, 2020
5,140
Well, you are looking to reduce 32V in DC, so, Zener and a Resistance? No, the efficiency is BAD(likely 5-15% efficient if the motor is on stand by) , a Linear Voltage regulator like the LM338K may work, but the efficiency will still suck, (around 50%), the best bet for efficiency is a switching Voltage regulator, a custom one maybe
An LM338 that takes 30A?
 

panic mode

Joined Oct 10, 2011
2,134
the only sensible way to do this is by using switching regulator. linear mode using any technology will still produce 1000W of heat
 

Papabravo

Joined Feb 24, 2006
18,422
the only sensible way to do this is by using switching regulator. linear mode using any technology will still produce 1000W of heat
As has been pointed out numerous times this is not a weekend DIY project, and the TS should not entertain the notion that it is.
 

bassbindevil

Joined Jan 23, 2014
422
You'd be better off using the cells from the batteries to make a new battery for the bike. That's not a minor project either, but more straight-forward. There's lots of info out there on DIY battery packs for e-bikes.
 
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