Undervolting a 48v geared hub motor?

EMGX

Well-Known Member
I've installed a 48v 500w rear geared hub motor with a 48v 15ah battery on an old mountain bike and found that I like it a lot. I'm thinking I might take it on a 2-3 day camp and ride late May in fairly remote areas of eastern Oregon. If it works I'd like to take a 36v 15ah battery that I already have as a backup. Controller is a 11a (22a peak) 36/48v KT controller. The display settings don't have a battery voltage choice. Low voltage cutoff is somewhat adjustable but not for choosing a specific battery voltage (setting "4" is default value which is 30v for 36v battery or 40v for 48v battery). Does the controller automatically choose the correct voltage for the battery and will a 36v battery work with this setup? I've read that the motors themselves aren't voltage specific.
When the weather clears I'll try the 36v battery but in the meantime wondering if others have tried this or have knowledge in this regard.
 

harryS

Well-Known Member
The KT controllers usually get the battery voltage right when you hook up the battery. If you go from 48 to 36, give it a few minutes for the circuits to discharge so it can recognize the lower voltage. Turning on the bike w/o a battery will also do it. Sometmes the battery display is wonky, but as soon as you start riding, it snaps in. If you have the right display, you can see the actual voltage, as you probably know.

When you go above 48V like to a 52V battery, they don't adjust.
 

EMGX

Well-Known Member
Stopped raining long enough to give it a try. Very limited ride on level 1 but couldn't tell the difference 36v vs 48v assist wise. I'll have to give it a more rigorous testing but I'm hopeful that this will serve as a good backup for long hilly multi-day rides. I don't want or need more than 2 ebikes, one for wife and one for me, so if this bike continues to impress the BH Rebel Gravel X with Yamaha PW-SE might go up for sale.
 

harryS

Well-Known Member
You ought to see 20% less wattage in a given assist level if your display shows that parameter. Of course, a 36V pack of similar AH rating will have 30% less watt-hr too,