Accessories Wiring Help!


New member
Local time
3:01 PM
Mar 4, 2022
Hey there!

I am in the process of putting together my first ebike and have hit a wall when it comes to the final stages of the wiring. I am trying to wire up accessories such as a headlight, brake light, etc. which are all rated at 12 volts. My battery is a 72volt 20Ah. In order to get the accessories to work I bought a 72v to 12v step down converter. The converter works great and powers all the accessories when it is the only thing wired directly to the battery, but when I tie the converter into the battery leads going to the controller, the converter doesn't really work and gets super freaking hot to the touch within a minute. Is it not getting enough power when plugged into the chain that the controller is plugged into? Any help to get the accessories powered up would be greatly appreciated!

I'm going to guess that when you tested the converter as the only thing connected, you did not use it for very long. Getting HOT, is absolutely normal for these and should have happened whenever it is functioning.

The best way to go is to get lights that will run off of direct pack voltage, OR if you have a controller with a lighting function built-in, but these do not seem to provide sufficient power for multiple accessories.

Transformers get HOT, nature of the beast.

Now, it should have worked OK spliced in, no reason it would not, UNLESS the converter will not handle a lower voltage than 72, most have a range, like 60v-72v, for correct function. When you add a load to the battery, voltage will drop a bit. Double check specs on the transformer, double check the wiring splice, voltage test with controller connected.

Also note that your fully charged voltage is likely quite a bit HIGHER than 72V, you may be ABOVE the spec limits for the transformer. 18s would be 75.6V, 20S would be 84V. Worth testing AGAIN as only thing connected to the battery to verify it has not been damaged. CHECK THE SPECS.

BUT, -AGAIN- best way to go is to have accessories that function on unaltered pack voltage.

Separate small battery pack is an option, need another charger, but there will be no parts on the bike likely to catch on fire, as small, inexpensive transformers on a mobile platform subject to shock and vibration are somewhat prone to do. Consider a power-tool battery pack with an adapter mount, these are rugged, easily available, and you may already have one with the charger.

Also, just so you know, 72V is a dangerous voltage, high enough to kill quite readily. Few if any commercial vendors who would be subject to liability lawsuits use such a voltage for this reason. Exercise caution.