Hybrid Moped Dual power source lights and diodes

Thread Starter

BruceLindholm

Joined Feb 15, 2018
5
Hi All,
I am building a hybrid moped - gas engine power to the rear wheel - 48v power to a front hub motor. It all works well except I am unsure of how to design the circuit for the headlight and tail light. The bike has a lighting circuit to power the lights - it also has a rectifier so the light uses 12v dc power. I have a 36w dc-dc converter to have 12v power out of the 48 v battery. I want to have the lights work on engine power only, battery power only, and also if both engine and battery power are being used - and all through a single switch. I believe I need a diode on the 12v output of the dc-dc converter, but don't know if I need one on the positive side of the lighting circuit. Is there anything else I am missing?

Thanks for any comments or help you can provide.

Bruce
 

wayneh

Joined Sep 9, 2010
17,134
If I understand correctly, you need only the one diode because the rectifier already contains diodes to prevent reverse current.

You are OR-ing power supplies together, and the typical solution is a diode for each supply to prevent reverse current being driven into that supply. As I said, I think your rectifier already does that for the moped's built-in electrical system. Does your moped have a magneto-based power system? I've never seen one with an alternator.

Does the 48V battery get recharged by the moped's electrical system, or is that separate?
 

Thread Starter

BruceLindholm

Joined Feb 15, 2018
5
It is a magneto based system. The gas engine will charge the 48v lithium battery above a certain voltage. Thanks for your response - it was helpful.
 

wayneh

Joined Sep 9, 2010
17,134
It is a magneto based system. The gas engine will charge the 48v lithium battery above a certain voltage. Thanks for your response - it was helpful.
How does the built-in lighting system get it's 'normal' 12V supply when running? Was the DC-DC converter also built-in?
 
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