I am currently eyeing installing an electric starter to my pocket bike 49cc engine. This question is purely about the electrical part of it, but I am going to give a little context.
The starter engine is very simple, it has 4 anchors that drive a rotor when powered. There is no one way bearing or disengagement mechanism except cutting power. They are mounted directly onto the crankshaft between the engine and the clutch shoe. For completeness at the bottom is a picture of such a starter.
I have watched several videos where people installed and wired them and (successfully) demonstrated starting the engine. It boiled down to this:
- Starter case connected to negative of battery
- Positive of starter connected via starter relay/solenoid to positive of battery
- Button to close the relay
From an electrical point of view the starting makes sense:
- button is pressed
- relay is closed
- power flows to the starter turning the rotor
- engine starts
Now this is where I get confused. Unlike in a car the starter mechanism has no way to disengage when the engine starts (like one way bearing, ratchet, centrifugal, ...) except letting go of the button for the relay. When the engine starts it will also start to drive the starter shaft effectively turning the starter into an inefficient generator. From my understanding that means that until the relay is disconnected current will flow to the starter battery instead of from it. I checked the starter relays used and they don't have any protection for reverse voltage or current.
So my question boils down to: Do these people risk their starter batteries or am I misunderstanding something?
