Topic: Starting amperage

[beemerbum]

Does anyone know what sort of amperage is coursing thru the wires during starting (electric) on a 72 CB 750?

[TwoTired]

Depends on how hard the engine is to turn over.  In good nick, it draws about 25 amps.  But if the engine is jammed or started motor stalled about 100 amps.

[beemerbum]

Thanks. Makes sense. Needed to know for a custom wiring situation

[scottly]

Depends on how hard the engine is to turn over.  In good nick, it draws about 25 amps.  But if the engine is jammed or started motor stalled about 100 amps.

The factory manual says that with no load, the starter draws 35A max, with load 120A, and stalling load 280A.
Beemer, the current through the starter button and solenoid coil is about 5A, IIRC.

[beemerbum]

Thanks gentlemen. To me electricity is a black art, not to be trifled with

[Bodi]

All depends on load. Measuring one off the engine, the starting current is well over 100A (for so short a time I could not get an actual reading) then it goes down to about 20A while it screams at full speed.
The motor itself will melt if run continuously - I think the thermal rating is 30 sec on and 1 minute rest - so you don't need to use cable rated for the max amperage. Heating the cable even perceptively is super unlikely - voltage drop is negligible (6AWG goes 0.5 Ohm per thousand feet).
If you want to be super careful 4AWG is impressively thick but overkill, 6AWG is certainly sufficient and close to the factory starter cable gauge. I would probably use 6AWG. Welding cable is best, "normal" stranded wire is too stiff. Hobby shops may have "wet noodle" wire but IMO that's to flexible for a battery cable.