Onan Generator Cranking Amps

CA Traveler wrote:
What is the expected cranking amp draw for a Onan 10K generator?

Mine is cranking slow due to excessive voltage drop on the + wire and I want to estimate what the voltage drop should be for the wire size and length. The - side uses frame ground is is OK.

Looked through my generator info and could not find the actual amp draw for the starter.

When I bought my coach, the generator cranked slowly and often would not start at all. Even with the "boost" switch pushed to combine house and chassis batteries, it was a reluctant starter.

I went through the entire 12V supply and cleaned all connections at the battery plus a post on the front wall. It helped a bit, but was not a satisfactory solution. If I remember correctly, the 12V supply fell to 11.5 Volts when cranking.

It is a very poor design to use house or chassis batteries located in the rear to start the generator at the front. Not only because of the long distance with resulting voltage drop, but because, often when you need the generator is when you have run your batteries down to 50% or lower. Just no enough power to start the generator reliably.

What I ended up doing was to install a dedicated battery at the generator and using a diode, charge it from the house system.


My generator now starts quickly. Even if my house batteries are down, I don't need to worry that my generator will not start.

My 4KY uses about 100A, very roughly speaking, when cranking. The initial surge is somewhat higher.

If it cranked well in the past, the wire size is presumably not the issue, but rather some poor connection somewhere. It may also be worth checking the starter motor to make sure all the brushes are properly functioning; I had to replace my generator starter a few years ago after it burned out, and discovered that for as long as I had owned it, during which time it was rather lethargic and marginal at starting the generator, one of the four brushes was not working properly and so the starter was only half working. Unlike many motors it has two sets of poles around the rotor and four brushes. Of course, it's entirely possible that your starter is a different design since it's a different generator.