Subaru EX21 charging coil / regulator rectifier

[xyzer]

I know this is a little out in left field but I know there are some very knowledgeable guys on here when it come to electronics. Here is my problem....I picked up a Subaru Robin EX21 7hp gas engine. It already has the charging coil in place under the flywheel and it puts out 13volts at idle and 21volts at higher rpm. The engine comes with 3 charging systems. 15watt 40watt and 200watt. I doubt there is a 200watt hiding under the flywheel. The question I have is there a way to measure resistance of the coil and be able to tell which diode/rectifier (15w 40w) the charge system needs to properly charge a small motorcycle battery without pulling the flywheel? I have found the proper regulators but don't know what I have.
Thanks
Dave

[BruceM]

Dave, I think you've got the right idea but will have to get the coil resistances from a friendly service center or parts dealer.  You could also just hook it up to a battery via a diode bridge without regulation and see what the charge current is.

 I also wonder if you couldn't just use the 40W regulator, since it would have the capacity for either 15W or 40W.  I'm not familiar enough with these magneto charging systems to help much, alas.

Best wishes,
Bruce

[xyzer]

Bruce,
Thanks!
Subaru Robin wants $27.00 for the 15w and $67.00 for the 40w. The engine is in a motorized kayak and I thought I could cheaply and easily get a 12volt system for a cell phone or dept sounder.
http://www.mokai.com/
I think I will call the company and maybe they know which one is in them. There newer models have electric start and mine is a rope start with no battery system......just tinkerin
Dave

[OneStep]

I am no expert  but since it did not come with electrics and it has charging coils go with the 15w.

My experience with dirt bikes says lots of system can be swamped. older motocross usually didn't have but did have the place for the coils, the enduros version did have coils since street legal, Some MXers and specialty bikes that had optional lights did have the extra coils in em.

So it depends on the options but since no electric start its kinda surprising it has any charging coils at all.

OS

[BruceM]

Love the Mokai concept.

I'll bet OneStep is right- if the engine is pull start it most likely has the small coil.

[xyzer]

I am leaning in the same direction. It was also suggested if I put a 40watt bulb on it and it is dim it is probably a 15w? not sure but worth a try to see how it behaves........