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Starter Generator output vs rpm

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I need some help.

My HB-112 has finally been put back together but we have something going on with the starter generator that I don't understand.

At sub 2,000 rpm the ammeter shows around 10 amps and up.

When we open up the throttle the amperage drops to close to 1 or 2 amps at 3,500 rpm.

What am I missing here?

Thanks Tim Reed

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It sounds more like the voltage regulator is pulling back. As the generator speeds up so does voltage and amperage and the regulator is pulling back to much at higher speeds. I have the same situation on my 101.

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Also make sure the ammeter is not connected in reversesm00 Check the voltage between the V/R Bat terminal (+) (closest to fuel tank) and ground. At idle and at 3500 RPM. It should normally increase with RPMs.

Is the battery new? An older battery could have a shorting cell at the increased current,associaed with higher RPMs.


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I had a S/G that had a wire on the armature that was broken. It would charge at an idle, but would stop charging when revved up. Think of the speed the armature is turning at when the engine is running at 3600rpm. The centrifigul force would open up the break in the wire, therefore opening the circuit. Idle it back down, and the wire would go back in place. Took some time figuring it out. The shop that had rebuilt it swore it worked fine. I asked to see their test stand - it would only spin the generator a few thousand RPM at most, which wasn't enough to tick mine off. On a running engine, the generator is humming along at at least 10,000 RPM - look at the pulleys and do the math. Disassembled it again and when looking very closely, we found a broken wire - had some carbon tracking from arcing as the wire flexed. Good luck. Tim

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Hey TimJr,

Thanks for this comment. I had an identical problem with my 3314H S/G doing the same thing. It would charge OK around the nominal 13.8V output range up to mid-RPM's, then above that drop off and the GEN light would come on(discharging). We tested the armature with the "growler" and found nothing wrong. Then after replacing the armature, it worked fine. Further inspection the copper windings using a magnifying glass showed a fractured conductor at a commutator segment. You're spot on about how these S/G's are spinning at over 10,000 RPM's at those engine speeds and "static/low RPM" test jigs do not tell the entire story.

To m(PK)

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