Onan generator DC issue

mcgivor · July 2017

The test light has an alligator clip with a wire to a probe which has a lamp inside, you clip to ground or negative and use the probe to search for a positive in a circuit. Because it actually draws curgent when it lights up, the lamp inside, it eliminates, to some degree, false readings associated with digital meters. It can also be used in reverse by clipping to a known positive such as the battery terminals, then probing ground points.

BB. · July 2017

Use the bulb like your volt meter...

Connect across coil (if separate leads). If lights, then you (probably) have enough current (good enough electrical connection) to drive the coil.

Try other connections. I.e., only lead of light to battery negative terminal.

Other lead to B+ of coil, if lights good electrical connection (to B+).

Then move to negative to coil, if lights/glows, then coil has bad ground connection (with B+ energized).

Move lead to frame ground of engine, try cranking, if lights then you have bad bonding from engine to battery negative.

Etc.

-Bill

Aguarancher · July 2017

Like I said previously..." It doesn't even try to crank"

you should be able to jump the starter solenoid and get the engine to turn over regardless of any wiring issues except battery cables.

Is this how you're jumping the solenoid?

Estragon · July 2017

@mcgivor and @bb - will try to rig up a test bulb. If I'm understanding this correctly, using the bulb causes non-trivial current flow through a circuit, whereas the meter flow is trivial and may indicate a closed circuit where for practical purposes non exists?

@aguarancher - functionally, yes. At the b+ terminal, there is also a fused wire that supplies 12v power to a controller box with relays for fuel etc. I jumped that to the wire in the box that leads to the solenoid terminal marked ignition switch in the illustration. Both wires appear good (I see 12v in the box on the 12v lead, and continuity to ground on the ignition lead), but the above discussion on using a bulb has me questioning my readings.

Aguarancher · July 2017

I would go right to the source and jump at the solenoid only. Cuts out all the middle men..lol

mcgivor · July 2017

You stated that when battery + was applied to the coil connector, there was a spark, that would probably indicate the coil is functional, given the resistance reading. Inside is a plunger which forces the pinion gear out to the ring gear on the flywheel, also causing the internal contacts to make, which in turn powers the motor . If the mechanism inside, or the plunger is stuck, the coil will be unable to move, resulting in nothing happening, just as you are experiencing. This is a common problem, a picture would be worth a thousand words, as there are different designs, some use the Bendix method, others/most a fork to engage the gear, a picture would enable identification. The image posted by @Aguarancher is the fork type, Bendix is not that common, usually seen on older starters, namely British.

Estragon · July 2017

It looks very similar to the picture. I tried to remove the motor late yesterday as it's in an awkward spot for testing and after taking out the two bolts on the flywheel end it wouldn't budge. I assume it's just the two bolts normally attaching it. Maybe it's stuck engaged to the flywheel?

Aguarancher · July 2017

It might just be paint and rust from age holding it in. Give it a wack with a rubber hammer or a 2x4.. I would bolt it back in and test like I said first. I'm starting to think you might have a starting battery problem if it won't crank by jumping it. jmo

Estragon · July 2017

The starting battery is quite new and voltage is good. Can't rule out a connection issue yet though. Maybe I'll reconnect wiring and try direct jump first before 2x4 whack.

Haven't been able to find a 12v lbulb yet. I do have a little 100w msw inverter though. Will try hooking a trouble light through that.

Estragon · July 2017

Bah. Hooked the starter back up and tried the direct jump and it kicked, so back to looking for wiring problems. Thanks @Aguarancher - at least one more thing ruled out.

The fact it didn't kick when jumping in the control box has me wondering. The other wire in common with the starter ignition is glow plug relay, so they heat during cranking. I unhooked the glow plugs from the relay, but maybe a problem with the relay with another path to ground.

The little inverter idea isn't working out so far - need to find a better way to connect as alligator clips keep slipping, or just find a bulb. I have LEDs that might work.

Estragon · July 2017

Progress!

The LED light worked. The B+ wire I tried to jump the starter with showed 12.9v, but dropped over 2v with the little puck light in the circuit. It lit, but just. No way the wire would carry the higher current for glow plugs etc.

I think I've narrowed it down to the inline fuse holder. It looks pretty old, and the shaking when the generator shut down probably caused an intermittent connection problem. Now that I've been messing around with it, it's opened pretty much completely.

Thanks @bb and @mcgivor for the light tip!

Aguarancher · July 2017

glad you got her to crank over. I was thinking along the same lines that the shaking caused your problems. i've had wires break before at the connectors inside the insulation.looked perfect but barely making contact and failing under load. drove me up the wall until i found it. lol

Onan generator DC issue

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