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 > elec test help on Onan gen

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path1

Varies with weather

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Posted: 06/06/19 12:52am Link  |  Quote  |  Print  |  Notify Moderator

I know there must be a common since answer to my problem.
My gen doesn't want to start. As in "starter engages-disengages" What describes my problem the best. Working my way thru the trouble shooting checklist,
(A)battery state of charge, (12.77)
(B)try starting gen with vehicle running (didn't work),
(C) clean battery cables and battery posts...Here is where I could use some help. Only one end of cable I can get to without pulling the genny. Appears the cable has a wire bracket clamp (better known as a P clamp)that holds the cable, so cable doesn't rub on other stuff I guess. I really don't want to drop the genny just to test a cable, big hassle to get it out and back in.

So I'm thinking how to test this... without the pain of pulling the genny. Thinking about running a regular auto jumper cable directly from battery to genny. In other words I'll by pass the cable being used now (that might be bad) and see what happens. My concern is the other electronics I might not see. Is there anything I could screw up doing a test like this? On genny's, the cable goes directly from battery to genny or is there anything in the cable routing such as a fuse or relay or ?


(I didn't post genny info because this is a elec test question, really not model specific).

Thanks

Tom_M

New Hope, MN

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Posted: 06/06/19 03:42am Link  |  Quote  |  Print  |  Notify Moderator

It would be helpful if you did state model number and coach information.
Is coach gas or diesel? If diesel, is gen diesel or propane?
What does "starter engages-disengages" mean?
Does gen crank over?

If gen cranks over you do not have a battery problem. Check if you are getting fuel. If gas or propane check if you are getting spark.

I have an old Onan gas gen that I use for home backup power. It failed to crank over one time. Turned out that a chunk of carbon had broken loose and blocked the piston. Had to pull heads and clean out the carbon build up.


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Sam Spade

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Posted: 06/06/19 05:46am Link  |  Quote  |  Print  |  Notify Moderator

Tom_M wrote:


If gen cranks over you do not have a battery problem.


That simple fact is not conclusive proof.
Neither is the resting voltage at the battery.

As was mentioned, a locked rotor is a possibility too.

I recommend that you find a Cummins/Onan dealer and let them diagnose the problem. In my experience, they are very competent and reasonably priced.


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MEXICOWANDERER

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Posted: 06/06/19 03:54pm Link  |  Quote  |  Print  |  Notify Moderator

Maybe disengages too fast?

Starts cranking but then spins-out before the engine starts?

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Chris Bryant

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Posted: 06/06/19 04:32pm Link  |  Quote  |  Print  |  Notify Moderator

You can certainly jump to the battery input on the genset, and don’t forget to jump the ground as well.
You can also just measure the voltage while trying to crank.

But, don’t really understand starter engage disengage. Does it run and not crank the genset? That’s usually a broken part in the starter, but some models are more prone than others.


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path1

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Posted: 06/06/19 04:37pm Link  |  Quote  |  Print  |  Notify Moderator

(Sorry was typing same time Chris was posting)…
Quote:

But, don’t really understand starter engage disengage. Does it run and not crank the genset? That’s usually a broken part in the starter, but some models are more prone than others.


To me sounds like a weak bindex gear on a starter. Only thing that comes close in the trouble shooting guide is what they describe as "starter engages-disengages" (cranking voltage dips below 6 volts-low battery charge, poor connections, long cables)

OK seems OK to run jumper cable from starter to genny.


(Typing same time above posts were)

I'm trying to trouble shoot the battery cable from genny to battery. But don't know if there is any electronics are installed in this cable, and I don't have access to seeing entire cable. Looks like when the genny was installed, installers lay'd out the cable then used a couple "P" clamps to hold cable in place (in back of genny) and then jacked up genny and bolted into place. So jacked up into place, I can't see entire cable. And don't know if I should blindly bypass this cable.

Do most battery cables, (positive side) run directly from battery to starter on genny?

MrWizard

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Posted: 06/06/19 05:23pm Link  |  Quote  |  Print  |  Notify Moderator

Yes, most generator installs cable runs directly from battery or nearby terminal block to the generator

No electronics between those points

12v battery up front, or 12v battery sitting on the ground beside RV
It is still only 12v battery

You can not harm anything if you connect the jumper cables correctly


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opnspaces

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Posted: 06/06/19 05:35pm Link  |  Quote  |  Print  |  Notify Moderator

Does the starter engage the flywheel and start cranking the engine and then mysteriously just disengage before the generator starts? Or does the started just click, you hear the gear fit the flywheel, and then it immediately retracts and shuts down?

Can you put a meter on the starter battery terminals and then watch the display while you're cranking the starter over to see if it hits 6 volts? Either that or as MrWizard suggests put a battery on the ground right by the generator and run some jumper cables to the terminals on the generator.


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Sam Spade

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Posted: 06/07/19 06:43am Link  |  Quote  |  Print  |  Notify Moderator

Chris Bryant wrote:



But, don’t really understand starter engage disengage.


IF....the voltage falls low enough it will disengage.

In addition to the "normal" things that can cause the voltage to drop....like loose connections or bad solenoid or weak battery....a locked up engine or rotor will draw a HUGE amount of current and the voltage will go WAY down.

If that is the problem, jumping in a second battery probably is NOT a good thing to do.

D.E.Bishop

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Posted: 06/07/19 08:24am Link  |  Quote  |  Print  |  Notify Moderator

I'm going to ask a really important question, have you read the manual? There was nothing wrong with my Onan engine, oil level, battery charge, damaged wires... I finally deciphered the little set of flashes on the display. Mine wouldn't start because the generator was not outputting. So you may find the answer in the manual. If it's not there, what have you lost, nothing but a few minutes.


"I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to go". R. L. Stevenson

David Bishop
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