Onan generator problem

Submitted: Tuesday, Feb 26, 2019 at 19:00
ThreadID: 137870 Views:1567 Replies:7 FollowUps:12
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Hi All
I have an onan 3600 genset in a Winnebago. Have had some work done on it at the official Adelaide onan dealer (Frostec). but picked it up and didn’t last more than 5 minutes before it was running rough again, I renewed the fuel filter and made sure there isn’t a fuel supply problem. Checked spark, it sparks while turning over but as soon as let the start button off the spark stops immediately. Which is exactly what it was doing before Frostec worked on it. While turning over does try to fire but won’t run.
If anyone knows about these I would appreciate some knowledge.
Other than that anyone know of any experts in Adelaide or Melbourne we are heading that way next week
Cheers
Shane
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Reply By: RMD - Tuesday, Feb 26, 2019 at 19:30

Tuesday, Feb 26, 2019 at 19:30
G’dayShane.
It is a long time since I worked on an Onan powered unit, but, seeing it tries to start but won’t run after releasing the button, indicates the starter solenoid or relay system is at fault and it is either disconnecting the ignition supply or shorting the ignition wire to the coil.
If you can, look for wires which are close to, or rubbing on moving parts.
Having checked fuel supply etc it indicates a lack of electrical correctness.
I am presuming it is a magneto system of ignition.
AnswerID: 624097

Follow Up By: mike39 - Tuesday, Feb 26, 2019 at 20:18

Tuesday, Feb 26, 2019 at 20:18
Is that an inverter generator or 2 pole alternator.
If an alternator, that situation indicates a problem in the "flash" circuit that excites the alternator to make it generate.
A capacitor or diode fault.
mike
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FollowupID: 897500

Follow Up By: RMD - Tuesday, Feb 26, 2019 at 22:42

Tuesday, Feb 26, 2019 at 22:42
mike39
It is the engine which won't run, if the engine doesn't run then no alternator will generate anything. Best to have engine running first which seems to be the issue.
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FollowupID: 897504

Follow Up By: mike39 - Wednesday, Feb 27, 2019 at 07:44

Wednesday, Feb 27, 2019 at 07:44
Sorry I failed to make myself clear.
Some gen's use a wire from the engine coil low tension circuit to flash the alternator into life. An intermittent short in this circuit may allow the engine to start but stop shortly after.
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FollowupID: 897507

Follow Up By: RMD - Wednesday, Feb 27, 2019 at 12:31

Wednesday, Feb 27, 2019 at 12:31
Mike39
Not having seen the wire you mention, which you say apparently exites the alternator, what then disconnects the coil low tension side from the alternator so the coil energy can be delivered to the HT coil of the ignition. Anything connected to the low side will use energy and the level would then be insufficient to porvide enough magnetic flux in the coil. ie, that is what a kill switch does. Kills the low side energy.
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FollowupID: 897510

Follow Up By: mike39 - Wednesday, Feb 27, 2019 at 19:48

Wednesday, Feb 27, 2019 at 19:48
The unit I have is a Lincoln welder/generator. 5kva gen. / 180 a. welder.

Not used for some time, it would fire then immediately stop. Tried everything, full fuel cleanout, carb. etc......just fire a few revs. then no more.
New ignition module, same result.

Traced the wire from the start stop switch to the low oil alert, removed it and the engine started and ran immediately.
However, there was no electricity being generated by the alternator.
Replaced and back to no go.

A wire ran from the oil alert to the inside control box of the gen. Removed the cover to see the wire terminating at a capacitor/diode arrangement. Disconnect this wire and the engine runs as normal, but no generation.

With the engine running, touched this wire to its terminal, the engine immediately starts to behave as if it was switched off, quickly remove it, the engine picks up and the generator starts to deliver power.

This is the "flash" circuit, and either the capacitor or diode block have shorted.
I bought a new capacitor and diode assembly from a local electrician, installed and no more problem.

Hope this explains the suggestions I made, some alternators have a permanent magnet exciter which does not require this external electrical impulse.

The circuit diagram of my unit shows it all quite clearly.
mike
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FollowupID: 897518

Follow Up By: Member - Tony H (touring oz) - Thursday, Feb 28, 2019 at 10:46

Thursday, Feb 28, 2019 at 10:46
To me .....this sounds like a crook ballast resister, does it have one of these on the ignition circuit?
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FollowupID: 897531

Follow Up By: RMD - Thursday, Feb 28, 2019 at 12:20

Thursday, Feb 28, 2019 at 12:20
mike39
That is a good explanation of the system. Thank you. I agree the capacitor was likely to be at fault. It would drain a bit of current initially to excite the alternator, then, effectively drop out of the primary circuit after the capacitor charged up, which is pretty quick and wouldn't normally be noticed in normal starting.

Tony H
Although the system is spark ignition, the Onan has a magneto and a system having a ballast resistor is a Kettering system. First has no ign system battery the Kettering does, hence the resistor to keep up coil energy efficiency to make sparks at high revs. Ballast resistor can give similar trouble symptoms on vehicle engines.
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FollowupID: 897534

Reply By: Member - shane r1 - Tuesday, Feb 26, 2019 at 21:06

Tuesday, Feb 26, 2019 at 21:06
G’day RMD and Mike
I agree definitely spark. Weird they got it running and it’s stopped again.
They replaced the carby ( which I didn’t really believe was the problem) and spark plug.
By my googling , I thought it should run for a second or two before shutting down from the “flash” or if it’s not producing 240 , but it did run the aircon for say 10 minutes even tho it was missing and farting about. Then wouldn’t run at all when I tried it again after checkin fuel delivery. It’s a puzzle! And frustrating!
AnswerID: 624098

Follow Up By: mike39 - Tuesday, Feb 26, 2019 at 21:33

Tuesday, Feb 26, 2019 at 21:33
Here's another thought....low oil alert.
A dicky sensor there can create this problem, also some gen's. have a wire from there to "flash" the alternator.
Suggest you remove every accessory wire from the engine (other than starting) and see what happens....think most unlikely carb., more like an electrical fault cutting off power to the coil. Have you checked the "on/off" switch, they also can fail.
mike
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FollowupID: 897501

Reply By: Member - sweetwill - Wednesday, Feb 27, 2019 at 07:46

Wednesday, Feb 27, 2019 at 07:46
first of all, I'm not electrical minded, but is saying that my Honda will run for a few minutes then cut out if I don't unscrew the air breather on top of the filler cap.
AnswerID: 624103

Follow Up By: Frank P (NSW) - Wednesday, Feb 27, 2019 at 12:13

Wednesday, Feb 27, 2019 at 12:13
Certainly that happens to my EU20i with a full to the brim tank. Not so much with some air space in the tank.
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FollowupID: 897508

Follow Up By: RMD - Wednesday, Feb 27, 2019 at 12:27

Wednesday, Feb 27, 2019 at 12:27
Do you not think the OP who has used the generator in his motor home and now has a problem is suddenly unaware of any breather requirements for the fuel tank which he has filled many times?

Honda EU20i handbook says to open the vent in the cap before use and close after use. That is to prevent vacuum lock overcoming the pulsing fuel pumps ability to transfer fuel.
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FollowupID: 897509

Follow Up By: Frank P (NSW) - Wednesday, Feb 27, 2019 at 14:58

Wednesday, Feb 27, 2019 at 14:58
"Do you not think the OP .....etc"

If that was for me, RMD, yes, I do.

I was responding to sweetwill.

The OP clearly has enough knowledge to discount a cap breather issue. Perhaps in my follow-up I should have said something to that effect to save any misunderstanding..
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FollowupID: 897511

Follow Up By: RMD - Wednesday, Feb 27, 2019 at 16:29

Wednesday, Feb 27, 2019 at 16:29
Frank P
That is ok, it is just the cap issue is of concern when they shouldn't block and are hard to find the cause sometimes.
If I forget to close the one on my EU20 it stinks a bit when in the canopy.
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FollowupID: 897512

Reply By: Alan M21 - Thursday, Feb 28, 2019 at 16:12

Thursday, Feb 28, 2019 at 16:12
Hi Shane,
I am an Onan agent in Thomastown vic
This type of generator has all sorts of faults that result in one thing, they shut down.
Give me a call on 0418330123, also if you want to see what I do, search ExactaGen on facebook.

Regards
Alan
AnswerID: 624116

Reply By: Member - shane r1 - Saturday, Mar 02, 2019 at 21:22

Saturday, Mar 02, 2019 at 21:22
Thanks everyone for your replies,
I am heading for Alan of exactagen, I spoke to him after he posted a reply.
Will post the results , Alan certainly gives me the feeling he knows the Onan product very well.
He fluked seeing my post as it came up on a google feed and he just happened to have a look.
Wish it wasn’t so hard to find good technicians! ( in all sorts of things)
Cheers
AnswerID: 624152

Reply By: Jon L3 - Tuesday, Mar 05, 2019 at 20:30

Tuesday, Mar 05, 2019 at 20:30
Hi Shane try holding the start button for 2 or 3 sec after it has started I think it has to have power from the generator to keep running.
Cheers Jon
AnswerID: 624229

Reply By: Member - shane r1 - Monday, Mar 25, 2019 at 22:14

Monday, Mar 25, 2019 at 22:14
Hi all,
If anyone is interested and haven’t seen it .I put up a new post (moderators locked it saying I should have not started a new thread) with my result with getting the Onan going.
Hope the info may help anyone else with Onan problems.
Thread no. 138028
Cheers
Shane
AnswerID: 624626

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