energizing generator glow plug

[bill209]

hmmmm...

while working on a generator (Onan M643 5kw) issue, i put the voltmeter on the glow plug rack (?) and it came on to ~12v when pushing in the glow plug/safety bypass button prior to cranking and held that during cranking. great so far.

but when the engine turns over and i release the buttons, the glow plugs continue to be energized, ~11.6v not under load and can jump to 13v when the generator is under load. i was under the assumption that once the generator was started, not only do the glow plugs no longer required energizing but can be damaged if energized continuously (while the genset is running). the electrical schematic seems to support the idea it should turn off once the glow plug switch is released.

if it should NOT be continuously energized, then I am looking at the glow plug switch itself or possibly a bad preheat relay. not sure which would be more likely or if i am missing something else entirely.

i appreciate any guidance you can provide on this matter.

tl;dr
* should glow piugs continue to be energized once the genset is started and the buttons are released?
* if not, what would be some of the likely culprits?

thanks for your help,
bill

 

[SteveK]

I have a westerbeke, for comaprison the volt meter is seen to draw a load while holding switch to glow plug and then releashing when I let go.
That suggests your thought is correct, it should not be powered after start.

 

[Lepke]

The contact points are burned and sticking, probably in the relay.
On my Onan the glow plugs get power when pressing the run button. I wanted them to come on before the starter so wired in a separate switch. Works better because in cold weather the first gulp of air is hotter and the generator starts quicker.

 

[luna]

On my 8 & 20 kVA 1996 Onan diesel Gensets, the preheat system (glow plugs) is energized when you press and hold the Stop side of the Stop/Start momentary rocker switch.

This system seems to work well as with a cold and stopped engine you press and hold the Stop side of the momentary rocker switch for a maximum of 30 seconds, energizing only the preheat system and then roll over to pressing the Start side and bingo, on comes the starter motor.
Magic, the engine starts in about a revolution or so. No separate switch required.

Why the preheaters would be energized by a "run button" is beyond me. Is there another purpose for this "run button"?

 

[BruceK]

Ours is a 7KW Onan EQD. The Start button energizes the glow plugs. Press and hold, the lights in the button flash for a few seconds but it doesn`t start, then the starter operates and it does. Next the light stops flashing, you`re up and running.

 

[Mischief Managed]

That is absolutely not normal and you should probably test all the glow plugs once you figure out the problem. Odds are good they are shot. That said, unless you have an AC battery charger for the genset start battery, I would expect functioning glow plugs would wipe out your genset start battery pretty quickly if they were always on.

 

[bill209]

I am not sure how long this particular problem has existed, but fortunately the glow plugs are still operational though may be compromised, and the genset battery is still cranking at the appropriate voltage.

@Lepke , I was going to mention how i mulled this over in the middle of the night and decided it could not be the relay. This conclusion did not make me happy as I have three working relays in my possession plus it’s a relatively easy replacement, just constrained by location. And then I read your comment and gave more consideration to the idea it could be the relay and realized I was conflating the energy provided to the relay with the energy provided to the glow plugs. So the relay is in fact still a contender for culprit. Thank you so much for your comment!

I’m going to change out the relay this morning and will report back on the result.

Thanks everyone!

 

[luna]

Could it be that your generator is a Northern Lights M643, not an Onan?

If it is such that your generator uses Mini Relays (1" cubes) to control the preheat circuit then this article may help you troubleshoot what is going on.

https://www.electricalrebuilders.org/techlib/tech_articles/four_uses_for_relays.pdf

I find that first identifying the problem and then fixing the problem, is far better/cheaper than replacing parts until the problem goes away.

This should not be too hard to diagnose as it can only be the switch, the relay, or a wiring issue.

 

[Davil1]

you are correct
"I was under the assumption that once the generator was started"

Relay (solenoid) faulty, or electrical connections to/from, more likely, stuck on closed and continues to energize plugs.

An excellent replacement in Amazon

White Rodgers 586-902/586-105111 DC Power Contactor Solenoid, SPST-NO, 12VDC, 200A, BRACKET​

$109.97$109.97

 

[Davil1]

one way to test IF your generator has a preheat button/switch to press BEFORE pressing the start motor is to check the voltage drop on the panel, when pressing the switch the voltmeter shows the needle moving, releasing the switch the needle goes back to neutral

 

[Greg QS]

I would check you glow plug switch. Could be bad and stuck in the on position

 

[ronobrien]

hmmmm...

while working on a generator (Onan M643 5kw) issue, i put the voltmeter on the glow plug rack (?) and it came on to ~12v when pushing in the glow plug/safety bypass button prior to cranking and held that during cranking. great so far.

but when the engine turns over and i release the buttons, the glow plugs continue to be energized, ~11.6v not under load and can jump to 13v when the generator is under load. i was under the assumption that once the generator was started, not only do the glow plugs no longer required energizing but can be damaged if energized continuously (while the genset is running). the electrical schematic seems to support the idea it should turn off once the glow plug switch is released.

if it should NOT be continuously energized, then I am looking at the glow plug switch itself or possibly a bad preheat relay. not sure which would be more likely or if i am missing something else entirely.

i appreciate any guidance you can provide on this matter.

tl;dr
* should glow piugs continue to be energized once the genset is started and the buttons are released?
* if not, what would be some of the likely culprits?

thanks for your help,
bill

It sounds as though one of the latching relays is not unlatching. A wiring diagram would help in diagnosis. I was able to download one but it is too large to attach. Search Onan M643 marine generator. It will come up as Northern Lights. Good luck