Generator randomly shuts down

Flybull · Jul 27, 2019

Flybull said:
Following closely as I just had a genny problem on my 15kw Onan (Cummins)...

A week ago I shut it down after noticing less water output and steam flashing indicating higher exhaust temps (at least in my mind). I pulled the intake pump and found the impeller in bad shape as anticipated.

I had a spare impeller from PO as this is a new-to-me boat, and I changed it out and fired up to normal operation. Being dockside on shore power, I switched the load gradually to genny and let it test run with full loads for about 20 minutes and all seemed normal. As a side note... although this Onan has oil pres., temp., and DC volt guages on both the genset in the ER and on remote panel in main AC/DC panel, the temp guages do not work on either.

So the other day, we left for an all day cruise and all was working fine as usual, both ac's running, full size fridge, ice maker, water heater... and for about 7 hours nothing unusual. I think I looked over the port side a thousand times watching water/exhaust flow...

At some point, in the last 45 minutes of the cruise, she stopped. I was not aware until I went down below while underway and noticed no ac working.

I have yet to be able to start any troubleshooting at all due to having company at the time and started work the next day. Thursday is my day off so will start checking into things, and am glad this thread started as there are some great ideas here. I haven't even tried a restart, as I haven't had a chance to break down the sound box for even a 1st step visual check of things.

Sorry for any derail/hijack of your thread, OP... glad there's so much knowledge here to tap into. I have no problem starting a separate thread after initial observations if that is the proper thing to do.

Thanks, and good luck getting to the bottom of it OP...

UPDATE:
Finally was able to get to the genny issue on Thursday. The fault breaker was tripped, which trips for water temp, oil temp, oil press. Pulled the sound shield box and removed inlet side hose to water pump to inspect impeller without pulling... it looked really good after bumping start switch a few times.

What I found upon restarting the generator with no load was that the intake hose from the strainer was collapsing from the suction. Strainer was clean. The hose felt very soft and was restricting flow to the pump.

After replacing the intake hose with new, she's throwing water out of the exhaust at a higher rate than I've ever seen since owning this boat, and we were out all day yesterday at heavy load with no issues.

:dance:

Flybull · Jul 27, 2019

UPDATE:
Finally was able to get to the genny issue on Thursday. The fault breaker was tripped, which trips for water temp, oil temp, oil press. Pulled the sound shield box and removed inlet side hose to water pump to inspect impeller without pulling... it looked really good after bumping start switch a few times.

What I found upon restarting the generator with no load was that the intake hose from the strainer was collapsing from the suction. Strainer was clean. The hose felt very soft and was restricting flow to the pump.

After replacing the intake hose with new, she's throwing water out of the exhaust at a higher rate than I've ever seen since owning this boat, and we were out all day yesterday at heavy load with no issues.

:dance:

twistedtree · Jul 27, 2019

Nice job! And a good easy fix.

ben2go · Jul 27, 2019

Glad it was a simple repair.

BrianSmith · Jul 29, 2019

SailorGreg said:
This is not a fuel issue. It is electrical. Everything stated here is a relay from various NL tech support. I would ignore well meaning suggestions that are not specific to NL gensets. Good luck. PM me if you like.

Agreed. When I had my problem (16kw NL), I looked at the schematic about a hundred times, to try to figure out what to test. Finally, I wrote out a detailed description of exactly what all those relays do, at what stage of operation (Pre-heat Button on, Start button on, etc.). Also, at each stage, what the electrical status should be of each terminal on each relay (12v or GND). Once I had it written up, I was able to step through it and test each connection, and quickly found that one of the diodes was blown.

I have attached a PDF copy of it, for anyone who has a NL gennie.

P.S. - This solved only one of the problems. The other, more perplexing, problem was the intermittent failure of the resettable fuse. I don't know how to test for that, other than to jumper around it.

SailorGreg · Jul 29, 2019

Thanks, Brian
Very thorough. I went through years of problems with mine and this would have helped. First issue was an oil temp switch. Then some other weird action that was solved by moving the oil temp switch from the block to a Tee off the same line as the oil pressure switch.
This last issue was a diode that had a broken lead under the potting. Vibration would cause it to open randomly.
I hope OP's recent success holds...but mine didn't. It would run fine for months, then fail every other hour. We would fix one thing, then another gremlin would raise its head.
During the diode period i would go down and re-seat the relays and it would work for a week or so. Fixed maybe? Nope. I pulled every connection on every relay, after I replaced the relays. How I actually found the broken wire under the potting is a story too long for this thread.
Over the years had a succession of techs on the boat. Each insisted on fussing with the fuel system. Wasted lots of hours and money. Hard to get efficient help when the fault shows up every 3-4 hours, or 3-4 days. Finally took over myself, with advice from NL techs over the phone. Did get some good help from Washburns in Solomons.
One common failure with the older models has been mentioned before by others here and that is the circuit breaker on the outside of the electrical box. Redesigned before my genset was built.

Generator randomly shuts down

Flybull

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Flybull

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twistedtree

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ben2go

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BrianSmith

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SailorGreg

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