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Old 07-09-2019, 07:41 AM   #1
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Generator randomly shuts down

Some generator/engineering/diesel mechanic guru thoughts would be appreciated.

We have a Northern Lights 16kw generator with about 6000 hours on it. It was well-maintained by previous owners, starts easily, and will power our three a/c zones, two refrigerators, and hot water heater simultaneously with no problem.

About three weeks ago, we did a week-long cruise in Florida waters and ran the generator to power the a/c during most of the trip. It ran normally.

A week ago, we filled up our fuel tanks at our marina. They pride themselves on clean fuel. As is our usual procedure, we gave each tank a maintenance dose of Biobor JF before fueling.

A few days later, I changed the oil in the generator, changed the oil filter and the fuel filter. Afterwards, I started and ran the generator for about 20 minutes. All went normally. The oil level is between the marks on the dipstick.

Last weekend, we did an overnight trip. The generator started easily, had good water flow out the exhaust, and was running when we left the dock. About an hour later, we discovered it had shut itself off while we were underway. I checked the strainer and it was clean. It restarted easily and the gauges showed normal loading, normal temp, and normal oil pressure. The exhaust water flow continued to be excellent. About an hour and a half later, it spontaneously shut itself off again.

The spontaneous shutdowns continued at random intervals throughout the evening and through the night, never running more than 3.5 hours before shutting itself off. It always restarted easily and the gauges always showed as normal. There was no pattern to the shut down timings. The next morning, we restarted the generator and it ran normally for the six hours or so that it took us to get home and docked.

The mains ran normally so we weren't really suspecting dirty fuel. The Racors are clean.

From an engineering perspective, diesels need clean air, clean fuel, and compression and they'll pretty much run forever. Of course, it gets more complicated when you start adding electronic sensors and such. We have good water flow and good coolant temps. The amp meter shows it's under a medium load around 12 kw. I suppose it could be a loose or bad connection at a sensor... maybe?

We're stumped. This weekend, I plan to pull off the water pump cover to check the impeller and pull off the heat exchanger end cap to look for anything unusual but, honestly, I'm not expecting to find any surprises.

Any ideas?

Thanks.

John
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Old 07-09-2019, 08:23 AM   #2
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You may want to check into the stop switch, check the resistance to make sure it's not failing. They're typically a momentary NC switch that opens when you operate the switch. There's likely a second switch near the genset that duplicates that function. If those switches are not making good contact, they could be heating up and creating a situation where there's enough resistance to drop out the holding circuit that keeps the engine running. Any one of the engine safety controls are daisy-chained in that circuit and poor connection or a failing safety switch could be at fault. I'd check the exhaust temp switch at the exhaust manifold, pull one lead and check with an ohmmeter, it should be no or low resistance, tap on it and see if it wavers. Check the connections to all those switches, a loose spade terminal could be the culprit. A PITA, but if you can check those switches as soon as it shuts down, you may be able to get some clue as to which switch is opening, that'll go a long way in pointing you to the solution.
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Old 07-09-2019, 08:40 AM   #3
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I've fixed several NL gennies that had a failing DC control breaker. Wires vibe in the control box and connections get loose on the breaker, or the breaker gets damaged from the vibes. Result is random shutdowns. Check that first.

Also look in the box for any other loose connections.
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Old 07-09-2019, 08:50 AM   #4
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Some great suggestions, guys. Thanks! Now I have a place to start.
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Old 07-09-2019, 08:51 AM   #5
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There are a few other threads on this problem so a search will provide all types of suggestions. We have a 12k NL and had similar issues. Troubleshooting:

Check wire connections to alternator, starter, sensors and fuel solenoid. The smaller control system wires can vibrate loose.

I changed the fuel solenoid but donít think that was the problem. You can hear/feel it activate when pushing the bypass switch. Also purchased spare sensors but they seem to be OK so have not replaced them.

Fuel supply and return checked OK. Have changed generator and Racor filters recently.

Water flow, coolant level and temps were OK. Checked with IR gun. You probably know not to crank for too long if the engine does not start - problems with battery, starter and water backing into exhaust manifold.

Purchased spare sensors online through eBay or from Diesel Parts Direct. Changed the raw water pump due to shaft seal leak. Ordered by eBay from the UK, significantly lower cost than I could find in US but took a few weeks for delivery.

The most prevalent problem was (is) the control relays vibrate loose in their sockets. The 12K has four cube relays (start, preheat, bypass, run) which use sensor and switch inputs to enable start, run and shutdown states. When one vibrates loose the engine will shutdown and/or not crank. I have reseated them, moved them from socket to socket, and replaced them. I wedged them in with a small piece of wood and rubber strip. This holds for several days but eventually loosens.

We have been running it 2x1hr every day for the last six months and have always managed to start and run.

Good luck.
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Old 07-09-2019, 09:03 AM   #6
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The most prevalent problem was (is) the control relays vibrate loose in their sockets. The 12K has four cube relays (start, preheat, bypass, run) which use sensor and switch inputs to enable start, run and shutdown states. When one vibrates loose the engine will shutdown and/or not crank. I have reseated them, moved them from socket to socket, and replaced them. I wedged them in with a small piece of wood and rubber strip. This holds for several days but eventually loosens.

We have been running it 2x1hr every day for the last six months and have always managed to start and run.

Good luck.
Well, that's an interesting solution. And good information. Seems to support what others are suggesting, too. Thanks.
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Old 07-09-2019, 09:07 AM   #7
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Originally Posted by Ski in NC View Post
I've fixed several NL gennies that had a failing DC control breaker. Wires vibe in the control box and connections get loose on the breaker, or the breaker gets damaged from the vibes. Result is random shutdowns. Check that first.

Also look in the box for any other loose connections.
The "joyful" part of this is going to be the difficulty reaching the box, to begin with. That end of the generator is buried in the corner of the engine room. The most visible part is the breaker reset switch on the backside of the box. It can only be seen with a flashlight from a certain angle. You can reach it only by feel; it can't be seen when your arm is in there. It's going to be fun getting that part of the housing off to get to the backside of the box. But I shall persevere and find a way!
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Old 07-09-2019, 09:08 AM   #8
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Does the engine stop quickly or does it sputter for a few seconds before it dies. If it sputters it might be a sign of a faulty fuel pump or loose wiring to the fuel pump.
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Old 07-09-2019, 09:11 AM   #9
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Does the engine stop quickly or does it sputter for a few seconds before it dies. If it sputters it might be a sign of a faulty fuel pump or loose wiring to the fuel pump.
Hey TR,

No sputtering. It shuts down quickly. The more I hear, the more it's starting to sound like an electrical issue, like a loose relay or wire.

John
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Old 07-09-2019, 12:39 PM   #10
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I think Ski nailed, as usual. The DC control breaker in those gen sets frequently become intermittent over time and exhibit the exact symptoms you are seeing. It's labeled "fuse" at least on some of the gen sets, which creates confusion.


Once you gain access, the connecting wires have typical spade lugs. Pull the wires off and connect them to the blades and an automotive fuse of similar rating. The wires should push right on. Then tape it up or otherwise protect the terminals from making contact with other things in the control box.


I'll bet you a beer that it will work fine after than, and you can order a replacement circuit breaker at your convenience.
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Old 07-09-2019, 12:54 PM   #11
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I think Ski nailed, as usual. The DC control breaker in those gen sets frequently become intermittent over time and exhibit the exact symptoms you are seeing. It's labeled "fuse" at least on some of the gen sets, which creates confusion.


Once you gain access, the connecting wires have typical spade lugs. Pull the wires off and connect them to the blades and an automotive fuse of similar rating. The wires should push right on. Then tape it up or otherwise protect the terminals from making contact with other things in the control box.


I'll bet you a beer that it will work fine after than, and you can order a replacement circuit breaker at your convenience.
That's a pretty brilliant diagnostic step. Thanks. I'll give that a try this weekend.

John
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Old 07-09-2019, 12:58 PM   #12
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That's a pretty brilliant diagnostic step. Thanks. I'll give that a try this weekend.

John

Don't credit me. I got it from one of the Northern Lights guys.
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Old 07-09-2019, 12:59 PM   #13
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Don't credit me. I got it from one of the Northern Lights guys.
My statement still stands, regardless from whom it came. 😃
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Old 07-09-2019, 02:00 PM   #14
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Hey TR,

No sputtering. It shuts down quickly. The more I hear, the more it's starting to sound like an electrical issue, like a loose relay or wire.

John



I was about to suggest a bad seal on the fuel filter at the engine but you say it shuts down with no struggling to run issues. I too agree that it sounds like an electrical issue. I bet it will be a simple fix when/if it's found.
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Old 07-09-2019, 02:20 PM   #15
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i agree with the above. check the thing ski said first if that doesn't pan out check the safeties for oil psi, water temp, ect. i have more than a few cause random shutdowns on big gens.
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Old 07-09-2019, 03:52 PM   #16
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This may be pertinent based on discussion.

https://www.northern-lights.com/medi...on_M_NL673.pdf
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Old 07-09-2019, 04:17 PM   #17
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This may be pertinent based on discussion.

https://www.northern-lights.com/medi...on_M_NL673.pdf

In the pictures, it's the red push-button breaker that's the DC control breaker. That's the one that can fail in a way that causes seemingly random shutdowns.
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Old 07-18-2019, 09:25 AM   #18
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I was getting mentally geared up to disassemble the frame of the sound box and remove a cooling fan in order to crawl far enough back into a hole to get to the screws on the J box and open it up to check out the relays and the DC control breaker.

Before doing that, I had a sudden inspiration to call Northern Lights and ask them about the situation. I spoke to a guy named Joe at their Ft Lauderdale office. He listened carefully and said what they were seeing on these random, intermittent shutdowns is a failing coolant temperature switch. He said the temperature sender will still be good and the gauge will show it's within normal operating temps but the switch will randomly kill the engine. He said they've seen it frequently. The switch is on the front and much easier to access.

I mentioned the DC breaker maybe being the source and he said it was possible but they had seen far more temperature switches as the issue.

I've decided to give that a try... partly because Joe was so confident in what he was saying and partly because it's easier to get to. I'll report back on the results.

John
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Old 07-18-2019, 09:56 AM   #19
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Fingers crossed.
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Old 07-22-2019, 01:01 PM   #20
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Hi John,


A bit late to the party but here's one other simple thing to try if the coolant temp switch is not the problem. I had very similar symptoms with my NL 5 kW generator stopping randomly. It would start normally and then run for a while and then die. As time went on the periods of "on" became shorter until it would not even start.



The culprit was the foam air filter. It had been deteriorating over time and was clogging the air intake. I removed it, used a shop vac to clean out all the bits from the airbox I could reach and installed a new filter that I had. Working great now!


NL recommends annual removal of the foam air filters and washing in warm water and dish soap. Like twistedtree, if it helps don't thank me, we both have the same source at Northern Lights!


~Christopher
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