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Old 09-01-2011, 10:46 AM   #1
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Backup Generator Lost Power?


Wow, I just found this forum and it seems to have a lot more activity than other DIY forums I have visited. I hope someone can help.

We've had a backup generator, Northstar 5500, that we have used about ten times a year for ten years. It has always worked perfectly, until last week when Irene hit. I'll give a detailed description, sorry to be long winded.

Gen ran fine for about 3 hours. Then funny things started happening. Our computer would shut down, the TV would shut off, the microwave clock would go out. Each would turn back on but not last for very long. Then after about 1/2 hour of "funny thngs" the only power we got was a very dim fridge light and the LED light on the cable box. I thought it may be a problem with the wire, but I plugged a power tool directly into the gen plug and it barely moved, but did move. The engine was running great, but the gen was only producing a tiny amount of power.

The gen is hardwired into a transfer panel with all the same circuits that have worked for ten years. But, it is possible that I did overload the gen by plugging in the freezer into the aux outlet on the transfer panel. However, the freezer was plugged in the whole time, but the "funny stuff" didn't start happening til 2-3 hrs later.

Again, sorry for the long story. Any ideas where to start or what to check? The gen is HEAVY and installed in a small dedicated raised shed, so I can't readily take it to a repair shop. Thanks for any ideas!!

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Old 09-01-2011, 10:50 AM   #2
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Backup Generator Lost Power?


What about a reset button?

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Old 09-01-2011, 11:01 AM   #3
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Backup Generator Lost Power?


Unplug everything except for about 100 watts (incandescent lights?), on each side if 240 volts. Measure the voltage.

Does the generator hace any built in receptacles? Try plugging in small loads there (use extension cords ro give receptacles to stick meter probes into) and measure the voltage there.
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Old 09-01-2011, 11:02 AM   #4
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Backup Generator Lost Power?


Loose wire connections?
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Old 09-01-2011, 11:08 AM   #5
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Backup Generator Lost Power?


i understand computers and generators not such a good mix
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Old 09-01-2011, 11:12 AM   #6
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Backup Generator Lost Power?


No breakers, resets were tripped. Plugged hand drill directly into outlet on gen with no other load on it and the drill barely moved, but it did move. I'm not home right now, but plan to measure voltages this weekend with multimeter. I read something about capacitors in the manual, do these burn out, are they replaceable? I also read about the "exciting voltage" trick by turning a power drill backwards by hand to "excite" the generator, but if the drill is slowly turning already when I plug it in how can I turn it backwards?

Edit: no loose connections, and the computer worked fine on the generator for ten years.
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Old 09-01-2011, 11:27 AM   #7
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Backup Generator Lost Power?


Generators maintain constant voltage thru the use of a voltage regulator that controls the current in the exciter coil. It's a good bet that the voltage regulator failed or that one of the slip rings that transfers current to the exciter coil is defective.

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Old 09-01-2011, 11:54 AM   #8
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Backup Generator Lost Power?


I have see some of the portable generator did use the capaitour as well they can go bad as well.

But few case I have see the didoe on rotor go bad or connection frizted up the last portable generator I just service not too long ago did have a 12 volt stator winding and it was shorted out and end up replace the stator { it cost about half of what new generator cost } and after that it work good.

So take it to the generator shop they can assit you on that. { or you can call them to come out to your place as well }

Merci,
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Old 09-01-2011, 11:57 AM   #9
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Backup Generator Lost Power?


I would say that the problem is in the generator unit. Flip the transfer switch back to utility power (whether or not live) and work on just the generator.

Does the generator have replaceable brushes (for the slip rings)? Check the existing brushes for excessive wear.
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Old 09-01-2011, 12:06 PM   #10
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Backup Generator Lost Power?


exciters, brushes, slip rings -- all sound Greek to me (or maybe French, "FrenchElectrician" haha) I'm no electrician. So, I'm guessing it is not as easy as changing spark plugs or such? Is this something I can check? If not, I guess I'll have to call a serviceman if I can't get any current this weekend when I test it.

Thanks for all the replies, this forum is awesome and much more helpful than other DIY forums!
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Old 09-01-2011, 12:10 PM   #11
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Backup Generator Lost Power?


If it's a "inverter" model, it has diodes in the rectifier. I was assuming that this is a "standard" generator. A generator with a failed voltage regulator will work like an induction motor and make some (inconsistent) voltage. The OP's comments seem to support that it is putting out something, but not 120/240V. That makes the VR or exciter a likely culprit.

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Old 09-01-2011, 12:38 PM   #12
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Backup Generator Lost Power?


Bad or failing SCR's would be my guess. Ten years is a long time for a genset to be used, without some kind of regular maintenance being done on it.
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Old 09-01-2011, 01:33 PM   #13
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Backup Generator Lost Power?


Here is a link to my model generator, which is no longer sold at NortherTool:

http://reviews.northerntool.com/0394...ws/reviews.htm

Here's a link to the manual/parts list: http://www.northerntool.com/download...als/165911.pdf

It appears to be "brushless" and "maintenance free". It was only used for a few hours during power outages a few times a year. I did the usual engine maintenance like plugs and oil.

busman, where would one find this "voltage regulator" on the gen and how do you check it?
gregzoll, what's an "SRC" and how do I check it?

Last edited by Oh-Fudge; 09-01-2011 at 01:44 PM.
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Old 09-01-2011, 02:12 PM   #14
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Backup Generator Lost Power?


Since this is not a solid state gen, I would be looking at the Varistor & Diode as the two possible problems.

http://www.littelfuse.com/data/en/Ap...tes/an9773.pdf
http://www.elexp.com/t_test.htm

The best thing to do, would be to buy a new generator if costs for repair on this one, out weigh cost to continue owning. With units better than they were 10 years ago, it may be more cost effective, to just purchase a whole new unit. I am sure there is someone out there, that would buy the old one for parts, or scrap value.
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Old 09-01-2011, 05:05 PM   #15
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Backup Generator Lost Power?


The voltage regulator has no handyman serviceable parts inside and may or may not have an adjustment for the desired voltage. It is generally removable and replaceable as a complete separate module. It is most llikely in the vicinity of the built in receptacles. It is generally a boxlike module, the size and shape suggestive of a book or a brick. Or it might not be enclosed and look like a circuit board. It may contain any or all of the fancy items (diodes, etc.) mentioned except brushes and slip rings and spark plugs and rotors.

Slip rings and brushes maintain an electrical contact between parts on a rotating member and parts on the (stationary) frame. The slip ring is analogous to a brake drum or disk and the brush is analogous to a brake pad or shoe except the pressure is constant and gentle. The brush does not bear down harder or less hard for the purpose of regulating anything.

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Last edited by AllanJ; 09-01-2011 at 05:18 PM.
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