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Old 13-07-2019, 07:21   #1
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Burned up capacitor on generator

Our generator was happily humming along making power when we heard the engine speed up from no load and all AC power was lost. It was at about 80% load.

When I opened up the compartment, I could smell the hot wires (or ozone) and I tracked it down to this capacitor.

The generator is a Paguro 9000 and has about 8 hours on a new engine that was replaced when the old engine sucked a glowplug at 200 hours.

The first thing I noticed is that this capacitor looks really beat up for a new or even 200 hour install.

I noticed that beginning yesterday, the generator would show zero hz when started and wouldn't start reading anything until I started putting a load in it.

My question is what could cause this? Is this caused by a bad capacitor or did setting cause the bad capacitor?
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Old 13-07-2019, 07:40   #2
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Re: Burned up capacitor on generator

Typically, a cap is the first to fail. Whether or not that failure causes subsequent problems is unlikely. Make sure you replace with the equivalent or higher voltage rating.
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Old 13-07-2019, 07:44   #3
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Re: Burned up capacitor on generator

It really looks like a rush job was done on the install (zip ties, banged up cap). I'm thinking the terminals may have been loose but I can't check not since they are all melted. ��

I plan on getting a technician out to look instead of replacing the cap myself. Just in case they see something I might miss. Ahh, the joys of telling the admiral that we are on power and water rations...
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Old 13-07-2019, 07:48   #4
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Re: Burned up capacitor on generator

Thatís a 209 hour generator?! Whatís with the zip ties?
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Old 13-07-2019, 07:51   #5
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Re: Burned up capacitor on generator

With a capacitor regulated generator, cap failures are common. Enough so that I carry at least two spares as I often end up giving one away.
The all fail by overheating, but Iíve not had one burn up the connections, it does look as if they could have been loose.
My current Cap has been in there for quite awhile. It is a General Electric (Sold as Gentec) rated at 440V.
It has far outlasted the cheaper Chinese 370V capacitors.
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Old 13-07-2019, 07:54   #6
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Re: Burned up capacitor on generator

That engine has only 8 hours. The new engine was installed a month ago. It was a rush warranty job because I was buying the boat and the engine had died just before the survey.
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Old 13-07-2019, 08:28   #7
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Re: Burned up capacitor on generator

Quote:
Originally Posted by a64pilot View Post
With a capacitor regulated generator, cap failures are common. Enough so that I carry at least two spares as I often end up giving one away.
The all fail by overheating, but Iíve not had one burn up the connections, it does look as if they could have been loose.
My current Cap has been in there for quite awhile. It is a General Electric (Sold as Gentec) rated at 440V.
It has far outlasted the cheaper Chinese 370V capacitors.

I bought a nextgen 5kw about eight months ago and my battery charger has recently stopped working when running off the genset, but it still works fine on shore power. I suspect that the capacitors are not long for this world and the wave form has gotten to poor for the charger to use. Even turning on the water heater has not helped. A friend who has owned one of these gensets for years told me his used to eat capacitors about every six months. To solve the problem me moved the capacitors out of the sound enclosure into a waterproof box mounted on a bulkhead a couple of feet away. He hasn't replaced a capacitor since and that was about 8 years ago. This pretty much shows that heat is the problem. I intend to do the same thing.
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Old 13-07-2019, 08:38   #8
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Re: Burned up capacitor on generator

The last month, I've had to turn the battery charger and water heater on to get the generator "kick started" so the breaker for the air conditioners would close. It wouldn't stabilize the voltage or hz wouldn't stabilize without a load. My guess now is that was the early warning sign that I didn't recognize.
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Old 13-07-2019, 11:21   #9
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Re: Burned up capacitor on generator

My Nextgen also ate up capacitors, average life was about eight months in the tropics. While it was in originally mounted in the generator end fan flow, it did not provide enough cooling for the capacitor. Finally remounted it away from the genset and increased wire size. Life of capacitor increased to every three years.
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Old 13-07-2019, 16:37   #10
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Re: Burned up capacitor on generator

I have a Next Gen 5.5 which has gone through one cap and now the hz are crazy so the bat charger does not work. The charger is a Pro 20 amp which works fine on shore power. I tried putting a resistence load on but no change. Paid Next gen for a cap costing $80 and will replace the existing cap to see if the charger works on the Next Gen. The charger is new. May try moving the cap outside the sound box to reduce heat. Any suggestions??
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Old 13-07-2019, 18:29   #11
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Burned up capacitor on generator

Yes, buy GE caps off of Amazon for $30, which is likely twice what a Chinese Cap costs.
Iíve not remote mounted mine, but concede the logic in doing so.
Often caps come as dual caps. One for the compressor and one for the fan, they are usually 40+5 or so, you can use them just fine, just ignore the third leg, that is the 5 uf cap.
Of course if you shop around you can find a single 40 uf cap, but if your out and can only find the common 40+5 that works fine too.

Donít use the one marked fan, use the ones marked C and Herm.
I have no idea why the compressor one is marked Herm.
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Old 14-07-2019, 04:24   #12
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Re: Burned up capacitor on generator

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Originally Posted by a64pilot View Post
... Donít use the one marked fan, use the ones marked C and Herm.
I have no idea why the compressor one is marked Herm.
An Air-Conditioning Dual Capacitor has three connections HERM, FAN and COM.
HERM connects to the Hermetically Sealed Compressor
FAN connects to the Condenser Fan Motor
COM connects to the Contactor and provides power to the Capacitor.
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Old 14-07-2019, 05:02   #13
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Re: Burned up capacitor on generator

So a capacitor is just 2 'plates' separated by a chemically treated 'paper'.

They are basically 2 long strips of very thin aluminum foil and a piece of special material treated with an electrolyte. The electrolyte and separator are part of what makes a good cap. The made in China no name brands will not have qual control and may be just poorly stolen copy of say a GE cap chemistry. Some will fail out of a box.

Now I am being kind of general as these caps can be on anything. The really big caps in power supplies or motors to the small ones found on computers. They fail.

The heat can cause the chemicals to go bad. Yes, keeping them a bit cooler can dramatically increase their life.
The vibrations can cause mechanical failures.
Poor connections can burn the tabs.

My guess is you want a major name brand cap and if you can get a higher voltage/ heat rating you will be better off. It does have to be the right kind as you have AC and DC capacitors. Putting the wrong one in can lead to a nice explosion and pieces of aluminum everwhere.

You have to be careful about relocation. Sometimes it is important to keep the leads shorter as the purpose of the cap might be tuned and could affect its job.

For best results, buy major name brand parts. If the part is available in a higher voltage or temp rating buy that.
Regularly inspect the connectors for heat and replace if they are questionable.
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Old 14-07-2019, 12:09   #14
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Re: Burned up capacitor on generator

Quote:
Originally Posted by GordMay View Post
An Air-Conditioning Dual Capacitor has three connections HERM, FAN and COM.
HERM connects to the Hermetically Sealed Compressor
FAN connects to the Condenser Fan Motor
COM connects to the Contactor and provides power to the Capacitor.


Yeah, I had read that before.
I would still have labeled it Comp myself, same number of letters.
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Old 15-07-2019, 05:49   #15
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Re: Burned up capacitor on generator

They will fail quickly because of overload due to temperature also if the outside temp is high and even on low load. just my two cents :-)
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