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Old 13-10-2019, 14:29   #1
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Melting wires on gen capacitor

I keep having problems with the capacitor wiring on our Paguro generator that uses the capacitor to regulate voltage.

The previous owner replaced the stock capacitor with a much larger 50uf cap because they wanted higher voltage for everything they ran.

The cap died and when I removed it wires were burned as well. I've lowered it to a 40uf (no idea what stock is) and the wires again melted. Volts have been running at 128 with no load.

Is this issue because of the cap size?
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Old 13-10-2019, 14:59   #2
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Re: Melting wires on gen capacitor

Just a guess.

Burned wires, hot usually means too much current. I’d start by figuring out what a factory spec capacitor is and try to match the parameters. I think of capacitors in this instance to tame an inductive load such as a collapsing inductive field. In such a situation, the field will induce a high voltage spike with a certain total power. An overwhelmed capacitor or one with too low a peak voltage capability might simply short. Once shorted, it remains as a short or nearly so. My forte is PE Mechanical. I’m recalling some EE ancient college history. I have been surprised occasionally by field collapse. I was replacing the foot switch on our windlass last year. Bumped the motor and was shocked by the induced voltage spike. Same principle as an old fashioned ignition coil and breaker points.
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Old 13-10-2019, 15:34   #3
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Melting wires on gen capacitor

The cap regulates voltage, lower uf value lower voltage I believe. Itís not going to change current.
Usually melted connections means loose connections, lose the plastic cap, it serves no purpose most likely except appearances and replace the terminal ends, and it helps to use a dab of silicone to prevent corrosion and make it easier to slip on.
Loose means resistance, and resistance means heat.
Now if the cap itself is burnt, Iíve had real good luck with GE gentec Caps, the higher the voltage rating the better the cap I have been told.

These are of course usually air conditioner compressor run capacitors, often come as 40+5 caps as they are two caps in one, just ignore the extra terminal if that is all y9u can find, it will work fine. The extra 5 uf cap is usually for the fan on an airconditioner unit.

These things donít last forever, carry a spare, it may last a week or two years doesnít seem to be any logic to it, my current one is a couple of years old.
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Old 13-10-2019, 16:00   #4
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Re: Melting wires on gen capacitor

Some capacitors have an AC rating. Does this one?

If you use a non AC rated one in place, it might overheat.
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Old 13-10-2019, 16:45   #5
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Re: Melting wires on gen capacitor

The cap seems fine. It's rated at 450v AC.

I noticed the generator sounding like a load was changing (it wasn't) and then I noticed the voltage flucuating. That's why I checked the cap after shutting things down.

I'm guessing with the 40 amps of motor load we had running when the wire to the cap was going bad it was causing the voltage to drop meaning the amps had to increase this the generator was loading for a bit.

That's just my guess.
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Old 13-10-2019, 17:08   #6
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Re: Melting wires on gen capacitor

Quote:
Originally Posted by a64pilot View Post
The cap regulates voltage, lower uf value lower voltage I believe. Itís not going to change current.
Usually melted connections means loose connections, lose the plastic cap, it serves no purpose most likely except appearances and replace the terminal ends, and it helps to use a dab of silicone to prevent corrosion and make it easier to slip on.
Loose means resistance, and resistance means heat.
Now if the cap itself is burnt, Iíve had real good luck with GE gentec Caps, the higher the voltage rating the better the cap I have been told.

These are of course usually air conditioner compressor run capacitors, often come as 40+5 caps as they are two caps in one, just ignore the extra terminal if that is all y9u can find, it will work fine. The extra 5 uf cap is usually for the fan on an airconditioner unit.

These things donít last forever, carry a spare, it may last a week or two years doesnít seem to be any logic to it, my current one is a couple of years old.
I'm going to try to find a 30 uf cap tomorrow.
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Old 13-10-2019, 17:44   #7
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Re: Melting wires on gen capacitor

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Originally Posted by crayiii View Post
The cap seems fine. It's rated at 450v AC.

I noticed the generator sounding like a load was changing (it wasn't) and then I noticed the voltage flucuating. That's why I checked the cap after shutting things down.

I'm guessing with the 40 amps of motor load we had running when the wire to the cap was going bad it was causing the voltage to drop meaning the amps had to increase this the generator was loading for a bit.

That's just my guess.


I am going to guess that the voltage was fluctuating because you had a loose connection to the cap, regulating voltage is its purpose.
If you go to a 30 uf cap, assuming you can find one, I wouldnít connect anything to it until after you verify voltage, 10 uf is a big jump and I donít think voltage will be within limits.

See this to see what your voltage limits you should see, use these for voltage under load, ideally even with no load you should stay below the max and above the min even under a heavy load
https://www.pge.com/includes/docs/pd..._tolerance.pdf
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Old 13-10-2019, 18:15   #8
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Re: Melting wires on gen capacitor

It was 128 no load, 121 at 50% and 116 at 80%. Also, I was wrong, I had a 35uf cap installed.
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Old 13-10-2019, 20:33   #9
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Re: Melting wires on gen capacitor

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It was 128 no load, 121 at 50% and 116 at 80%. Also, I was wrong, I had a 35uf cap installed.


To me that is nearly perfect. Remember 120 is target, not 110
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Old 14-10-2019, 05:33   #10
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Re: Melting wires on gen capacitor

Generally for electrolytic capacitors and especially aluminium electrolytic capacitor, at high temperatures (over +85oC the liquids within the electrolyte can be lost to evaporation, and the body of the capacitor (especially the small sizes) may become deformed due to the internal pressure and leak outright. Also, electrolytic capacitors can not be used at low temperatures, below about -10oC, as the electrolyte jelly freezes.

Quote:
Originally Posted by a64pilot View Post
I am going to guess that the voltage was fluctuating because you had a loose connection to the cap ...
Spade Terminals are notorious for becoming loose, generating high resistance connections. This may be the commonest cause of capacitor overheating.
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Old 14-10-2019, 06:16   #11
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Re: Melting wires on gen capacitor

Poor connections and allowing the generator to be shut off or run out of fuel while under load is what prematurely kills these capacitors.
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Old 14-10-2019, 09:34   #12
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Re: Melting wires on gen capacitor

I'm out of ideas on this generator. It's so frustrating.

I replaced the capacitor and the wiring to it. It runs great for about 30 minutes then it sounds like it's bogging down and the RPMs drop to 3540 and go back up to 3600/3660 after about 2 seconds. It repeats this cycle every 15 seconds.

It doesn't matter if it's at 80% load or 30% load.

I changed all the fuel filters 8 run hours ago.
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Old 14-10-2019, 11:04   #13
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Re: Melting wires on gen capacitor

What kind of RPM regulation does it have?
Old lawnmower engines used the cooling fan air blowing against a vane.
The linkage got sticky with clippings etc, and the symptom was exactly like what you describe. Vroom, vroom, vroom....
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Old 14-10-2019, 11:14   #14
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Re: Melting wires on gen capacitor

It could be a stuck governor, but itís usually fuel delivery, clogged hose, or sucking air etc.
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Old 14-10-2019, 12:39   #15
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Re: Melting wires on gen capacitor

https://youtu.be/oWilSwLNxg0
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