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Generator Bogs Down No Load After a Few Miniutes #5163539 07/17/19 03:12 PM
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Lewis Offline OP
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I've just bought a small 6KW diesel generator, it's only 2 years old but has about 2500 hours on it. Anyway, the engine seems fine, oil is clean and it starts right up no smoke like a dream. However 5 minutes after starting the engine bogs down and the voltage drops, then the unit cut's off due to low speed (has a digital controller). If I disconnect the generator capacitor it will run fine for hours, so I think the actual generator is faulty however it generates the required voltage fine before bogging down and the windings ohm out fine. The generator is the brushless type without an AVR but uses a capacitor. I've come across generators that have shorted windings and bog the engine as soon as it starts but, in this case, it works fine for 5 minutes I can even put a load on it and works fine, then it'll slow down like I'm overloading it and cut out even with nothing plugged in. What could this be, bad alternator, capacitor? Has anyone come across this??

Re: Generator Bogs Down No Load After a Few Miniutes [Re: Lewis] #5163588 07/17/19 03:55 PM
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Kamele0N Offline
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Sounds like when CDI unit on a gasoline OPE is faulty...

CDI stops giving sparks as soon as it heats up....

Insulation/resin around your "windings" is cracked....inside those little cracks when generator is operating you get small micro sparks....those sparks later make carbon (from burnt Insulation)....

Carbon then has different resistance when hot or cold...when "windings" are still cold (enough) everything runs fine....but when they heat up...your generator became shorted (hope that I was clear enough)

Last edited by Kamele0N; 07/17/19 03:56 PM.

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Re: Generator Bogs Down No Load After a Few Miniutes [Re: Lewis] #5163673 07/17/19 05:46 PM
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Donald Offline
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Originally Posted by Lewis
I've just bought a small 6KW diesel generator, it's only 2 years old but has about 2500 hours on it. Anyway, the engine seems fine, oil is clean and it starts right up no smoke like a dream. However 5 minutes after starting the engine bogs down and the voltage drops, then the unit cut's off due to low speed (has a digital controller). If I disconnect the generator capacitor it will run fine for hours, so I think the actual generator is faulty however it generates the required voltage fine before bogging down and the windings ohm out fine. The generator is the brushless type without an AVR but uses a capacitor. I've come across generators that have shorted windings and bog the engine as soon as it starts but, in this case, it works fine for 5 minutes I can even put a load on it and works fine, then it'll slow down like I'm overloading it and cut out even with nothing plugged in. What could this be, bad alternator, capacitor? Has anyone come across this??


if you remove the capacitor and short it with a screwdriver. Look for bulging or leaking. If so it needs replacement. With an ohmmeter you can set the meter to ohms and attach the leads and watch the ohmmeter change as it charges with the tiny current from the ohmmeter

DVMs that measure a capacitor are becoming more common.

If you want to start checking out the actual generator you will need a 4 wire ohmmeter and the troubleshooting specs for the generator head. Typically very low resistance like .5 ohms.


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Re: Generator Bogs Down No Load After a Few Miniutes [Re: Lewis] #5165129 07/19/19 09:34 AM
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cronk Offline
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Is the capacitor available fairly cheap? Typically capacitors don't cost a lot of money, if you can find one cheap, I'd be tempted to throw one in it and see if that fixes it.


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