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Justme

How does a genny work?

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I know that the engine turns the alt to make the elec. I am after a bit more than that.

 

Without going in to to many details just yet. I have a genny (no not a cheapy ebay jobby one but a £2k plus one) that has stopped making power. Its been diagnosed as having a faulty cap. They are saying that the cap blew / failed due to the engine running at to low & variable speed.

(which they are blaming on a slightly dirty air filter & the fuel filters that still flow fuel freely so cant be blocked at all)

 

Now I would assume that the caps job is to smooth out any variances in the speed especially as the genny was fitted with the add on AVR module so that the power produced was suitable for sensitive equipment.

 

Also of note is that the power is fed to the appliances via an inverter charger that monitors the power for V & Hertz & will disconnect if the values are not up to spec. The inverter has not been doing that.

 

 

So what does the cap do (the genny has two, the second is wire to the AVR but I dont know which one failed) & why would it fail. The engine sounded lovely to me, never missing a beat, easy to start & stop

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The capacitor is effectively a battery which will store a certain amount of electricity to meet the demand of small surges or times of low use.

 

I have seen caps blow through having too high a voltage applied to them but not too low a voltage.

 

Hope that helps, if not try the website http://www.howstuffworks.com

 

Kev

Edited by Kev Stephenson
.com not .co.uk

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You haven't quoted the rated output of the generator. But you hint at its size given the inverter mentioned. Q: is this a set which requires sychronisation with the mains? Did it fail to synchronise? Do you build up load to a set pattern i.e after sync and not too quick?

 

Subtle misfires can upset the rpm and cause disconnection...?

 

Think the cap took the brunt of what the inverter should have been doing...

Edited by TimberCutterDartmoor

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I always thought that he engine turned a wheel that had a load of cats strapped to it. As the wheel spins, it rubs the cats against a bunch of glass rods, making electrickery. Maybe your cats have died?

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You haven't quoted the rated output of the generator. But you hint at its size given the inverter mentioned. Q: is this a set which requires sychronisation with the mains? Did it fail to synchronise? Do you build up load to a set pattern i.e after sync and not too quick?

 

Subtle misfires can upset the rpm and cause disconnection...?

 

Think the cap took the brunt of what the inverter should have been doing...

 

 

Its a 4.8kw / 6kva unit. No sync with mains as we have none. Does not need to sysn to inverter as the inverter drops out & passes through (but still monitors) when genny is on. The inverter lets the genny start under no load then once stable will pass through the power. The load it takes over is quite small (1 or 2 amps) & then the inverter will ramp up the charger slowly adding the load. On shut down the charger will have lowered its demand & the inverter again senses the shut down & switches back to inverter power before the genny shuts down. So I dont think its a sudden loading / unloading problem.

 

Will check out that how to link thanks.

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Sounds like a little bit more of a problem than the capacitor.

 

It will more than likely be the AVR, capacitors dont blow because of rev fluctuations, that is bull.

 

The person who sold it will have already had a quote for repair and thats why its being sold.

 

I had a genny in for repair which turned out to be the avr, the genny was about £600 new, the avr as a spare was £430

 

Generators have a small magnetic field in the for of a small magnet in the rotor, when it starts to spin it generates a tiny current which then passes through the avr and which circulates it round building up more and more current untill it reaches a stage where it regulates it at the required voltage. Simply put

 

Some gennys dont have an avr but do the same via the capacitor, through a small winding buried in the stator or outer winding, sometimes when the capacitor have gone this small innner winding can burn out so the process will not begin even with a new capacitor

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