Generator output

[Hadenough]

I have a Geko diesel genset, nominal output is specified at 230V. Had a feeling that the immersion was slow to reach temperature so I tested the output at a socket and am getting 221v to 222v steady. Is this acceptable? And is a shortfall of 8v to 9v going to affect the 750W immersion heater very much. Everything else that we use, charger, appliances are working satisfactorily.

 

[NormanS]

I'm no expert, but when I had a small diesel generator, I was able to increase the voltage, by increasing the revs, simply by adjusting a screw on the governor.

 

[Hadenough]

Thanks, did consider that especially as I had filter / running problems with it earlier this year. I don't have the kit with me at the moment to check the engine revs so really wondered about the short term affect of the 220v output.

 

[NormanS]

Thanks, did consider that especially as I had filter / running problems with it earlier this year. I don't have the kit with me at the moment to check the engine revs so really wondered about the short term affect of the 220v output.

I didn't check the revs. I just used a volt meter, and fiddled with the governor adjustment until I got the required voltage. I assume that the two are directly related. I'd be surprised if the drop from 230v down to 220v would make any significant difference.

 

[theoldsalt]

I thought that voltage was controlled by a voltage regulator and engine speed affected AC frequency ?

However I may be confusing small portable generation with industrial generation ?

 

[VicS]

I have a Geko diesel genset, nominal output is specified at 230V. Had a feeling that the immersion was slow to reach temperature so I tested the output at a socket and am getting 221v to 222v steady. Is this acceptable? And is a shortfall of 8v to 9v going to affect the 750W immersion heater very much. Everything else that we use, charger, appliances are working satisfactorily.

The power produced is proportional to the sqare of the volts applied (W = V²/R ) so changes in volts do lead to bigger changes in power output than you might sometimes expect.

However in this case if you do the arithmetic you will find that a element which produces 750 watts at 230 volts will produce approx 690 watts at 221 volts. Not a huge difference.

 

[Hadenough]

Thanks for that, a non problem by the look of it!
As far as maths is concerned, I failed my maths O level 4 times but I needed it to get onto a construction course at the Tech. Luckily in the 1960's there was an O level in "Building Maths" which if you could work out the area of a square you passed. Served me well for the next 45 years.

 

[superheat6k]

I have a Geko diesel genset, nominal output is specified at 230V. Had a feeling that the immersion was slow to reach temperature so I tested the output at a socket and am getting 221v to 222v steady. Is this acceptable? And is a shortfall of 8v to 9v going to affect the 750W immersion heater very much. Everything else that we use, charger, appliances are working satisfactorily.

Was the voltage measurement made with or without the immersion heater load switched on. You don't state what the capacity is, but I assume around 4kVA. These simple generators do tend to control voltage by rev setting, which really only controls the frequency properly, but voltage will rise as revs rise, but will fall as load increases. Higher output generators use the revs to control the frequency only, e.g. 3,000 RPM = 50 HZ, with a separate circuit controlling the field current, which regulates the voltage.

If your no load voltage is already low at 220v then the 'on load' voltage level could drop significantly, and this could more noticeably reduce the effect of the immersion heater. Ideally a frequency meter or digital tacho will let you see if it is simply going too slow, if you can actually see a rotating part, as these units are well shielded.

 

[William_H]

Just to confirm what has been said. The standard gen set will rotate at 3000 RPM to produce 50 hertz AC (or possibly 1500 RPM with double gen poles). It is desirable to keep the frequency close to 50 hertz to keep transformers and induction motors happy. This type of gen can be confirmed by the fact that the engine runs or tries to run at constant speed.
A more modern design in smaller gens is to run the engine at variable speed driving a DC generator (alternator then rectified like a car alternator) the Dc is turned into AC in an inverter built in so AC is always 50 hertz but engine runs slow for li8ght loads and faster for full power.
Anyway as said the voltage should be set by the regulator whic samples the AC voltage feeding some back as DC to the field coil to control the AC volatage output. There may be a voltage adjustment somehwere in the regulator box near the AC outlet connections.
It is likely that with the load of the water heater the engine is running at full power but slowing down under load and the regulator is running at full power but failing to maintain desired output voltage. This may be because the engine is not producing full power due to old age or some other problem. good luck olewill

 

[mattnj]

I have a 6kw diesel genset here....recently had a similar issue and can confirm(in my case) a small reduction in speed made a huge difference to the output power......tweaked a screw to get it back to 3000rpm.

 

[jerrytug]

I have a 6kw diesel genset here....recently had a similar issue and can confirm(in my case) a small reduction in speed made a huge difference to the output power......tweaked a screw to get it back to 3000rpm.

That's exactly what they do with the national grid as well!

 

[Hadenough]

It,s a 4.5KVA, 3000rpm unit and the reading was taken with the load of the water heater and a couple of phone chargers. I can get at the spinning parts easily so will get hold of a rev counter got check out the engine speed. Thanks for the responses.