Reducing Generator RPM?

Coach Dad · October 2012

Lowering the RPM in a generator reduces noise and fuel usage. It also reduces the frequency of the generator output but it doesn't reduce the voltage output as drastically.

So I was wondering....
What would happen if I lowered the rpm on my generator so that it was putting out 50 hz instead of 60 hz.

Would the 50hz cause damage to any components that are designed for 60hz such as my well pump, refrigerator? What about electronics TV, Microwave etc? Would it make clocks runs slower?

Would it cause damage to the generator?

Cariboocoot · October 2012

Re: Reducing Generator RPM?

It's "non answer" time!

The answer is: it depends.
Some things will not care if the frequency is off by 10 Hz, other things will have fits. What it depends on is what's inside the particular item in question. An analog clock that uses just a motor will be inaccurate, but a digital one that uses a power supply won't (crystal regulated circuitry).
Induction motors will run harder, drawing slightly more current for the power output and thus generating more heat. How great the effect will depend on how heavily loaded the motor is. For instance this could be a problem with a water pump or refrigerator (affecting it over time) but it's not likely to harm a table saw.
The same goes for the generator. Since it would have to work harder at 50 Hz if it is heavily loaded there will be some noticeable affect. If like most it is loafing at 50% capacity it will never notice.

Personally I doubt the sound and fuel savings are worth the effort. If you want to try it, connect the gen to non-critical resistance loads only. Note the Voltage, current, and frequency. Then slow it down to 50 Hz and see what changes you get. Don't forget to monitor the fuel consumption and the sound level (got a dB meter?). You'll have a time judging whether your load output is "acceptable" too (measure the lumens from lights?).

For other things, check the electrical specs on them. You'd be surprised how many things are labeled "50-60 Hz". That makes it easy!

Blackcherry04 · October 2012

Re: Reducing Generator RPM?

Making some generator's output 50 hz may be a issue if you have a AVR ( Automatic Voltage Regulator ) on the exciter winding. It's not as simple, depending on the governor and the windings on the generator head to just lower the RPM. The AVR may be able to have the jumpers set for 50 hz. It would be a shame to burn up you generator. On mine it's a detailed setting procedure for the AVR, as the RPM slows the AVR increases the output to match it's settings, so it would be fighting the lower output and RPM trying to match the settings. The AVR also has all the voltage limit settings ( Upper & Lower & HZ ) in it.

Vic · October 2012

Re: Reducing Generator RPM?

Hi CD,

First, believe that the Inverter would NOT qualify the 50 Hz input frequency ... doubt that the range of adjustment is that large, but I am unfamiliar with the Magnum Inverter.

Anything that has a 60 Hz transformer would probably not like 50 Hz. I would NOT run any motor that is designed for 60 Hz on 50 Hz. Many Microwave ovens still have line-operated transformers ... Not a good mix. Yes, clocks would run S . L .. O ... W.

And also agree with others, even if the genset would run well and regulate V at the slower speed, doubt that it would save very much (if any) fuel or reduce noise by much at all. A diesel genset would have the best fuel savings vs gasoline/LP. The surge capability of the genset would probably be reduced (lower inertia) at 50 Hz.

My 25 Kva Diesel has a 50 Hz position on the Govenor, and is designed to work well at 50 Hz, but my inverters will not qualify 50 Hz as suitable power. Just opinions, Vic

waynefromnscanada · October 2012

Re: Reducing Generator RPM?

Anything with an induction motor, such as fridge water pump, table saw etc will run roughly 18% slower, and of course, like with 60 Hz transformers running on 50 Hz, they will draw more current and run hotter due to having insufficient inductance for 50 Hz operation. The only saving grace re extra current and heat, could be the reduced input voltage. The induction motors will however, definitely run slower, meaning you're fridge will have to run longer, and you're submersible pump, along with having to run longer, will have it's max output pressure reduced. If you already have lots of pressure to spare, there shouldn't be a problem that way, but if it's already near it's max before the pressure switch finally shuts off the pump, you could run into a situation where the pump can't get the pressure high enough to trigger the switch, and would thus end up running continuously.

inetdog · October 2012

Re: Reducing Generator RPM?

Coach Dad wrote: »

Lowering the RPM in a generator reduces noise and fuel usage. It also reduces the frequency of the generator output but it doesn't reduce the voltage output as drastically.

So I was wondering....
What would happen if I lowered the rpm on my generator so that it was putting out 50 hz instead of 60 hz.

Would the 50hz cause damage to any components that are designed for 60hz such as my well pump, refrigerator? What about electronics TV, Microwave etc? Would it make clocks runs slower?

Would it cause damage to the generator?

The reduction in generator noise and wear is significant if you double the number of poles on the generator so that it produces 60 Hz while rotating at 1800 RPM instead of 3600 RPM. The change in going from 3600 to 3000 or from 1800 to 1500 without changing the system design will probably not be worth the hassle. And you may have a problem with your engine producing full output power at the lower RPM!

Some of the other pitfalls have been covered well in earlier replies.

Surfpath · October 2012

Re: Reducing Generator RPM?

Coach Dad wrote: »

What about electronics TV, Microwave etc? Would it make clocks runs slower?

I don't know about damage to the generator or if the inverter would allow it, but FWIW, any 60hz appliance that relies upon a digital timer may potentially malfunction. We live in a 50 hz area and all 60hz appliance that rely on digital clocks or internal digital timers (like fridges, freezers, alarm clocks) won't work on 50hz.

waynefromnscanada · October 2012

Re: Reducing Generator RPM?

Overall, all things considered, it's just not worth doing. Far better to switch to an inverter generator like the Honda that will idle down on light loads, yet still provide 120 VAC @ 60 Hz. Things will work properly and not be prone to damage / burnout.

oil pan 4 · October 2012

Re: Reducing Generator RPM?

I have ran just about everything found in a house or shop off 50hz power for years when I lived in japan.
Digital clocks are useless. Thats the main problem I found.

Unless you have a higher end generator with an external 50/60Hz regulator chances are if you slow it down it won't put out any voltage.

I picked my generator very carefully for this feature. The ability to run 50 and 60 Hz was a must have for me.

You are going to have to let us know what generator you have, it may not be possible to run what you have at lower speed and get power out of it.

Coach Dad · October 2012

Re: Reducing Generator RPM?

Thanks to all... this confirms my suspicions.

jvbram · November 2016

But can i use a 220 vac 50hz 5kw alternator off an old genset on my waterwheel that runs around 300rpm. The genset does not have a battery so the alternator must be self exciting. I want to generate 12vdc. 10 amps will do. I realise that I must bypass the regulator and install a bridge rectifier.

mike95490 · November 2016

jvbram said: But can i use a 220 vac 50hz 5kw alternator off an old genset on my waterwheel that runs around 300rpm. The genset does not have a battery so the alternator must be self exciting. I want to generate 12vdc. 10 amps will do. I realise that I must bypass the regulator and install a bridge rectifier.

Not likely, but try anyway. The alternator in my genset has a self-exciting harmonic winding, but it does not produce enough voltage till it's up to about 50% of rated RPM. Then it really takes off. I suspect if you try loading the output while at low RPM's the voltage will collapse and you get nothing but heat in the windings. Just my guess

oil pan 4 · November 2016

If you only need 12v just engine drive an automotive alternator with a small gasoline engine.

Reducing Generator RPM?

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