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Power stability with PTO generators
The critical thing about generators is speed. To get 60Hz power, most generators need to run at 3600 RPM which happens to be 60 revolutions per second. They produce one power cycle with a full rotation of the alternator. (This is not required by the physics of power generation, but by alternator design. Alternators could be made to operate at 1800 RPM and a nine pole generator could even be designed to work at 540 RPMs directly) Current producing capability of the generator is related only to its wiring size and steel content.
Having about 2 PTO HP per KW generated is a good factor to use. It provides some reserve and takes into account the efficiency loss of converting 540 PTO RPM to 3600 RPM at the generator shaft. Having three or four PTO HP available per KW generated will provide more stable power and high overload cabability at the expense of higher running costs at low loads.
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Power stability with PTO generators
You can connect your generator through a second breaker in the panel. This is a good added insurance policy and you can select the style and capacity of the breaker to set whatever protection point you want.
I would select a two pole breaker rated for 4 amps per KW of power generated or the nearest standard value. So for 5KW of Continuous power generation I would use a 20 Amp two pole breaker connected to the 220/240 VAC outlet on the generator. A breaker sized this way will allow for some peak running. For additional safety, you can reduce the size of the breaker. A 15 amp breaker will handle a 5KW generator connection for a significant period of time.
The type of breaker used is important. Typical breakers can handle high overloads for a significant period of time. Some breakers are rated for 200% rated capacity for 1 hour. Others will trip at 125% after a few minutes. The second type is better for protecting a generator. These are used specifically to protect electronic equipment rather than general purpose or motor circuits.
Depending on your codes, this may be a breaker in your main panel, or it might have to be a small separate panel installed with your transfer switch. Remember to connect the neutral to handle unbalanced loads on 110 VAC.
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Power stability with PTO generators
If my generator is running, I want it running at full speed ready to take a load if it develops on the line and provide 60 Hz power to that load, immediately. If I get to a point that I don't need ANY power, like the idle down situation, I will turn the genset off. When I am running on generator power, there are very few times when the genset will be delivering ZERO power to the panel and could idle down.
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Power stability with PTO generators
I can see why a generator might idle down with one person using it at a construction site, but for backup power, which I expect includes most everyone in this discussion, it should not be an issue. The difference in fuel usage during the very short periods of ZERO load will not be significant in any way.
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Power stability with PTO generators
I understand about the noise. The sound deadening qualities of the mufflers and air intakes are not good on some brands. My first generator was very loud and I replaced the muffler and welded on a copper plumbing union fitting onto the muffler outlet to increase the length of the exhaust pipe with a removable section. That improved the raspy exhaust sound considerably.
My backup generator is a 7KW with a Honda engine. I don't think that it is as loud as the old smaller generator that I modified before. But, it has more low frequency noise. I was thinking of adding the copper union fitting to that Honda muffler also and then running the exhaust through an automotive "turbo" muffler. I forgot to mention on the previous generator, I did try a glasspack automotive muffler and it helped, but there was more high frequency noise from the first generator.
You will have to draw your own conclusions about safety, but I have run the older generator inside a building with the union fitting securely attached to a pipe that was mounted in a vertical exhaust stack for an old furnace. I know that there are pros and cons and you have to make your own decision whether you think that you could do this safely. I did have a vent fan providing positive fresh air into the building and it ran on the generator power.
We started this thread about PTO generators, and that is a different story entirely. Idle down is not even an option. I doubt that fuel usage is a problem with my tractor idling at PTO rated speed, but the noise might be in certain situations.
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