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Old 5th November 2011, 03:09 PM   #1
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Default Home generator questions

I am finally looking into buying a generator for my house. I have most of my problems with mounting and hookup sorted, but I am confused about what to do about the quality (or lack of) of the AC coming out of these things. I know the inverter generators produce a nice, fairly clean sine, but they are very expensive. Putting individual iso transformers on sensitive equipment is an option I guess and should be fine for filtering spikes and HF noise, but what about the actual AC waveform coming out of your average generator?. I saw some scope pictures of "average" generators, and what I saw was disturbing to me. Am I thinking to much, or can this be a wear and tear issue for equipment powered by a generator. We have had 2 events in the past 2 years that have lasted 5 days, so some of the run times can be substantial.

some pics towards the bottom of page showing cheap generator output

Anything that can be done at the generator output to improve things?
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Old 5th November 2011, 06:17 PM   #2
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There are a lot of ways to approach your solution. Clearly those generator outputs were poor, and I dare say not typical. You will need to consider both prime mover/governor control, as well as regulation method if you really want decent power quality. A stable prime mover with electronic governor will help keep your frequency relatively stable. If you get one with a mechanical governor you will find both speed and voltage regulation will be poor relative to electronic. The older style two cycle engines or cheap gas powered Briggs/Tecumseh types really don't do well for a clean output- they operate bang-bang-bang. The newer natural gas or propane models are much smoother running, which will help keep the sine wave clean.

Consider that the way to produce a sine wave is to rotate a DC field in a circular path, forcing a magnetic field into windings wound around the stationary perimeter. The cleaner the rotation, the cleaner the sine wave. Deeper design issues such as winding pitch also affect harmonic output, but that is beyond the scope of your question. Choose your prime mover carefully, and select a decent electronic governor.

Regulation of the field will affect voltage regulation more than wave quality. There is inherent time delay (you need to measure the voltage before you can correct it, and it takes time to measure AC) with regulators, which is why transient load changes will cause voltage fluctuation.

If you are serious about running audio equipment off a generator, I would select an oversized ferroresonant transformer to provide power. The unit will completely clean up the sine wave and regulate output as well. They do produce a little bit of harmonics, but nothing that should adversely affect a decently designed amplifier. All other equipment (HVAC, computers, lighting) should be all right.
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Old 5th November 2011, 06:46 PM   #3
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Even the bad generator is clean enough! A filter will load the generator.

The bad generator will most likely fail soon as it appears there is movement in parts that should not be moving.

All generators have distortion!
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Old 7th November 2011, 02:02 AM   #4
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Thanks for the reply's guys. One of the pictures on the link I posted was from a Honda generator with an inverter. It produces a very nice clean sine. The problem with an inverter generator is the price for 6K watts is between 3-4K$

I looked at the CVT type transformers, they sound like just what I need except they are large, heavy, expensive and don't handle much current. I will put these into my search engines, may find a few for cheap to add as point of use type protection.

Not looking to power any serious audio, but just not sure if I invest in a generator solution that I want that kind of crap coming out of it. I guess pretty much like all else, you get what you pay for.
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Old 7th November 2011, 02:46 AM   #5
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You can get two Honda EU2000i generators for under $2K total and run them in parallel to get 4kW of very quiet and efficient clean sine wave power. There is a significant advantage in that each unit only weighs about 46 pounds so it is easier to handle than a single larger machine. I have owned an EU2000i for about 10 years mostly used to top up my boat batteries when on extended anchoring. I have also used it in a pinch during outages to keep the refrigerator and basic service going. It has been bulletproof!
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Old 7th November 2011, 04:59 AM   #6
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It's tough to beat a Honda generator.
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