# Building a generator, need some advice

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I am in the process of building a generator. I have a horizontal shaft 11HP engine, that will drive an alternator. My question is, I will use a converter, to convert 12Vdc to 120Vac. Can I step up the 120 to 240 with a transformer? Thanks

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Yes you can if you can put up with the transformer losses. Just keep in mind that there is no magic about it. 5000 Watts is a little over forty amps at 120 volts and not quite twenty one amps at 240 volts. Will the inverter that you have in mind produce that much output?

-- Tom H

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Thats a good question. I don't think that it will. Well shit...I am out of ideas now. I have built 4 or 5 ac to dc inverter for mobile CB's and HAMs. Is it out of the question to just build an inverter that will convert the

12Vdc to the 240Vac? That way I can build the > > I am in the process of building a generator. I have a horizontal shaft 11HP
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in article snipped-for-privacy@corp.supernews.com, John Robertson at snipped-for-privacy@cox-internet.com wrote on 12/12/04 8:41 PM:

You might consider using an autotransformer. That will cut down on how much copper and iron will be needed. Depending upon the application, you might also want to:

1. Go to a higher frequency to reduce transformer size.

1. Use electroning switching directly from the 12 volts dc to 240 VAC.

Bill

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Building your own inverter for 12 v dc to 240 ac at 15HP'ish is far from a trivial. There are alternatives. Putting a transformer on the output of a 12vdc to 120vac inverter can be fraught too - a high efficiency inverter is only going to produce a crude approximation to a sine wave - that the transformer may not like at all. A true sine wave inverter is likely to be very expensive and inefficient. Both types are going to be much less efficient at very light loads.

The first is obviously to generate at 240vac. But I assume that you can't do that for some reason -such as battery backup.

The second is if the load is partionable into many, lower wattage, loads and power each from its own inverter. 300W

12vdc to 240vdc are on sale in the UK for
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How you design your generating system depends on the load you plan on powering. Can you give any specific details, such as current and power factor. Are you switching loads?

Dwayne

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| Thats a good question. I don't think that it will. Well shit...I am out of | ideas now. I have built 4 or 5 ac to dc inverter for mobile CB's and HAMs. | Is it out of the question to just build an inverter that will convert the | 12Vdc to the 240Vac? That way I can build the inverter to handle the higher | wattage? Thanks so far

Build an inverter as big as you want.

Now how big is your alternator? How many amps can you get out of it? If you want 5000 watts, you're going to have to pull 416 amps at 12 volts, plus more for the inverter losses. If you can get an alternator to go directly to 240 volts, and a stable enough engine to keep the frequency close, you might be better off by eliminating the inverter. But if you do want a DC system, for example so that you can run batteries, too, then a higher voltage DC might be in order. Double conversion UPS systems in the 5 kW range typically use 48 to 72 volts in the DC section. If you can get an alternator to do that, it might help.

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Lemme see now... 63 amps * 13.8 volts = 869.4 watts. I think the elements in a domestic hot water heater are 3000 to 5000 watts at 240 volts, depending on size. Your 11 HP engine will drive a 5500 watt generator, but you need a a governor if you want to maintain anything near 60 Hz. The generator head only, 120/240 volts, is \$389.99 at