Home made generator?

Hi
I don't know as much as i'd like about electrics, but i thought someone here might be able to help.
Here's the thing...I need a generator. New, they're around £100 for a 750W,
but I've got an old 3.5 bhp engine which, i imagine is half of what the generator actually is.
What i'd like to know is there anything i can buy (like just the generator bit) or use (like a car's alternator) to 'bolt on' to the engine to produce electricity to power lighting/power tools etc..to save buying a new genny?
Any thoughts appreciated! \sh
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On Thu, 12 Mar 2009 15:15:55 -0000, "news.zen.co.uk"

You could certainly get 750w out of a big car alternator but this won't be the one in a Mini. Big old Detroit iron had alternators in the 70-100a range. An old cop car or a Caddy is a good start. Your 3.5 HP engine should spin it up. The problem is that is 14v or so. You will still need an inverter to make that mains voltage. I am doing a similar thing here for hurricane outages but I only run small loads and some are 12v
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     snipped-for-privacy@aol.com writes:

The Lucus alternator used in old UK minis (and some other UK cars of that era) generated up to 42A at idle speed, but only went up to about 48A max a little above idle, and produced no further increase in power output as you raised the engine speed further. Nowadays, alternators are controlled digitally by the engine management unit, and won't work standalone.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
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On 14 Mar 2009 10:10:38 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

I guess all the more reason to try to find an old American alternator. Most of them are "one terminal" alternators. Spin them up and ~14.7 volts comes out.
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snipped-for-privacy@aol.com wrote:

Big alternators are everywhere these days. The factory Bosch unit in my Volvo 740 is 100A and it has a convenient internal regulator. I have an extra one in the garage awaiting just such a project, since I also have a perfectly good 3HP engine sitting around. Any luxury car from the mid 80s on should have at least a 70A alternator. Seat heaters, power windows, power seats, all that stuff sucks a lot of juice.
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I recall many moons ago Wireless world did an article where someone used a lawn-mower engine with a car Dynamo and, I may be wrong, but I think he rewound it to give 240V.
See if your local library have back issues but you may have to spend a lot of time looking, it's a long time ago.
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On Thu, 12 Mar 2009 18:11:15 +0000 (GMT), Stuart

There was a hack to the voltage regulator that allowed you to get 120v out of one (over on this side where we use it). They sold the kit at places like JC Whitney but I haven't seen it lately. It is not in the 50/60 hz range at all though. This is high frequency AC. It was sold to run drills and other "universal motor" type tools.
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snipped-for-privacy@aol.com wrote:

If you run the field coil flat out, you can get even more than that without rewinding. You have to spin it pretty fast and obviously you will not get anywhere near the full rated load current. The output is unfiltered DC unless you tap off prior to the diode pack in which case it will be 3 phase AC.
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wrote:

Many thanks for all the replies, folks. You've all given me something to think about.
And now I think I'm going to try and get hold of a decent sized alternator and give that a go.
Cheers again! \sh
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"news.zen.co.uk" wrote

It will probably cost you more in materials and parts than it would to buy a new unit.
It will certainly cost you vastly more in terms of your time and effort
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John wrote:

Clearly if you were to go buy all the parts it would, however he has an engine already, and a used alternator can be had for anywhere from free to $30 bucks or so, can't really factor in the time and effort if you're the sort who enjoys this stuff, and what decent engineer doesn't?
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On Mar 12, 11:15 am, "news.zen.co.uk"

There are generator heads available at farm supply outlets here in North America that are intended to run off of a tractors power take off. You may want to see if the equivalent kind of thing is available there. The ones here have a gear box to speed them up from the tractors 470~ RPM up to 1800 in order to get the sixty Hertz that is used here. Yours would be 1500 or 3000 RPM depending on how it is wound. 3&1/2 BHP will only give you 1000 to 2000 watts though.
-- Tom Horne
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