Home-made generator

Even if you could get the alternator to output 240, which may or may nor be possible (it's insulation probably isn't up to it ) why bother it would output about 1KW max any more and it would overheat (and the drive belt slip) . it would be very inefficeint with a car engine driving this. Also how would you govern your engine to 1500 rpm or 3000 rmp depoending on how many poles the alternator has. You need accurate governing to keep your frequency at 50hz....

Just buy a 5.5 hp honda powered job, will output 2-3 kva and will run any normal power tools.

if your set on diesel, (not much point for a low output intermittant use genny) you can pick up a cheap lombardini or lister genny for a few hundred.

Jimbo

Hi Bryan, Alternatively, have you considered buying a 12V DC to 240V AC converter? This might be a convenient option for powers less than around 1000Watts. Maplin

do a range of them.

- Steve

This is the way I would do it - as do several of my friends who live on narrowboats, and use a similar system for their electrics. The important thing is to have some big batteries in the system, so the inverter runs off the batteries and the engine/alternator recharges them. This keeps the DC side of the system nice and stable, and prevents the alternator getting stressed by too great a load. Cooling the engine shouldn't be a problem, just fit the normal radiator complete with cooling fan and switch. Might be worth fitting the biggest alternator you can find at a scrappie, too.

I don't think you'd get anywhere near 1kW at 50 Hz. You'd have to run it pretty fast for maximum output, and the frequency at that speed would make it unsuitable for many uses.

I use an inverter and an old lorry battery. This will run an angle grinder or drill or lights or sander. In fact anything up to 800 watts. The inverter came from ebay for 60 pounds, the battery from the side of the road!!

The real advantage to this is that it is easily portable and quiet. If you want a small generator then just buy a cheapie at about 80 quid , that is all they are now !!

MrCheerful

Why bother? Lidl have a generator in their special offers this week. 650w continuous, 720w max, 2 year warranty. £89.99 incl VAT!

Because I find it more interesting and challenging to do something like this. According to the DIY manual on

it is possible to get 230v from a car alternator. As for the RPM, I have a hand throttle assembly from a Land Rover that I could use to alter and maintain the RPM of the donor engine.

I'm not familiar with generator technology, but how can such a small engine produce such a useable voltage output when a car engine (with much greater capacity) fails to be able to do this... granted they were never designed to do this, but surely it is possible to get a good supply from such an engine.

Thanks, Bryan.

-- Bryan Lurring snipped-for-privacy@ntlworld.com

1959 Hillman Minx :

Voltage isn't the problem. Your car produces a steady supply of 12V AC, which is changed to DC by the rectifier pack inside the casing. You can get an AC output by connecting to the windings before the rectifier. You can then run this thorough a transformer to get 240V (or anything else that takes your fancy.) The limit to the power is the size of the alternator - a car one will supply around 50A at 12v, so around 600w power. The portable genny has a similar sized unit, same power range but wound differently to provide around 3A at

240v. But your car engine is seriously oversized for the job, as it can produce ITRO 50Kw - 100 times more power. So the alternator can only use a very small percentage of this. The tiny engine on the portable unit is better sized to the task.

But 230 volts isn't all the story unless you're just using it to drive a resistive load like a light or heater. The frequency is important too for many things, and for this it needs to run at the correct and constant speed. This also is the trouble with cheap generators and invertors.

Well, an alternator has a high efficiency, so (near enough) you'll get 700 watts per engine horsepower.

But the alternator has to be designed for the required output as well as having a powerful enough engine driving it. And even the biggest common car alternators are only about 1000 watts.

Hi Bryan, I can certainly appreciate why the challenge of making your own system appeals. Perhaps the "atlantean arts" plans are not what you expect, however ? Note that on their own web site they say: "Car alternators are unsuitable for AC generators" Not meaning to be negative, just be certain that their "plans" will give you what you need before spending money!

- Steve

If you really want to go ahead with this project take a look on machine marts website as they sell alternators without engines, whack a pulley on one of these and away you go, drive it straight off your crank pulley. Your engine will still be way oversized running at the 3000 rpm needed to make

50hz and you would have problem hitting 50 hz as every time you load the engine the revs would drop using the hand throttle. Also imagine the engine is under a moderate load, then you unload it the revs will shoot up. Can be done quite easily, but i'd use something like a honda GX stationary engine as these have governors you can set at 3000 rpm. A bought machine would be close coupled running at 3000rpm, but why not try and find a 13hp honda gx run it at 1500 rpm and gear it to a freestanding alternator running at 3000 rpm using belts and pulleys that way you get to make the thing yourself and it's aguably better than a bought jobby as it runs quieter and will last longer.

Jimbo

In generator technology....which is fairly simple..... Not only do you need to monitor voltage... but frequency also.... you NEED

50 -60hz at all times.....want advice...... go to ebay and search "inverters" ... pick up one that will run 800watts or so and get a descent car battery and this will run drills, grinders, lighting e.t.c for you at the site.... as well as that you can pick up the battery take it home and fully recharge it for less than a cupful of petrol...... if the battery goes down when using it at the site then hook up the inverter to your car while idling and this will back up whatever you need. Just my tupence worth.

Mine is rated at 120 amp (, and is one of the biggest alternators you'll commonly find.

-- James

Fairly obviously, because the primary purpose of the car engine is to move the car. The alternator is only designed to charge the battery and power the relatively small electrical items in the car. A car engine would be hugely inefficient as a generator - try a lawnmower or something like that.