OT : generating 240v AC...?

Try the boat supplies people. This is quite a standard trick. What surprised me is that you don't have to have constant revs for 50Hz.

nigelH

It will be very difficult to do, unless he has precise control of wheel speed, unless he is NOT driving any kind of sensitive load, like motors in fridges etc.

Real hydro stations can control the speed of the turbines accurately by adjusting the pitch of the turbine blades dynamically, and by adjusting the water flow rate.

The best way for small hydro is to use gear the wheel up to a sensible RPM, like 1500 or so, use a conventional alternator, rectify it, and stuff it onto a battery bank then invert it.

Alternatively, he could have a varispeed gearbox - the kind that the Hillman Imp achieved with belts, and servo the input speed to his alternator, by measuring output frequency. Do-able, interesting, but probably more expensive than a system built like I described.

Steve

Its an undershot wheel too. Can you fill in the numbers on this site at all ?

Steve

On or around Fri, 25 Jan 2008 12:13:19 -0000, "Nigel Hewitt" enlightened us thusly:

buggered if I see how, with any normal sort of alternator.

You also have to look a the power output of the wheel, and the cost of a big alternator - a mate of mine has a 13KVA Lister to run his miles-from-anywhere place. The other day the lights went dim, and he went out to the shed to find magic smoke escaping from the alternator. It's going to cost the thick end of a grand to replace said alternator.

My plan involves surplus car parts, batteries, and inverters to run the low-power loads such as lighting, fridges, freezers and computers. I've no intention in the short term of trying to run the 2HP-ish motors in the machine tools from microgeneration.

Imp? Daf?

Are you custom-making a microCHD or getting a commercial system? I'm thinking of redoing the heating for my house (provided I get enough work to keep up the mortgage payments) and might go in for a pair of MicroCHD units to do heating and electrickery.

How is he going to regulate the rotational speed of the generator as the load changes to maintain 50Hz within acceptable limits? Better than +/-

10% you'll probably get away with but real mains is more like 1% short term and bang on in the long term (24hrs).

Has he done any calculations on the power available from the wheel? It's small and undershot, neither of which are conducive for maximum efficiency or power. I'd be surprised if you could get more than 10W from it, if that.

If the wheel was pitchshot(*1) and 1m radius I think the maximum energy available with a bucket holding 5l is 5 x 9.8 x 1 = 49 joules. 1J/s is 1W so if the wheel was rotating at 240rpm you'd have a shade under 50W potentiality available but take losses into account and you might be able to get 25W from the generator...

That is with four 5l buckets. Make it 16 buckets and I think you'll have about 100W from the generator but you need 20l/sec (*2) of water which is quite a lot of water...

If he has that sort of flow available and a decent head say 10m then he could be looking at over a kilo watt of electrical power given a proper pelton wheel turbine. This would be a far better approach and would actually produce something. Have the undershot wheel driving a bicycle generator and some fairy lights...

(*1) The most efficient waterwheel at about 90%, undershot is about 20%.

(*2) 1200l/min or 1.2 cubic m/min, think of emptying one of those large cubic metal caged containers in 50 seconds.

Simple AC generators rely on the input rotational force being of the right speed, so anything he tries is going to be complicated, in things like aircraft they use a hydraulic clutch like the torque converter in an automatic car, with which they control slippage to keep the input to the generator constant. Not very efficient. In big wind turbines they seem to use a DC generator and a DC to AC circuit, plus turbine rotational speed control through turbine pitch.

So if he solves it, might be an idea to patent it ;-)

I may be wrong about this as I can't find one now.

What I remember was basically a DC generator but the 'input' coils were driven from a small inverter so you got fixed frequency AC out. You used them on your main engines and they gave reasonably consistant output as you changed speed although they had a habbit of stalling things on idle if the load was too big.

Maybe they've been discontiued as a bad idea. Sorry an all.

nigelH

All the (small) boats I have been on have nice big leisure batteries and either run everything off DC or have an invertor for those things that insist on mains.

You generate DC and then invert it to AC.

That's what I keep saying, but he is adamant that he wants to create

240v AC. I don't know the ins and outs, but the replies have confirmed what I thought - that you need a constant speed to generate AC properly, which he ain't going to achieve without some clever trickery.

Initially he wants to connect it to a pump circulating water from two solar panels around the swimming pool, and to heat the hot water supply in the house. He doesn't want to use it to replace the general domestic supply.

I think the simple answer is that it is not going to be simple! Or at least, it is going to be expensive!

Cheers,

Matt

I like that use idea an alternator to generate DC storage batteries to ensure a consistant supply and an inverter for the conversion to AC quick and dirty solution tho' I would tend to attach a driven pump to the setup for moving the water about rather than convert to DC electrickery to AC and back to flowing water depends really how far the pool is from the mill./house

Derek

That's the one ! One of my Cnc machines has exactly the same drive idea on the spindle.

Steve

In the setup in the video he just isn't going to have very much power available. Maybe enough to run a small windscreen washer type pump which is all you need to circulate water through solar panels. But you only want to do that when there is enough solar energy about to warm the water. Do it when there isn't and you'll cool your swimming pool rather than heat it.

As for useful heat for the DHW, oh dear... And why does it have to mains? You can get 12v heating elements from car kettles or the like. But note they run at about 100W and take 15 minutes to boil a mug full of water...

Forward to go forward, back to go back. Some were raced with very little success IIRC.

Rover 25 CVT transmission!

My mate's subaru justy 4wd has metal belt variomatic and a magnetic particle clutch, seems to work well.

AJH

It's simple enough, just not legal without permissions and certified interconnects. Choose a 3ph induction motor much bigger that the wheel can output, connect it with pulleys such that the motor never falls below its rated speed, plug in to mains, the motor load will synchronise the wheel.

A chap on the business.agriculture group has been describing his water turbine which is a pelton wheel running at ~15kW and 50Hz and some of the problems are unexpected. Mind his drop is 60 metres, it's amazing how little you get out of a low head flow.

AJH

I agree, without spilling water I cannot see how to easily maintain wheel speed.

I'd bet a permanent magnet generator would be far more efficient and the cogging effect won't be as much a problem as with a wind turbine, have a look at the homemade designs based on a Volvo front disc and hub, given enough magnets it would work with no gearing.