DC to 240AC !!???

[billyandkim]

I am new to this scene and have got a daft questions.

We are hopeing to put a turbine in our stream.  Why can you not get the turbine to make 240AC rather than 12/48DV?  I am thinking along the lines of a petrol generator?
What I want to do is buy a petrol geny and dismatle it and rebuild it so the drive is powered by a wheel turned by water, with may be a bit of gearing in between, is it possible?

Regards Amanda

[AndySV1K]

I dont see why not, although the electrical process will be the same.

The generator part will more than likely generate a lower voltage than mains which will then be rectified to DC to then be controlled and inverted to match mains electricity.

The idea of power your generator from a water wheel is sound though as long as you have enough water flow and pressure to turn the generator, this you may only find out by trial and hopefully not, error.

Andy.

[Alan]

Hello Amanda

You do not say what you will do with the 240 V.A.C. generated from the alternator driven from your water wheel , you will not be able to directly connect this voltage to the supply grid system. The energy can be used to feed the grid system by using a grid connect inverter if required.  If you intend to use the voltage direct for use in a water heating element say in your water tank the voltage fluctuation would not be a problem. If you use the available energy in a lighting system the voltage fluctuation caused by the flow changing across the wheel will be a problem. In a hydro power station they  control the volume of water that feeds the turbine depending on the load they want to produce. That way they can maintain a constant out put from the turbine, you will not easily be able to maintain a constant flow of water to your wheel.

Some petrol generators drive a shaft connected alternator that produces a variable voltage A.C. which is then rectified to D.C.  The D.C. is then fed to a inverter that produces 230 volts A.C. ( this can not be connected to your grid system )

Some petrol generators drive an alternator direct to produce 230 V.A.C. ( this can not be connected to your grid system )

More info required as to what you intend to do with the energy produced.

Regards

Alan

[chaso]

Alan, I have just got some info from the Navitron FAQ

WATER

What is the voltage/frequency output?
220v 50Hz single phase a.c.

Why not low voltage DC?
Because the higher voltage allows you to site the water turbine further away from the house without incurring heavy powerline losses. Also, it allows you to use these turbines directly with household wiring, without the expense and efficiency losses provided by an inverter system. It is of course necessary to ensure that the incoming mains electricity and the turbine-produced electric are kept separate using a changeover switch.

What about load variations?
All of our turbines come with an integral dump load connected to a voltage stabiliser circuit. Some manufacturers supply these at additional costs of hundreds of pounds. The voltage stabiliser ensures that a constant maximum load is placed on the turbine at all times. The circuitry reacts to changes in applied load, and feeds any excess power into the dump load, thus maintaining voltage and frequency.

[PEMTEK]

Using an alternator from a generator is not an ideal thing to do as it will not allow mains connection without careful synchronising with the mains AND a high quality AVR with a droop kits to enable backfeeding.

A diesel engine generator will typically have a 4 pole alternator that will give 50Hz at 1500rpm
A petrol engine generator will typically have a 2 pole alternator that will give 50Hz at 3000rpm

If your frequency (alternator RPM) varies by much it wont help anything connected to it especially on a cheap alternator that has a poor voltage control system.

A better bet if you are considering backfeeding or supplementing your suppy is if you can somehow manage 1500rpm from your turbine and use a 4 pole induction motor. You can turn it on when there is sufficient water flow rate to make the motor go faster than 1500rpm. This by its very nature will ganerate electricity in synch with the supply. As long as the force of the water is not greater than the electrical rating of the motor things will happily generate. (this can be measured by measuring the current output of the motor)
This however creates several legal and safety issues if not dealt with correctly.

I posted under the chp subject in the diesel engined section about induction motor generation also..