Wednesday, June 3, 2009

AC Grid Tie update

Well, good news. I successfully pumped 42 watts into the grid last night. As you can see, I'm just testing using a DC motor to drive an AC induction motor from a clothes dryer. The DC motor is on the left. It is geared at 3.5 to 1.5 or 2.33:1. Just a word about pulleys. I know that the pulley on the right is 1 inch, but the outside of the belt is the load carrying part. So, measure from the center of the pulley to the outer edge of the belt and then double.
Below, you can see a close up of the AC motor.
I can't find any numbers on it but I believe it is a 1/4 hp. But something to remember about dryer motors with centrifugal switches is that they have two sets of windings. They both start in parallel and once the speed is up to a certain point, then just one winding is used to maintain speed. So, a 1/4 hp motor is really closer to 1/2 hp when both windings are being used. But you can't run them both together once it gets up to speed due to the start winding being out of phase with the run winding. It will work but sound funny and be very inefficient. And if this were used in a windmill, then the wind would be a natural cooling. In the summer time that would mean a doubling of possible power and in the winter about 3 times the power can be expected. So, if you bypass the centrifugal switch and connect to just the run windings then you can expect .5 hp up to 3/4 hp as a max. So, 375 watts in the summer up to about 550 watts in the winter.

I also played around with using the centrifugal switch to connect to the grid once the speed was up. But just like I thought, it would stay connected even after the DC motor was turned off. So, I figure a simple trigger mechanism that triggers on at a certain windspeed and shuts off again once the wind slows down again.

Later today or tonight I'll measure amps and voltage going into the DC motor and compare the input power to the AC grid tie power to determine efficiency of this setup.

Also, I don't like using the V belt on that little tiny pulley on the AC motor. It means that the tension on the belt has to be quite high to keep it from slipping at the higher wattage. It also means the belt heats up quite a bit more due to the constant extreme bending around that tight radius. If I used a 3 inch pulley on the AC motor and used a 7 foot blade set turning a big homemade plywood pulley, it would have to be about 18 inches to start grid feeding at about 10 mph wind.


1 comment:

  1. Well, instead of using a DC motor and different sized pulleys to couple with an AC motor to be used as a generator for gird-tied arrangement, the better option in my opinion can be to use two AC motors. The first one to be driven by an inverter where by varying the frequency of the ac current from the invertor you can control the speed of the AC motor and control how much power you want to deliver.
    Just a suggestion, I have not tried it myself.

    Rafat M Jamal, Karachi Pakistan.