Newbie Questions

[Derick Johnson]

I am making a DIY V.A.W.T., and being a beginner to electricity, I have a lot of questions, so bear with me.

The plan is this: to take a 3-phase, 208V, 1.5A, 3450 rpm, 60 Hz motor and spin it with a home made wind catcher attached to the top of my shop. The High Desert of Oregon has plenty of wind, but the air is a little dirty due to a couple of Juniper trees on either side of the shop, so its going to have to go up on a pole. The wild 3-phase AC will run from the generator to the control station, which is right next to the shop service panel and soon-to-be net meter.

If watts is just V x A, does that mean that this motor will kick out 312 watts max as an alternator?

How do I know which rectifier to buy?

I want to add more wind turbines and solar panels in the near future. How do I know which inverter to buy?

Any help is appreciated!

[Rob Beckers]

Hi Derick,

Welcome to the forums!

The motor you have, is this a permanent magnet motor? Usually those would be servo motors. Since you mention 208V 3-phase 60Hz it sounds like you have a regular induction motor; those can be used as a generator but it's not straight forward (you'd have it auto-synchronize to the grid and feed back, no rectifier involved).

If you do indeed have a PM alternator that can kick out wild AC, this would then go into a 3-phase rectifier. For the rectifier diodes all that counts is the maximum current and Voltage. Since wind turbines can overspin and the Voltage go up high it's good to look for diodes that can handle a higher Voltage than needed. Also keep in mind that 208V is the RMS value, peak-Voltage is 1.4x higher. It's easy to find either ready-made bridge rectifiers or diodes that handle 800 or 1000 Volt, those would be a good choice. The current is determined by the maximum your alternator can handle, plus a safety factor. If yours is just 1.5 Amp maximum then 10 Amp diodes should be fine (or anything with a higher rating).

Watt equals Volt x Amp x Power-Factor. With the power factor anything between 0 and 1. So only if the motor/alternator has a decent power factor would Wattage be around 300 Watt.

I'm a bit worried about the rated RPM of 3450. That would make it hard to use as a wind generator, where RPMs are MUCH lower, or you need gearing of some kind.

Let us know how it goes!

-RoB-

[Derick Johnson]

Hey Rob!

YOUR KNOWLEDGE IS GREATLY APPRECIATED!.

I think that you are right about my motor being an induction motor. There is some literature on it that says "starting type: squirrel cage induction". So, moving forward.

Would it make my life a lot easier to buy a PMA?

Which type of motor would be more efficient if the wind turbine was a long distance from the meter, say 100'?

If I did decide to use this induction motor, would I need a special type of grid-tie inverter for the auto-synch/feedback process?

As far as the RPM's go, my plan was to put a small chain drive running from the turbine shaft to the alternator shaft. It would be easy to play with the speeds, in theory at least. If I didn't want to mess with all that (which I do), what would be the best RPM rating for a VAWT in your opinion?

a million thanks
-Derick J

[Rob Beckers]

Derick, it's possible to use an induction motor to feed back to the grid. It does not require an inverter in fact, you just feed back 3-phase directly. What happens is that the grid will "motor" the turbine up to speed, and the wind will then make it run ever so slightly faster, which will cause the current to reverse and feed back to the grid.

It will of course be utterly illegal...

-RoB-

[Derick Johnson]

Hey Rob, those days are behind me. I went back to the drawing board so I can keep it LEGAL.

Looking at a couple of different PMA's to buy. Do you sell any? I didn't see any your site. If not, could you recommend a brand? The one from Missouri Wind and Solar seems like a likely candidate. Or maybe WindGenKits?