Renewable Energy Questions/Discussion > Wind and Hydro

And so it begins

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ksouers:
Look what the Big Brown Truck brought today!



Not knowing where to start or what to do I ordered 40 of these little magnets. They are 1x1/2x1/4 inch and intended for a small alternator. I’m not expecting much power, just getting some experience in building a working alternator. Gosh these little things are expensive! And powerful! I had one stack I was working with trying to separate one of the magnets. I set the stack down on the bench and it pulled one of the change gears for the lathe from almost a foot away! I’m going to have to make sure my work area is very clear of any iron when working with these things.

I hope you guys are up for some stupid newbie questions cause I’ll have a bunch. I don’t even know where to begin.

First I have a lousy site for wind. Most days are 3 – 15 MPH except in the dead of summer when it’s dead calm for July and August. I have lots of trees and there is a subdivision right behind me. I have a half acre but it’s covered with trees, large old maples. The only real place I have for the tower is mounting on the garage, it’s detached so I’m not worried about the noise but I know it’s going to be turbulent. As if the trees weren’t bad enough, all the buildings are going to mess up the air flow. I have to keep the tower low so the fall zone stays within my property boundries (county ordinance).

I don’t know what kind of power to expect out of these little magnets but I’ll be happy with anything that works. I hope to get about 10 watts out of it in a good breeze.

The design parameters I’ve set out to achieve are:

3 foot rotor
Cut-in about 150-200 rpm
At least 2 amps and 15 volts but I’ll settle for .5 amps.
5-6 inch magnet rotor with 8 or 12 magnets, 6 or 9 coils.
Figuring on a 3/8 inch air gap.

What do you think? Is this do-able with these little magnets?

Thanks,
Kevin

dang:
First off - magnets are new to our five monkey senses, there is no instinct to follow with them. GET THEM PROTECTED, back in the delivery box and up on a high metal-free shelf. If you must, find one that is already scratched/chipped/dented to play with and leave the others ALONE until the hour & minute you're going to be placing them... in a clean room w/o other metal items.

My shipment of magnets? I was flipping one around and trying to gauge the strength etc. and was disappointed... then went back to the pile of others and watched the whole stack go frictionless away from my hand enough it almost leapt to an ugly situation.  If you've ever used a metal grinder, cut metal or cleaned up rusted iron in your shop the particles will find their way to the magnets. Duct-tape adhesive is about the only way to clean it off once that happens. Littler ones have given me blisters, larger ones like you have can break bones.

EDIT: I see they are smaller than I thought, not quite bone-smasher's but when they attack in packs.... Same rules apply, call it good practice for larger ones  ::)

WooferHound:
That's a Lot of magnet
 

Watt:
Where is Sir Flux when you need him?  :(

I come up with just over 8.25" for rotor diameter if you use all magnets, 20 per rotor for two rotors and have .5" spacings at the closer points.  Just over 5.75" diameter with 12 magnets.  I guess you are going to go three phase with this turbine as you have indicated 3 coils for 4 magnets. 

I think I'd decide on the type of bearings, spindle and hub, get the rotors built and get on to a test coil.  I seem to think more magnets is better so, all you have to do is decide on magnet count before you can really start the build. 

Anyway, keep us posted with your progress.   8)

Janne:
Hi,

My rule of thumb on designing alternators has been, that when you double the turbine diameter it will take 8 times the amount of magnet to make as stiff generator. That is because the power output is quadrupled, while speed is halved.

If we use that rule of thumb, and compare it to the early 10' machines, which had 24 pcs of 2*1*0.5inch magnets, your magnet lot comes in about 1/5 of that. Cube root of 1/5 = 0.58, so your magnet lot should be able to support a 5 footer, mayby even 6 if you'd be pushing it a little.

There are of course other factors that play, like how efficiently the magnets are being used, are the (turbine)rotors going to be the same performance etc.. It's important to compare it to something, that makes good use of magnets and also focus on your own design into doing the same. In the end it will only give you an estimate with all the variables in play, but these "rules of thumb" have worked quite ok for me.

The first you'll need to do is to figure out suitable size of magnet rotors. It would be best if you can size the rotors so, that there is space for one magnet in between of each magnets, but a bit smaller gap(like Watt suggested) than that is ok too. That will get you most out of your magnets.

When your magnet rotors are complete, you will then need to make the final design about the rotor size, as suitable cut-in voltage depends on the rotor size. Once you get there. This includes wounding a test coil, and then calculating the number of turns based on the required cut in voltage, and selecting a wire that you can fit into the stator with the required amount of turns.

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