Results improving, but is it enough?

[mettleramiel]

Well, to continue from my last posting http://www.fieldlines.com/story/2006/11/11/215814/47

I have added a second steel rotor to my genny as per DanB's suggestion, however, spinning it by hand, I can't get the voltage over 8. So, I'm left to wonder, will I be able to charge a battery in anything less than a gale force wind? I know that the wind will turn my genny faster than I can, but DanB surmised that I wouldn't reach cutin until at least 300 rpm. How strong a of wind would I need to get that? If memory serves, it seems that most people around here say that they need somewhere around 10mph to reach cut-in, now I don't have a tach or any other way of testing my rpm output, but will that be enough wind?

Maybe I'm just too pesimistic here. Here's a lovely picture for anyone interested.



It's strange how building a windmill can be mind-boggling, depressing, frusterating, and yet tons of fun all at the same time!

fixed your pic you had some realy wacky code in there.......
Kurt

[Flux]

I am not sure what you are doing but with 60 turns per coil 12 magnets and a second disc to return the flux you should have no trouble reaching 12v at a reasonable speed.

You should easily reach 12v below 200 rpm.

How thick is your stator. The magnets and the second disc should run with a gap of 1.5 mm clearance from the stator so if your stator is 1/2" thick your gap between magnets and disc would be under 3/4". 2 x 1 x 1/2 magnets should easily get you 300mT so with 60 turns you should see 12v dc at somewhere near 180 rpm. You should be able to turn it by hand to about 250 rpm so you should see well over 12V.

How have you connected the coils you should have 3 in series per phase and star connected.

Count how fast you are turning it, let's have some decent details, preferably a picture, it should work.

Flux

[kurt]

when adding pictures upload them to your "my photo uploads" on the right in the box with your nick at the top. and then use the add a photo thingy it is at the bottem for comments and on the right if you are posting a new story.

[mettleramiel]

my gap between the two rotors is about 7/8", so it's a little too big, I suppose. I'll try sanding down some of the resin on the magnet rotor a bit to bring it a little closer. I am turning it at around 200-250 rpms and it's about 6-7 volts. The coils are connected just like you suggest, 3 per series, in star.

[DanB]

is it 6-7 Volts AC your reading there?  Or DC - after the rectifiers?

If the reading is alternating current then you're not too far off the mark perhaps for a 6 or 7' diameter blade.

[mettleramiel]

DC after the rectifiers.

[Flux]

Short the output of the rectifier and turn it. It should be very stiff but smooth, if you can feel it lumpy when turning you have some coils connected wrongly.

I rather feel that your gap is very wide. For that single rotor  with blank disc and the 60 turns (which you say you guessed and may be less) you ideally need to get the magnet within 5/8" of the other disc. Lumps of resin etc just count as air gap.

With those turns and that size wire, if carefully wound you should get into a stator of 1/2" thick including resin, so the whole thing should go into a 5/8 gap including resin on the magnets. You would probably be ok with a 3/4" total gap but with N35 magnets you will be fairly fast.

Unless you have a connection problem the trouble can only be too big a gap or less than your guessed 60 turns. Without exact details of what you have it is difficult to comment.

Ideally with that single rotor construction you would have been better off with a thinner stator ( say 3/8"). If you can't get it below 250 rpm you will need a faster prop or need to make a more suitable stator.

If you keep to a higher speed 6ft prop you could work with over 300 rpm cut in and still cut in below 10 mph but it will be better if you can sort out the speed and if you can get down to 200 rpm you could use a fairly fast 7 ft prop and get more power.

Flux

[mettleramiel]

yes, it must be the airgap as when I short the wires, it is smooth yet stiff. I took a closer look at my magnet rotor and decided that the resin was done quite poorly, so, I scraped all of it off and am going to start over again.