Volts per Coil

[wind pirate]

I just wound a single coil to see if I can increase the output of my gennie. The setup is as follows:

Dual rotor setup 14" rotors

12. mags per rotor - Round 1.25 x 1/2"
    
9. coils - 3 phase - Star
   
   

Current stator 85 turns #19 wire - 1/2" thick

24. VDC @ 120 RPM (estimated by counting vs time)
    
8. ft swept area - tsr 5
   
   

Looking to increase the output

Milled the rotors to decrease the airgap - had approx 1/8 of resin over the mags, machined that off. Hit a couple of mags in the process - saw sparks but hope there is no damage.

Wound a single coil, #15 two in hand, 40 turns - at 120 RPM got 1.5 VAC

Wound another coil, #15 single, 80 turns - at 120 RPM 2.6 VAC

If I figure correctly, #15 single - I have 2.6 VAC X 3 = 7.8 VAC X 1.73 = 13.5 VAC

I need 24 V so as I see it I need 5 VAC per coil to get there. 5 V X 3 = 15 x 1.73 = 26 V.

My question is - Am I figuring this right?

If I need to go to 100 turns #15 to get the 5V cutin, I don't have room on the stator. I may be nuts trying to get more than I can get, but as always, need more power!!

Maybe I just need to leave things as they are and build another one bigger......

Thanks for your thoughts and input.

WP

[Flux]

Do you mean 8ft diameter tsr 5?

I suspect your cut in is low at present for 8ft even with your lower tsr of 5.

I certainly wouldn't make any attempt to lower the cut in speed.

Volts does not mean power, this seems a common mistake. More turns as you have found out means thinner wire and that adds resistance and reduces your potential power. The low cut in also means that you stall early and also loose out on the power available from the prop.

For 24v cut in , assume 26v to allow a bit for diode loss.

Ac line voltage is 26/1.4  = 18.6v

Phase volts   18.6/1.73  = 10.7v   volts per coil is 10.7/3  = 3.6vac.

That is at cut in speed. For your low tsr prop I would choose to cut in about 150 rpm, normally I would use 180-200 rpm for 8ft.

Far easier to work from your existing stator, if you have 24 v cut in at 120 then for 150 rpm you would need 68 turns with the original air gap. If you have reduced it you may get away with a few less turns. The reduction in turns will likely let you go up a wire size.

If the original stator is up and flying, I think you may be stalling. Try it into 30 or 36v if you have a spare battery. If it is livelier and produces more power ( not amps) then you will do better to increase the air gap or add some resistance in the line.  If this is the case you will be better off with fewer turns of thicker wire.

If you don't get any improvement then the cure is a bigger machine, that's the only real way for more power in the same wind speed.

Flux

[Flux]

I have had another look at this, I was tired last night.

Your ac figures for the test coil don't tie very well with your dc ones  from the complete stator.

It is not easy measuring low voltage and low frequency ac possibly with odd waveforms.

Working from your stator is likely to be more accurate.

From my figures you should have been able to use much thicker than #19 for the 85 turns. You seem to have confirmed this by managing to get 80 turns of #15 in the test coil.

Check for stall as I suggested above, I think you are stalled badly. If it works much better into 36v then I would wind the coils with 60 turns of #15 or possibly 2 in hand #19. You may be able to use thicker than that if you have the option.

You should be able to get down to nearly 1/4 of the present resistance.

Flux

[wind pirate]

Thanks Flux

"Your ac figures for the test coil don't tie very well with your dc ones  from the complete stator."

I am thinking you are correct - measuring DC from the stator is probably more accurate than measuring a single coil. I'm leaning towards trying 85 turns #15 single and see what that gets me. I may also go to 10" blades with tsr 8.

Thanks for the help

WP