Voltage for single coil?

[zenpi314]

I am at the point of testing my first test coil.

I'm following the design of our hosts concerning rotors and stator. There are 2 X 12 magnets (2x1x0.5) on dual disks. The main difference is that I am in a low wind site, in an urban area, which severely restricts the height of my tower, and that I will be using 2m props instead of 10'.

I made my first test coil purposely with too many windings because it is easier to take some off than to add some.

Here are the results:

Volts versus RPM

3. 1  109.3
   
3. 3  117.7
   
3. 4  118
   
3. 7  130.5
   
4. 3  152.3
   
4. 8  165.1
   
5. 1  177.3
   
   

The coil was 75 windings of #14

Now here is my question. With a 2m prop is it reasonable to aim for a cut in speed (14.5 volts) at 160 RPM? Or is that too low? Will I stall when the battery kicks in?

I would like to keep the rpm's down to keep it save. I also want to furl somewhat early even though I would not harvest the power out of the higher winds. Just to keep it save.

Another question is that according to my calculations I should get about 2.2 volts at target RPM out of a single coil in order to achieve cut-in at target RPM (160). Is that correct?

That is assuming 15.9 volts (14.5 + 1.4 for diodes).

Last question is this. Interpolation of my test results gives me 4.6 volts at 160RPM out of my test coil. In order to get 2.2 volts I need to drop from 75 windings to about 36 windings. (0.0613 volts per winding) Should I stay with single strand #14, or should I go to double strand #14? Again, I don't plan to run extremely high Amps through the alternator. When a Hurricane is approaching (Florida), I will lower the turbine.

Sorry for all the questions, but I'm getting excited about finishing up the alternator.

Hopefully I provided all the info needed to make sense of it all.

Clear skies,

Arno

(potpower.com)

[Flux]

with that magnet set up I think you will stall badly with a 2M prop with a cut in as low as 160 rpm. Even at 2.4m you may reach stall with that cut in and those magnets.

I realise you are aiming for low wind speed , but I still think you are aiming too slow. There may not actually be any useful energy in the low winds of an urban site, even if the wind seems to be there.

I would not aim lower than 180 rpm, you could always increase the gap if even that proved too slow.

So I think you may be ok at aiming for 2.2v per coil at 180 rpm. Your present winding is slow ( very slow) even for 24v.

I think you will be looking at nearer 30 turns per coil and you might as well use the 2 in hand #14 as you obviously have plenty of room. The alternator should be bomb proof for that prop size and should stall hard. It will be slow and completely safe and nice and quiet. You can use cheap leads for the line as you will need to add some resistance. If the cable run is short you may even need to add a resistor in the dc line, but it is far better to make heat there than in your windings.

If you don't get much in the way of strong winds you may be happy to leave it pretty well stalled and not have to worry much about furling. If you get better wind than you expect then it will pay to add enough resistance to get it out of stall and get far more out of it, but then you will need to make sure you can furl safely to keep the noise down for the urban area. I should use 4" offset and don't make the tail weigh a ton.

Flux

[zenpi314]

Thanks Flux,

As always, your comments are very helpful. Thank you.

I will go for 180 RPM and most likely 2 in hand #14.

If single strand gives me cut-in voltage with, for example, 30 turns, do I also need 30 turn with 2 strands to reach that voltage, or do I use less? In other words, does it only influence the amount of amps that can flow through, or does it also influence the voltage?

I was planning on making the furling system that our hosts are using (if my welding abilities allow me). With or without stall, it can't hurt to have furling available, I guess.

Thanks again for sharing your knowledge. It will definitely spare me from winding a couple of wasted coils.

[hiker]

go with the same amount of turns--the 2 in hand will give you more amps..

[zenpi314]

Got it!

Hopefully I'll have a chance to try it tomorrow.

Thanks,

Arno