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3 Test Coils for18" Rotor
By mitcamp, Section Wind Posted on Sat Jan 28, 2006 at 02:32:34 AM MST
18

Hi,this is my 3rd post and I,m no pro at this. I have built 2 hugh,s 8 ft and a Hugh,s 4 ft for my camp. They all are performing.
I was admiring Dans 14 foot machine and was going that way with a larger disc as Dan said he would have used a slightly larger disc next time. I checked wondermagnet and they only had 4 big mags on hand at the time.
I then run across a couple post on 18 in. disc with 1*2*.5 mags with 18 coils, 3 phase @ 12 volts and decided I would go with this since I had the smaller mags. I placed my mags at 15 degrees and put paper (trial) coils around my 22 in stator to make sure there was enough room.
I wound 3 coils, #1 85 turns of #15 (I had this one from hugh,s 4 ft. machine) and got 3.2 volts ac @ 60 r.p.m, 0.7 ohms #2 34 turns of #14.5 (2 in hand) and got 1.1 volts ac @ 60 r.p.m 0.8 ohms #3 Someone suggested 12 turns of # 14 (4 in hand) and I got 0.2 volts ac @60 rpm 0.7 ohms These test were done with one coil and both disc on the axle.
How do I go about calculating (lets take #2 coil for instance) the total voltage, for when the 18 coils are on the stator. What voltage must I get from this one coil, in order to get a cut in of 80-120 r.p.m and what can I expect for power from this machine.
Dan, if your reading this post, I will be on the phone sometime next week for information on the availability of them mags you used on the 14 ft machine with 14 in. disc/ 9 coils ,3 phase. I already have that stator cast (24 wraps of #14 4 in hand wired for 12 volts) and hanging on the wall, just waiting for magnets. Thanks to anyone out there that can help me. email me if you like: mitchelllake@yahoo.com
Mitcamp

3 Test Coils for18" Rotor | 18 comments (18 topical)

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#1)
by gator on Fri Jan 27, 2006 at 09:31:07 PM MST

I can't answer your question but am so glad you asked. I too am looking for similar information. We have, on graph paper, with scissors, cut out shapes for coils based on readings and pics from this post. I got my protractor and compass and dominos and the kids, I and the wife occasionally have been drawing out our plan. We just received our Hugh Piggot books and have been reading them. DanB's articles have been a great inspiration as well. We also,finally, figured out an optimal tower sight and based on that we are fixed with a max height of 55 feet (good enough). Now we are leaning towards a 16 inch rotor, 15 coils and 20 of the readily available 2*1*.5 mags from wondermagnet in a 48 volt configuration. The kids cut out paper pretend coils (to my specs of course) in a somewhat wedge shape (to match the 18 deg profile my mags will sit at), I assumed a 1/2 inch diameter of the coiled wire for fitting purposes(I really have no earthly idea what to even start with when winding test coils for this machine). With the mags tops placed out at 16" the bottom corner of one mag to the next is almost an inch. Don't know if this is good or bad but I like the fact that flux has further to go than across to the other stator. Also the paper coils (inside hole is 1" at bottom and about 1 3/8" at top)playing with them looks like a good fit(catching both poles at times for full power). The fun part of this is we used dominos for mags (not nearly as dangerous) and they are exactly 2*1. The kids are showing an interest so as I learn I'm teaching my children the theory by letting them play with this stuff. Of course I will have to buy them little bitty neo mags when I order my 40 1*2's from wondermag. This is a wonderful learning experience and it's fun! I do have another question that I couldn't answer for my kids, I understand electricity (electrons getting bumped from one molecule to another I think) but what still baffles me is magnets! Is flux electrons or what? What is it that is perpetually moving from one pole to the opposite? Does it burn out? What makes it stick to steel? How does flux bump electrons in the copper coil? I certainly would better understand how to educate my kids on this if I knew.

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#4)
by gator on Sat Jan 28, 2006 at 05:57:16 AM MST

After reading about magnetism and electricity on a hyper physics web site I am starting to see that theory is best left to the intelect...not me. I'll just build my machine based on you guys advice.

[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#5)
by Flux on Sat Jan 28, 2006 at 06:20:30 AM MST

You are very wise and many could benefit from your advice.

It's good to have a basic understanding of what you are doing, but to make working things it is not necessary to understand things at the electron level.

When Gilbert, Faraday and all taught us to use these things they had no idea of what the lines of force were but they gave us a concept that was good enough for every day use. Others later explained it all and made it very scientific, then someone invented Quantum theory and threw it all into chaos.

It is far more useful to understand the simple basics of circuits, magnetic and electric and know how to use them than to have intimate knowledge of fundamental theory and no idea of how to use it to make useful things.

You are teaching your kids good basics, they may later go on to learn things at a more fundamental level if it interests them but even if they don't they will have a head start on the rest.
Flux

[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#2)
by willib on Fri Jan 27, 2006 at 09:51:34 PM MST

" How do I go about calculating (lets take #2 coil for instance) the total voltage, for when the 18 coils are on the stator. What voltage must I get from this one coil, in order to get a cut in of 80-120 r.p.m"

First off double check the resistance you got for the coils.it's way too high.!
try this site , take the ohms per 1000 feet and divide it by 1000 to get ohms pre foot then multiply that number by the feet per coil.this should get you closer to the real resistance..
http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/wirega.html

as for the total voltage ouput of 18 of the #2 coil @ 60 RPM
is the 1.1v reading RMS?
assuming it is , then.
1.1Vac * 6 coils per phase =6.6 V per phase
6.6 *squareroot(3) = 11.43 V three phase @ 60RPM.
this is close to cutin so a little more RPM should start charging your battery..

Carpe Ventum (seize the wind)

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#3)
by Flux on Sat Jan 28, 2006 at 01:03:47 AM MST

The rectified dc voltage will be 1.4 times the 11.43 ac line voltage. this will be about 16v. Less rectifier drop will be about 14.5v and that means that you will be above cut in speed at that point.

Your cut in for a nominal 12v will be about 50 rpm.

Flux

[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#6)
by willib on Sat Jan 28, 2006 at 03:33:34 PM MST

Flux ,we were both wrong.
http://www.otherpower.com/images/scimages/2965/Picture_103.jpg

V(RMS)* sqrt(2)= Vpeak

and V(average or dc value)for a full wave bridge rectifier =2*V(peak)* sqrt(2)/Pi

so for the 1.1v outout that the origional poster got , if it was V(peak)..

V(dc)=2*1.1*sqrt(2)/Pi=0.990Vdc

0.990*6*sqrt(3)=10.29Vdc

so we were both wrong.
it gets worse if the 1.1V reading was allready V(RMS), because it comes to 6.62V(dc)

Carpe Ventum (seize the wind)
[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#9)
by Flux on Sun Jan 29, 2006 at 01:49:12 AM MST

Willib

He said he measured 1.1v ac. With any ac meter on a true sine wave it will be rms.

For the waveform he is likely to have got it will be near enough even if it is a cheap meter reading mean and scaled to read rms, which the cheap ones are.

You correctly said that with 6 coils this comes to 6.6v and is phase voltage.

With star connection the line voltage is as you originally stated root 3 x phase voltage. That is 11.4 v still rms ac.

When rectified with a 3 phase rectifier conduction into the battery will take place when the peak of the dc exceeds the battery voltage. This is root 2 x the ac rms line volts and is 16.1 v ( neglecting diode drop)

Without the battery the dc output from a 3 phase bridge is fractionally lower than the peak line voltage, due to a small 6 pulse ripple, but for our needs you can take it as being the same thing (it's almost smooth dc).

Flux

[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#7)
by mitcamp on Sat Jan 28, 2006 at 07:59:57 PM MST

I checked my #2 test coil (34 turns, 14.5 ga. wire, (2 wires in hand) and my $30.00 digital multimeter on the 200 setting says 00.7 ohms. I checked the table on the site you provided and # 14.5 has a resistance of 0.002855 per ft multiplied by my 24 feet in the coil is equal to 0.06852 ohms.
When I connect 6 of these coils together (finish to start) in the stator will the resistance be:0.06852 multiplied by 6 and a total of 0.41112 ohms
My 1.1v ac measurement was also taken on the same $30.00 multimeter. It has 2 settings 700 and 200 on ac side and is probably (peak) voltage and not RMS voltage.
If you think this experiment is going to be a dud, would I be wise to use my 2 18 in rotor disc and 48 magnets on a Hugh Piggot multi-phase and use 20 coils (similar to the 8 ft with 10 coils,5 phase)
Your probably going to say I,d be better off if I built 2 dual 8 footers and put my magnets and copper wire to better use. Thanks anyway. Mitcamp

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#8)
by willib on Sat Jan 28, 2006 at 10:46:34 PM MST

What does the meter say when you touch the leads tip to tip?

But you have that coil wound with two in hand ? right? or no?
If that is two 12 feet lengths in parallel then the resistance is 0.01713 per coil,
and the per phase resistance 0.10278 for six coils .

Carpe Ventum (seize the wind)
[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#10)
by Flux on Sun Jan 29, 2006 at 02:18:00 AM MST

mitcamp

You are doing fine. your cheepo meter will actually measure mean volts but it will be scaled to give the answer as if it was rms on a sine wave. there may be a small waveform error but that will not be significant. Reading low voltages is more likely to cause you trouble so I would ignore the 12 turn coil results.

With your 34 turns I predicted a cut in of 50 rpm from your figures. From calculation and making a guess at your flux density I got 40 rpm so your measurements are in the right order.

You would need about 17 turns for your intended cut in and you should manage 4 in hand of those wires (was it #14.5?)

If you are happy to have 10 rectifiers on the machine you could do it Hugh's 5 phase way with 20 coils. This would give more convenient wire sizes, but it wouldn't be practical to have the rectifiers at ground level.

This is a big machine for 12v and is going to be awkward whichever way you do it.

It is absolutely impossible to measure the resistance of those coils on the resistance range of any multimeter so ignore your resistance readings.

On a discussion board like this it is inevitable that you will find conflicting advice, all given in good faith. You have to form your own opinion and go for which you think you trust.

Go back and read all that DanB has written about using test coils to predict cut in speed and about this size of machine in general, it should work out ok but you will have an awkward winding and more losses at 12v.
Flux

[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#11)
by willib on Sun Jan 29, 2006 at 09:38:02 AM MST

flux wrote"It is absolutely impossible to measure the resistance of those coils on the resistance range of any multimeter so ignore your resistance readings."

That is what i was getting at, because if he tested his meter by touching the tips together , he would probably get the same reading as testing the coil..
But i suppose i should have said that..

Carpe Ventum (seize the wind)
[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#12)
by Flux on Sun Jan 29, 2006 at 10:22:58 AM MST

Yes I was agreeing with you, you said that he could calculate the value nearer than he could measure it. I was being a bit more blunt and saying not to try to measure it with a meter.

I agree about shorting the leads but I don't want people to get the impression that subtracting the zeroed lead reading will make the result satisfactory.
Flux

[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#13)
by mitcamp on Sun Jan 29, 2006 at 11:55:22 AM MST

Hi Willibur, Q: What does the meter say when you touch the leads tip to tip?
A: when I touch the leads tip to tip I got 00.6 I see why flux says to ignore the restiance of the coils.
Q:But you have that coil wound with two in hand ? right? or no?
If that is two 12 feet lengths in parallel then the resistance is 0.01713 per coil
A:Yes, I have the coil wound with 2 in hand, and it is two 24 feet lengths in parallel.

Hi Flux, (you say #1) With your 34 turns I predicted a cut in of 50 rpm from your figures. From calculation and making a guess at your flux density I got 40 rpm so your measurements are in the right order.

(you say #2) You would need about 17 turns for your intended cut in and you should manage 4 in hand of those wires (was it #14.5?)

Yes it is #14.5 gauge wire.

My Question regarding the above (you say # 1) Is this 40 r.p.m to low a cut-in, keeping in mind that this coil 34 turns and 2 wires in hand.

In (you say #2) If I were to use 17 turns,(4 in hand), is the cut-in the only thing that would change.
Thanks again Mitcamp

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#14)
by Flux on Sun Jan 29, 2006 at 12:29:22 PM MST

Yes I think a cut in of 40 rpm is far too slow for a 14' prop. you need to keep slow enough to capture low winds but there is a lot to loose by going too slow. There is no useful energy in winds below 7 mph and if you try to get some you will wreck the performance in the higher winds and loose all ways.

Second question, no it is not just the cut in speed that will change, you will have 1/4 of the resistance by using half the turns with twice the cross section. This drastic drop in resistance will give you the loading to hold the speed down and also allow a decent output without frying the stator.

Flux

[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#15)
by mitcamp on Sun Jan 29, 2006 at 07:58:00 PM MST

Flux, I wound 12 of the 18 coils today. Went with the 17 turns of 14.5 ga. wire, 4 in hand. I,ll be back at it tomorrow to finish the 6 remaining coils. I think I,ve got the wiring of the coils in my head. I may draw a freehand diagram and run it past you before I cast the stator, if you dont mind. I appreciate the help,that you and willibur have been with this project. I have named this project "Renegade" as it has been way over my head when it comes to the coil calculations. Is it alright to post a picture now and then on my progress, stator, frame, rotors. Do I attach them to this post. Thanks Mitcamp

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#16)
by ghurd on Sun Jan 29, 2006 at 08:22:04 PM MST

http://www.fieldlines.com/story/2003/9/11/84741/6758

Ghurd.info
[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#17)
by willib on Mon Jan 30, 2006 at 07:40:02 PM MST

yes please do , i would like to see your work so far

Carpe Ventum (seize the wind)
[ Parent ]

Re: 3 Test Coils for18" Rotor (3.00 / 0) (#18)
by mitcamp on Tue Jan 31, 2006 at 08:51:15 AM MST

Hi Wilbur and Flux
Take a look in my files. I am wiring my 18 coils together over the next few days. Will post pictures of my work on this generator over the next month. Including hoisting it with the help of my jin-pole to the top of my 65 ft tower(my towers in files) Will post a few pictures of other wind machines that I built for my family, friends,and local (off grid)cottage owners.
Mitcamp

3 Test Coils for18" Rotor | 18 comments (18 topical)

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