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coil testing
By JB, Section Homebrewed Electricity Posted on Fri Mar 26, 2004 at 05:28:29 PM MST
can someone check my math

Can somepeople help me out here with my math. I wound a new coil 40 turns of 14 gauge. Im doing this test at 266 rpm with 12 magnets a 9.5 inch rotor just one of the 2 rotors for right now. OK at the dc bridge rectifier I am getting on this one coil.80 dc volts and .15 dc amps. OK i am going to use 9 coils 3 phase star. so im thinking I will get 2.40 volts per phase 3 times .80 = 2.40 times 3 phases 3 times 2.40= 7.20 dc volts times 1.73 for star=12.45 volts times 2 for when i put the back rotor on=24.91 volts. Am I pretty close here??? What might my current or amperage be and how can I figure this out. What would this reading be in delta. I appreciate the help. JB

coil testing | 25 comments (25 topical)

Re: coil testing (none / 0) (#1)
by windstuffnow on Fri Mar 26, 2004 at 06:31:19 PM MST

JB,
If your using 9 coils and 12 magnets you have 3 coils in series for the 3 phase so you'd have .8 x 3 = 2.4 volts x 1.732 for star wiring = 4.15 volts at 266 rpm. In delta you'd have 2.4 volts but the resistance would be 1/3 of star.

To find out the amps at a certain rpm...

Open voltage - charging voltage / ohms = amps at that rpm. For instance...

At 500 rpm, using your numbers. You have 266 / 4.15 volts = 64 rpm per volt so at 500 rpm your looking at 500 / 64 = 7.8 volts. If you were charging a 6 volt battery you'd be charging at

7.8 - 6 / 2 = .9 amps

I used the 2 ohm as an example since I don't know exactly what your coils would be in series.

Hope this helps

Windstuff Ed

Have Fun! Windstuff Ed

Re: coil testing (none / 0) (#2)
by JB on Fri Mar 26, 2004 at 06:51:27 PM MST

Hello Ed. It does help to point but may you have made a mistake or am i mistaken??If i have .80 volts in one coil of this first phase times 3 =2.40 for that 1st phase. Now I have 2 morse phases yet to add both at 2.40 volts wouldnt this be 7.20 volts for the 3 phases times star 1.73 =12.45 volts for the 9 coils??. or am I wrong//. Thank You JB

[ Parent ]

Re: coil testing (none / 0) (#3)
by Hank on Fri Mar 26, 2004 at 07:19:19 PM MST

JB,
Ed is correct. In a 3 phase machine the voltage output in star (Y)is 1.73 times the voltage of any one phase. If you will be using a dual rotor on your project your voltage should increase 2.5 to 3 times.

Have fun,
Hank

[ Parent ]

Re: coil testing (none / 0) (#4)
by JB on Fri Mar 26, 2004 at 07:28:42 PM MST

Thanks Hank. Looks like this machine might be a real dud. Id have to have typhhon type winds to get this thing up to 12 volt charging range. Thats kind of hard in the desert. JB

[ Parent ]

Re: coil testing (none / 0) (#5)
by Hank on Fri Mar 26, 2004 at 08:44:46 PM MST

Well not really,
If you use your coils w/dual rotors you will need about 340 rpm to start charging 12 volt batteries.

If you go to a smaller wire, let's say #16, then you can make coils with about 70 turns. Your voltage will go up proportionatly or 1.75 times.

So lets say you are currently getting 4.15 volts at 266 rpm one rotor no laminates with #14 40 turn coil.

By going to #16 with 70 turns the voltage should increase to 7.26 volts. Putting on the second rotor will increse the voltage 2.5 times (at least) and you are up to 18 volts ( you are charging). This comes out to about 14 rpm/volt and you should start charging at about 200 rpm.
Depending on your prop and your PMA design you should be charging in 10 mph winds + / -.

[ Parent ]

Re: coil testing (none / 0) (#6)
by JB on Sat Mar 27, 2004 at 06:30:04 AM MST

Hello Hank, Ed and others. I ve been doin math late last night and very early this morning. I used Hanks number of 4.2 volts with 18 gauge wire 70 turns and Eds number of 2 ohms just for the math. I did it in star 3 phase and used 2.5 for the other rotor assuning the other rotor would increase the voltage 2.5 times. Then I did some math assuming that I would use this coil configuation. I would wire coil 1 to 4 to7 in series and to a bridge. coil 2 -5-8 to a bridge and 3-6- and 9 to a bridge . I came up with Hanks number of 14 rpm per volt in 3 phase star at my test speed of 266 rpm. Using this other configuaration with a base factor of 4.2 volts per a set of 3 I came up with 8.48 rpm per volt.Total volts for the 3 phase star without the ohms factor was 19 for 3 phase star and this other configuration was 31 volts at 266 rpm. Then I used Eds 2 factor for ohms though I know that will change with 18 gauge and I came up with 9.5 volts for 3 phase and 16.5 volts for this other configuration. If my math is correct Im not getting charging voltage to a 12 volt battery yet with 3 phase at 266rpm but im getting 4.5 amps into the 12 volt battery with this other wiring scheme.I may be right or I may be wrong. Good Morning.JB

[ Parent ]

Re: coil testing (none / 0) (#7)
by JB on Sat Mar 27, 2004 at 06:33:59 AM MST

Sorry, the above posting should be 4.2 volts for 16 gauge not 18 gauge. JB

[ Parent ]

Re: coil testing (none / 0) (#8)
by Hank on Sat Mar 27, 2004 at 07:22:15 AM MST

JB,

I'm not sure what you mean by the other method.

Don't get hung up on the coil resistance yet it will not change your open voltage. You will coil resistance to determine current (amps)
First you need to get the open voltage above battery voltage + rectifier loss.
So let's say you need to get about 14 open volts before you start to charge. Coil resistance will be about 1.3 ohms using 70 turns of #16 wire (probably less).
So using my example in the earlier post of 18 volts at 266 rpm or 14rpm/volt.
(Open volts - Battery+Rectifier volts)/ resistance (Ohms) = amps into battery.

(18-14)/1.3 = 3 amps

If the PMA turns faster let's say 350 rpm you will get 25 volts (350rpm / 14rpm/volt).

Your charging current will then be about 8.5 amps.
(25 - 14)/1.3

The higher the open voltage the higher charging currrent you will get.

Hank

[ Parent ]

Re: coil testing (none / 0) (#9)
by JB on Sat Mar 27, 2004 at 07:53:18 AM MST

OK Hank. I got ya on the ohm thing but as far as open voltage goes my other method seems mathmatically better than star.I think ?? Let me explain what I did. I just did this in math only. Lets say 4.2 volts for 3 coils, coil 1 -4--7 of the 3 phase OK. I take that 4.2 volts times star 1.73 = 7.2 volts OK.Thats what we end up with. OK. 7.2 volts for all 9 coils cause it is in star. Correct?? Now lets do this. Lets take Take coil 1-4-7 at 4.2 volts to one rectifier. We got 4.2 volts.OK Hope you got me. OK now lets take coil 2-5-8 to a rectfier, we will series that to the first rectifier so we now have 8.4 volts . OK Now lets take coil 3-6-9 and do the same. We now have 8.4 + 4.2 volts = 12.6 volts. With the star we had 7.2 volts in comparison to the 12.8 volts. I may be right or I may be wrong. Thanks JB

[ Parent ]

Re: coil testing (none / 0) (#10)
by DanB on Sat Mar 27, 2004 at 08:51:34 AM MST

Perhaps I missed something in the other comments...
but - if you have 3 coils per phase, and you've got .8 volts DC after the bridge rectifier, we need to consider the rectifier losses (Which wont apply to every coil...)

so if its .8 VDC from a single coil, (after the 1.4 V rectifier loss) then you've got about 2.2 VAC per coil. 2.2 X 3 = 6.6, and then multiply that X 1.73 for the Star connection for 11.4 Volts AC @ 266 rpm. Then we can subract your 1.4 volt loss from the rectifier for 10 Volts DC @ 266 rpm. So when you drop the second rotor on you should be around 22.8 VAC @ 266 rpm, and 21.4VDC after the rectifiers.

It sounds like your in the ball park to me for a 12 volt machine, but I could've misunderstood something.

Re: coil testing (none / 0) (#11)
by JB on Sat Mar 27, 2004 at 09:02:00 AM MST

That is correct Dan. I have .8 volts on the plus and minus side of the bridge rectifier. It makes it simpler for me and I can hook up to my analog meters. Did You understand my other wiring scheme just out of curiousity. Thanks for the comment.JB

[ Parent ]

Re: coil testing (none / 0) (#12)
by DanB on Sat Mar 27, 2004 at 09:08:22 AM MST

Hi JB - yes, I think I understand anyhow!
Its the same 3 phase system I use...
You can take your readings on the DC side of the rectifier... but remember that 1.4 volt loss will only apply once after the whole alternator is together (not in each coil).
so, at 266 rpm, you need to figure 2.2 volts DC per coil, multiply that times 3, multiply that X 1.73 (for Star) and then subtract the 1.4 volt loss for the rectifier. It puts you in the ballpark for sure.

[ Parent ]

Re: coil testing (none / 0) (#14)
by DanB on Sat Mar 27, 2004 at 09:36:48 AM MST

JB...
I wonder what magnets you're using here?
I've been sitting in my shop thinking about this and I may take back what I said about "being in the ballpark" here...
I think, if you built your stator up with coils like the one you described (40 turns of #14) you'll have a cutin speed perhaps about 130ish rpm - which is good for perhaps a 10' diameter prop. But the problem is... the resistance of a stator which is made up from 9 coils like that (40 turns of #14) will be pretty high if its wired in star, so I think perhaps the alternator would not be powerful enough to handle the power from a prop which is appropriate for such a cutin speed.

My guess is perhaps you're using fairly smallish magnets? 12 Volt 10' machines I've been making have about 35 windings of #11, or #12 wire (about half the resistance of what you'd have going there...). Perhaps you have "room" to wind your coils from some heavier wire? If not, then perhaps I'd consider fewer windings of heavier wire so the cutin speed is higher and you can run a smaller prop. (Im probably just thinking too much...)

It would be interesting however to know what size magnets your using here. I believe there is a direct relationship between the "power" of an alternator (which determines what size prop you can use on it) and the size of the magnets used.
(it'd be fun to come up with some kind of chart, or basic guidelines about that for dual rotor machines)

[ Parent ]

Re: coil testing (none / 0) (#15)
by JB on Sat Mar 27, 2004 at 09:43:28 AM MST

No Dan . Not Quite . This wiring scheme i calculated i dont think ???is neither star or delta. It might be single phase I dont know??. Im electronically challenged but the cutin voltage I calculated comes in at lower rpm than either star or delta. The method Im talking about Using the color diagram from the 10 footer you built will be like this letter A start and letter X finish go to a bridge letter B and Y start and finish go to a bridge and letter C and Z start and finish go to a bridge. These 3 bridges are serised and off to the batterys they go. Im pretty sure the letters are right. The are the start and finish of every third coil wired in series. Thanks JB

[ Parent ]

Re: coil testing (none / 0) (#16)
by DanB on Sat Mar 27, 2004 at 10:03:56 AM MST

running those bridges in series like that.... hmmm
it's hurting my brain!

I'd wire it in Star, although you could rectify each phase seperately and run it all in parallel. (that should give about the same as Delta, although Ed did some tests a while back suggesting that output was higher that way... although to me it still seems like Delta makes better use of the conductors in the stator) Delta can be inefficient if the coils are not perfectly wound and perfectly placed. (perfection is unlikely...)
So, if it were me, I'd wire it in Star...

What size magnets are you using?

[ Parent ]

Re: coil testing (3.00 / 0) (#25)
by JB on Sat Apr 26, 2008 at 02:19:12 PM MST

Ok. Im back to finish this project up Hopefully . I got a new hydraulic tower. I got the motorcycle bug and put on a few miles and havent done my homework.Now its getting time . It looks like jerry rig way or Jerry delta way of wiring is what i was talking about 4 years ago before I gave people a headache. LOL. Im making a new coil winder and was wondering why we went with the 2 in hand winding coils in place of the single wire like before and what does it do. Thanks JB Dayton Nevada

[ Parent ]

Re: coil testing (none / 0) (#19)
by JB on Sat Mar 27, 2004 at 12:15:44 PM MST

Hello Dan , Hank , Ed and others. Just got back from a yard sale scored a bunch of cable and cable clamps for a buck and a hardcover book called electronic principles by Albert Malvino for a buck. The magnets i am using are 1.5 by .250 round neos. My wind speed up here on this hill is hard to say. Yesterday it was about 65 mph. Ive seen as high as 120 mph. In the summer there is usually a good afternoon breeze. I have a real good furling set up on my other mill. BillF posted it on the old board and my new tower I should be able to drop from 30 to 15 feet in less than 5 minutes. For some reason I thought the way I was thinking to do it would let me add the voltages, only cause when I did the garbogen a couple years ago I thought ?? I was able to add the voltages coming out of the dc side. Actualy in the back of my head for some reason Im thinking 24 volts is the way to go. I got jacks windpower book here. Maybe I should look at it again Thanks JB

[ Parent ]

Re: coil testing (none / 0) (#17)
by Hank on Sat Mar 27, 2004 at 11:46:14 AM MST

JB,

What you are proposing should have very similar results as Star connection.
I tried the same thing on my 3 phase PMA and the results were the same as when connected in Star. I believe that is because of the phase shift. The voltage is not additive as it would be in a single phase unit.

Did some calculations/guesstimates on the resistance you will be getting winding 40 turns #14 wire.
You should be getting about .065 ohms per coil (perhaps less as you said your rotor will be 9.5 inches), 3 coils/ phase, 3 X .065 = .198 ohms/phase.

Basically only using 2 phases at any point so your stator resistance should be about .4 ohms. Not to bad.

Attached are some formulas for determining your prop size ref. "The Wind Power Book" by Jack Park.

What are the average winds in your area? This will be important for choosing the right TSR for your prop as well as determining how much power you can get.

Actually I have a similar unit (higher resistance at .65 ohms) with an 8 ft. prop that has been running very well. It furls in about 30mph winds and produces about 50-60 amps just before it furls. You are there!!
Hope this helps some,

Hank

[ Parent ]

Re: coil testing (none / 0) (#18)
by DanB on Sat Mar 27, 2004 at 12:01:35 PM MST

Thats interesting....
I'd think your "guess" about his resistance is probably close.
To me it gets a bit scarry though, when we think of the power available in larger props.
Figure your machine, 60 amps at furling....
while its producing 60 amps your .65 ohm stator is a 2340 watt heater.... that's a lot of heat to dissapate. Hard to know for sure where the limits are -it probably depends a lot on the location of the machine.

Wards machine, which we built a couple years ago came in around half an ohm (it was single phase)... I'm doubtful if it could handle a sustained 50 amp output, although for moments in very high winds we've seen 120 amps! (thats a LOT of heat in the stator)
It has a 7' 3" prop and no furling system.
It'd be interesting to come up with some sort of chart for stator resistance vs prop size, it wouldn't hold true in every case and location... but it would be fun to have basic "guidelines" about what we could expect to get away with.

[ Parent ]

Re: coil testing (none / 0) (#20)
by Hank on Sat Mar 27, 2004 at 12:33:19 PM MST

Hi Dan,

I hear you and I share your concern about frying the stator. Fortunatly (or unfortunatly) these winds are not sustained for to long at my site and this was in winter with temps at 15 degrees F. Actually the PMA I'm refering to is similar to Wards and is single phase in series,16 coils. Hell, I learned most of this stuff from you.
I was thinking of taking it down and adjust the furling system so it furls earlier, I'll sleep better.

It would be good to know how many watts a stator can take before it fries. Quite a few variables in that equation I bet. But if you knew that then you could design everything for optimization, not the least of it the furling system.

This whole thing is a trade-off If you want to make power at low wind speeds and rpm's then you run the risk of making smoke in high winds or making no power in low winds and hoping for a gale for a high speed machine.

Having fun nontheless,
Hank

Hank

[ Parent ]

Re: coil testing (none / 0) (#21)
by JB on Sun Mar 28, 2004 at 08:55:30 AM MST

Hello Hank and others. Just another question. I hooked up my ohmneter on these 40 turns. I set it to Rx1/10 that is r times one tenth. It reads one and a half 1 1/2. So would the resistance be .015 for this coil. Thanks JB

[ Parent ]

Re: coil testing (none / 0) (#22)
by TomW on Sun Mar 28, 2004 at 09:05:36 AM MST

JB;

Math is not my strong area but where I come from 1.5/10=.15 so I vote .15 ohms.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

[ Parent ]

Re: coil testing (none / 0) (#24)
by JB on Sun Mar 28, 2004 at 10:39:55 AM MST

Very Well Tom. That actually comes in super close to Hanks Numbers. .Im going to use that number and do some recalculations as that number seems to be more important that I thought it orignally would be. Electronically challenged but dont mind learning. Take er EZ. JB

[ Parent ]

Re: coil testing (none / 0) (#23)
by JB on Sun Mar 28, 2004 at 09:07:10 AM MST

Im thinking that coil should be .150 not .015 times 3 coils would equal.450 or approximately 1/2 ohm per phase. Thinking out loud here. JB

[ Parent ]

Re: coil testing (none / 0) (#13)
by Hank on Sat Mar 27, 2004 at 09:28:25 AM MST

Good point Dan,

I totally missed that one.

Hank

[ Parent ]

coil testing | 25 comments (25 topical)

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