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My Box Fan Conversion
By bug bit, Section Wind Posted on Wed Sep 14, 2005 at 04:19:07 PM MST
Multimeter tells me i did something wrong

I read the post on the box fan conversion. Thank you for all the ideas Ghurd. I had one here and tore into it. The old wire came off and re-wired using 20-gauge wire I pulled off a couple of blenders I had. 100 winds per coil. Alternating cw-ccw all the way around the stator. 6 coils.
The rotor I cut to 8 sides using dimensions off the turbo-cad calculating for ½ x ½ x ¼ neos I had here.
Now for my problem. I wired it 3-phase star and got only .05 volts. Wired it series and got the same thing, parallel even got the same thing.
I even tore the mags off and put only 4 of them on (N-S-N-S of course.) and got the same result.
Could the mags be not big enough? Not enough windings? Not getting it to spin fast enough?
Any thoughts would be very helpful.

My Box Fan Conversion | 15 comments (15 topical)

Re: My Box Fan Conversion (3.00 / 0) (#1)
by ghurd on Wed Sep 14, 2005 at 10:39:26 AM MST

""Could the mags be not big enough? Not enough windings? Not getting it to spin fast enough?""

No. Its got to be something else.

The magnets left on the rotor are N-S-N-S right? Just checking.
If there were 8 N-S-N-S-N-S-N-S. And every other one was removed, the 4 left are all the same polarity.

Series is going to be goofy, so I'm not suprised by that one.

Check the ohms of each coil. Maybe something is shorted.

Put coils 1 and 4 in series, check the output. If it is low (like under 1V), switch one coils ends and try it again. One way should be something, the other way nothing.
Same thing with coils 2 and 4, then 3 and 6.

If there is still a problem, check each coil one at a time.

When they all get working, put them in star.

Not sure, but with 1/2" magnets, 100 turns each may be a little low.
My guess, just a lame guess, is maybe 250 turns per tooth.

Some of the phasing on these is "different", so I think 2.3 instead of 1.73, because of some of Ed's data. Still, I don't know.

Glad someone tried it!
G-

Re: My Box Fan Conversion (3.00 / 0) (#2)
by ghurd on Wed Sep 14, 2005 at 10:44:11 AM MST

I see the NSNS is right, sorry about that one.

Check AC volts if before the rectifiers, and DC volts after.
I always think I broke something if I forget to switch the meter.
G-

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#4)
by Dreadstar on Wed Sep 14, 2005 at 02:38:28 PM MST

Question for you Ghurd on the conversions you did. I never found any output specs for them for performance. What did you end up with and how big a prop did you use?

Could you just stuff it back in the box it came out of with the same fan blade and get anything at all out of it? of course you would have to manually position it to get advantage out of the winds.
But it may be an idea for someone with a truck or other battery powered vehicle to get some power back while sitting still or moving. Not sure if the extra drag would hurt it or it could be used to run some 12 volt appliances suchs as a small fridge.
Take out the (at) and substitute @ for replies via email
[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#7)
by ghurd on Wed Sep 14, 2005 at 04:45:01 PM MST

That one is on the back burner for a rewind, because 2 of the factory coils are bad.

Assuming all 3 phase worked...
If they were rectified separately the total of all 3 was about 2.3 amps at 1000RPM, or 0.8A per phase, into a 12.8V 7AH battery. About 1.5A at 650RPMs.
I don't have a way to check cutin with any accuracy, but it maybe about 275RPM.

As for 3 phase, there would be some strange things going on. It does not work the way it first seems on this one.

I cut this post in 2 in the wrong place, there is more below.
G-

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#5)
by hiker on Wed Sep 14, 2005 at 04:01:45 PM MST

if your going to do a box fan coversion--try this type of motor[photo]..
just knock the lams out and replace with mags--cut the old wire off and replace with thicker wire..lights up a 12volt spotlight by hand..or a couple of 50watt headlights under power..[i bypassed the inner coils on this alt..wire to fine]..
with the mags on the inner side of the case you dont have to worry about the mags flying off..powered by harddrive mags..single phase.............later.

WILD IN ALASKA
[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#14)
by allthumbs on Sun May 27, 2007 at 11:19:17 PM MST

I would love to see your photos but they don't show up. Just the box and no photo.

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#15)
by TomW on Mon May 28, 2007 at 07:44:54 AM MST

Thumbs;

Thats because web browsers need an extension on the filename: filename.xxx or picture.jpg otherwise it doesn't know what they are. That file has no extension. Another [certain OS] problem not playing by the established standards.

Ignarus can exsisto rememdium. Sardus est forever

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#3)
by ZooT on Wed Sep 14, 2005 at 12:13:50 PM MST

Ed over at windstuffnow has an article about three phase in which he says that if you're doing three phase you wind all the coils in the same direction and only switch the leads on phase two as phase two is out of phase with the other two.
http://www.windstuffnow.com/main/3_phase_basics.htm

I can visualize how the 4 magnet design works in that only 1 phase is being energized at any time with the other pair of magnets being between coils so it is three phase

If this is true, then if wound in alternating directions all the way around and then wired three phase, phase one(assuming coil 1 was wound clockwise)would be coil1 and coil4, coil1 would be wound clockwise while coil4 would be counterclockwise.

Is this correct? or would the two coils be cancelling each other out?

Re: My Box Fan Conversion (3.00 / 0) (#6)
by ghurd on Wed Sep 14, 2005 at 04:41:48 PM MST

As for 3 phase, there would be some strange things going on. It does not work the way it first seems. I think 2 phases are active and one is low.

I'll quote Mr Flux...
"Voltage is proportional to rate of change of flux. When a magnet is directly over the leg the flux is a maximum and the voltage is zero. As the magnet approaches and departs from the leg the flux change is rapid and the voltage peaks."
From this story...
http://www.fieldlines.com/story/2005/5/4/15729/16162

Add that information to this information from Windstuff Ed...
http://www.fieldlines.com/story/2004/6/7/21190/34164

Also look at Ed's numbers for overlapping coils, like the 18 magnet, 27 coil "Alt from scratch" on his website.

And there is a post that went off topic where UGL had some more pertinent info., but I can't remember the post.

So I believe this set up in 3 phase will take a lot less turns than single phase or "normal" 3 phase, because the magnets make the most power when it has half the flux down 2 adjoing 'T's or teeth.

I am mixing apples and oranges to get pears. Not sure how correct my extrapolations are, but I'm trying. I don't see any major flaws in the theory.

I tried a LONG time to figure out what was wrong with the bad coils. Lots of handling, lots of time sitting while in parts, etc. Then it real got busy at work.
Then the bushings and shaft rusted. Dang. It wasn't too great when I got it.
With the rusted bushings and shaft holding it back, the blade it came with will turn it about 90 RPMs in 11 MPH winds. By hand it feels stiff and gritty when it did not before. The 'dead' coils are still in it, and they will hold it back some too.
The factory blade would have got it up to cut in I'm sure, before the rust. Not sure how the blade would have stalled, but I figure it would have stalled kind of early.

Bug Bit,
I hope the wire is not shot.
"Strange Coil Troubles"
http://www.fieldlines.com/story/2005/6/28/16259/6856

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#8)
by bug bit on Wed Sep 14, 2005 at 06:13:07 PM MST

if i read the multimeter correctly, it is telling me .02 when i check resistance on each coil. looking at it i think i should have gone with twice as much wire as there is plenty of room left. i checked the coils seperatly and get .3 volts dc. this is really bugging me.
i have little .9hp 4 coil fan motor all i did was put mags on, it puts out 10 volts at about 100 rpm. go figure???

someone is always changing the rules

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#9)
by MountainMan on Wed Sep 14, 2005 at 07:54:21 PM MST

You might have to use a scope to really see what voltage you are getting on each coil.

Remember, it is "AC" coming from the coils, so a DC multimeter reading is meaningless at the coils. DC reading even after the rectifiers is only valid if you have a capacitor there to average out the pulses of voltage produced by the alternator. A typical modern multimeter is a sampling device. It samples the voltage frequently, rather than averaging. The pulse type output from alternator plus rectifier (with no capacitance or battery) would probably really confuse the digital multimeter.

Reading right at the coils (before the rectifier) with a multimeter set to AC is also problematic, because of the pulsed output from each coil. Depending on the relationship between the rotational speed of the alternator and how many magnets it has, and the sampling frequency of the meter, who knows what you will read on the meter. With an "old fashioned" needle meter set to AC, you would probably get something reasonably close to the RMS value of your AC voltage waveform ( which is not the same as the peak to peak voltage).

Despite the innacuracies involved, I would think you could still use a digital VOM set to AC to COMPARE the different coils, but not very accurately to get an actual voltage reading.

best,
jp
MountainMan, Julian California
http://www.real-home-based-business-opportunity.com
My ultimate hobby project is to build a ten foot tall robot.
[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#10)
by ghurd on Thu Sep 15, 2005 at 08:02:10 AM MST

It is starting to sound like the coils could be shorted out.
With 100 turns at ~3.25" per turn is 27'. #20 is 10.15 ohms per 1000'. 27/1000x10.15=0.275 ohms.

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#11)
by ZooT on Fri Sep 16, 2005 at 12:38:52 AM MST

Maybe one of the phases "isn't" the same length as the others but instead either much longer or much shorter......I'm thinking it is, after all, a three speed motor, and the hoops they junp through to build these things "on the cheap" might include some funky winding tricks.....

[ Parent ]

Re: My Box Fan Conversion (3.00 / 0) (#12)
by ZooT on Fri Sep 16, 2005 at 01:32:21 AM MST

bugbit,

I can't understand eight magnets creating a low output.......unless......the laminate cores that the coils are wound around are wide enough that there's never a time when only one magnet is directly over a coil core.(always two and possibly three over a core)
With both a north and a south pole being over a coil core at any given point in the rotors arc it'd be no surprise if output was low or even nonexistant due to a south and a north cancelling each other out thus not saturating the coil before switching polarity, which is, if I'm understanding correctly, what produces a current.

Re: My Box Fan Conversion (3.00 / 0) (#13)
by OlBuzzard on Wed Oct 19, 2005 at 05:14:24 AM MST

I think you may need to think about how you wound your coils, CW-CCW !

My Box Fan Conversion | 15 comments (15 topical)

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