Muffin Fan PMA
By ghurd, Section Diaries Posted on Tue Jan 15th, 2008 at 07:09:20 PM MST
Might be better than the average stepper

Yet another power house! Started with a 24VDC 350ma ball bearing fan. Removed the sticker, exposing the plastic retaining ring. Removed it. Pulled off the blades. A small bearing on the back was loose. Two screws removed the circuit board and motor. This motor has 3 connections to the 4 series coils. 1 on each end, and one in the middle. Cut the traces to the coil leads.  Removed a pair of diodes that were connected to one of the outputs.  Moved the input wires to the far ends of the coils. Reassembled. It makes 6VAC easy finger spinning at about 180 RPM(?).   Short circuit is about 65ma DC after the rectifiers.  Shorted doesn't feel any different due to the cogging. The coil resistance is 55~60 ohms. The diodes on perfboard is my testing unit.  10 diodes, 7 clips, 100% worth the effort. Bad things. The laminations had 4 legs, 1 under each coil. 2 legs were broken before I started. The crappy magnet ring has no flux path on the back side. It is all plastic, though there is an area that could be filled with steel wire, not sure how much it would help. Things I should not have done (AKA: fungus' favorite part). I quickly unsoldered (not the same as desoldered) the 4 legs, leaving stray solder on the legs and board. It took a lot of heat to get them back in. The solderable legs were plastic covered, meaning they melted before it was finished, leaving no way to get everything lined up perfectly. Broken legs didn't help matters. There was no reason to take the motor off the board anyway. Super Glue did not stick were I thought it would, but it did stick to everything else. Meaning the magnet ring seriously rubs the laminations. And it is not a solid unit. Anyway, I think this would have worked better than most small steppers for 12V charging. The far lower frequency would be better, by my understanding.  This shouldn't be as limited by inductive reactance of most small steppers. Might have made 200ma at 12V. Why did I try it? Wife needs remote power for the cell phone and GPS for some bike trip. Thought about the fan PMA to the back wheel when the bike was up side down, hand crank the pedals a few minutes at night.  Connecting something permanent is out of the question.  Probably end up going solar. I want an LED desk lamp powered by wind. And it is cheap entertainment.  Cost me a nickle, best guess. G-

Muffin Fan PMA | 6 comments (6 topical, 0 editorial)

Re: Muffin Fan PMA (3.00 / 0) (#1) by claude on Tue Jan 15th, 2008 at 12:57:46 PM MST (User Info)

I bet if you build a wall made entirely out of 24V fans, that would really be a powerhouse :-). But somehow I doubt super glue will do that job. You know me, I'm a stepper fan. No, not the cooling kind. Claude

Re: Muffin Fan PMA (3.00 / 0) (#2) by fungus (info@reenergy.co.uk) on Tue Jan 15th, 2008 at 01:03:44 PM MST (User Info) http://www.reenergy.co.uk/

Tried the same thing with a 70ma 24v fan, lights a couple LED's easy, puts out about 10ma turning (not very fast as I couldnt) shorted, this one had screws on the pcb so was easy to solder the wires.. They're pretty nice :) 'Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.'-Albert Einstein Fungus - www.reenergy.co.uk

Re: Muffin Fan PMA (3.00 / 0) (#3) by dinges on Tue Jan 15th, 2008 at 05:44:38 PM MST (User Info)

Good to see you haven't run out of hotglue yet. No project is complete without it. I may have to give converting an old fan a go then. There should be a suitable candidate in one of the three boxes with old fans. Another use for old PC PSU parts... Good to see I haven't been saving those fans in vain. I -knew- they'd come in handy some day. BTW, if I mount such a fan on each tip of a regular HAWT (say, a 10 footer), can I then beat Betz ? Perhaps even (gasp) overunity ? Would be sort of a combination of a HAWT and three small VAWTs I think. <ducks and runs> Seriously. Nice little project for the next rainy sunday. Costs a nickle, fun for a dime. Peter.

Re: Muffin Fan PMA (better) (3.00 / 0) (#4) by ghurd on Wed Jan 16th, 2008 at 08:21:48 AM MST (User Info)

A better write up was lost to the top of the hour bug. Mostly, how Peter should stack 3 fans, modify 2, power the 3rd fan from 1... I figured the meter couldn't react fast enough to the changing voltage. Added a cap to the open output.  It gets past 12VDC easy. Tried it into a battery at 12.50V. Meter reads 6 to 8ma about every time. Once it went past 14ma.  The meter is having trouble reacting to the current too. It no longer rubs after a bit of heavy-handed adjusting. Might just make some small fast blades for it.  Snowy days here. G-

Re: Muffin Fan PMA (3.00 / 0) (#5) by ghurd on Tue Jan 22nd, 2008 at 10:38:10 AM MST (User Info)

The thing gets just past 12VDC under the bath tub faucet. Our faucet doesn't flow nearly as much as most. It wasn't turning all that fast, so it will get blades.  Eventually. G-

Re: Muffin Fan PMA (3.00 / 0) (#6) by ghurd on Thu May 1st, 2008 at 03:02:40 PM MST (User Info)

WARNING: I ruined it. The magnets are weak to start with.  The laminations in the motor act like a keeper. I let the fan off the motor for a month and now it makes about 1.5V when it made 6 or 8V before. Don't leave the thing in pieces any longer than it takes to do the work. G-

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