Yet Another DC Box Fan

[ghurd]

Got the 48V motors on eBay.  Thought they may be good for a tiny windmill.  Wrong!  1200RPM cut in for 12V.

Gave them to my off-grid solder guy, who quickly put them to good use.

A couple L brackets and hunk of plywood hold the motor.  The rear encoder cover was left on to cover the rear shaft.

The factory pulleys were turned down with a chisel, when the motor was running on 12V.  Then sanded a flat to match the blade.

I think he used the factory switch.  Not sure how he did it.  The switches and motors are not like they were a couple years ago.

High uses 700ma, straight from 12V (13.5V at testing).

Medium runs through a 5W 8.2 ohm resistor, and uses 400ma.

Low runs through a 5W 25 ohm resistor, and uses 200ma.

Nothing very scientific about the values, simply had them on hand.

The power (speaker) wire is shown under the fan. The coil that looks like it goes to the switch is an air line 10 feet behind it.

It uses about double what the "$10" treadmill motor fan uses, but it fits in the case pretty well.

Running on High, through a 555 based PWM controller, adjusted to be about the same RPM as low, takes about 150ma from the battery.

The thing is super quiet!  Almost can't hear it on Medium.  "Silent" on low.

G-

[RogerAS]

Gurd,

Way to be. That's cool. Argh no pun!

Do you mind showing us your 555 based speed controller?

[deloiter]

ghurd,

I have also been looking for a good 555 controller circuit.  I hope you will show us the diagram.  Thanks.  

[wooferhound]

Check out the very last post on this page for a circuit . . .

http://www.fieldlines.com/story/2007/5/1/212155/6372

[ghurd]

Well guys, hate to disappoint you, but I didn't really build ANY of it.

All I did was waste more money on more motors that won't work for a windmill! And take pictures.

And the PWM circuit is pretty old, like my memeory.  It is just on breadboard.

Probably, maybe, I think, not sure...

I "think" "maybe" it is "probably" Samoa's Ametek ceiling fan circuit, but "not sure".

What I recall for certain...

Used a IRFZ44N for the fet, and changed his 1N4007 to a 3A 60V Schottky.

The fan was high pitched "squealing" at low speed, so added an additional 220uF to the output (shown as 100u, but the circuit's output cap looks bigger than 100u, so it may be 440uF total), which helped a lot.  It would be quieter with even a 47uF on the motor.

I think he jacked the HZ up a bit too.  Maybe not.

Probably has less than 100 hours use, but it works and nothing gets hot.

Samoa's circuit,

http://www.otherpower.com/images/scimages/5176/PWMCont.gif

G-

[RogerAS]

Hey,

The deal is I've built a lot of 555 toys and they're fun to dink with. I also like to see other folks efforts with soldering irons 'n such.

I would think the FET would have to be a beefy one to run these motors as ceiling fans with variable speed. I must say the low power requirements caught my eye!

later,

[tecker]

 

 Good circuit but the 100 ohm out to the gate turns the fet on a little hard to get good relax times maybe a 220 and a 820 the 820 reference to ground

will give full on an a solid quick off time .

[ghurd]

Been thinking about this, and I'm confused.

I have a distaste for things with more than 3 legs, mostly caused by 555 and 723.

The Gate to ground now is 100.  With what you said it would be 173.5.

Seems like 100 is better.  I figure I'm missing something important about the 555?

Or lower Vgs means less gate charge to get rid of?

Anyway.  Why 220 and 820?

The fet tab (no heat sink) doesn't raise a (finger test) noticable degree even with 2A.

G-

[tecker]

First order is to stay below 4 volts ( max treshold ) .At 3k you should be able to hear the circuit with an AM radio . There won't be a whole lot of adjustment at around 25 percent the make space duty cycle  will be rapped up by the frequency and be  just like having a resistor in there . If it works for you then there's not a lot of reason to make changes . The impedance of the 50 volt motor is keeping the fet cool running aT 12 volts. I'm a little confused sounds like the 25 k pot is not your speed adjust.

[CmeBREW]

That is very nice!  Thanks for sharing those pictures. I like the simple idea of the 5 watt resistors.  I only really use 2 speeds myself with my big floor fan.

With Electric bills starting now to go thru the roof and beyond, I think everyone is going to need one of those in EVERY room when they HAVE to shut the air conditioners off.  I like that box fan since it is kid safe and can fit into the window.

Do they give the ratings?

I use a 10" "camping fan" (7Watts/low) now to put in my window each night for a few hours (9pm-midnight) to pull  in cool night air from outside into my bedroom. And I always have the big floor fan on me all night!  Its starting to get really Hot around here now--but these make it bearable.

[ghurd]

Factory motor? They probably gave ratings, but being off-grid, he removed the motor instantly.

Then he gave it to some nut who made it into a PMA.  :-/

"Feature Comforts". A Lowe's brand?

No sticker on the PMA motor now.  Tiny motor, maybe 3.25" dia?

Might be a sticker on the bottom of the 'box'.

The Pittman motors only say 48V, and a bunch of number strings Google and Ametek can't find.

He's working on another better suited to a 7" fan.  Guessing 350ma 1700RPM 12V?

Stupid eBay 24V Hanson 360RPM motors are really 3600RPM.  Glad I only bought 10.

Pulled over 2A, near stalled, with the above box fan blade.

[bsafe]

I was considering replacing my bathroom ventalation fan (70w, 80 cfm) with a 120mm  dc fan. some of the  dc compuler cooling fans will pull less than 10w and move 90+cfm. Should I be concerned with the moist air moving over the dc motor storting it out,or just jump in install it, and look for majic black smoke?

[ghurd]

I would just jump in...

I don't think a muffin fan is very prone to failure from moisture.  Been running a 110V muffin in the damp (wet) basement for 10 years. Sometimes add a 12V too. No failures at all.

I smoked more than my share of muffin fans. Can't recall one failing to short circuit. They just stop turning.

G-

[ghurd]

The real speed adjustment is the resistors.

The PWM circuit was sitting there, so we tried it.  Fan on High (no resistors).

It didn't save as much power as we hoped.

Mentioned the PWM circuit and noise to someone a few weeks ago, so it was more an interesting side note.

G-

[bsafe]

Jumped in ...and I learned that a 12v transformer from a 12v television rated 12v d.c. 1000mA actualy outputs 19.9v initially and "transforms" a 12v  .58 mA fan into a twitching sculpture and ...magic smoke. I will be reading up on the pwm circuits unless someone has some ideas on a 120 to 12v power suply that can stay within 15% of 12v. I might try a 120 volt muffin fan to reduce complexity but they seem to consume twice the energy as a 12v fan with a transformer. Either way it should be easy to beat the "stock" fan that uses 73w and is rated 80cfm.

[ghurd]

The transformer...  It had a bridge rectifier on the output?

If not, it was feeding the fan AC.  (hence "Twitching")

An unloaded transformer has higher than nominal voltage.

Usually a small load will drop the voltage quite a bit.  A 0.58A motor on a 1000ma tranformer, after the rectifiers should have been around 15~16V.  The motor should have been able to handle that, even if it was a tiny bit over the design parameters.

Standard disclaimer, YMMV.

I know for certain an under-loaded 50A 12VAC transformer, after rectification, blows up expensive car stereos.  :-(

The vent fan motor, and stupid 29-cent #1141 bulbs lasted longer than the camper, on the same system.

G-

[bsafe]

Yep, I pried the transformer apart it has a cap and 4 diodes to rectify. Would the addition of a resistor be usefull, or should I look for a "regelated" transformer while studying pwm circuits.

[ghurd]

It should have been fine.

The cap should have helped a lot too.

The "twitching" makes me thing there was a problem with the transformer, a diode, or the motor.

I am pretty sure with motors that size (0.58A), the PWM isn't worth the effort.

At best, the fan above saved a hair under 25% at low speed.  Much less savings at higher speeds.

Myself, I'll stick with simple power resistors until the motor is quite a bit more powerfull, maybe 3A?

Samoa's circuit is easy to build.  Works fine with the changes I told my friend to make (Schottky Flyback, and better mosfet).

You can build a "regulated" transformer.  Same as what you had, but a bigger cap.

Then feed the output to a low drop-out 7812 (TO-3 size, with heat sink), and a small cap and 1M resistor across the final output.

It is not efficient.  I wouldn't do it for a motor.

Really, a "12V" motor should handle 16V no problem.

G-

[ghurd]

Only 2 months late.

The factory 3-speed motor was rated 120VAC 60Hz 0.75A.

Far cry from the old box fans.  2.1A.

G-