Lots of air for 30 seconds....

[Aedan]

I was busy modifying a fan, as you do on a saturday afternoon. I'd got hold of a nice impeller from a blower, and had hooked that up to a Minicraft motor (from one of their drills). The drill was rated at 12V 30W, so I figured it wouldn't be too much of a problem. I grabbed one of my little PSUs, designed to power electronic things, and used that with the drill. The results weren't too bad to be honest, but those little PSUs are only really good for some 20W.

I grabbed my slightly better power supply (120W at 13.8v), and decided that would be god for a go. Hooked it all up, and turned it on. Whoa, was there a speed increase or what! That impeller was now rotating at a really good speed (probably in excess of 10-15KRPM), but something didn't quite smell right. Shut everything down, and noticed that the motor was a little warm.

Decided to break out the multimeter to find out just what was going on here. I put the multimeter in line with the PSU, and powered everything up without the impeller attached. Idle current on the motor was about half an amp (~7W). Figured that was ok for a 30W motor, powered it all down, and hooked it back up to the impeller. Fired it all up again, plenty of air whooshing from the unenclosed impeller radially outwards. Check the multimeter, and the motor is pulling some 9A from the PSU, and that the voltage had risen to about 14V. That's a little more than the 30W the motor was rated for. It's more like 126W, so perhaps it's not surprising that the poor little motor was getting so hot so quick.

Now I just need to find a motor of a more sensible size to power the impeller. A 120W fan is perhaps a little more noisy than I really want.

[Pitch]

So...

120W PSU + Drill Motor + fan = uber fan?

If only we had the weather to need such a beast.

I think I need an uber umbrella...

[danrok]

You could always put the fan on your head, blowing upwards = uber umbrella

[Pitch]

Hmmm.... Yea but my head would vibrate and kill off the last remaining braincells.

[Aedan]

Originally Posted by Pitch

120W PSU + Drill Motor + fan = uber fan?

120W PSU + motor + impeller = dead motor, if you're not careful

[Gizmo]

I'm a little confused. That motor shouldn't be ABLE to pull 9A unless the impeller were putting more load on the motor than it was designed to handle (i.e. the motor is running at a significantly slower speed than it was designed for)?

[Aedan]

The motor was designed to operate at 30KRPM. I don't think spun up to that speed, due to the load of the impeller.

[Gizmo]

Ah, I see. That makes sense then. I think you'd know if it had even come close to 30K RPM. LOL.

[Aedan]

Yeah, I suspect I'd have been greeted with the impeller turning into lots of bits of flying plastic.

[Cerium]

flying plastic going really fast. I dont know if anyone saw the myth busters show where they tested the myth of explodeing cds. Took one up to 50'000 rpms then it exploded leaving shrapnal in their balistics dummy like 5 in. deep. oww!

[Aedan]

Not surprised there, as CDs are hard plastic that forms fairly jagged spikes when it shatters! Mind you, CDs have been known to shatter at much lower speeds - 16,800RPM (56x) seems to be about the maximum limit. 15,600RPM (52x) seems to be a much safer speed, as opposed to the 50,000RPM (166x) they tried!

[Gizmo]

I'm also a bit dubious about the Myth Busters test. Ok, they spun a CD up to 50K RPM before it shattered. But how long did they let it run at, say, 16K RPM. A component might be able to take 16K RPM for 30 seconds, but what about 300 seconds, or 3,000? There is such a thing as stress fractures that can develop over time. The British Comet didn't suffer from explosive decompression on its first flight, but only after several hundred hours of flight. Same thing with the Tacoma Narrows bridge.

[Staz]

Originally Posted by gizmo

I'm also a bit dubious about the Myth Busters test. Ok, they spun a CD up to 50K RPM before it shattered. But how long did they let it run at, say, 16K RPM. A component might be able to take 16K RPM for 30 seconds, but what about 300 seconds, or 3,000? There is such a thing as stress fractures that can develop over time. The British Comet didn't suffer from explosive decompression on its first flight, but only after several hundred hours of flight. Same thing with the Tacoma Narrows bridge.

Agreed.

On "The Screen Savers" they said that they thought it was a myth at first, until it happened to them with an old CD-R.

If you are really looking for a high power high velocity fan (and you are already deaf) then I would suspect that disecting a hair dryer would give you a very powerful fan.

[Aedan]

A damaged CD can shatter in the drive at high speed. From what I've gleened from CD drive manufacturers, 56x is pretty close to the margin in terms of stress a CD can take over the long term.

As for the hairdryer, I was trying to avoid the noise, and maintain a reasonable flow into a radiator that's got closely spaced fins.

[Phat Pat]

Originally Posted by gizmo

I'm also a bit dubious about the Myth Busters test. Ok, they spun a CD up to 50K RPM before it shattered. But how long did they let it run at, say, 16K RPM. A component might be able to take 16K RPM for 30 seconds, but what about 300 seconds, or 3,000? There is such a thing as stress fractures that can develop over time. The British Comet didn't suffer from explosive decompression on its first flight, but only after several hundred hours of flight. Same thing with the Tacoma Narrows bridge.

everytime they test a myth I am left asking about 20 "but what if" questions. I guess they cant test every possibility in one show but they do seem to leave some big things out every time.

but check this out, random fun with destroying cd's http://www.powerlabs.org/cdexplode.htm

I love powerlabs, all the stuff I wish I could do lol. "Mom can I build a rail gun?"

[Cerium]

Yea . . . If i ever convinced my mom htat id (Whatever it is) be safe she could get all the chemicles i need. Science teacher. But that would never happen. . .


Cool site. Chemicles in small but expensive portons. Avalable to consumers. http://www.unitednuclear.com/supplies.htm

[danrok]

They seem to have run out of uranium ore, just when I was getting low.

[Daniel ~]

Worlds first Nuclear power plant, advanced instrumentation console.
( Just wanted an excuse to share this beauty!)

[danrok]

I am fortunate enough to live just 15 miles accross the water from France's largest nuclear crap reprocessing plant. They pump the waste in to the sea, which is nice.

Anyone for lobster?

[Daniel ~]

So France joins with the other far-sighted nations of the world!