12V fans query

All the fans I've seen were 'brushless' AC polyphase with protection to the driver board (inside the fan) to prevent damage.

I suppose if you were reallyi creative you could turn one into an alternator and generate (a small amount) of power with it...

Unplug the fan before blowing if unsure.

--
Blattus Slafaly  ? 3     :)  7/8

Older DC Muffin Fans use DC permanent magnet motors, you can feel magnetic detents as you rotate the blades.

Michael

They all have permanent magnet motors, but they're brushless. You can feel detents on those too.

I've never given it a second thought. Nor have I ever damaged anything by it. As a young lad I loved to turn my bicycle upside down and turn the garden hose on the pedals and wheels and watch them spin.

Meat Plow wrote in news: snipped-for-privacy@news.alt.net:

I was having problems with my car. Was in a small town garage watching while the guy removed the noisy wheel bearing from my front wheel. He washed it a couple of swishes in solvent and grabbed the pressurized air hose. As he started to blow the solvent out, the bearing started to spin. It sounded like a warning siren.

Within a few seconds, it went 'BANG' and roller bearings ricochet around the garage like bullets.

He yelled and started to nurse a sore hand. His boss came out and explained to him why he should never do that. (I think he had already learned the lesson.)

Well, I needed new wheel bearings, anyway.

--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+nanae@ch100-5.chem.lsu.edu

I used to turn my bicycle upside down and spin the devil out of the rear wheel and then slam on the brake.I own a 1961 made in Germany moped with sixteen original miles on it, it has bicycle pedals on it. You can rig up an old computer hard drive motor if you want to make your own wind speed aeronometer.I saw how to do it on the internet. cuhulin

On Tue, 25 Mar 2008 11:04:22 -0400, PeterD put finger to keyboard and composed:

Brushless DC fan motors use integrated Hall effect sensors/ICs for electronic commutation.

See these datasheets for examples:

These ICs have integral reverse voltage protection, as you have said.

Here is a more elaborate example:

I'm wondering how the EMF produced by the motor windings can generate a current that passes through the switching elements, either in the form of discrete transistors or internal to the commutator IC. I suppose that in the latter example the current could flow through the diodes.

As an experiment, I suppose you could attach two fan rotors back-to-back with a suitable spacer (eg velco?) and use one fan to drive the other.

- Franc Zabkar

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Please remove one \'i\' from my address when replying by email.

LOL great story.

I blew the rear end out of my 70 Dodge Charger R/T at a drag strip when I was kid. A couple of the bolts that hold the ring gear to the carrier blew right through the cover. Luckily nobody was standing behind me.

An Army buddy and I decided to head to Florida on a long weekend. We got about 50 miles from Ft. Rucker when he threw a connecting rod, and sent the piston through the oil pan. I found the piston about 150 feet away with part of the sheared wrist pin and broken rod bolted to one side. I took it back to the barracks and cleaned it up, and removed the piece of the connecting rod. If you were careful, you could balance it on the desk, on the one good surface. The next day we had some smart ass sergeant along with the captain for Monday morning inspection. The Sergeant grabbed it up and started yelling, demanding to know what it was, and why it was on my desk. The captain had a big grin on his face, so I smiled and told the jerk "It's a hemorrhoid extractor, would you like me to demonstrate it on you?" He stormed out of the room, while the Captain struggled to keep from laughing at him. :)

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I wasn't clear, I was thinking rip out the electronics in there now and add rectifiers...

It works. A hard drive spindle motor also makes a decent miniature 3 phase AC generator. You can even wire one up to another similar motor and it will run, just like a regular 3 phase motor.

When anybody ask me about what something is for, I tell them it's a windshield wiper for a billygoat's a..

You should never spin a dry bearing.One dry spin can ruin that bearing, and often does. cuhulin

They had DC muffin fans in the 60s? I don't recall ever seeing one, what were they used in? I've seen AC muffin fans powered by shaded pole motors, and a few DC fans that were just a fan blade stuck on the end of a little DC motor, but I've never come across one I'd call a muffin fan.

Indeed this is true for modern versions, but DC Muffin fans from the 1960s had brushes (electronic comutation would have been large and of prohibitive expense).

Michael

msg wrote in news: snipped-for-privacy@corp.supernews.com:

I salvaged and ratholed some 12V fans from PC power supplies,and after Hurricane Charlie knocked out power,I used two of them with a 12V/20 A-H SLA battery to give me some quiet air circulation at night so I could sleep in the 90+ deg temps. It was just enough to make me comfortable. I also had a 8-AA cell 12v fluorescent lamp that I made an ext.power cable to connect to a 12v SLA or car battery for lighting.

I was without power for 7 days.

--
Jim Yanik
jyanik
at
kua.net

I knew you'd ask ;) My recollections are from govt. contract gear that used

24 or 28 VDC fans. These may not have been "Muffin" brand fans but I am unable to inspect one any more as the gear is long gone. Anyone else with these recollections?

One remarkable fan that I wish I still had was the 400 Hz "Minicube" blower; about one inch on a side, it could easily levitate or blow itself off of the bench under power. These were used on F111A avionics boards (and no doubt other platforms as well)

Michael

I had one out of a military radio or test set that was 24 VDC. It was about 1.5" square, and about 2.75" deep. It was a regular brush motor, about the size of the early dust buster with a regular fan blade.

The GRC-106 used them, too. I had a handful of ones pulled for noisy bearings at the CE plant where we built the 106.

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When I lost power some many years ago, I got six 200 AH deep cycle 12V marine batteries (factory cosmetic seconds) to power a Sola 2.5KVA UPS which I wired into the breaker panel, first disconnecting the utility service. To charge the batteries I mated a 10 HP Briggs horiz. shaft engine to an old military DC generator set; it's duty cycle was governed by the batteries' specific gravity. The power was cleaner than what I normally had and the UPS was continuous duty rated ;)

Michael