Re: AC Fan use in PC??

Its not such a good idea to have mains power leads wander around inside a PC. You might touch one of them. Also spikes on the mains get an opportunity to jump into your logic circuits, oops....

The original IBM PC and XT supplies used AC fans.

Where do you come up with this crap? Millions of AC fans were used inside mini and mainframe computers without any of your gloom and doom ever happening.

Before the ATX form factor, the AT power supplies had AC running to the power switch on the front panel. Again, none of your projected crap happened because of this. They use DC fans in PCs because they are cheaper and lighter than cast aluminum fans.

Just make sure that you use safe wiring practices, and route the cables along the metal chassis, away from the data cabling to keep from picking up any RF from inside the case.

Noise? The AC fans don't have brushes so the only radiation would be at the line frequency from the motor's windings.

And they were contained INSIDE the powersupply that even had tamper proof screws to prevent silly people getting electrocuted on the supposed safe 120 volts.

Oh! and those power switches were mostly carefully insulated, but better practices have evolved so ancient things are not always the way we should stick to just because they worked when we did not know better. Real IBM AT power supplies had the switch within the powersupply case. It was only cheap Taiwan knockoffs that had remote AC switches.

Nope. Ac fans are nice.

Not that will affect a computer. Hum from a fan can inject microvolts into low-level analog circuits, but the brushless DC fans are just about as bad as the AC fans, just different waveforms and frequencies. The DC fans can do horrendous things to shared power supplies, since they draw current in nasty peaks.

John

I have a 120V fan in my computer, it runs just fine. I had it for years and I never turn this computer off. (it runs linux).

Yep. I once had to "quick-fix" a GenRad portable tester that had wavy lines in the CRT due to a "DC" fan.

I fudged it by measuring the ripple current in the fan and drawing additional current to keep the draw fixed at a constant amount... sort of a smart shunt regulator ;-)

...Jim Thompson

So, you've never seen a properly installed AC fan with the insulated plug in connector or finger guards? Its a pity that your education is so lacking. Real computers have air filters on their AC fans. Too bad you've only played with toys. Some of them have the DC fan mounted outside of the "Metal Box", and have no finger guard.

BTW, there never were any "REAL IBM AT" power supplies. IBM never made a power supply for the AT because they all came from outside vendors. The same vendors that made the power supplies with external power switches made supplies for the crappy AT case with the switch on the back corner of the case. If that design was such a good idea, why did IBM abandon it on their PS/1 PS/2 and Aptiva computers?

People who post meaningless s*it and proclaim it as Gospel.

I think this approach is kinda elegant:

(an active, shunt noise-canceller)

Cheers, James Arthur

The GenRad PSP was pretty high current so little conventional shunt regulators wouldn't work.

So I added a small resistor in series with the fan ground connection, a current mirror whose output device (NPN) emitter was connected to the top of that resistor, and the collector to B+.

So it drew a current equal to the current mirror setting, the transistor drawing what the motor didn't.

...Jim Thompson

Slick!

James

Lotsa reasons:

(1) The soft-on power protocol in a PC means there's no place where

(2) There's gigahertzes of noise running around inside the case. Are you sure you want to couple that noise to the AC line?

(3) The line power wires are hipot tested to 1500 volts or more. Are you sure your fans are rated for that?

(4) There's no good way to control the fan speed--those AC motors have a rather steep voltage/cfm curve when they get below a certain point. And running AC line to a front-panel pot is not recommended.

(5) Most DC fans have a tachometer output that can be fed into the motherboard monitoring bus. Do your fans have that?

Otherwise OK.

This appears to be just a single unit mod.

There should allready be filtering on the mains.

I have used dimmer type controls before. I have used a thermister to control the speed by sensing th heat.

No, but the DC fans are much more efficient.

I still use some fans out of a PDP 8, Linc 8's They still work and are sleve type.

When I worked at DEC, those things really howled. They still do.

greg

Probably because by then they had figured out that it's a PITA to reach all the way around the back of the computer every time you had to do a hard reset. ;-)

But, back to AC fans - I've installed AC fans, plugged and unplugged those little connectors that Michael has described here, but, in all honesty, I couldn't testify under oath that the ones that I did that to were in home PCs.

But that's neither here nor there. Splork sounds like he/she knows what he/she's talking about, and knows 115V from a lollipop, so I say go for it! ;-)

Me, Too! ;-)

Cheers! Rich

Kewl! You've reinvented the Ripple Regulator! I once worked on a switcher that for its day and age, was mind-boggling. 300 watts out, in a package about nine inches long, four inches thick, and about six inches tall, with one of the long corners cut off so that it could slide into a 9" tube alongside another one that was a mirror-image, at least mechanically.

In 1971.

It had subfunction names I'd never heard of (what the hell is a "Slave Inductor?"), and I had just aced Tech School! (well, a couple years previously.) Totally bleeding-edge state-of-the-art wartime military design. Everything about it was classified.

Except, I hope, the term "Ripple Regulator". It was a series pass, not a shunt, but it used the same principle as yours there.

Thanks! Rich

Michael, There is no need to get personal. I only mentioned a few facts. Yes I fixed IBM mainframes for many years (1440 onwards )before the PC was announced and yes they had 120 volt fans as you say. The PC was designed for a different market and had some stricter safety objectives. Some of the later IBM PC PS/2 etc had the power switch still inside the power supply but operated by a push/pull wire from the front panel still to keep all the mains AC within the PS box.

Times have changed some for the better some for the worse.

Have a nice day.

Not mine, JT's and (for noise reduction) Charles Wenzel's. Wenzel's website (the link I gave) is full of kewl stuff. Check it out Rich, you'll luv it. But, as far as "ripple regulators," I thought the ATF handled that.

Cheers, James