AC EMF Radiation

[KnightMarauder]

I got my hands on some fans from something like a fridge or clothes dryer, something like that: Muffin XL and Muffin

Someone mentioned to me that AC equipment produces crazy EMF radiation that may pose a threat to the delicate electrical components in my computer. I don't have a gaussmeter to actually verify the existence of any substantial levels of EMF, so I'm in the dark on this one. Just wondering if it's something that I should be concerned about. (Because, you know, the integrity of my data is more important than the possibility of contracting cancer from something like that).

 

[dkozloski]

Fans like you describe have been used to cool electronic equipment of all types for at least half a century with excellent results. In fact, that's what the fans were designed for.

 

[RossGr]

Your house, your neighborhood our intire country and most of the world it pathed in the same 60Hz ratiaion that runs the Computer therefore the fan. It is not the EM Radiation that is of concern, it is the

Electric Fans are inheirently noisy electrical devices, I am not refrereing to acoustic nosie but ELECTRICAL noise. Where I see a potential for troubles is when people use the 5V and 12 Volt lines to get a 7V fan. While this works fine, you have inserted a electrical noise generator right into the middle of your power supply. This makes me nervous, many PSs may be able to filter the noise fine, others may not. The 5V line is used to drive most of the electronics on the Motherboard and periferal cards, nosie on that line can casuse lots of problems.

 

[KnightMarauder]

The Muffin fans I have are both AC.

So you could not hook them up to a power supply in any event (if you did, the fan would spasm for a moment and then be still because DC doesn't change polarity like AC)

Figure, could keep electrical noise on the line under control by using a separate circuit for the Muffin fans all together. Have a stripped down power bar stuck somewhere inside there with maybe a dimmer control switch (like the ones that control lights for a room). Because the fans work on 120V @ 60Hz (same as native line voltage in your house) there are a lot of options open that aren't really available with 5V and 12V DC circuits.

It was just that EMF issue that I was curious about. But as dkozloski mentioned, they have been used to cool electrical devices so they must be relatively harmless from an EMF stand point.

 

[RossGr]

Its not clear to me why you would be concerned about the 60hz radiation from this fan. It is the exact same radition that every ligth bulb or ANY device(virtualy every electrical device in your house) that runs on 60Hz emits.

 

[f95toli]

Originally posted by: RossGr
Its not clear to me why you would be concerned about the 60hz radiation from this fan. It is the exact same radition that every ligth bulb or ANY device(virtualy every electrical device in your house) that runs on 60Hz emits.

Fans are more noisy. They generate more 60 Hz noise than light bulbs. What I mean by this is that some 60 Hz goes into the "local" electric ground (GND) of your device (in this case computer), this means that the GND in your device is not really GND (the "real" GND beeing the GND connector in the wall). Hence you will have a 60 Hz signal going from your local GND (close to the fan) to the mains. This is the reason why proper grounding is so important in electronics.

You can see this effect easily if you use an oscilloscope: Measure the voltage between a place on your computer (for example) that should be grounded and the main GND, you will almost always see a 60 Hz signal (that can be significant).

Another problem is that fans tend to generate higher harmonics which means that you will also have 120 Hz, 180 Hz etc.

 

[KnightMarauder]

After doing a few impromptu tests (plugging in the fan and moving towards my monitor), there did not seem to be any visibly significant amounts of EMF radiation. Of course, this is highly unscientific, but lacking any other testing methodology to tell me differently, I'm going ahead and putting the fans in.

If my hard drives need formatting in a week, I'll let you guys know

 

[RossGr]

Shall I repeat myself?

Electric Fans are inheirently noisy electrical devices, I am not refrereing to acoustic nosie but ELECTRICAL noise. Where I see a potential for troubles is when people use the 5V and 12 Volt lines to get a 7V fan. While this works fine, you have inserted a electrical noise generator right into the middle of your power supply. This makes me nervous, many PSs may be able to filter the noise fine, others may not. The 5V line is used to drive most of the electronics on the Motherboard and periferal cards, nosie on that line can casuse lots of problems.

This statement is true for AC fans as well as DC, I just hope that he is taking proper care with these AC fans inside his box, because you are correct they do generate a lot of electrical nosie, as I already stated.


If you are seeing it on a Oscope then that is what I was talking about in my first post.

This is different then EM radiation, 60hz EM raditiation is 60hz irregardless of the souce.

To see the 60Hz radiated noise, simply set your oscope to a mV scale and hold the probe up in the air you will see plenty of 60Hz

It is not clear how you could get any indication of the presence of 60Hz, or any other electrical noise without test equipment.

 

[blahblah99]

Modern switching power supply does a good job of filtering out unwanted noise anyways...

The noise is further filtered on the motherboard, i/o cards, cd-rom, and hard drive circuitry with bypass caps.

The only problem you will ever have with AC EMF radiation is with the FCC, which has set standards on these issues.

Your not going to be able to do any in-home emf testing without the expensive equipment. At the very least, your going to need a spectrum analyzer and a faraday cage.

 

[f95toli]

60 Hz is tricky to filter out. You need huge bypass caps unless you load resistance is very big. I would avoid using anything that generates a lot of 60 Hz noise in a sensitive enviroment.

 

[KnightMarauder]

Correct me if I'm wrong (which I may very well be), but by placing the fans on their own AC circuit (separate from the computer's power line), that would eliminate electrical line noise caused by the fans because they wouldn't really have no way to contaminate the computer.

This was the reason for this post in the first place: as far as I can see, the only way the fans would interfere would be if there were significant enough EMI to affect other components.

 

[f95toli]

Correct, as long as the fan is not in the same circuit it should be ok. The 60Hz "radiation" is negligable.

 

[RossGr]

The only concern would be if you failed to electrically isolate the fans from your case. Be sure all wires are well insulated and do not allow any metal to metal contact. you do not want to create a new path to ground for 120VAC through your case.

 

[PowerEngineer]

I think your concern over "crazy EMF radiation" can be put to rest.

As f95toli says, the current from the AC fans will pass through your ground wire (going back to your local distribution transformer); and because that ground wire has some resistance (and reactive impedance) associated with it, there will be a small (largely) 60 Hz voltage difference between the ground measured at your PC and the ground measured elsewhere (your circuit breaker box for instance). Actually all your electrical devices contribute current to their ground wires this same way. This little bit of voltage is very seldom an issue for electrical devices.

What might be an issue is the magnetic fields that motors (both AC and DC) intentionally produce (because it is the interaction of the magnetic fields in the stator and rotor that produce the torque that turns the rotor). Some of these fields will leak out of the motors and have the potential for inducing currents in nearby circuitry. Of course, fans intended for use with electronic equipment are shielded to keep this kind of interference to a minimum, but your "fridge" fans might have proven to be a bit leakier.

Your test using your monitor is pretty clever. You should be okay, regardless of where you plug them in.

 

[KnightMarauder]

Thanks, powerEngineer -- you hit my main concern right on the head. I just didn't know the terminology for it: "inducing currents in nearby circuitry" is what I should have said right from the start.

Glad to know things will be relatively safe. As for the monitor thing, figured if my FPS2000 sub causes magnetic distortions in the monitor, then this crude test would be sensitve enough to detect any worrisome amounts of interference.

 

[rimshaker]

Relax. Just look for that "Class B" certification and you're good to go