# question about electric fan motor

• posted on January 21, 2006, 3:01 pm

I have six electric fans that were salvaged from an old computer equipment cabinet (not a PC, but data center size equipment). I'd like to repurpose them for either a downdraft cabinet or air filtration system. The label states that they are 230V. Is there any possibility of running them on standard 110V house current?
Thanks
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• posted on January 21, 2006, 3:25 pm
Your options are : a) Get a 110/220V transformer (not cheap) b) Run a 220V line for this purpose. Your house will likely have 220V capability. The normal 110V feed is two separate phase 110V line. You get 220V by having a breaker join both lines. c) Get rid of the 220V units and replace with 110V units.
If you run the present fans on 110V they will burn out. The motor is designed for a certain wattage. Watts = Amps x Volts. If the Voltage is half design, the Amps will be twice design and normally burns out the motor, typically very fast and "energetic".
Dave Paine.

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• posted on January 21, 2006, 8:26 pm

Running at half voltage will not double the current consumption, it will basically halve it, resulting in about 1/4 of the rated power.
A motor has a particular impedance seen "looking" into its cables. This has nothing to do with the voltage you apply, but rather is a function of the coils inside the motor. The motor isn't some magical piece of machinery which draws constant power (wattage). It follows Ohm's law: V=I*Z, where Z is the impedance. If you solve this algebraically for the current I, you get I=V/Z. Since Z doesn't change, the current drawn is directly proportional to the voltage applied. Hence, half the voltage results in half the current.
I suppose I need to add an asterisk to this comment because motors are somewhat unique. The impedance of the motor is dynamic; it gets much higher as the motor spins up, because the mechanical motion of the motor acts as a generator, essentially creating its own current to some extent (usually called back-EMF). That's why motors draw a lot more current upon startup and when they are heavily bogged down than when they are running at full speed. Thus, since a motor running at half voltage is likely going to be spinning more slowly than one at the full rated voltage, it's dynamic impedance will be somewhat lower and it may draw somewhat more than half the current, but definitely NOT twice the current.
At any rate, I still agree with Tyke's conclusion - don't do it.
One way you could possibly get luckly: If you have more than one 110V circuit in your shop, two of them may be on different legs. In that case, you could run two plugs from two outlets over to your table and use the hot (black) wires from each to form the two legs of the 220V circuit. You could just wirenut the neutrals together. This may violate your electrical code, though.
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• posted on January 21, 2006, 8:33 pm

[...]
On the other hand: Fan motors are sometimes made slower by putting a transformer in, sometimes even biggish (several kW) three-phase fan motors are slowd by adjustable three phase transformers. (Seen that once when a cooling fan of that type used to cool some delicate electronics blew so much air that the airflow made the electronics boards vibrate too much, so the fan had to be slowed down, and an electronic dimmer was out of the question because of the electromagnetic noise it would produce...)
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto: snipped-for-privacy@physik.uni-bonn.de Phone: +49 228 73 2447 FAX ... 7869
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• posted on January 22, 2006, 12:28 am
Those things work by changing the phase angle between the voltage and current. The voltage itself is not reduced.
Really though anything that the OP tries will cost a lot. Jim
Phone: +49 228 73 2447 FAX ... 7869

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• posted on January 22, 2006, 12:42 pm

If the fans are the square "muffin" or "boxer" type fans you might be able to successfully run them off of 110v. Years ago we would scavenge these type fans for use in cooling the home brew stereo amps we constructed. Running them at 110v made them run at 1/2 speed which would move some air but would not add any significant unwanted noise if implemented carefully. We never had a problem with them overheating that I am aware of, they were supposed to be internally thermally protected, but we never had any shut down or do nay thin else out of the ordinary.
It seems to me that even now that the ac powered fans are more effective than the PC's 12v howling monsters. I found a reasonably good source of both 110v and 220v ac fans at surpluscenter.com. I always use them with an add-on fan filter mounted so it can easily be changed/cleaned without having to disassemble whatever you are using them for. I have used them for everything from replacement/upgrade for commercial refrigeration condenser units to embedded cooling inside built-in home theater systems. good luck, regards, Joe.
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• posted on January 22, 2006, 11:30 pm
Thanks all for the info. The fans I have are 10" diameter round aluminum case fans made by Nidec Torin. They are no longer made. According to the manufacturer, they each have an airflow of 530 CFM. The motors are thermally protected and are abll bearing type. If I had 230V power easily available, I think they would be quite useful. Maybe I'll Ebay them.
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• posted on January 21, 2006, 3:27 pm
snipped-for-privacy@gmail.com wrote:

Probably not, although they should work fine on 220V house current.
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• posted on January 21, 2006, 3:58 pm
Look around for a 50-100W transformer built for overseas appliances. The fans don't take much power. Any transformer with a 120/240 primary can also be used, if big enough. There are lots of these in industrial control systems. How good a scrounger are you? to use the dual voltage primary, feed 120 into one end and the 120 tap. Take 240 from the same end and the 240V tap. Leave the secondary open. Wilson

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• posted on January 21, 2006, 4:05 pm
Cheaper to buy a 120 V. fan than do all the conversions/wiring. Bugs
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• posted on January 21, 2006, 4:21 pm
On 21 Jan 2006 07:01:21 -0800, snipped-for-privacy@gmail.com wrote:

Make an auto-transformer to step up 110V to 230V. This needs a large transformer (three times the total fan rating) with a primary winding that's centre-tapped for 0-110V-230V. These are common in European electrical equipment from the '50s to the '80s - not sure how easy they'd be to find in the US.
Then feed your 10V current in on the 0-110V tappings and take a fan supply from the 0-230V tappings. Ignore the secondary (leave it unconnected). Place this inside the fan cabinet, earth as appropriate and insulate/label all the 230V side as if they're all "hot" (i.e. don't rely on anything being neutral or at low potential)
I'd expect these to make a usable air filter that's very quiet, but maybe a bit underpowered. I wouldn't expect them to work for a downdraught sanding table.
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• posted on January 22, 2006, 12:11 am
Look around for a 50-100W transformer built for overseas appliances. The fans don't take much power. Any transformer with a 120/240 primary can also be used, if big enough. There are lots of these in industrial control systems. How good a scrounger are you? to use the dual voltage primary, feed 120 into one end and the 120 tap. Take 240 from the same end and the 240V tap. Leave the secondary open. Wilson

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