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ferdb · 10-07-2004, 01:10 AM

a lot of 240v fans won't spin at 120v, although some will - very slowly. You're better off getting a 120V fan and running it at reduced voltage.
You can use a Variac or variable transformer to crank the AC voltage up and down and control the AC fan speed that way. I've seen variable transformers for $50 at Fry's that would be great for fan speed control. Fan speed is not linearly related to the AC voltage by the way, it drops off fairly quickly as you drop the voltage.

You can also use a fixed transformer, which is what I use on the desk fans I have placed under tables. Fry's had a 40VA transformer with 120/208/240 volt primary and a 24V secondary. I wired it up as an autotransformer with the 208V primary winding connected to the 120V AC wall. This gave me ~69V on the 120V primary tap on which I stacked the 24V secondary winding adding another 14V (not 24V since the 208V primary is only running on 120V) giving me a total of ~83V. This is pretty much ideal for the fans I have so they run almost silent at the lowest of their 3 speed settings. I put the whole thing in a little box with a switch to select the 83V or 120V and made a small extension cord out of it all.

10-07-2004, 01:10 AM	#6
ferdb Cooling Neophyte Join Date: Sep 2004 Location: texas Posts: 68	a lot of 240v fans won't spin at 120v, although some will - very slowly. You're better off getting a 120V fan and running it at reduced voltage. You can use a Variac or variable transformer to crank the AC voltage up and down and control the AC fan speed that way. I've seen variable transformers for $50 at Fry's that would be great for fan speed control. Fan speed is not linearly related to the AC voltage by the way, it drops off fairly quickly as you drop the voltage. You can also use a fixed transformer, which is what I use on the desk fans I have placed under tables. Fry's had a 40VA transformer with 120/208/240 volt primary and a 24V secondary. I wired it up as an autotransformer with the 208V primary winding connected to the 120V AC wall. This gave me ~69V on the 120V primary tap on which I stacked the 24V secondary winding adding another 14V (not 24V since the 208V primary is only running on 120V) giving me a total of ~83V. This is pretty much ideal for the fans I have so they run almost silent at the lowest of their 3 speed settings. I put the whole thing in a little box with a switch to select the 83V or 120V and made a small extension cord out of it all.