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Re: fan wiring

In a message dated 1/14/2001 12:50:40 Pacific Standard Time, 
Aquatic-Plants-Owner at actwin_com writes:

> cheapest light dimmer I could find at Home Depot and hooked
>  it up to one of the four inch RadioShack AC cooling fans (they only
>  sell one model that fits this description).  It did work.  However,
>  I found that I could only control the fan in a narrow range of
>  speeds, and that there was some sort of noise from the fan when
>  I slowed it very much at all.  The net effect was that it did not
>  make it very quiet.

AC motors are designed to run on what is called 60 cycle sine wave current.  
Some  of the cheaper speed controllers or light dimmers put out what is 
called "square wave" current, and some fans and electric motors chatter and 
complain loudly when run on square wave current.   They also tend to run hot, 
and can actually burn up when run on square wave current.  Although wasteful 
of power, that's one of the advantages of a Rheostat:  sine wave in, sine 
wave out.  I suspect if you switch to DC motor fans (such as are used in your 
computer power supply), you'll get better speed control and quiet-running 
fans.  I believe Radio Shack sells little 12v DC power supplies with variable 
voltage, although they many not be the cheapest things you've ever bought.  
Expect to pay $40-100 for a small variable voltage DC supply.  However, you 
can also expect very quiet and controllable fan operation as well.