Before plugging in an old fan first note what the voltage and type of current the fan is designed to operate on. The current will be either AC (alternating current like your house current) or DC (direct current which was once common but is rarely used today in the home for appliances). Fans run by a battery are DC fans. Do not connect a fan to a current type it is not designed to be run on to avoid damage to the fan motor.
If you have a DC fan you can still run it from your house current but you will need to connect a small and inexpensive BRIDGE RECTIFIER between the house current and the fan. This will change the AC current to a rough form of DC that the DC fan motor can run off of. In addition, a Variac may be needed to decrease the AC voltage to the fan's rated voltage or less. The Variac will be in the circuit BEFORE the bridge rectifier.
If your fan has an AC motor the only thing you might want to change is to lower the voltage to what the fan was designed to run on or even a lower voltage to run the fan slower and quieter. This is where the Variac comes in handy. Most Variacs are rated for 120 volts in and 0-140 volts out. If you fan is rated at 104 volts for instance, set the Variac to that voltage. From there you can decrease the voltage to where the fan still runs well on high and does not stall out. The fan should also be able to start from OFF at this lower voltage. If not you should increase the voltage to one that the fan will start up on. Set the fan speed switch on HIGH speed when using a Variac.
The two Variacs on the left, above are ones you are likely to come across. From left to right: 10 Amp Powerstat Type 116B (the similar but earlier Type 116 is 7.5 A.) made by the Superior Electric Co. in Bristol, Conn., 5 Amp Variac brand (the original) made by General Radio Co., Concord, Mass.; 5 Amp metered Variac. These probably all date from the 1960s or a little later. There are a few other brands made in the USA as well as plenty of chinese made "variacs". I like the quality of the older US brands. The Variac came in 5 and 10 amp versions as well as larger. The Powerstat came in 7-1/2 and 10 amp versions, possibly others. You can find these on ebay or at some swap meets, fan meets, radio swap meets, etc. The 5 amp. size is entirely adequate to run a couple of desk fans. Prices can be from $20 to $100 or more. Plug in an incandescent lamp to check to see that there is a smoothly increasing output at all points of dial rotation.
|A nicely restored c.1950 "classic" Variac 10 amp. Model V10MT10
I plug a fan into the outlet of the Variac then turn down the output voltage until the fan runs at a slower speed to my liking. I find that some of my 104 to 110 volt fans run very well and quietly around 90-95 volts. If you want more breeze just turn up the voltage toward the rated voltage.
CAUTION: When using a Variac to run a fan or motor that has a centrifugal start switch which is common on many of the earlier fans be sure to not run the motor at a slower speed that will cause the start switch to engage. That will energize the start winding which is not meant for constant running and cause the start winding to burn out. Please familiarize yourself with what a Variac can and cannot do and adhere to proper operating proceedures. If you don't know what is correct please ask someone who is an expert.
When running low voltage DC fans, (1.5, 6V, etc.), you must remember that the current required is much higher. It may exceed the ratings of the smaller Variacs on larger fans.
Do NOT use a light dimmer for a fan.
PLEASE spend the extra couple of bucks for a real "fan" speed control.
John McComas (used by permission 11-27-11)