On Mon, 24 Jan 2011 13:17:46 -0800, "Jon Danniken"
wrote:
wrote:
I am fabricating a small box that will house a couple of "muffin" fans
to direct air behind a fireplace insert. I have a 3 position switch
(0, 1 , 2) so that I can run either one or two fans. I need a "check
valve" (diode?) to prevent both of the fans from running when the
switch is set for a single fan. I am having a bit of trouble with
selecting a diode. I did a quick google search that leads me to
believe that the diode needs to be specified based on reverse current
to be blocked and the voltage. The fans draw 20W each. For such a
cheap simple part, I wish to buy it at Radio Shack but looking at
their web page:
http://www.radioshack.com/family/ind...goryId=2032269 I am
having difficulty trying to pick one - many of the diodes do not
even show a spec sheet. Recommendations please. Once I complete this
task I can get down to forming the sheetmetal. Thanks
You don't neet a diode, you need a switch. Specifically, a DPDT Center-off
switch.
Ground out both fans, and use the switch to switch the hot. Here is a
picture of how you would wire it up:
http://img510.imageshack.us/img510/9725/dpdtfan.jpg
As you didn't provide specifications for your fans, determining the correct
ratings (and size and mounting hole) for your switch is up to you.
Personally, I would order it online and get the switch you want, instead of
buying whatever radio shack has laying around made by God only knows who.
Jon
IF he is running DC fans a center off double throw single pole switch
will work with a diode. With the diode connected between the positive
connections, and the negatives tied together, putting power to one
side of the diode will run the one motor, with current to the other
fan being blocked by the diode.
Put power to the other side of the diode and the first fan will run
through the diode, and the second fan will run full power.
Not a bad way to do things - and the diode just needs to handle
adequate voltage and current for one motor. If the fans are 12 volt,
he needs a 25 voltpiv, 2 amp diode at the very minimum. I'd use a 50
volt 5 or 10 amp diode if I was doing it. The 3 amp barrel diode on
the rat-shack site would do the job. It doesn't say on that site, but
it is a 50 volt PIV diode. (some are actually 200PIV) - look up
ecg-5800 for 50 volt,5801 is 100 volt, 5802 is 200 volt.
A 6 amp diode would be a 5850, 5854, or 5855 and would be a
stud-mount.(DO4 case)