12v dc cooling fan for a hot-running Icom 2200H 2 meter rig questions

[tom]

My brand new Icom 2200H 2 meter rig runs really hot when it transmits, so I
put a 12v dc cooling fan on top of it's cooling fins. The fan is supposed
to be for a computer power supply and it has 3 wires, black, red and white,
but I just put the red wire on +, and the black on -, and the white wire
isn't connected to anything. Because the rig only heats up when
transmitting, the fan doesn't need to be on all the time, so I put a 10k
variable resisitor in series with the fan and I can adjust the speed of the
fan or stop it altogether (if I had an on-off switch I would have used that
instead, but I don't right now and won't be able to get one for a while).
So, my questions are:

-- Is this arrangement OK?
-- Am I running the risk of burning something out or damaging it?
-- What is the white wire on the fan for?

 

[Chris]

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My brand new Icom 2200H 2 meter rig runs really hot when it
transmits, so I
put a 12v dc cooling fan on top of it's cooling fins. The fan is
supposed to be for a computer power supply and it has 3 wires,
black, red and white, but I just put the red wire on +, and the
black on -, and the white wire
isn't connected to anything. Because the rig only heats up when
transmitting, the fan doesn't need to be on all the time, so I put a
10k variable resisitor in series with the fan and I can adjust the
speed of the fan or stop it altogether (if I had an on-off switch I
would have used that instead, but I don't right now and won't be
able to get one for a while). So, my questions are:

-- Is this arrangement OK?
-- Am I running the risk of burning something out or damaging it?
-- What is the white wire on the fan for?

Hi,
I think you should be fine doing this. The white wire is for RPM
reporting (you should be able to pick up an electrical pulse on this
wire once every revolution or so); leaving it unconnected is fine. As
long as you are sure that your power supply is about 12V, the fan
shouldn't have any problems. I'm not quite sure about the speed
control thing; fans in computers are usually speed-controlled via
pulse-width-modulation rather than by changing the input voltage; it
might be safer to run it at on/off. On the other hand, I've used
computer fans before (admittedly only once) in my own circuits and
they worked fine with variable-voltage supply.

Chris
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