| Author |
Message |
    
Starface
Advanced Member
Username: Starface
Post Number: 629
Registered: 1-2005
| | Posted on Tuesday, May 30, 2006 - 5:11 pm: | 
|
I am working on a portable radio cabinet and have installed a 5"
cooling fan in the back. The fan is out of a PC and runs on 12VDC.
When I hook it up to the power supply, it runs perfectly - except
that it's a bit fast for what I want. (Also noisy)
I want to slow it down so I added a simple variable resistor pot
rated at 25 ohms. This helped some. It slowed the fan down enough
where it doesn't blow the knobs off my radio but I would like to be
able to adjust it more. What would be perfect is to add a resistor
in series to drop the voltage even more...
The question is... What value resistor and what size should I use?
It would be nice if the pot would go from "off" to "mid speed"
instead of from "mid speed" to "very fast" as it is now.
Anyone have any ideas?
Starface
KI4NBE |
Tech291
Moderator
Username: Tech291
Post Number: 395
Registered: 11-2004
| | Posted on Tuesday, May 30, 2006 - 8:13 pm: |
|
George,
Most of those fans have a tach circuit in them and wont run below a certain speed.look up a simple varible voltage regulator using a LM-317 i.c.,Also check on a fan controller/tempeture display for a computer tower.
TECH291
CEF#291/CVC#6
KC8ZPJ |
Chad
Advanced Member
Username: Chad
Post Number: 874
Registered: 11-2004
| | Posted on Tuesday, May 30, 2006 - 8:16 pm: |
|
Most computer fans are brushless designs and are not driven from current. Inside there is a small PC board and driver circuitry to enable it to... you guessed it... maintain a constant speed. This is important in a computer because as the power supply is under load it's more important to maintain fan velocity. There are adjustable speed fans out there, check the local computer warehouses, they are niot that much more money.
Chad |
Starface
Advanced Member
Username: Starface
Post Number: 631
Registered: 1-2005
| | Posted on Tuesday, May 30, 2006 - 10:17 pm: |
|
Thanks for the help
George
KI4NBE |
