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Rheostat

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RJ

Member
Joined
Apr 12, 2001
Location
Michigan ,USA
Since the Swiftech rheostats are on B/O I decided to make my own for my FOP38 I went to Radio shack and bought one, well the specs on the fan say 3.5 watts The rheostat is rated 3watts, Its working fine and not getting to warm, however I'm kinda nervous about it. It sure made a difference in the DB's of the fan with only sacrificing 1* Can anybody give me there opinion on it?Or should I just break down and by the Swiftech or go with water cooling? I really don't have a big cooling problem I would just like to improve it.Right now it's running 40*c idle and 45*c with a load. by the way I also tried going with an 80mm 42cfm fan on the FOP38 and the temps went up 3*.
 

bdf24

Senior Member
Joined
Feb 15, 2001
Location
Harford, WI.
If your happy with where your at I would'nt worry about that .5w's. It should be ok. Instead of the Rheostats I used DPDT toggle switches to change voltage from 12v to 7v's. Got some cool LED's as well. But the good thing about the rheostats is you have a lot more control over fan speed. Where as I olnly have 2 options.
 
OP
RJ

RJ

Member
Joined
Apr 12, 2001
Location
Michigan ,USA
Thanks for your reply,I'll keep an eye on it for the next couple of weeks and see what happens
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
Electronics Class is now in session.

The wattage your fan consumes is when you are operating it at 12V. The Rheostat lowers that voltage to produce the slower speed. At the reduced voltage, the wattage your fan consumes goes down.

You would have a valid issue if you were using, say, a 15V supply and using the Rheostat to lower the 15V down to 12V.

Class dismissed

Hoot
 

coldmop

Registered
Joined
Mar 4, 2001
but how does the rheostat drop the voltage? by adding resistance. Therefore to pump the electrons (at a given speed,ie Voltage) through the wire you need more force which has to be handled by the power supply in the form of Amperage. (over time the good Dr. Watts) Wish I had one of those inductance field Ammeters to get some exact measurement on how rheostats affect the power supply. Tough calculation on DC brushless fans running out of spec. The cure all is a Pulse Width Modulator but I keep burnin' them out.
 

Yomama

Senior Member
Joined
Dec 18, 2000
Location
The battle born State
I am using the same rheostat. I actually inserted it into the 12V lead of a 4 PIN P/S cable extension. I am running it controlling 2 fans with a total of 7.4W. The rheostat is in series with the fans' resistance and therefore the wattage by which the fan is reduced is applied to the rheostat.

Mine gets quite warm if I reduce the speed a lot but it's running alright.

Yo