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View Full Version : Bout' to build a Rheobus ...

DKYoda
10-06-02, 09:41 AM
And I have a few questions for you EE's out there :beer:

I always like to "Overkill" my hardware to keep things rock stable ..
I found a place to aquire 15 Ohm ,15 Watt Ceramic Rheostats..

I keep seeing peeps using the 100 Ohm stats and was curious if the 15 ohm rating was an issue ..

Is the Ohm rating on a stat the total resistance when in the lowest speed position ??

Please advise ...:cool:
DKYoda
10-06-02, 03:11 PM
Any takers ??
athlonnerd
10-06-02, 09:35 PM
yeah, 100 ohms will let you run slo0wer than 15 ohms. rheostats are so ugle though, why not use pots and transistors
rUfUnKy
10-06-02, 09:40 PM
If you havn't checked this out it might help ya out.. http://www.fanbus.com/thelab/rheostat.htm
DKYoda
10-06-02, 10:16 PM
Yeah .. I saw that earlier today ..
Seems fairly simple ..
I have a 120 on my Heater core rig and wanted to make sure I had a Rheostat strong enuff to slow her down without overheating ..

Thanx Peeps !!

I'll try to find a 100 Ohm pot with a little more watt capacity than those Jameco's have ..

If that doesnt pan out I'll go this route ..

http://www.overclockers.com/tips910/
Since87
10-06-02, 10:44 PM
Originally posted by DKYoda
I'll try to find a 100 Ohm pot with a little more watt capacity than those Jameco's have ..
http://www.overclockers.com/tips910/

Hold up. That rheostat is probably fine.

What is the total current rating of the fans you want to control?
(Add up the Amps numbers printed on the fans.)

If it is 0.8 Amps or less, that 15 Ohm rheostat will allow you to turn your fan voltage down to 6V or lower. Also, if the fans draw less than 0.8 amps at 12V, the worst case power dissipation in the rheostat will be 2.4 Watts. That rheostat is probably quite adequate for what you want to do.
Since87
10-07-02, 08:35 PM
I got that all wrong. Posting too late at night.

If the fan load is 0.8 Amps or MORE, that 15 Ohm rheostat will allow you to turn your fan voltage down to 6V or lower. You'd need a fan load in excess of 10 Amps to hit the max power rating of that rheostat.

Again, if you can send me your total fan load I can calculate the idea rheo value.