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rheostat
- Thread starter j2me_tech
- Start date
- Joined
- Dec 17, 2001
- Location
- Houghton MI, MTU, up in the UP eh!
Could you be a little more prescise in what you are asking? I don't really understand....
LuckyBob
Disabled
- Joined
- Mar 19, 2003
- Location
- Seattle, WA, USA
He's asking if the rheostat he bought for use as a speed control device for his fan will burn out the fan.
No, it won't, but it might burn the rheo if it gets hot enough. Rheostats just absorb the flow of electricity through a circuit, so the worst it can do is just restrict so much electricity that the fan won't spin at all. Speaking of which, with a 50k ohm rheo, you'll get zilch control over the fan. I'd be willing to bet that you'll get about 10 degrees of rotation with the rheo between full on and full off.
One option is to use a resistor in parallel with just the rheostat, which will lower the effective resistance of the rheo (IE if you used a 50k ohm resistor soldered across the appropriate pins of the rheo, you'd get a maximum resistance of 25k ohm). The formula for this is 1/((1/R1)+(1/R2)+...+(1/Rn)) = total ohms. You can try different values to see what you like. Generally I use 1k ohm potentiometeres (as they're cheaper than rheos anyway).
One last suggestion - if you plan to use the rheo to control the fan all the way to a stop (and there's enough resistance to do it), keep in mind that there will still be electricity flowing through the rheo at all times, and it gets disapated as heat. If you "stop" the fan, the rheo's absorbing almost all of the +12VDC power that the fan would've been taking, so it's just wasted power. A simple fix - tear the rheo apart and you'll see the "track" which the actuator runs on - if you cut a swath in the track with a boxknife just before the track ends on the "off" side of your rheo (depends on how you solder it up), it'll actually function as a switch and a rheo. Only problem is if you've put another resistor in parallel with the rheo, then that resistor gets all the electricity from the +12VDC line, so this trick only effectively works if you're OK with the amount of fan control you get with the rheo alone.
Good luck.
No, it won't, but it might burn the rheo if it gets hot enough. Rheostats just absorb the flow of electricity through a circuit, so the worst it can do is just restrict so much electricity that the fan won't spin at all. Speaking of which, with a 50k ohm rheo, you'll get zilch control over the fan. I'd be willing to bet that you'll get about 10 degrees of rotation with the rheo between full on and full off.
One option is to use a resistor in parallel with just the rheostat, which will lower the effective resistance of the rheo (IE if you used a 50k ohm resistor soldered across the appropriate pins of the rheo, you'd get a maximum resistance of 25k ohm). The formula for this is 1/((1/R1)+(1/R2)+...+(1/Rn)) = total ohms. You can try different values to see what you like. Generally I use 1k ohm potentiometeres (as they're cheaper than rheos anyway).
One last suggestion - if you plan to use the rheo to control the fan all the way to a stop (and there's enough resistance to do it), keep in mind that there will still be electricity flowing through the rheo at all times, and it gets disapated as heat. If you "stop" the fan, the rheo's absorbing almost all of the +12VDC power that the fan would've been taking, so it's just wasted power. A simple fix - tear the rheo apart and you'll see the "track" which the actuator runs on - if you cut a swath in the track with a boxknife just before the track ends on the "off" side of your rheo (depends on how you solder it up), it'll actually function as a switch and a rheo. Only problem is if you've put another resistor in parallel with the rheo, then that resistor gets all the electricity from the +12VDC line, so this trick only effectively works if you're OK with the amount of fan control you get with the rheo alone.
Good luck.
- Joined
- Mar 11, 2003
doesn't the TT smart fan 2 already have control?
