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Old 10-21-2010, 10:44 PM   #1
Ichthy
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Default Semi-urgent Potentiometer help

I just bought a new potentiometer for my DIY stirplate. *disclaimer* I don't understand very much electrical lingo.*

The potentiometer is rated at 25 ohms and 3 watts - it is the part recommended in the often used stirplate thread. I'm powering a 12 volt computer fan and am using an AC converter that is rated at 9V output.

My issue: I soldered the connections to the potentiometer and when I turn on the power the potentiometer heats up rather quickly and becomes too hot to hold in your hand. There is no smoke or sparks and the fan is turning fine. I have full range of speed adjustment.

My question: Is this heating problem an issue? I'm wondering if I've to powerful an input and it's overloading the potentiometer?

And advice would be much appreciated!

Cheers



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Old 10-22-2010, 12:32 AM   #2
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Man, I am trying to tap into knowledge at least 15 years old from when I left my former career as an electronics tech, and from the posters here I would expect someone w/ active knowledge to chime in at some point.

BUT, that being said- a potentiometer is simply a variable resistor, which will normally heat up during use. Sometimes very hot depending on the load. This sounds a bit extreme to me and the answer would lie in the input voltage- or more likely - the amperage. I run a 9v 500 mA with no crispy-finger heat - knowing your amperage would probably help with proper advice.



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Old 10-22-2010, 01:13 AM   #3
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Ok, thanks for your help, but I figured it out after some extensive googling.

To start I'm a moron. I had the ground from the power and the fan wired to the 3rd pin of the pot. I removed them from the 3rd pin and no more problems. I just assumed you need all the wires connected to the pot. Lesson learned.

Thanks again for responding, I really aprreciate it.

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Old 10-22-2010, 01:46 AM   #4
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Maybe you adapter is AC-AC9v instead of AC-DC 9v

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Old 10-22-2010, 03:04 AM   #5
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Quote:
Originally Posted by Ichthy View Post
I just bought a new potentiometer for my DIY stirplate. *disclaimer* I don't understand very much electrical lingo.*

The potentiometer is rated at 25 ohms and 3 watts - it is the part recommended in the often used stirplate thread. I'm powering a 12 volt computer fan and am using an AC converter that is rated at 9V output.

My issue: I soldered the connections to the potentiometer and when I turn on the power the potentiometer heats up rather quickly and becomes too hot to hold in your hand. There is no smoke or sparks and the fan is turning fine. I have full range of speed adjustment.

My question: Is this heating problem an issue? I'm wondering if I've to powerful an input and it's overloading the potentiometer?

And advice would be much appreciated!

Cheers
If your aiming for 9V and you have 12V the resistance of the pot (potentiometer) should be set to 3/12ths of the total resistance (the other 9/12ths being the fan). This also means the 3/12ths of the power going into the circuit it turned into heat by the pot (the other 9/12ths to power the fan).
But more on topic, if the third wire doesn't fix it fully; you may be exceeding the 3watts the pot is made for. Many small fans use 10+ watts. Is there any markings on the fan as far as wattage or amperage?
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Old 10-22-2010, 12:37 PM   #6
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Quote:
Originally Posted by DrJerryrigger View Post
If your aiming for 9V and you have 12V the resistance of the pot (potentiometer) should be set to 3/12ths of the total resistance (the other 9/12ths being the fan). This also means the 3/12ths of the power going into the circuit it turned into heat by the pot (the other 9/12ths to power the fan).
But more on topic, if the third wire doesn't fix it fully; you may be exceeding the 3watts the pot is made for. Many small fans use 10+ watts. Is there any markings on the fan as far as wattage or amperage?
Fixing the ground wires solved my problem completely. The pot doesn't even warm to the touch now. It's been spinning all night without any problems.

I was probably being overly cautious but I had to order the part in because radio shack in my town doesn't stock it. Was trying to avoid burning the thing up.

Thanks everyone for suggestions!


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