The potentiometer that I used for the tranny control is not the best part for the job. It's rated power handling is .5 watts. This is not enough. How do I know?

IT CAUGHT ON FIRE!!!!!!

I'm gonna try to find one with a higher power rating, if not, I'll just use an on/off switch.

Stay tuned.

 

Woah.....Time to get a bigger Pot....

I hope this didn't cause any damage......

 

If I remember my ohms's law, 0.5watts should have been plenty enough.

E(electromotive force) = I(current) x R(resistance)

12V = I x 100,000ohms
12V/100,000ohms = I
I = 0.00012Amps

0.00012Amps x 12V = 0.0014Watts

What do you think? Is my calculation wrong or maybe a bad pot from Radio Shack?

 

hehe......nm

 

Your calculations for the current through the pot are right. But, you didn't consider that the resistance of the pot is variable. There was no fire when I had it turned up. It burned at the lowest setting. At the low setting there is almost no resistance so the current goes way up. Up enough to burn the contacts and my hand. If I cant find a pot that can handle the current and has a low price, I'll just go with a switch so I can turn it on and off. I can live without the adjustability.

12V / .01 Ohms = 1200 amps OUCH!

 

Yes, your're right, I was calculating high side insead of low. However, on the lowest setting, you still have the factory resistor in series. I measured it yesterday at 13K ohms, so shouldn't it look something like this?

12v/13,000 ohms = 0.00923A
0.00923A x 12V = 0.011W

 

Some of your measurements looked suspect so I did some re-checking. The factory resistor isn't 13K ohms...it's 13 ohms. Well, 12.2 on my car.

12V / 12.2 ohm = approx 1Amp (through the factory resistor)

P = I^2 X R

(1 X 1)amps X .5 ohms = .5 watts

The .5 ohm setting is essentially the minimum setting on a device that has a range from 0 to 1000000. It seems as though this pot was destined to burn from the beginning.





[Edited by mzmtg on 02-13-2001 at 11:38 PM]

 

err
You can fry yourself pretty good with 1 Amp...
ouch...
You need to put "Proceed with Caution" on this mod

^_^

 

Very true, but current is function of resistance too. You would need a hell of a lot of voltage to get 1 amp to flow through a person. People have pretty high resistance. This is why getting zapped a little by 120V hoiusehold current doesnt kill you...usually.

 

I should have known not to trust an electrical engineer with a multi-meter. Using a Fluke digital, my resistor measured 11.9 ohms. I also measured the voltage at the plug with the engine running and it measures 6.12 volts.

6.12v/11.9r = 0.514A
6.12v x 0.514A = 3.15W

I'm going to check some electronics catalogs today to see if I can come up with a suitable pot.

[Edited by sinewave on 02-14-2001 at 10:46 AM]

 

I just got done. I took back the pot. I got an automotive flip switch that is rated for 10 amps at 12V. So now I just have on off control...good enough. I mounted it in one of the little coin holders on the console.