Your exactly dead on except I'm using a 50 ohm 5 watt pot to heat a loads that vary from 16-72 ohms. to dissipate dew from my telescope and different eyepieces. So why is this amp. meter not passing current, I'm bewildered that such a simple circuit is drawing up to 4+ amps in the pot before it smokes? Thanks for seeing the simplicity of the circuit.

With no load on the wiper, then the pot is rated to handle 316mA. You need to be careful exceeding this even when the pot is actually dissipating less total power because the current is going through only a portion of the winding before exiting via the wiper. You have two issues at play -- total heat that the package as a whole can handle and localized heat within the part of the windings that are actually carrying current.

At 12V your total resistance (load plus the portion of the pot winding between tap and supply) should probably be kept above about 35Ω. When your load is down in the 16Ω, then turning the pot more than about 60% of the way toward the wiper is probably starting to stress the windings.

 

What Brownout said.
I think most of the confusion resulted from the fact that you have a 4-wire ammeter, which I had never heard of until now.

Most probably it's a digital Amp-meter, where the smaller wires supplying the power for the chips inside to work. You can find plenty of those cheaply on eBay.

Allen

 

If A meter is not working, might check resistance of heavy leads, a common shunt produces 50mV @ 10A or 50mΩ. Fuse maybe?- but then pot used as rheostat woul not get hot-- back to square one. Dead chip? If it is drawing up to 4 A, then possibly load is being bypassed; rheostat @ 3 ohms then passes 4A- 48W?? = Hot.

 

Turn the wiper fully the other way (or disconnect the wiper and hook the other fixed end of the pot to the meter). What is the current that is indicated?[/QUOTE]Man who argue with wife during day, has no piece at night. Confucius
Two of the wires are for powering the LE D's. The other two for inserting between circuit. Chinese

 

This is not a case of Chinese junk, but of fundamentals.

I have a tutorial on LEDs you might like...

LEDs, 555s, Flashers, and Light Chasers

If you want a good way to regulate LED brightness, look at chapter 5.

Also, I have a beginning album on the subject...

LED Drivers

 

Two of the wires are for powering the LE D's. The other two for inserting between circuit. Chinese

What LEDs?

PLEASE! What is the make and model of this meter?! I want to try to look up its specs so that I can get an idea of what is and what is not reasonable in terms of how to use it or how it should behave.

 

If you keep smoking the pots, you might get a urine analysis test.

 

If the meter is one of the ones they sell on Ebay, they aren't to be powered by the same power supply as the circuit. Also they need a "shunt" resistor to measure the amperage in the main circuit. Probably blew/smoked the ammeter and it is shorting the circuit your trying to measure.

 

Did you hijack your own thread??
http://forum.allaboutcircuits.com/showthread.php?t=70901