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Having issues with my power supply

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O built a power supply several months ago and it worked fine. It measured all the right voltages at the correct spot. But now when I went to go and fix some of the wires connected to the pretentsheomiter that got diconnected. Then all the sudden the resistor starts to smoke for some reason. I am very confused by this and would like some other ideas on why.
 

MikeMl

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Most Helpful Member
Welcome, Zackary,

The reason that resistors smoke is that you exceed the power dissipation rating of the resistor! Heating of a resistor is (more-or-less) proportional to the power dissipated there-in. Resistors have power ratings, like 1/4W for a small film resistor up to 10s of W for large cement or wire-wound resistors. Pots are usually 1W or less.

What did you smoke? Post a schematic and indicate which resistor got hot.
 
well this was a school project, and I probably can't find the schematic again. But I can tell you that there is one resistor in the circuit [a 90Ω 5% restistor]. I
 

jpanhalt

Well-Known Member
Most Helpful Member
At 12 V across it, that resistor should be at least 2 W, 4 W or more would be better. The resistor should be labeled. Assuming it has leads, it should be the diameter of a pencil or larger.

My concern focuses on your problem statement. Namely, that the power supply worked fine until you "fixed" wires attached to the potentiometer. That is where I would look for problems, and without knowing what the potentiometer does or how the wires are attached to it we will all be at a loss.
 
Last year was my first year, so I was looking over my work again for improvements and I replaced a short wire and got a longer to replace. But it was only one wire though. I'll give you a picture towmorrowwhen I get into the shop.
 

atferrari

Well-Known Member
But, did you actually alter the circuit, right?
 
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