# Bench power supply potentiometer for 20v?

Hello!

I am trying to build a bench power supply from a laptop power supply and i need a potentiometer capable to handle 0-20v. I have tried many times with different potentiometers but they all start smoking and later starts burning :(
i don't know that much about elektroniks circuits so be gentle :)

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RavensCraft3 years ago

Try using an old sewing machine speed control pedal.

The old ones are basically variable resistors.

3 years ago

They are indeed variable resistors, but not suited to this task. The action of a bench power supply is to maintain a constant output voltage- the output from a variable resistor would need to be adjusted constantly

3 years ago

Ah! fond memories of carbon pile regulators.

Although the ones I worked with were MUCH bigger then thins example.

FarmerKJS3 years ago

i would just buy a 20-30 dollar supply from amazon or something

jchumpfree13 years ago

A potentiometer is very inefficient and unpractical way to control voltage as most its energy is wasted in heat (as you found out). Your best bet is to use an LM317 adjustable voltage regulator. It is a very simple 3 pin IC that has an input pin, a ground pin and an output pin. Google LM317 and their are tons of circuits using this adjustable voltage regulator. Good luck. We all have to start from the beginning and learn.

3 years ago

......the 317 generates just as much waste heat as a pot..... Just not in the pot

3 years ago
That's not true. If you stay within its rated parameters it runs fairly cool. And its current output is 1 amp from 1.5 volts up to the supply voltage. Try getting 1 amp out of a voltage divider circuit (pot). Your would need a low ohm rheostat that REALLY gets hot.
3 years ago

please do the maths and report back when you have corrected your errors

3 years ago

Steve IS TRUE ! it is you who don't know how to calculate regulator power.

Be it a resistor or regulator Power as the delta V multiplied by the current that defines waste heat which is increasing the entropy of this part of the galaxy as I type while my brain burns dear Padawan learner :-)