425Views11Replies

# Bench power supply potentiometer for 20v? Answered

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 :)

Tags:

## Discussions

Try using an old sewing machine speed control pedal.

The old ones are basically variable resistors.

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

Ah! fond memories of carbon pile regulators.

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

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

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.

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

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.

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

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 :-)

If you really want to learn the best way to go about this then i suggest you watch this series of videos.

He will discuss multiple design options for making your own bench top power supply.

Your laptop PUS won't give out enough voltage to provide 20 volts. or will it?