Potentiometers - What determines the max voltage rating - Page 1
Forum section: electronics / beginners

author: pigtwo
author_rank: Regular Contributor
timestamp: February 24, 2016, 09:52:48 pm
content: Hello all,I have a pretty simple question involving potentiometers.I want to use a potentiometer as a voltage diver for 24 volts. Because of physical limitations there aren't very many to choose from and I even have to buy from the factory. The one that I have found that is 'perfect' has a max voltage rating of 20 volts. My system will have a max voltage on the poteniometer of 22 volts. The power rating is 50 mW and the max power I will apply will be 14 mW.Do you think it would be safe to use this poteniometer? And what exactly determines the voltage rating?For example, the voltage rating for a cap is the dielectric brakedown(?) but I can't think of what is determining the voltage rating of the pot. Arching maybe? I understand the power rating will be because of heat, so I thought that the voltage rating might just be there to limit the power.The pot I am using is a PTV09A-4030F-A104 (100k ohm)Thank you for any input!

author: TimFox
author_rank: Super Contributor
timestamp: February 24, 2016, 09:57:45 pm
content: I would be surprised if the 10% over-voltage would cause a problem here, but if it does you can't blame the manufacturer.

author: pigtwo
author_rank: Regular Contributor
timestamp: February 24, 2016, 10:33:52 pm
content: That's what I thought, but I wanted to make sure there isn't something big I'm overlooking.

author: Shadetreeprops
author_rank: Regular Contributor
timestamp: February 24, 2016, 11:29:36 pm
content: Quote from: pigtwo on February 24, 2016, 09:52:48 pmI do not see why not. I used a 1Meg pot from a artari paddle to make a PSU with variable voltage. But i have seen others use them for 24v systems, with only a 50k rating and less MwIm not a wiz at the maths. but my 12v 19.9A PSU was ruffly 240W and the 1Meg pot worked fine, it did not overheat or anything. i used another for variable resistance to power the hacked in Mulitmeter, to act as the voltage readout. so i would know how much was coming off my bananna plugs..thats probally the best thing i have made to date.the rest of my stuff is just novlety blinky lights, with functions that really do not do anything other than look pretty.but i also saw a video of a guy, using a step up or down boad, with a power supply. and he wired a pot on it for the voltage control. worked great, and his pot was connected to the pot that was not really meant to be used like that. and his board was putting out 300Mw min..but im no expert just a fast learning hobbist.

author: mstoer
author_rank: Contributor
timestamp: February 25, 2016, 12:37:37 am
content: Quote from: pigtwo on February 24, 2016, 09:52:48 pmThat part you quoted is an audio pot. I don't believe they typically see higher voltages. The voltage ratings are usually to stay withing the power dissipation rating and to avoid breakdown/arcing. Perhaps they have lower ratings to maintain their quality for sound/volume control, etc.There are plenty of other pots/trimmers with higher voltage ratings, so do you need an audio pot?Shadetreeprops: I don't think you had the 1Meg pot sink 19.9A, otherwise the smoke would have surely been let out of it.

author: Shadetreeprops
author_rank: Regular Contributor
timestamp: February 25, 2016, 02:23:39 am
content: http://www.ebay.com/itm/ATARI-2600-PADDLE-CONTROLLERS-ORIGINAL-VIDEO-GAME-WORKS-WELL-/141911731946?hash=item210a992eea:g:9EgAAOSwB4NWzKtJbest price so far 2 bucks free shipping get 2 pots, rated 1Meg cheap works, and not wildly known. but i repair vintage consoles, and sell vintage games too, so i have many of these things all over my house, as well as the consoles, at least 200 carts for em.http://stardustarcade.com/2015/04/atari-rheostat-volume-knobs/another site to tell you about where to find something better. for 2 bucks.....VS look below100 Watt 100 Ohm Ceramic Disk Rheostat Variable Resistor$13.16 from Walmart - Tasharina Corp100 Watt 100 Ohm Ceramic Disk Rheostat Variable ResistorAll Points 42-1582 150-200 OHM Speed Control Rheostat - 208/240V$79.00 from 2 storesthe one in the atari was wired next to the power, and not after it, so it was a rheostat capable of 120 to 150v 100+ohm give or take.. another hidden jem in old electronics.

author: edavid
author_rank: Super Contributor
timestamp: February 25, 2016, 02:27:56 am
content: If you are actually using the pot for audio, it's poor practice to have a DC voltage across it.

author: pigtwo
author_rank: Regular Contributor
timestamp: February 25, 2016, 04:24:02 pm
content: @Shadetreeprops Thanks, but this is for something I need to send to production so I can't have them order from ebay and I need about 100 of them. And there are very specific size requirements(essentially very small package but long shaft). Thanks though.@edavid They're not for audio. I'm using the to generate a arbitrary dc voltage for a sensor.

author: edavid
author_rank: Super Contributor
timestamp: February 25, 2016, 04:59:08 pm
content: I think the voltage limit is due to degradation of the wiper to track contact from tiny arcs. If there isn't any voltage difference between them in your circuit (i.e. not passing any current through the wiper), this probably doesn't apply. Ask the manufacturer to be sure.