How to Build a 24V DC Power Supply With Adjustable Output Using Potentiometer

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How can I make an adjustable DC output from a 24 V, 0.8 A adapter using a potentiometer and passive parts?

A potentiometer voltage divider is not a good way to make a regulated adjustable supply, because the output voltage changes when you connect a load; it only works reasonably when the load resistance is much higher than the pot resistance, and even then the voltage depends on pot position and may need DVM monitoring [#21675249] If you want a real adjustable output from your 24 V adapter, use a fixed or variable linear regulator instead of a plain divider [#21675249] A small regulator kit or module that is rated to accept 24 V DC input is a cheaper option than buying a whole lab power supply [#21675251] A simple passive divider is the cheapest and simplest approach, but it is inefficient and not suitable when the load varies [#21675247][#21675249]

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Potentiometer divider is not a suitable regulator
#1 21675246 23 Jan 2016 14:50

Gran Ingvarsson Gran Ingvarsson

Anonymous

Potentiometer divider is not a suitable regulator
Post #1 21675246 23 Jan 2016 14:50

Hi. I thought I might fashion a simple D/C power supply using a surplus switched A/C adapter that used to power my flatbed scanner. It puts out 24 volts @ 0.8 amps.

The plan is to construct a simple voltage divider network using a potentiometer and the necessary passive components with the adapter as input. I used to be able to do this as easily as I write this but that was 30 some yrs ago...

Thank you.
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#2 21675247 24 Jan 2016 02:37

Justin Spencer Mamaradlo Justin Spencer Mama...

Anonymous

Post #2
21675247 24 Jan 2016 02:37

Hello Goran,

I'm not really a fan of voltage divider networks via passive resistors because of their inefficiency but they're
the cheapest and simplest.
Attached to this reply is the implementation [in the picture].

Hope this helps.
Regards,
Justin
#3 21675248 24 Jan 2016 08:00

Gran Ingvarsson Gran Ingvarsson

Anonymous

Post #3
21675248 24 Jan 2016 08:00

Thank you Justin. This is not my preferred route either but...it's the cheapest and simplest way as you say.

I'd much prefer, say, an Oltronix power supply with current limitation possibillites for serious lab-work like I had in the day, but...that's in the past and I really don't need that level of sophistication for what I want to do.

Again thanks for taking time with this Justin, it is surely helpful to me:)
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Potentiometer voltage shifts under load; use a regulator
#4 21675249 24 Jan 2016 12:41

richard gabric richard gabric

Anonymous

Potentiometer voltage shifts under load; use a regulator
Post #4 21675249 24 Jan 2016 12:41

You say that you need a regulator circuit. If that is truly the case, there is a problem with the potentiometer method, once a load is put onto the potentiometer, the voltage changes. The effect is small if the load resistance is much greater than the potentiometer resistance, and is obviously dependent on pot rotational position as well (non linear). You will have to monitor the supply with a dvm if you need a specified voltage, and if the load is not constant while running, then that will not be much help either.
If your load current is high, then a simple fixed or variable linear regulator (kit or built up)from places like Ebay(or probably local electronics hobby shops) will be cheaper than a high power variable pot.
Cheers,
Richard
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#5 21675250 24 Jan 2016 14:22

Gran Ingvarsson Gran Ingvarsson

Anonymous

Post #5
21675250 24 Jan 2016 14:22

Thanks Richard. I can sort of follow your reasoning, anyway well enough to know that you are right about the output voltage being load dependent.

Hmm...as I had been severely nostalgic for the stabilized Oltronix lab power supplies of my youth and which I mentioned before, I just might go the full distance and buy one.

A one-channel one, 1A max will do fine, yes...Alright - you talked me into it Richard. Done _and_ done. Come monday I'll go to the local electronics shop and pick one up.

Thx for helping me make my mind up;)
#6 21675251 24 Jan 2016 16:46

richard gabric richard gabric

Anonymous

Post #6
21675251 24 Jan 2016 16:46

You could still use your 24V DC supply, connected to a variable regulator.
There are a lot of kits around, you just have to make sure that they will work at 24V DC in.
A lot cheaper than buying a power supply as described.
If nostalgia and the need for better performance is more important, then.........
cheers,
Richard
#7 21675252 25 Jan 2016 09:01

Gran Ingvarsson Gran Ingvarsson

Anonymous

Post #7
21675252 25 Jan 2016 09:01

_"A lot cheaper than buying a power supply..."_ I know it Richard, and I really don't need lab-level performance but..._"nostalgia..."_ Not to be disregarded;)

Plus, I love the feel and look of a fine piece of professional equipment!
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#8 21675253 25 Jan 2016 09:21

Gran Ingvarsson Gran Ingvarsson

Anonymous

Post #8
21675253 25 Jan 2016 09:21

Afterthought: thanks to all friendly ppl who have contributed suggestions and tips for my little project. It is sure heartwarming!
#9 21675254 15 Nov 2016 08:47

Justin Spencer Mamaradlo Justin Spencer Mama...

Anonymous

Post #9
21675254 15 Nov 2016 08:47

Yes, I'm so silly. What was I thinking when writing this? *sigh*

Sadly, I couldn't delete this reply anymore so my stupidity is etched here forever. Ugh!
#10 21675255 15 Nov 2016 18:59

idealwriter2 idealwriter2

Anonymous

Post #10
21675255 15 Nov 2016 18:59

I think I'll go with what you said. I'm in a similar problem right now. Thanks for the little piece of information anyway.
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Topic summary

The discussion centers on building a 24V DC power supply with adjustable output using a surplus 24V, 0.8A switched AC adapter and a potentiometer-based voltage divider. The main concern is the inefficiency and load-dependence of voltage dividers with passive resistors, which cause output voltage fluctuations when the load varies. It is recommended to use a variable or fixed linear voltage regulator circuit compatible with 24V input to achieve stable and adjustable output voltage. Such regulator kits are often more cost-effective and reliable than high-power variable potentiometers. The original poster expresses nostalgia for professional lab power supplies, specifically mentioning Oltronix models with current limiting features, and ultimately decides to purchase a simple 1A Oltronix lab power supply for better performance and user experience. The discussion highlights trade-offs between simplicity, cost, efficiency, and output stability in DIY adjustable DC power supplies.
AI summary based on the discussion. May contain errors.

How to Build a 24V DC Power Supply With Adjustable Output Using Potentiometer

How can I make an adjustable DC output from a 24 V, 0.8 A adapter using a potentiometer and passive parts?

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