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I would like to build a small DC power supply (or find a cheap way) that allows me to get voltages in 0 - 50V DC range.

I had a look on ebay and some electronic shops but most supplies dont get higher than 12/24V DC. I know about variacs, but they are quite expensive and seem to output only alternating currents (someone can confirm?).

I dont need a lot of amps, something around 0.5A should be enough. What I'd like to do : I have a few fans/ small electric motors (running 9/12V) that i'd like to use and push to their limits. Best I was able to get from now is 24V DC, by using -12V / +12V from a old computer power supply.

I'm thinking about buying several 12V transformers and putting them in series but it seems a rather expensive and not reliable solution.

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    \$\begingroup\$ @OlinLathrop That's what "edit" is for. You know what the OP means. Changing "currents" to "voltages" took me 5 seconds. \$\endgroup\$ – Telaclavo May 20 '12 at 15:36
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    \$\begingroup\$ @Telaclavo: I thought he actually meant what he said, which made it useful information to judge this OP by. \$\endgroup\$ – Olin Lathrop May 20 '12 at 15:51
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    \$\begingroup\$ @OlinLathrop So, after having written "0-50 V is not a measure of current", what benefit does your -1 do to him? \$\endgroup\$ – Telaclavo May 20 '12 at 20:15
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    \$\begingroup\$ @Telaclavo: It's not intended to benefit him at all. It's intended to indicate to others the poor quality of the question. That's how voting works around here. If you say something blatantly wrong, you're going to get downvoted. Obviously at least one other person agrees this is not a good question. \$\endgroup\$ – Olin Lathrop May 20 '12 at 21:20
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    \$\begingroup\$ It seems to me that people here keep forgetting that in our FAQ we have line that says:Be nice. Treat others with the same respect you’d want them to treat you. We’re all here to learn together. Be tolerant of others who may not know everything you know. Bring your sense of humor. , especially the :Be tolerant of others who may not know everything you know. part. \$\endgroup\$ – AndrejaKo May 20 '12 at 23:00
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You should be able to find cheap 48V DC power supplies on e.g. ebay. Those are commonly used in industrial applications. Not clear if you are looking for an adjustable power supply or not...

If you have a floating power supply you can also connect them in series (e.g. two 24VDC supplies in series can give you 48V DC). If you have two lower voltage adjustale floating power supplies (most lab ones I've seen are) you can use them in series to get adjustable higher voltage. Shouldn't be too expensive, a quick google shows you can get a 30VDC adjustable supply for less than $100.

Building your own adjustable DC power supply is going to be a bit more complicated. If you go that route by the time you're all done it will cost you more than buying one (though you will learn a lot). Cheapest option is probably a bunch of 9V batteries in series (just don't short them).

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  • \$\begingroup\$ Would 9 V batteries be able to give 500 mA and work correctly? Wouldn't that be over 2 "C" for most of them? \$\endgroup\$ – AndrejaKo May 21 '12 at 8:20
  • \$\begingroup\$ @AndrejaKo: It obviously depends on the battery. This one data.energizer.com/PDFs/522.pdf apparently can. Surprsingly most battery vendors don't seem to specify a maximum current. Voltage will drop at higher current... \$\endgroup\$ – Guy Sirton May 21 '12 at 18:31
  • \$\begingroup\$ @AndrejaKo: This one batteryonestop.com/baotongusa/products/datasheets/ni-mh/… max 600mA continuous discharge current. \$\endgroup\$ – Guy Sirton May 21 '12 at 18:35
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First, DC transformers don't exist. Transformers take an AC signal and can transform the voltage that way. A basic transformer will need at least a bridge rectifier and probably a capacitor at the load to give you something that resembles DC.

You can almost always get a transformer that will meet your needs. For example, this transformer would get you to over 60V with no load, and still supply you with enough current to get your 0.5A current. Keep in mind that the voltages that these transformers are rated at are Volts AC RMS, which means that the peak voltage will be sqrt(2) times larger. There are lots of transformers available, you just need to look at someone's catalog (e.g. Digikey, Mouser...) who actually has a wide selection. Make sure that you get a transformer rated for the load you are drawing, and then add a safety margin.

Don't make your own transformer, especially if you are hooking it up to mains voltages.

Buying several transformers and putting the secondaries in series is a perfectly fine way to get your target voltage, but as you suspect it may be a bit more expensive. I don't think there is any impact on reliability as long as you're making good connections between the transformers.

I would recommend against doing this, and if you do, make sure you have a fuse and a switch in series to give yourself some safety with your circuit. If you keep increasing the voltage, you will eventually exceed some component's breakdown voltage.

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