32v laptop style power supply. What can I use it for?

[Luke51411]

I found a 32v 680mA power supply at a second hand store. Would this be easy to convert to pedal/amp use? I was thinking of running my valvecaster at higher voltage with an added voltage regulator for the heaters. That seems like it would be a lot for a regulator... Would I need a transformer? Would there be a simpler/better use for this power supply? If I can't come up with a way to use it, I'm out a buck so no big deal. I just didn't know where to start.

[thelonious]

I've used one before to feed a regulator that output 18V (it was heat-sinked, bc that's a lot of voltage to drop), but I was always irritated by the slight whine I could hear. Those are usually switched-mode power supplies that are designed more for cost-efficiency than for quietness. You could probably add an LC filter and kill that, though. In fact, I think there was a thread about that not too long ago.

[GibsonGM]

Yes, you can use this for 'things', Luke.  Depends on how much work you want to do!   These supplies tend to be noisy, so any audio circuit you used it with would require additional R>C filter sections, but no big deal.

You can use a diode voltage doubler to get about 60V, for tube work.   Yes, you'd need a 2nd trafo for the heaters...

Or you can make an adjustable supply...neat project, see this .PDF to see what's going on with that:  http://home.iprimus.com.au/nuggles58/Making%20A%20Basic%20DC%20Controller.pdf

Mind that the lower you dial the voltage, the more HEAT you must dissipate, mainly in the 2N2222 transistor...a bigger load (lower resistance) also will increase the heat generated....the 2N222A transistor might need heatsinking or other protection, unplug if it gets HOT.....anyway, I use this kind of regulator once in a while and have no trouble at 30V, going down to like 1V, as long as the load is kept small, like in the 10's of milliamps.   Most of our stuff IS in that range, with the LED being the single largest draw.


You could also split this into say, +12 and -12V and use it to power some Anderton filters, etc.   Do some reading up on how these things are done!  Virtual ground etc.  Good chance to learn a lot by working with little power supplies.  

For general use, you're better off getting a 9V 1A supply, IMO, but you can do a lot with a variable supply, even if it's cobbled out of PC power brick or whatever.  Just be careful, use your head, and do some Ohm's Law work to be sure you're not going to pop anything (the 2N2222 WILL pop if you get it too hot, so watch your eyes, oy!)

[Luke51411]

Thanks for the info! I have plenty of 9 and 12v wall warts so I'm not concerned with that. I would like to have at least an 18v supply and I haven't managed to come across one at the thrift store. Another question, I have a 12v unregulated wall wart rated for 1A. When I check the voltage with it unloaded it puts out about 15v. Can I put a regulator and filter after to get a constant 12v supply or will it load down too much to put out enough above 12 for the regulator to put out 12?

[psychedelicfish]

If you wanted to run your valve caster with this, there's no way you could use a linear regulator, at least not in a stompbox. If you were powering 1 heater (12.6V, 0.15A) you would have to drop 19.4V to get 32V down to 12.6V, and at 0.15A, this would mean your regulator would have to get rid of 2.91W as heat, which, in a stompbox situation, is a lot of power. You might be better off using a transformer, or, even better, reading about switching power supplies, and in particular, buck converters. The transformer would be a quick and easy solution, whereas the buck converter would be a cheap, small solution. The buck converter option would mean you learn a lot about switching power supplies, and learning is always a good thing.

[psychedelicfish]

I have a 12v unregulated wall wart rated for 1A. When I check the voltage with it unloaded it puts out about 15v.

12V@1A means that it will put out 12V when you pull 1A.

Can I put a regulator and filter after to get a constant 12v supply or will it load down too much to put out enough above 12 for the regulator to put out 12?

Most regulators have a dropout voltage of about 2 volts. This means that in order for the regulator to work, you need the input voltage to be 2V greater than the output voltage, so with a 12V regulator, you'd need 14V input. As soon as you start pulling current from your wall wart, it's voltage will drop and your regulator may not work. I'd suggest using a 12V zener diode and a resistor, say 100r. This will mean, however, that if you pull more than 30mA (3V/100r) the voltage will drop below 12V. If you want to pull more current, use less resistor.

[GibsonGM]

What fish said...or, get a 7809 regulator, and set it up for 9V...

Yeah, if you set up the thing I linked to, you could use that 32V doobie to get 18V no problem.  It should stay pretty close with varying current draw, and you can always tweak it with the pot - within limits.  The PS itself is rated <1A, so don't expect to be running power drills this way!   The thing with (unregulated) power supplies is the drop....the "18V @ 50mA" statements....you can use zener diodes to keep it pretty well-regulated (again, Fish said this above) - but I'd get a hefty one, maybe 2W, 5W and make sure the dropping resistor is rated well, too....just as a precaution.   

You HAVE to do a bunch of power calculations and know what the dissipation is with these setups to avoid the magic blue smoke.  E*I, I^2*R....
make sense?

http://www.electronics-tutorials.ws/diode/diode_7.html

[Luke51411]

Yeah I didn't think running the VC would be possible in that setup but I'm not up on the science/math at this point.

[GibsonGM]

That's ok, man. Takes time.  Ohm's Law / Power calculation are 2 of the simplest equations in the universe, and sometimes have the power to totally boggle someone for hours!    Just keep working at it, esp. look at online tutorials/youtube vids on the subject. 

One day it just snaps into focus. 

<I'm still waiting for that day, LOL>   

[Luke51411]

Who knows when I'll actually get around to this project. I have a tendency to get distracted by shiny objects.  I also like to spend money I don't have. Currently eying some of madbean's new pcbs...

[duck_arse]

If you run two twelve volt valve heaters in series, you'll only need to drop 8V from your 32V supply. less heat. and you'd only need a doubler for 64V plate, much less work and complexity.

you can also buy or make your own low drop out v regs, that need much less than 2V across them to keep them regulating.

[DougH]

Jack Orman Minitubes:

http://www.diystompboxes.com/smfforum/index.php?topic=55407.0

http://www.muzique.com/amz-cd.htm