Electronics > Beginners

Power supply advice please (I live in the UK)

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bd139:
I spent most of my life using a non current limited supply, made from the remains of some scientific equipment I skip dived. I got in the habit of sticking 10 ohm 1/8W resistor in series with whatever I was building. If that disappeared in a puff of smoke, then there was too much current!

Where there’s a will there’s a way!

I would NEVER use an ATX. Those things can shift 100A very quickly very suddenly.  Things just disappear if they go wrong.

boffin:
This is the video/thread you want to read about cheap power supplies.

https://www.eevblog.com/2017/10/11/eevblog-1030-20-diy-bench-power-supply/

cdev:
By disappear he means vaporize.

very good point, bd139, very good point.

And in one of Daves videos about the RDtech devices, maybe this one, one of the units he was testing caught on fire, it partly burned up, because a ceramic capacitor in it failed, causing a localized fire. It didn't quite totally self destruct in the Mission Impossible sense, but had he not been there it might have caused a fire.

cdev:
rstofer, I have one quite similar to that and its pretty decent.

*It's totally silent*.

It has low ripple and a self-contained transformer and a bunch of different voltages and can deliver a substantial amount of current. I got it from All Electronics ages ago for just a few bucks.

It needs convection through the case. No fan, it does fine without a fan but it does need convection. So case with vents is a necessity. 

rstofer:
I never meant to imply that I didn't like or need current limiting.  It is one of the great features of the DP832.  I can set a foldback limit and a shutdown limit on each of the 3 sources.  This is a very powerful feature!

Is it worth $500?  Maybe, at some point in the evolution of the hobby.  It may have saved a few chips the other day when I was building up a Z80 project and there was a bus selection conflict.   But, somehow, I never trashed chips before I had the Rigol.

The 10 Ohm resistor idea is good, so is a small fuse or, better, a small transistor.  We joked in school that designers used transistors to protect fuses.  A long time ago...  It was funnier back then!

Still, I got along with whatever foldback the 7805 provided and I didn't lose too many parts.

Where I start to get nervous is when I see these DIY projects with multiple control loops and no real guarantee that they are stable.  Designing a real PS is a non-trivial affair.

There are two flavors of current setting:  The old way was to short the output and adjust the current knob to get the current you wanted (because there was no calibrated current setting capability) and the newer digital schemes like with the DP832.  That's another thing you don't get with DIY or low $ supplies.  That digital setpoint is worth every bit of $500 - a long time later on with the hobby.

There is something fundamentally wrong with shorting a PS output.  It just doesn't seem right!

The thing about 'learning' electronics is that you can also learn by modifying experiments to match what you have on hand.  So what if the transistor amplifier circuit calls for a 6V supply and you have either 5V or 12V.  Work it out!  There's some good learning when you have to recalculate the bias point and the collector/emitter resistors.

In fact, there is a LOT more learning when you have to calculate the components based on availability.  It's all too easy to simply Copy and Paste.

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