As I mentioned in my Shelly/Ellard post, it would occasionally be handy to have a “bench power supply”. This is simply a box with some knobs on it which can be used to produce a selectable/adjustable range of DC current and voltage. Since DC at lower voltages isn’t as dangerous to humans as the 230 volts of AC we use as our mains electricity in the UK, this is a better option for booting up Shelly relays on the bench for configuration, and also for charging up or powering an increasing range of modern electronics if you’ve lost the right charger.

I found a nice unit for sale on eBay - as it happens, by a well-known UK charity who do house clearances. Some top sniping later, I’d bagged it for about 20% less than the cost of a brand new one, which felt like a result. Sadly it arrived with no fuse in, the reason for which became apparent upon inserting one and firing it up: a loud bang, the smell of burning electrics, and the fuse blew.

You’d think that anyone selling electronic items would at least plug them in and see if anything appeared on the display before going to all the cost and hassle of listing them and shipping them. However, since they did give me an instant refund without making me post the defective unit back, I’m not going to name names.

At this point I lost all enthusiasm for eBay and coughed up the extra twenty quid for a new one, and here it is in action:

Bench supply in action
Look, Ma, 34 volts!

I’ll leave it to the reader to judge whether the cheap multi-meter or the moderately cheap bench supply is giving the more accurate decimal reading.

So next time I need to power a Shelly or something, it can be done in a much safer and more convenient manner.