Friday, May 1, 2009

Power supplies

I am very fortunate. I have a friend who works for Questacon, who has lots of fantastic electronic junk. One prime example of this is a trio of variable linear power supplies, each having a range of 9-18 volts DC. In my annoyance at having to recharge my SLA batteries after etching, I finally broke one of the power supplies out in the place of the battery. It's a wonderfully simple device, you just put mains in one end, and a preset and adjustable voltage comes out the other end. Because I had no proper electronics enclosure on hand, and lacked the motivation to build a nice box to put it in, I had decided to mount it in an abandoned lunchbox. This was necessary, because otherwise there would have been bare, live mains wires sitting on top of my workbench, which is both permanently covered in crap, conductive and non-conductive alike, and is within easy reach of my two lurkers. I wouldn't want to zap them, now, would I? Anyway, I set the voltage to about 10VDC, zip tied it in, put a switch and some connectors and a fan for ventilation in as well, and closed the lid. That was my power supply until today, when I mounted it up in a nice box, with adjustment knobs for voltage and the current limiter, and all the connectors. Still to come is an ammeter and a polarity switcher, which will allow me to plate with this supply.

You, however, may not be as fortunate in your friends as I am. Never fear. All is not lost. You can use other power supplies. As I mentioned before, SLA (Sealed Lead Acid) batteries work very well. They're basically car batteries, but they don't spill, and you can get them in different strengths. You will, however, also need to shell out for a charger, and keep the battery charged. What a pain. But, that's not the only alternative. Do you have a phone that's broken? (A land line, hands free phone that is.) Or a broken scanner? How about some dead computer speakers? Most of these devices are powered from a 'plug pack', a step down transformer that plugs straight into the wall. One of these plug packs will suffice as a power supply for etching. Just make sure the output is DC, and at least three volts. You may want to solder some alligator clips onto the end of the wires (after lopping the plug off), to help you identify +VE and -VE, and to make your connections easier.Pictured above are a 7 Amp/Hour SLA battery and some plug packs

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