Friday, November 10, 2017

9 volt power plug salvage

I bought this fantastic piece of equipment. it is a kind of multi-tester. Not like any ordinary multimeter, no a multitester.

Not only does it tests resistors but also capacitors, transistors (PNP and NPN) fet's, diodes etc. It can be found on all the well-known chinese web-shops for just a few dollar. But that is a different story all together. It has only one flaw: it works on 9 volt batteries. The availability of the 9 volt batteries is not such a problem as well as the cost and lifespan.

After some examining of the multiteter I realised it was powered by a 7805 5 volt regulator. Powering it with a slightly divergent power supply would therefore not lead to problems. And I had such a power supply at hand. It is a 9 volt power supply.

However my multimeter showed it supplies 11 volts when unencumbered. No sweat: the 7805 should be able to handle that.

I could cut the 9 volt plug and solder the wires direct to the multitester. But I wanted a more flexible solution that would permit me to use the power supply also for different purposes. Therefore I needed a 9 volt contra plug. And that was easily found.

There is a 9 volt plug on top of the battery. Now I have seen instructions on how to decap the battery and salvage the plug. I have never done such a thing myself and looking at pictures on the internet is not the same as doing it yourself.

I examined the battery slosely and saw that there was a juncture. So I started tweaking at the juncture and to my surprise it was the start of a label that was glued to the casing. So the label came off easily and beneath it was a plasic casing. You might not be so lucky as I know that many cases are made of metal so cutting them up might be more tedious.

Next step was to carefully saw the bottom off. And when I made a big enough cut I ripped it with some pliers.

Inside was a pack of 3 batteries soldered together with some long flat leeds.

I removed the batteries and the remains of the casing until just the plug was lying in front of me.

Then I cut the long flat leads off.

Next step was examining the battery and looking which pole was corresponding with VCC and which corresponded with GND. The small round pole is the VCC side and the large split pole is GND.

The only remaining step was then to solder the wires of the power supply to the poles and all was done.

A final test with my multimeter showed that everything was fine and indeed when I plugged it to my multitester it worked as expected.

This is an excellent way to save on batteries.
Just make sure that anything you plug this power supply into has to be capable of handling the supplied voltage which is in my case about 11 volts.

Till next time.
Have fun.

Luc Volders