Extech Power Supply: If It Ain’t Broke, Fix It Anyway

[Wolf] came into possession of an Extech power supply that wasn’t quite in working order. It has been used in battery manufacturing and was fairly corroded. He was able to fix it but found there was an issue with the power supply that wasn’t a defect. By design when you turn off the outputs, the voltmeters read zero. That means you can’t adjust the voltage to a known value without turning on the outputs. Sure, you ought to disconnect things before you adjust, but you can only hope you’ll remember.

At first, he tried to use the existing output control switch, but that really cut power. Instead, he turned to a small microcontroller board usually used for servo control. He added a few nice looking pushbuttons to the front panel. There was plenty of room in the enclosure to mount the controller board and four relays. You can see the final result in the video below.

You can guess the rest. The micro is able to read the controls, set the power supply, and switch the outputs off without killing the metering. This required some major mechanical surgery on the output terminals, by the way. In addition, the micro monitors the voltage output with an analog to digital converter and stores state when the power is dropping out. That way it can restore things on the next power event.

[Wolf] did eight videos covering each step of the process. You can find the result in the video below, but be sure to watch the ones that lead up to it as well.

The Extech supply looks nice, but we’ve noticed it is getting easier to build your own thanks to some interesting and inexpensive modules. Or you can build one in pieces if you prefer.

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