Digital Display Mod for Variac

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kolakidd

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I ?modified? a really basic Variac I bought from acdc.co.za.

It?s basic 4A model. I got it at a massive discount, and the dial and analogue display were woefully uncalibrated. I fixed the knob accuracy by simply changing the position and measuring with a multi-meter. The analogue display was still out though, and it's viewing angle wasn't great.

Here is the link to the variac, you can?t find it through the website search, and if you go to the head office (Edenvale Branch) you get a 20% discount if you ask: https://new.acdc.co.za/products/4a-220-0-240vac-variac-enclosed. Note: Just be prepared to wait, it took them around an hour to get it from the warehouse. Order it first and then browse.

The meter I used is off Aliexexpress, it is a AC 80-260V 20A meter (PZEM-021), it?s around $10. There are many hacks to this meter, the one I implemented was simply to get the reading down to 0-260V. It does volts, amps, watts and energy. The benefit of this display is that you can pretty much see any irregularity in the device you are powering immediately because of the readings.

The initial mod for the device is from here: https://www.youtube.com/watch?v=b2MXXSuzM2k (Quest for Zero Part 4).

This is the standard variac, the knob and the analogue dial were about 15V out. Excuse the mess, it was pre going on holiday, and this was one of many small projects



I added a big a$$ switch and pilot light on the input, that?s for me to know when it?s powered, I tend to get ahead of myself and forget where the power is sometimes, so this is my (don?t) kill (yourself) switch.



The wiring for the meter is pretty basic, you provide independent power to the meter by adding one additional wire. This is all in the https://www.youtube.com/watch?v=b2MXXSuzM2k video. Then you wire up the box as normal. The two red crocodile clip covers are hiding some additional output wires I added for some banana plugs I wanted to add to the Variac.



My printrbot printing the new cover. It?s a prototype cover, not very pretty or robust, but it?s good for a prototype, I?ve already started designing a new cover with the ability to rotate the display.



First power up. No device attached. I left it at 207V for the picture



queue BACK LIGHT. Accuracy is great, down to 0V



You can see the banana plugs, I?ll print covers for those when I do the final print? I have curious cats who don?t know they are at finding ground.

Testing with glue gun.



The only modification to this design I am going to make is to print a cover where I can swivel the display.

 
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