Detecting voltage change in the OFF state of an AC Load

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anishkgt

Joined Mar 21, 2017
529
I am trying to switch on a LOAD from its OFF state by detecting a change in the voltage. Here the load is a MOT(Microwave Oven Transformer), the voltage at the primary is 1VAC when OFF. My idea is to switch ON the MOT by detecting the voltage change at the primary when the Secondary are shorted when in the OFF state. I can see a voltage drop of .5VAC when shorted. How can i monitor this voltage change with an Arduino.

I hear this would be possible by level shifting the voltage to a range that an Arduino can handle but i am not sure how to handle the high voltage at the primary when the MOT is switched ON.

Below is one such circuit for level shifting a voltage, but not sure how i could use it with the ac Mains.
 

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AlbertHall

Joined Jun 4, 2014
10,554
That circuit isolates the MOT control signal from the Arduino but the voltage output to the ADC is not isolated from the mains. This won't work and is potentially dangerous.

You REALLY do not want to switch on power to the primary when the secondary is shorted. This WILL damage something. With LUCK, and assuming one is fitted, all that will be damaged is the fuse.
 

Thread Starter

anishkgt

Joined Mar 21, 2017
529
I'll try to explain the whole idea behind this,

Lets assume we have a push button switch to switch ON the spot welder. We press it and that switches ON the MOT and we spot weld nickel tabs to 18650 cells. All looks good and Hunky-Dorey. Now lets say you have to build a battery pack of 300 cells and pressing the switch 300 times or a foot switch would be........a little uncomfortable or your legs get exhausted while pressing the pedal 300 times to spot weld those cells.

Here we are replacing the 'SWITCH' by sensing when both electrodes makes a contacts on the nickel tabs. When it does current is drawn from the MOT and that draw will show a voltage drop at the primary and that voltage-drop is something that am trying to sense which would fed into an Arduino to activate the MOT.

Hope that's clear.
 
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