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I have a pasteurizer machine and I'm trying to find out the voltage of the heating element. The circuit in the image shows the connection. Hot wire goes into the thermostat at point A then exits at point B where it splits and goes into the heating and LED power indicator connected in parallel. The wires from the heating element and LED join at point C and go back to neutral.

What confuses me is that the voltage readings across points B and C as well as across points A and point C both show 110V when the mains supply is ~220V. When breaking the connection between the heating element and LED from point C (removing the red line in the image) I get 220V as I rightfully should. Can someone help me to understand why it shows 110v between point A and point C when everything is connected?

circuit

blah
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    Something sounds fundamentally wrong. Either your measurement technique or there is an issue with the supply wiring methinks. – Kartman Mar 09 '22 at 16:04
  • Is the thermostat a simple on/off thermostat, or does it potentially have the capability to act similarly to a dimmer switch using some kind of solid-state circuitry? – nanofarad Mar 09 '22 at 16:31
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    Points A and C are the 220V mains; something sounds fishy here. – rdtsc Mar 09 '22 at 16:41

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Is there any additional circuitry in the LED block other than an LED? You might be shorting out half of the 220V waveform, making it read 110V.

If this is the case, you probably have a current-limited source or a very impressive LED that can handle several amps without failing immediately.

It's also possible that the load of the heating element is dragging down the voltage. Maybe try reconnecting the element and LED individually to see if one causes the effect by itself.

Cristobol Polychronopolis
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  • What does it mean if the heating element is dragging down the voltage? I'm not sure what else might be in the LED block but when I remove the heating element from the circuit I get 220V between points A and C. When I remove the LED block however and leave the heating element, I get 110V. – blah Mar 09 '22 at 23:30
  • That means the source resistance from your mains feed is about the same as the resistance of the heating element. Since the mains are generally a low impedance source, specifically so they can drive low impedance loads like heaters, I suspect that there's some additional resistance between points A/C and the breaker box. Wherever that resistance is, it's probably dissipating about as much heat as the heating element, so that might help you find it...look for a warm wire, plug, etc. – Cristobol Polychronopolis Mar 10 '22 at 14:07
  • I did have an incident last week where the machine was plugged into an extension cord and the plug heated up and melted. Before that I've been plugging it straight into the outlet and getting a slightly warm cord but nothing hot enough to melt wires. Do you have any advice as to how this problem can be solved? – blah Mar 10 '22 at 21:56
  • Having the cord slightly warm isn't that much of an issue, but "not hot enough to melt wires" isn't that low a bar--heating appliances have high temperature insulation. Is it directly plugged in when you get >100V drop? Can you measure the voltage between the plug and the end of the cord? If your cord's dissipating as much as your heating element, it's kind of extreme. Heavier gauge cord (and heavy duty extension cord) can limit it. How much current is the device specified at, and how much is it drawing? – Cristobol Polychronopolis Mar 11 '22 at 17:49
  • I found the problem. The outlet was newly installed to replace a cracked one and the neutral and ground wires were interchanged. There was a huge voltage drop when plugging in just about any appliance. I switched back the ground and neutral and everything works fine now. – blah Mar 15 '22 at 21:30