# transformer to monitor HV circuit without taking too much current.

#### Gibson486

Joined Jul 20, 2012
355
I am trying to monitor a HV circuit and isolate it at the same time. I am kind of limited with scraps parts I have lying around. I have box of 1:3 transformers. The original feedback is just a series of resistors to bring the HV down to MCU level voltages. I tried putting a 1:3 transformer flipped around, between two 1M resistors, and it worked, but the issue is that when I swap out to a different transformer in the box, the voltage deviates a lot on some of them. I am guessing that the those 2 1M ohm resistors really limit too much current?

#### Externet

Joined Nov 29, 2005
2,220
Monitor its voltage, its presence, its current ? AC or DC ? 1KV, 10KV, 100KV ...?

#### Tonyr1084

Joined Sep 24, 2015
7,900
Happy to help IF we know the HV you're measuring. Just starting off, I'm assuming your HV is AC, not DC. But lets assume you're running 500VAC and want to measure it. With two 1MΩ resistors in series forming a voltage divider your voltage would be 1/2 the source voltage (the 500VAC). The amount of current the two resistors are drawing is Voltage divided by Total Resistance. In this example, 500 ÷ 2,000,000 = 0.000,25A (or 250µA) That's almost nothing. As far as affecting the circuit - I wouldn't worry about it. As long as it's only providing a reference voltage for measuring the output.

#### Gibson486

Joined Jul 20, 2012
355
Yeah, it is AC. It can be anywhere from 100VAC to 500VAC @ 15kHz. I was trying to use it to see what the exact Voltage was, but that does not seem feasible with the huge variance, so it will probably just be presence detection for now. I wanted to do presence detection with an optocoupler, but I do not have one in house.

#### Tonyr1084

Joined Sep 24, 2015
7,900
Regular transformers don't work well with 15kHz. They're typically designed around 50 ~ 60Hz.

#### Gibson486

Joined Jul 20, 2012
355
Regular transformers don't work well with 15kHz. They're typically designed around 50 ~ 60Hz.
It's an audio one.... MET 39

#### Externet

Joined Nov 29, 2005
2,220