Insulation Resistance Testing - Issue with Hi-Pot Tester

elmos

So, I have a HiPot tester with a minimum capable voltage of 100VDC.

I'm testing for any leakage between a string-pot and the housing case for the unit it goes into, with the requirement being 45VDC applied to it. With the HiPot tester incapable of supplying a voltage that low, I am thinking of using two power resistors to divide the voltage down to 50V, and then supplying that voltage to the EUT. I'm using power resistors to prevent the resistors from burning up in the event that I have leakage.

My question is: "what rated wattage should I choose for the resistors?" Is it a simple P=V^2/I problem? I'm guessing that leakage could result from fairly high resistances (kOhm range), but then it's entirely possible to have it down to 1 ohm or less if the wiring is bad.

I'm not a EE by trade (Aerospace), and I've been thrown into putting together this test for a qualification effort, so any advice would be much appreciated.

vk6kro

If you put resistors across your tester, the tester will read the value of the resistors.

Would it matter if you tested at 100 volts? If it was OK at 100 volts, it would be OK at 50, surely?

To answer your question, you work out the worst case and design your resistors accordingly.
Is it a simple P=V^2/I problem?
Yes, it is.

Assume the lower resistor is going to get shorted out. The top one then has 100 volts across it. If it was 1000 ohms, it would have to be rated for better than 10 watts. E^2/ R = 10 watts.
Normally, it would have 50 volts across it so it would be dissipating 2.5 watts.