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.

 

[oswaler]

As a scientist, it is important to follow proper testing procedures and ensure accurate results. In this case, it seems that the HiPot tester is not capable of supplying the required voltage for the insulation resistance test. While using power resistors to divide the voltage may seem like a solution, it is important to consider the potential risks and limitations.

First, it is important to know the exact voltage and current requirements for the insulation resistance test. This will determine the appropriate wattage for the power resistors. It is not a simple P=V^2/I problem because the resistance of the EUT (Equipment Under Test) is also a factor that needs to be considered.

Additionally, using power resistors to divide the voltage may not accurately simulate the actual conditions of the EUT in its intended use. The EUT may have different resistance levels and the power resistors may not accurately replicate that. This could affect the accuracy and reliability of the test results.

Furthermore, using power resistors may not be the safest option. They can generate heat and may not be able to withstand the voltage and current requirements for a prolonged period of time. This could lead to potential safety hazards and damage to the equipment.

As a scientist, it is important to consult with a qualified electrical engineer or technician to determine the best course of action for this test. They can provide guidance on selecting the appropriate equipment and procedures to ensure accurate and safe testing. It may also be necessary to invest in a different HiPot tester that is capable of supplying the required voltage for the test.