Testing the high voltage components and potting

Testing the high voltage components

Now that all components are soldered on the board, we will check that everything is functional. There is an automated script that checks the hvps-x can generate a high voltage, that the voltage reading circuit can monitor the voltage, and that the optocoupler output stage works. The script apply a voltage set point 20% of the full scale range. It is very important not to apply the full scale voltage at this stage. This can only be done once potting is done (see below).

If you have followed the instructions step by step, your hvps-x is already flashed with the hvps-x firmware and the initial configuration has been performed (refer to Testing communication with the micro-controller). Also remember that you need a jumper on header J10.

To access the script Run the Python library as a main script from the folder in which you saved the library:

  • python hvps_lib.py
  • Alternatively, if using windows, you can use the compiled executable hvps_lib.exe in the same folder as the interface main executable.
  • Once the program is launched and the hvps-x detected, use the option [2] Basic functionality test (to be performed after assembling the high-voltage components)
  • Follow the prompt. Text in the terminal will tell you whether your hvps passed the tests. Note that values used as a pass are based on a limited number of assembled boards at the moment. If one test returns “fail” look at the output and at the acceptable range. If your measurement is close to the accepted value, that’s all good. In case of doubts, send us your results and we can have a look.

Here is an example of the script output for a 4kV hvps-x:

Name: b'Zeta'
Vmax: 6000 V

Your choices:
[1] Initial configuration (to be performed after assembling the low-voltage components)
[2] Basic functionality test (to be performed after assembling the high-voltage components)
[3] Transfer a json file to memory
[q] quit

Your choice: 2

During the course of this test, a moderate (~20% of full scale) voltage will be applied to the output of
the hvps-x. Make sure that it nothing is connected to the output and that you are not touching the
instrument

Voltage set point 0V. Output off
---Testing HV enable switch (S1) ---
Place HV enable switch (S1) on position 1 and press any key
***PASS

---Testing Voltage monitoring at set point 0 ---
Raw reading at the output of the converter is 1 
This is within the tolerance range V < 5. Continuing...
Raw reading at the output of optocouplers 3 
This is within the tolerance range V < 5. Continuing...
***PASS

---Testing Voltage monitoring at set point 20% FS Output off ---
Applying 20% PWM value
Raw reading at the output of the converter is 1001 
This is within the tolerance range V > 900. Continuing...
Raw reading at the output of optocouplers 3 
This is within the tolerance range V < 5. Continuing...
***PASS

---Testing Voltage monitoring at set point 20% FS Output LOW ---
Output LOW
Raw reading at the output of the converter is 1001 
This is within the tolerance range V > 900. Continuing...
Raw reading at the output of optocouplers 0 
This is within the tolerance range V < 5. Continuing...
***PASS

---Testing Voltage monitoring at set point 20% FS Output HIGH ---
Output HIGH
Raw reading at the output of the converter is 987 
This is within the tolerance range V > 900. Continuing...
Raw reading at the output of optocouplers 977 
This is within the tolerance range V > 900. Continuing...
***PASS

***hvps-x passes all tests***

Potting the high-voltage components

!! Do not skip this step, the optocoupler footprint is not designed to be operated in air without potting. Applying high voltage to your board prior to potting will lead to arcing and damage !!

When you have verified that your hvps-x is working well, you can pot the high-voltage side of the board. Once potted, rework of the board on the HV side will be very difficult and cumbersome, it is therefore important to make sure that the board is working as expected prior to proceeding with the potting step.

Potting the high-voltage components plays two essential roles:

  1. Prevents any contact between users (or other foreign bodies) and any pin, track or pad in the high-voltage zone of the board.
  2. Adds insulating material between any high-voltage connection and ground or low-voltage track to avoid leakage or breakdown. Even if your board is working fine without potting after you finish assembling it, humidity, dust, or other contamination can contribute to increase leakage over time, which can result in breakdown between the high-voltage output and a low-voltage track, leading to possible damage to the board.

You can use the potting material you prefer. We use Ecoflex silicone dragon skin 20, because that’s what we have at hand, and it has just the right pot-life and viscosity. On the download page, you will find a potting frame that can be 3D-printed.

  • Place your board in the potting frame.
  • Dragon skin 20 will nicely flow through the creepage cuts and two holes to fill the bottom compartment, it is will also flow slightly behind the bracket and the board. If you want to avoid silicone from flowing out of the pool, apply some glue with a paint brush between the bracket and the PCB on the topside (we use universal white glue, but almost anything will do).
  • On the back side, place a piece of tape on the creepage slot, and you can also apply glue at the border between the board and the pool frame.
  • Very important: insert banana plugs in the two output sockets or they will be filled with silicone.
  • You will need ~28g of dragon skin to fill the bottom and top compartment.
  • Pour some dragon skin on the top compartment and wait for a few minutes. As the silicone flows to the bottom compartment, the level of silicone in the top compartment will drop.
  • Add more silicone to the top compartment
  • Repeat a few time until the silicone level in the top compartment remains constant and the pool is completely filled (the level of silicone should reach the rim of the pool and the top of the optocouplers.
  • Let the silicone cure for a few hours.
After testing the high voltage components, it is important to pot the high voltage section of the board to increase safety and remove the risk of breakdowns due to creep.
After testing the high voltage components, it is important to pot the high voltage section of the board to increase safety and remove the risk of breakdowns due to creep.

 

Your hvps-x is now ready to be used at full voltage. Download the interface and refer to software section to start using your power supply.

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