High voltage 1000V Isolation Tester 1kV Curve Tracer STM32

thingiverse

High voltage curve tracer , isolation tester Some time ago I ordered 230VAC LED modules, consisting of an aluminium coolplate and electronics, separated only by a thin layer of isolation. I wanted to check the safety of the isolation, and to see the breakdown voltage on a graph, not just static data. With this instrument, I could verify that the isolation is good up to 1000V. Drawing a voltage / current graph up to 1kV makes it possible to check VDRs, SCRs, diodes, other high voltage parts and isolation too. The instrument's output is 1kV but it is safe to use, the current is limited by high ohmic resistors and is very low. Main parts are : STM32 Blue Pill, ST7735 TFT 1.77" FPC, 15kV transformer, TP4056 module . Source : Aliexpress, Ebay, Amazon. The STM32 Blue Pill outputs 109kHz PWM signal on PB0, driving a Mosfet and a tuned (15nF) HV transformer. The HV diode charges the 10nF 2kV capacitor, its voltage depends on the PWM the STM32 is outputting. The DC voltage could easily be as high as 1200V. Testing the transformer, selecting the best driver frequency : In the Arduino program list, if bool trafoTest is true, the STM32 will change the frequency and the PWM and draw the output voltage diagram on the LCD. So it possible to determine which frequency value fits best for your transformer. Look for the best S-shaped curve. In my case , the default value freq=330 uses the least power as well, tested with many transformers. The Voltage-PWM diagram is not straight, but it makes no difference. We collect corresponding voltage-current pairs in the main program, so the measurement will be correct. A smaller black transformer (1.4x1.4x0.7cm) could be used too up to 800V, the tuning capacitor is 10nF. Main program : The PWM on PB0 goes up from zero in 120 steps. Each time, the output voltage (divided by 10M/27k) and the current (on 100k shunt, 35uA range) is saved in arrays. The result is shown on a graph, the breakpoint where the current reaches 10-15 uA is displayed too. Cycle is repeated every 10 sec. Construction : 3D printed box, round torch switch, 2mm banana plugs. Build the STM32 and the LCD in the frame. The high voltage unit is built on a perfboard. Any Mosfet will do if opens at 1-3V Vgs. TP4056 board : the 1 amper charge current is far too much for our Li-Ion cell. Reduce the charger current to 100-200mA , remove the 1.2k SMD resistor and solder 5.1-10k between pin 2 and GND on the board. Glue the charger board in place. Connect the 14500 AA Li-Ion battery, solder the HV cables (add extra shrink tube isolation in full length) to 2mm banana sockets. Load the program and test the instrument with inputs open. You should get a straight horizontal yellow line reaching 1kV. If the test voltage is less, change the coil polarity and/or try the trafo tester program and change the frequency. The secondary "upper" winding end should connect to the diode. For HV diode I've used one from a laser printer, this is made from more "normal" diodes in series and specified 5mA 20kV but don't have the exact type number (update : FV5M06). Aliexpress has 2CL77. Put isolation and shield layers between the cables , parts. Update 3 Jan 2021 : add C8 100nF 25V between input Low and GND, removes noise. Using the instrument : The instrument is safe, short circuit output current is only 0.45mA. This is no hazard at all, however can sting unpleasantly. My skin's breakdown voltage was 120V. I've destroyed some ceramic capacitors by testing, but semiconductors usually survive, they don't accumulate charge. Gas filled tubes and TL lamps, igniters produce interesting graphs. Additional information : https://www.thingiverse.com/thing:4631015 Note :Some photos are rotated by upload to Thingiverse, no reason why. Libraries : https://github.com/rogerclarkmelbourne/Arduino_STM32/wiki/Installation https://github.com/adafruit/Adafruit-ST7735-Library This object was made in Tinkercad. Edit it online https://www.tinkercad.com/things/36BNGKJgnie