MD10-POT problem

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MD10-POT problem

Postby JonnyDex » Fri Feb 18, 2022 3:35 am

I bought an MD10-POT to control power going to an electrolyzer. My input power measures as 28 vdc and 9 amps. I verified my connections and turned on my power supply. At first everything seemed to work correctly: Moving the knob counter clockwise reduced current smoothly and had a nice feel. I had reduced the amps from 9 to 4.2 right away. I was going to take a reading with my oscilloscope. Then, after only about 20 seconds -- maybe less -- oil steam jetted out of the base of the large cap. I shut the power off the second I saw the cap blow and evacuated the area.

What happened? Should I not have expected this board to work on a resistive load?
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Re: MD10-POT problem

Postby waiweng83 » Tue Feb 22, 2022 3:10 pm

Sounds like this is the problem of overcurrent. FYI, the input current is not the same as output current when it's under PWM control.

Input = 24V, 10A. Input power = 240W.
Assuming output power = 75% of input power.
Output power = 0.75 * 240 = 180W.

If PWM duty cycle = 50%, output voltage = 0.5 * 24V = 12V.
So output power = 180W / 12V = 15A.

From this example, we can see that the output current is always higher than the input current.
Moreover, the MD10-POT is mainly designed for inductive load (motor) and we never tested it on electrolyzer before.
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