Guidance: Measuring Capacitance of Capacitor Bank (0.24F) 400V

I have capacitor bank 0.24F 400V. I need to check capacitance periodically. I am able to find code for capacitance meter https://www.arduino.cc/en/Tutorial/Foundations/CapacitanceMeter

The code and schematic seems to be suitable for low voltage capacitors (not sure) becuase capacitor shown is being charged by Arduino supply (5V).

In my case (400V), i can use divider circuit to charge capacitor bank with suitable power supply and read corresponding voltage at analoginput to charge up to 63%. However, i am puzzled whether arduino uno can handle discharge current or 5V is sufficient to measure capacitance or do I need to make some changes in hardware or schematic to achieve this.

Please guide.

Can You post a wiring of the setup You want to do?
What is the "discharge current"? Arduinos hsndle 5 volt and 20 mA directly.

The link is broken, dies not work.

"I need to check capacitance periodically."
Will something happen to make it change?

Thanks for your responce.
please find link. Circuit diagram as per diagram given in link.

That link works.
That should work using 5 vilt controllers.

"I need to check capacitance periodically."
Will something happen to make it change?

I shall be calibrating further sequences once I am to able establish and record failure pattern.

I would not rely only on a resistor divider for this task.

A circuit energized to 400V poses a significant safety hazard and the fault of a single component could pose an electrocution risk.

Instead, consider using an optoisolator operating as a linear feedback element. Refer to this paper:

This type of feedback is often used in AC/DC converters to safely isolate the DC output from the hazardous AC mains. An example circuit from that paper:

Keep in mind that a DC voltage is not necessarily safe. Look up the terms "ELV" and "SELV"...

Thanks for your guidance and i shall be using optoisolator

My question is still unanswered,

a. can i use this scheme as it is to measure Capacitance of 0.24F 400V bank
b. whether Arduino will be able handle to current while discharging capacitor bank

pankajsharma200:
Thanks for your guidance and i shall be using optoisolator

My question is still unanswered,

a. can i use this scheme as it is to measure Capacitance of 0.24F 400V bank
b. whether Arduino will be able handle to current while discharging capacitor bank

The timing principle of measuring charge and discharge times is basically sound.

However, you cannot discharge the capacitor bank through an Arduino pin. Well, in a hypothetical case assuming no safety issues existed, you theoretically could but you would have to limit the discharge current to, say, 15mA because of the delicate structure of the AVR pin but it would take something like 100 hours to discharge.

You would need to use the charge and discharge pins on the Arduino to, though isolation circuits, command other circuits on the capacitor bank to charge and discharge the capacitor. If you want to charge to 400V you'd want to use something like an IGBT for the charge and discharge and precision series resistors in each path rated for the voltage and power dissipation they'd see.

pankajsharma200:
Thanks for your guidance and i shall be using optoisolator

My question is still unanswered,

a. can i use this scheme as it is to measure Capacitance of 0.24F 400V bank
b. whether Arduino will be able handle to current while discharging capacitor bank

That same circuit measures the resistance of the series resistor which will change with temperature and age. How will you be able to determine which is doing the change, the capacitor or the resistor?
Paul

capacitor bank 0.24F 400V

Are you serious!!!

  • I don’t think the microprocessor-based capacitor measuring techniques will work with capacitances as high as 0.24F. For discharge currents appropriate to a microcontroller (~20ma → 250ohms equiv resistance) you’d be looking at an RC time constant of about a full minute.
  • 38 kJ is in the “leave a charred spot on the ground” range, if you make a mistake. It’s not the sort of thing you’d just connect “a resistor voltage divider and an Arduino” to.

There are probably special techniques for measuring the capacitance of such high-power packs, involving discharge through a carefully designed load. I don’t know what they are. Maybe I’m over-reacting - 400V is pretty low for high-energy caps - but you’re still in the “instantly fatal” area, and you should be reviewing professional technical literature (electric vehicle?), and not asking on a hobbyist forum!

LOL my brain automatically added a µ in front of the F when reading the question. That’s a huge capacitance, especially for such a voltage. Quite some energy stored in that.

Do you need to check capacitance at the full voltage of 400V? Or is a measurement at 5V sufficient? The latter is easy to do with an Arduino, but capacitance may depend on the voltage.