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What are 4-pole capacitors and how to wire them in parallel?
Hello everyone. I'm currently designing a driver for a 5 HP BLDC motor that runs on 320 VDC. I've created the circuit for it using 6 power MOSFETS (I used six IRF840) and the microcontroller that will give trigger them is an Arduino Uno. Of course, since 3.3V from the Arduino is too low a voltage to trigger the gates, I also used 2N2222 behind each MOSFET to act as a switch and give out a much higher voltage to the gate of the IRF840s. Naturally, I'll be using power diodes too at the end, right before the connection to the motor so that the circuit is protected from any feedback when the power is cut off.
The problem that remains is the usage of capacitors. I realize that I'll need large 400V capacitors, and these were the ones provided for me. However, I've never used 4-Pole capacitors before and have no idea how they work. All I know is that the poles are actually connected to the corners of each plate instead of in the middle like regular 2 wire capacitors.
I have looked online and came across a couple of circuits that tell me how to wire them, but I can't simply rely on such circuits without understanding what is going on first. So can someone please explain how to connect not two but NUMEROUS 4-pole capacitors in parallel, as well as an explanation of how they exactly differ from 2-pole capacitors.
This is the diagram that I saw:
2 Answers
- roderick_youngLv 77 months agoFavorite Answer
Those look like stiffening capacitors for some kind of audio amp, perhaps a car? I haven't seen them used in the context of driving a motor. Sorry, can't help you there.
But you mention driving the motor with (6) IRF840. Do you mean to just turn the motor on and off with those, or will you be driving individual phases many times a second? If the latter, then switching time will be important, as it will dominate the power dissipation in the transistors. You might do better just buying a MOSFET driver IC, than trying to put something together with transistors.
You're right about the 3.3V not being enough to drive the gates. Get at least 10V, maybe 12, but will need to be sure not to exceed the maximum voltage. You might think that the drive signal couldn't exceed 10 volts if the supply voltage is 10, but due to overshoot and ringing, it could, and that would slowly eat away at the MOSFET until it failed.
A 5 HP motor is a lot of power. That's what - 10A at 370V? Even when fully turned on, that means a MOSFET with 1 ohm ON resistance would dissipate a power of i^2*r = 10^2 * 1 = 100 watts. That needs a very good heat sink, and active cooling.
Depending on the characteristics of your motor, you may also need a snubber circuit on the driver. Maybe that's what you were doing with the power diodes, but it's hard to tell without a schematic.
Source(s): Most likely, an Electronics forum such as https://www.allaboutcircuits.com/ could give better advice than Y!A. - PhilomelLv 77 months ago
Two of the connections are on one plate(A) and the other two are on the second plate(B).
solder a wire betheen the A's and another between the B's. Now you have a std cap.
