This is a switching circuit used for a switched reluctance motor. In this circuit there is a 47μF capacitor on the right side. What is the capacitors function in this circuit?
Electronic – the function of the capacitor between ground and 12V
capacitor
Related Solutions
Does this motor already have a capacitor built in ...
The car has 4 motors, one per wheel. If the motors do have capacitors added, each capacitor will be an easily visible part with two leads, connected to the two tabs of each motor, marked with the red circles below. So a visual inspection should suffice.
(Image source: DX.com)
Most likely answer: No.
If the motor does need a capacitor, what would be the formula(s) I need to study to find out how to match the right capacitor with the motor I'm using?
There isn't a simple formula to determine capacitor size in this context:
- My general suggestion for a motor this size operating at 6 Volts or so is to wire up the highest capacity non-polarized capacitor (e.g. a 1 uF film capacitor from DigiKey) that will fit in the space around each pair of motor contacts, and is rated for 12 Volts or higher. Non-polarized because the motor is likely to be driven both forwards and backwards, so polarity across the motor will switch around.
A definitive computed value for a capacitor is not a simple matter of a formula:
- The capacitance required would be determined by the load of the motor, how much noise the rest of your electronics can tolerate, the amount of radiated electromagnetic emission the operating environment can tolerate, the internal resistance of the power source (battery), resistance of connecting wires, the control mechanism used for the motor (PWM or not), the commutation frequency your motor will operate at, and I have probably missed a few other factors.
I would recommend using the values given in data sheet if possible. Order some more caps you will surly need them sooner or later. The data sheet also states:
"If large capacitors are used, a high current diode from input to output (1N400l or similar) should be introduced to protect the device from momentary input short circuit"
Not sure if this is valid when you are using it as a single supply.
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Best Answer
The 47-uF capacitor is not used to supply the inrush current, which would be needed to start the motor: it's value is too low to do the job (the IGBT handles 7A, so the motor will be quite powerful).
It is likely used as a noise suppressor.