Discuss Can someone once and forall tell me what a capacitor does in an AC circuit?Thanks. in the UK Electrical Forum area at ElectriciansForums.net
here endeth the first lesson.There are different ways to look at it, but one analogy is:
So when you try to increase the voltage across a capacitor you need to put current in to charge it, this makes it hard to change voltage suddenly as the required current is given by I = C * dV/dt so a capacitor provides "smoothing" and stores electric charge in doing so.
- Capacitors try to prevent voltage changing
- Inductors try to prevent current changing
An inductor need a voltage applied in order to change the current flow. So if you try to interrupt current in an inductive circuit (e.g. motor, relay coil, etc) you get a high voltage generate opposing that. The voltage is given by V = L * dI/dt and that can cause damage to switches or solid state controls, but is sometimes of use in cases such as car ignition coils.
The rate of change terms (dV/dt and dI/dt) for the useful case of a sine wave is given by 2 * PI * f which leads to the concept of capacitive and inductive reactance, analogous to resistance in opposing current flow, but not in-phase with the voltage as it is the changing aspect that matters. That is at its maximum when the voltage is crossing zero.
Yes but can I use capacitors to increase voltage across motor windings?There are different ways to look at it, but one analogy is:
So when you try to increase the voltage across a capacitor you need to put current in to charge it, this makes it hard to change voltage suddenly as the required current is given by I = C * dV/dt so a capacitor provides "smoothing" and stores electric charge in doing so.
- Capacitors try to prevent voltage changing
- Inductors try to prevent current changing
An inductor need a voltage applied in order to change the current flow. So if you try to interrupt current in an inductive circuit (e.g. motor, relay coil, etc) you get a high voltage generate opposing that. The voltage is given by V = L * dI/dt and that can cause damage to switches or solid state controls, but is sometimes of use in cases such as car ignition coils.
The rate of change terms (dV/dt and dI/dt) for the useful case of a sine wave is given by 2 * PI * f which leads to the concept of capacitive and inductive reactance, analogous to resistance in opposing current flow, but not in-phase with the voltage as it is the changing aspect that matters. That is at its maximum when the voltage is crossing zero.
Yes but can I use capacitors to increase voltage across motor windings?
If I had a capacitor across a winding in a three phase motor, then what difference would that make?Lots of things. It can smooth the bump of a rectified waveform.
It can block DC.
It can be used in conjunction with an inductor to reduce EMI.
And ashit ton of other stuff.
Why the "once and for all"? Has this been on your mind for a while?
Reply to Can someone once and forall tell me what a capacitor does in an AC circuit?Thanks. in the UK Electrical Forum area at ElectriciansForums.net
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