Electronic – Voltage dropping capacitor doesn’t work

accapacitancecapacitorpower supplyvoltage

I connected a voltage dropping capacitor in series with 220v AC supply and I measured the output voltage and it was 220 v too. I was expecting to get a voltage that is less than 220 volts. Did I make a mistake or the capacitor doesn't work ? I just want to test the capacitor before making the rectifier and load circuit.

One more thing, It is written on the capacitor 822j does that mean it is 8200 pF ?

It is about 0.9 uF when I measure it.

I know it is a dangerous circuit and I should use a transformer but I would like to make a transformer less power supply.

Thank you very much,

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Best Answer

Lets look at this another way. What is the voltage at the terminals of this circuit:


simulate this circuit – Schematic created using CircuitLab

Will the voltage drop? Simple answer: no. Long answer: Well there is no load on it, so no current flowing, so by Ohm's law, no voltage drop across the resistor.

The same is true for your capacitor, there is no current flow, so no voltage drop across it's reactance.

Now what a capacitor will do in an AC circuit if you have a load on it, is to limit the current flowing, which it can do without dissipating large amounts of power like a normal resistor would - it stores and releases charge. That doesn't mean to say it won't heat up, there are losses in it which limit how much power it can safely transfer. It will also change the power factor a long way from unity which can be bad for whatever is supplying your mains voltage (increased losses in transformers and transmission lines, etc.).

Using a capacitor in this way means you would be building a potential divider circuit with whatever you connect, so it won't be a very good regulator. With little load the voltage will go up (no load = open circuit = full mains voltage), and if you put a large load the voltage will drop as more and more voltage is dropped over the capacitor (so high enough rated X series capacitor!).