Hi folks.

Im sure this is a easy one for you but Im struggling.
I want to work out what capacitor to use as a series capacitive reactance.
I know 1/ 2.∏.F.C = Xc. what calculation do I do if I have resistance but want to calculate what capacitor to use?

Thanks very much

Carl

 

I have no idea what you're asking.

What resistance? What are you trying to do?

 

A complex impedance has two parts. The real part is the resistance and is plotted along the horizontal axis. Capacitative reactance is plotted along the neagative imaginary axis aka the jω-axis. The complex impedance is:

R - jXc

The magnitude of the complex impedance is
 ___________
√R^2 + Xc^2

and the angle is arctan(-Xc/R)

Does that help?

 

well what im trying to do is get a 12v fan working on 230v supply but using a capacitor in series with a bridge rectifirer to do this.

Supply = 230vac
Load = 12v @ 0.11mA.

so... 230-12 = 218v.

218/0.11 = 1982Ω

218x0.11 = 24watts.

so I know I need a resistor thats 2k @ 24 watts to do this.
But how can I do the calculation to give me the answer in capacitance... so I know what capacitor to use to do this?

 

Hello,

Sorry, we do not allow circuits directly connected to the mains.
Please use a small powersupply for the fan.

Bertus