# Resistor burnt in a phase shift circuit

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#### mohan.n2293

Joined Jan 23, 2017
60
Hi all i have used a RC circuit to get phase shift form 230v input with cap=22uf,450v and resistor=1k,1/4 watt ,but i dono when i connect to 230v supply resistor in the 230v got burnt .
can any one tell me why it happend?

#### Alec_t

Joined Sep 17, 2013
12,892
For the usual phase shift arrangement the R and the C are effectively in series across the 230V RMS supply.
The impedance of the cap at 50Hz is ~ 145Ω, so the RMS current through the resistor is 230/(1k+145) = 200.9 mA. That means the poor resistor has to dissipate ~ 230 x 0.2 = 46W . It's hardly surprising a 1/4W resistor gave up the ghost.

#### Kjeldgaard

Joined Apr 7, 2016
461
My calculations get the impedance of the capacitor approximately to be 145 ohms @ 50 Hz.
So almost all the 230 Volts is across the resistance, and it provides approximately 50 watts of power in the resistance.

#### LesJones

Joined Jan 8, 2017
3,745
You have not given a schematic of how the components are connected so I will assume they are connected in series across 230 volts AC I will also assume that the frequency is 50 Hz as you have also ommited this information. Based on these assumptions I do not find it surprising that a 1/4 watt resistor disipating 52.44 watts get very hot.
Edit This is based on vector addition of the capacitors reactance (144.7 ohms) and the 1K resistance which gives a value of 1010.4 ohms.
Les.

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#### ScottWang

Joined Aug 23, 2012
7,243
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