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 Power Factor in Capacitors

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Cliff Jones
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Join date : 2010-11-22

PostSubject: Power Factor in Capacitors   2012-02-14, 2:59 pm

As a note I have paraphrased this post from an article in the July 1957 Radio-Electronics Magazine.


Power factor in capacitors means nothing more than how much energy is wasted, charging and discharging a capacitor.
Energy used in this waste is a combination how well the capacitor can take a charge and how well it can discharge.
The power factor is rated in percentage compared to a perfect capacitor. Power factor cannot be measured in Ohms as we are dealing in frequency and capacitance of the applied voltage and the internal resistance of the capacitor.

In a perfect capacitor there is no loss, so the current would lead the voltage by 90% so the power factor would be zero. If a capacitor has an internal resistance exactly equal to it's capacitive reactance both in ohms, the current will lead the voltage by 45 degrees, so the power factor will be .707.

Less internal resistance allows greater lead and smaller power factors. So more resistance is just the opposite it brings the current lead more into time (phase) and increases the power factor. Capacitor Power factor is equal to the cosine of the angle by which the current leads the voltage. No cosine can be greater than 1.00 so 1 represents 100% so lesser values are represented by a percentage of 100 it is customary to convert these to fractions. So 0.707 becomes 70%. In an off handed way it is the ratio of internal resistance to capacitive reactance. This is just a simple explanation.

So the lower the power factor the better the capacitor is and is able to reduce ripple effects in power supplies.
A rule of thumb I would say after reading the article is if the power factor is close to 20-30% don't use it. The lower the percent(%) the better.

Boy you don't know how hard it was to read and smell the mouldy odor while transcribing this from the magazine. pale

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