Capacitors

Capacitors: Substituting for Unavailable Values

In a pinch, you can combine two capacitors to create one with the desired value. Simply remember that when two capacitors are wired in parallel, their values are added. When wired in series, their capacitance values are reduced.

For example, say that you need a .04-mfd capacitor, but all you have on hand are .02-mfd units. Wire two .02s in parallel, and you now have a .04-mfd capacitor. Likewise, wiring two 22-mfd capacitors in parallel creates a single capacitor of 44 mfd.

Conversely, wiring two .02-mfd capacitors in series produces a .01-mfd capacitor. The capacitance is halved.

Wiring in parallel or series also affects the voltage rating of the resulting capacitor.

For capacitors connected in parallel, the voltage equals the lowest voltage rating of either capacitor. For example, wiring two 22-mfd/150-volt capacitors in parallel results in a 44-mfd/150-volt capacitor. Both voltage ratings are equal, so the resulting voltage is 150 volts. If you wire in parallel one 22-mfd/150-volt capacitor and one 22-mfd/35-volt capacitor, the resulting capacitor will be 44-mfd/35-volt. The capacitance is doubled and the lower voltage rating is 35 volts.

For capacitors connected in series, the voltage is added up. For example, wiring two 22-mfd/150-volt capacitors in series results in a capacitor of 11 mfd and 300 volts. The capacitance is halved and the voltage is doubled.

Observe polarity when combining electrolytics. When wiring them in parallel, wire both positive ends together and both negative ends together. When wiring them in series, connect the positive end of one capacitor to the negative end of the other.

Here's a real-world example. I needed a .25-mfd capacitor rated for 200 volts. Not having that exact value, I wired in parallel a .22 and a .033, both rated for 630v. The result is a .253-mfd/630-volt capacitor, which worked perfectly.

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