Choosing New Capacitors

Each capacitor has two values: a voltage rating and capacitance value. Both are important. The general rule for replacing capacitors is to use values that are equal to or higher than the originally-specified values.

Voltage rating tells how much voltage the capacitor can withstand. It does no harm to exceed the original rating somewhat. For instance, it is fine to replace a 250-volt rated capacitor with a 450-volt one. A few capacitors may require a higher voltage rating, such as 500 or 600 volts. Don't waste money buying capacitors with voltage ratings vastly higher than the originals. Your radio will not work any better with 1000-volt capacitors than with 450-volt units.

Capacitance value indicates how big an electrical charge the capacitor can store. This value should also be equal to the original.

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—voila!—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.