Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!agate!ig!uwmcsd1!bbn!rochester!pt.cs.cmu.edu!sei!sei.cmu.edu!rsd From: rsd@sei.cmu.edu (Richard S D'Ippolito) Newsgroups: sci.electronics Subject: Re: (easy) capacitor question Message-ID: <6209@aw.sei.cmu.edu> Date: 13 Jul 88 14:45:55 GMT References: <24300028@silver> Sender: netnews@sei.cmu.edu Reply-To: rsd@ae.sei.cmu.edu.UUCP (Rich D'Ippolito) Organization: Carnegie-Mellon University, SEI, Pgh, Pa Lines: 36 In article <24300028@silver> Robert Schofield writes: > I have a question that should be easy for those in this group. > > Is the voltage rating of an electrolytic capacitor the maximum it can > handle or is it the voltage required to drive the capacitor? (If that > is even a correct thing to say) What I really want to know is if I can > substitute a 35v,47 microfarad capacitor for a 16v, 47 microfarad > capacitor. Easy, but with several twists: Yes, but electrolytic capacitors should be used at around 75 to 80% of the working voltage to maintain maximum quality factor (leakage/life characteristics). Electrolytics are formed, that is, have the oxide layer built up to the right thickness to withstand the impressed voltage. A unit run at a substantially lower voltage will eventually deform and become a lower voltage unit (with a thinner oxide layer). In other words, after many years, you'll have a 16-volt unit anyway. As a bypass component, this will not matter. The end result is that the (originally) higher voltage unit may take up more space and have slightly higher leakage in operation. The voltage rating (if only one is given) is the recommended maximum impressed circuit voltage (DC plus repetitive peaks) that can be applied to obtain the rated electrical characteristics and life. Higher voltages may result in higher leakage, lower service life, dielectric punch-through (shorting, although some capacitors are self-healing), or explosion due to internal heating. Oil-filled AC capacitors are especially impressive in that regard! By the way, there are such things as AC capacitors (even electrolytics) designed to handle the heating due repetitive charge/discharge cycles. Rich