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Date:         Sun, 10 May 1998 10:14:25 -0600
Reply-To:     Bill <billv2@PRODIGY.NET>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Bill <billv2@PRODIGY.NET>
Subject:      Re: Tantalum capacitors
Comments: To: Vanagon@VANAGON.COM
Content-Type: text/plain; charset=ISO-8859-1

> The problem with your 22mF/35V capacitor is that it's failed, not that it's > 35 volts. My guess is that the heat in the engine bay took it out. > Use the highest temperature spec available. There is a special "automotive" > spec, with reason. > > ************************************************************ > Johan Nyberg, Sweden N 59o E 17o 25" > '86 Caravelle C > ************************************************************

I agree. Capacitors have limits as to the amount of voltage it can handle across its plates. Thus, the rating givin' specifies the MAX dc voltage that it can withstand before failure. As a rule of thumb, you should always use a higher rating when designing circuits.

I suspect that the electrolytic (tantalum) capacitor was breaking down. Heat has a definite reaction to capacitors. This depends on the temperature coefficients. An example would be 100 ppm/C for a 1 micro farad capacitor calculates to 1 degree Celsius rise in temperature, the capacitor will decrease by 100 Pico farads. Yes, temperature vs capacitance is inversely proportional.

Bill '85 GL [*Magic*Bus*] Big Sky Country <><


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