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I have a battery charger circuit, this capacitor sits between the rectifier diodes and chunky set of inductors and diodes on the AC input side. The battery charger is 30A 12V car battery so pretty hefty.

WikHow says <number>R<number> means 3.9pF but does not explain why there are an additional two digits afterwards, also looking at high voltage 3.9pF capacitors, they seem much smaller than the one I found in the circuit. Also there is no guidance as to the R and L. The capacitor is shorted so I cant measure the values.

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It may be a varistor rather than a capacitor, you can see in this image where I took it from in the board, how can I identify a replacement for this component?

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It doesn't seem to be a capacitor. If this component "sits between the rectifier diodes and chunky set of inductors and diodes on the AC input side", probably it is a varistor. Ceramic disc capacitors usually have a mate finishing, and not a shiny smooth finishing like this component in the photo.

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  • \$\begingroup\$ I'm pretty sure it is a power thermistor from Semitec after more investigation - it has a resistance of about 3.9Ohm at room temperature consistent with the marking. Datasheet at pdf.datasheetcatalog.com/datasheet_pdf/semitec/… \$\endgroup\$
    – Brendan
    May 14, 2019 at 20:53

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