> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Russell McMahon
> Sent: 9 July 1999 08:59
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Determining polarity of electrolytic capacitors
>
>
> Here is an informal but effective method for quickly testing a
> working circuit to see if electrolytic capacitors are correctly
> polarised. I have never seen this method described elsewhere but I
> always use it after assembling circuits - it appears to be highly
> reliable and catches the occasional mistake.
>
> To check electrolytic capacitor (metal can version only) polarity in
> circuit
>
> - Ground negative meter probe
> - Operate circuit
> - Measure voltage on can of working electrolytics.

Bit of a problem here, in that in a very short time if the cap is in the
wrong way
around you could have some rather spectacular self destruction of the cap
occurring.
Good to see you disclaimer at the end of the message:-}
>
> Properly polarised caps will typically show a voltage of from about
> 0.1 to 0.5 volts.
> Reverse biased caps will have a can potential much closer to supply.
> ie the can is not AT, but is NEAR the potential of the true negative
> terminal.
> For a reversed cap in the 10uF - 1000uF range on a 5 volt supply the
> can is typically at 2 or 3 volts but anything over about 0.5v is
> suspect.
>
> This method COULD be used for testing a new cap of unknown polarity
> provided the voltage used was much lower than rated and perhaps
> current limited by a series resistor - no responsibility taken for
> valuable caps damaged by this test :-)
>
>
>
>
> regards
>
>
>             Russell McMahon
>