In sci.electronics.design, Michael
The plus is definitely neaer the side with the line. So if that is the
positve side - that means I connect it to the +5v line instead of the
ground line right? I can't believe I have to ask this...
Yes, the positive side goes to the +5V line.
I recall from a recent discussion of tantalums here that they are
very easily damaged by even a small reverse voltage, less than a meter
or the forward voltage drop of a diode would give. So if you tried
connecting it both ways with a multimeter measuring resistance as John
suggested, you may have damaged the tantalums you tested. Such damage
may be subtle - they may work now, but short out some time down the
road. I'd be wary of using them, and only use "pristine" ones that
you're sure haven't had any reverse voltage on them.
I (only now) recall that the bar indicates which lead the "outside"
film in the case is connected to. Caps are made with two foils and an
insulator/dielectric in between. Aluninum electrolytics (the popular
"normal" kind) are (almost?) always wound with the negative foil on
the outside, so the bar is at the negative terminal. Most or many
tantalum caps (which are technially a type of electrolytic, so the
full name is "tantalum electrolytic capacitor") are wound the other
way, so the bar would be on the + terminal.
What I vaguely recall is that this marking-a-capacitor-with-a-bar
business dates back to vacuum tube devices and capacitors made of
aluminun foil with wax paper dielectric, which were (and the ones that
survived still are) the sizes of an AA, C, or even D size battery.
These had a bar or band on one end (they had one wire coming out of
each end) to indicate the connection with the outside foil. This was
important when mounting it in a chassis - it was connected so that the
wire with the bar was the connection in the circuit that was the
closest voltage to the chassis (I hope you understood that - if one
side was 20V and the other was 330V, you connect the bar side to the
20V). This was done to reduce the chance that the outside foil would
arc through the outside insulation of the capacitor to the chassis on
which it was sitting. The voltages commonly used nowadays are nowhere
near what vacuum tube circuits use, so which terminal has the bar is
not important in (almost?) any application, but manufacturers still do
it. Putting the bar on must be some sort of standard.
