In a recent post to qrp-l, n4xy@avana.net had some comments about the
ARRL-recommended standard 12 volt connector. While I had nothing to do
with selecting that standard, I did write the QST article promoting it.
Both the handbook and my article clearly shows the recommended polarization
and keying of the connectors.
The triangular end of the connector
is the positive end, and the receptacle with female pins, is on the cable
connected to the power source (battery, power supply, cigarette lighter plug).
(The receptacle is the connector that fits inside the plug, and has the pins
closely surrounded by plastic; the plug is more of a shell, with the two pins
exposed inside.)
Fusing is strongly recommended for power sources.
As for accidentally mis-connecting them, give it a try. I just did, and
short of breaking the connector, there doesn't seem to be a way of plugging
it in backwards. Mobile and portable gear should, however, be set up with
reverse-voltage protection (series diode, reverse diode and fuse, P-channel
FET, etc) Even if you could short things out, the fuse in the power source
lead should protect against fire.
3-pin connectors would solve the reversability problem, but you still have
to be careful that you can't plug them together off by one pin. Also,
there didn't seem to be any really good 3 pin choices available at Radio
Shack (No, 3 pin XLRs aren't a good choice - they are used for mikes...)
/mike
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