OK... I completely disagree with that standard up front-for reasons I'll
state in a moment... but first, at to their standard, what was what? E.g.
Molex connectors like that have a pointy end and a square end... which was
positive, and which negative? And did they specify which pin type (M/F) and
which connector shell type (M/F or solid/open) went to the source and and
which to the load?
I disagree with a 2-pin standard for several reasons:
1. Although it is difficult to force together physically reversed Molex
connectors, it is quite possible. With only 2-pin connectors, the forcing
together of the two pieces, and subsequent connection between the wrong
polarity pins can be done-at least momentarily-with utterly disastrous
results: blown something (fuse/transistors/whatever) at best, and melted
wires & a fire at worst. One of the most obvious uses for such connections
involves batteries... and with the low ESR of NICADs tremendous surges can
pass through the pins, possibly spot-welding them together, and so on. A
3-pin connection, being reverse-proof avoids this.
2. With a 3-pin standard, the center pin is made NEG or GND, and is
connected no matter how the connector is pushed together-you always have
GND. Of the other two pins, one is used for the POS current-carrying lead,
and the other is either unused; used as a second, parallel POS lead; or
better, as the remote voltage sense lead for the power supply (or
DMM)-enabling the user to set the power supply voltage levels more
accurately. This sense lead is present on most modern power supplies. There
is no possibility of using this lead in a 2-pin connector (putting an
additional wire in the 2-wire cable, and attaching it to one of the
connector pins actually defeats the purpose of the sense-since it will only
be valid UP TO the connector attachment point and CANNOT be carried through
the cable to some point at the load-as intended.)
3. The point here also applies to other connectors: try and make their
reverse connection non-fatal where possible... and impossible if you can.
It only takes the slightest bit of cost and effort to eliminate several
nasty possibilities, and provide a much better, safer, and useful connection.
Finally, easily reversed connectors should ONLY be used for AC connections,
where their reversal will not matter.
72/73
Ed Tanton N4XY EMAIL: n4xy@avana.net TEL: (770)579-3933 V/MBX/FAX
189 Pioneer Trail
Marietta, GA 30068-3466
QRP-ARCI#7663 G-QRP#6779 OK-QRP#172 QRP-L#758 AdvRC#140
NORCAL#1779 NCDXF SEDXC
Life Member: ARRL AMSAT IDRA INDEXA QCWA
URL: Coming Sooner or Later
"Think you can, think you can't: either way you're right!" Henry Ford
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