[TowerTalk] APP issues

[Howard Hoyt]

Hi all,

I too use APPs for 12V amateur equipment, however I do have reservations 
about them and some work-arounds:

1) Retention force:  When assembled in a pair, the retention force is 
not high enough for all uses, lateral forces on the plug are translated 
by flexibility of the housing into a rotational moment at the center of 
the mated pair, encouraging dismating.  Indeed pushing cables around 
behind my K3 I have inadvertently unplugged the DC input.
Anderson makes a locking device:
(http://www.andersonpower.com/files.php?file=02628.pdf)
Powerwerks also makes a retention clip:
(http://www.powerwerx.com/powerpole-accessories/powerpole-retention-clips.html)
Both of these are very inexpensive, but manufacturers of devices with 
APPs must leave the part of the mated pair with the roll-pin hole 
outside the rig, and not have installed a roll pin for the locking 
device to be used.

2) Accidental reverse polarity engagement.  The most common arrangement 
for amateur use is a black/red pair side-by-side.  If you are fumbling 
around behind a rig with the plug out of sight, there is the possibility 
of accidentally plugging the plug one module over, i.e. just the red 
plug engages the black jack with the black plug hanging in the air.  If 
this plug is coming from your power supply which also has other cables 
powering associated equipment, you have just created a short circuit 
through the ground circuit of the rig, then through interconnecting 
cables to other equipment, potentially burning PCB traces or causing 
other damage. This problem argues for recessing the APPs far enough 
inside a rig panel so that they can only mate correctly.  Of course then 
the retainer is unusable.

All of this being said, in general the retention force and reliability 
of a 15/30/45 pair assemblies is adequate for non-critical use, and they 
are in wide use here and elsewhere.  They have exceptionally low contact 
resistance and small size for their contact rating and price.  These 
kinds of considerations will affect your choice of a connector when 
manufacturing a supply: we had considered them for our PAE-Kx33 Power 
Supply, but decided on the more direct to KX3 route of a DC Power Plug 
which, while having higher contact resistance, is more generic to QRP 
rigs and also eliminated these issues.  Of course then we had to offer 
an adapter for those who needed APP compatibility!

Cheers & 73,

Howie - WA4PSC
http://www.proaudioeng.com