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Emergency Power
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Intro
This page is not so much about power sources
as it is about the interconnection woes faced by the mobile ham. With the advent of the electronics
miniaturization revolution came practical mobile and portable operation for Amateur Radio. Now the market
abounds with examples of small, lightweight, commercial rigs. Every ham has at least one handie talkie and/or
2M mobile rig. Most of these devices are designed to operate from a 12 Volt power source, sometimes with the
help of an adapter. Add to this, the laptops, Packet TNC's and other station adjuncts, it becomes practically
impossible to keep up with all those wall adapters and cords. Heaven forbid that manufacturers decide on a
standard for those connector sizes. In this installment of the OIDpages, I will introduce a method of dealing
with all those various connectors and power sources that will allow choas to become order in your ham shack.
Where do I start?
A typical 12 volt powered device might be a Packet TNC.
This device usually comes with either a power pigtail to attach to a 12 volt power supply or, if the power consumption
is low enough, a wall outlet power adapter (wall wart). For ease of use and interchangibility (a requirement for
sane emergency operations), I modify all my 12V operated devices to use a standard connector.
Once upon a time, the ARRL suggested adopting a two circuit Molex connector as the standard for
emergency power. Radio Shack just happened to carry this component (274-222 and others). Since then, the
industry has proceeded to using connectors that are more capable of meeting the demands of both low and high current
circuits. Currently, the Amateur Radio community have standardized on the
Anderson Power Pole (power poles or PP for short), specifically the 1327 series.
{picture of pp connectors in package}
The power pole connector is an interesting system of shells and pins that can be stacked in various ways
to obtain a multitude of configurations. One of the neatest features is the mirrored connector mating interfaces.
One of the first tenets of safe interconnection design is that a connector that has open pins, shall not carry
live power. This design makes use of the right-left mirrror symmetry of the connector to allow the same contact and housing
to be used on either side of the power connection. Just flip one over and they slide right together. This means
no more exposed pins to short out, ever!
[picture of housings]
There is a generally accepted standard way of polarizing the connectors. When the connector pair is viewed from the end
and with the larger of the two 'U's on top, then the red (positive) connector housing should be on the right. Following
this convention ensures that when equipement from different shacks are gathered in one place (e.g. Field Day), everyone's
equipment will be interoperable at the power level.
[picture of two connectors on a cable, facing out]
The particular Anderson Power Pole connector system we use has three different sizes of connectors, 15A, 30A, 45A. While
most people assign the previously specified current values to these size ranges, the difference between sizes is really
the size of the wire that the contact can accomodate. Of course, this does determine the amount of current that can be
carried, but it can be a bit confusing.
| Current | AWG Wire Size |
| 15A | 18-20 |
| 30A | 14-16 |
| 45A | 10-12 |
[picture of contacts]
Now what?
We've decided on a polarization methodology for our connectors, but
we haven't talked about how we connect to the power sources. The method talked about in the previous section, inserting a
connector pair in the line of a wall wart, is fine for low powered items that connect one on one. But what about using a
larger power supply, or hooking multiple devices to that supply? The average ham shack typically contains at least two
different sources of 12 volt power, usually a 12 volt power supply operated from the AC mains and a 12 volt auto battery.
In each of these cases, the sources are capable of supplying a large amount of current on demand. It would seem that a
scheme for interconnecting larger sources and multiple devices might be desired.
There are several commercial power distribution products available, the two most commonly used are from West Mountain
Radio and Saratoga.
[pictures of devices]
These devices usually include some fusing as well as the power distribution feature. It is possible to create these
using just connectors and wire, so be creative.
These devices, with a high current (45A) input cable with connectors suited to the power source on one end (battery clips,
terminal lugs, etc), will allow the higher current circuit to be split out to multiple lower current circuits. In this
manner, several devices can be powered from the same power source.
MORE ON THIS
How to get them
Unfortunately, power pole connectors are not available through your local Radio Shack dealer. However,
there are various distributers that are known to carry them. Online ordering in quantity can bring the
unit price down to reasonable values.
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