A POWER SOURCE FOR PORTABLE OPERATIONS

After I built my Radio Station in a Box, a portable station containing an ICOM 706MkIIG, an LDG autotuner and an MFJ switching power supply, together with antennas, laptop computer, coax and so on, I realized that without portable power it lacked that last piece to make it truly a go anywhere proposition.¹ I began looking for a suitable power source for truly portable power. Having seen several operators using automotive jump-starter battery packs during the 2004 hurricane season, I investigated these devices further.

Unfortunately, most of the ones I could lift were too small to be of much use and those that had enough juice were too heavy and too expensive. Some had too many power robbing accessories like air compressors or work lights. Something more suitable for my personal use would have to be homebrewed.

I already had a good candidate for the battery under my operating position desk. I use a type 27 deep cycle battery as backup power for my home station. It is quite heavy, but with a suitable luggage cart, I found it easy to move around. The kind of cart I used is the kind that some travelers fold up and strap to their suitcase for those long walks from terminal to terminal at the airport.

The battery is contained in a standard marine type battery box with a vented lid. This meant that I already had an enclosure for the various switches and connectors that I envisioned for my portable power source. I also had a dedicated charger/maintainer to keep it charged up and ready.

Putting these elements together was a one afternoon project. I purchased a cigar lighter type power receptacle, a couple of automotive toggle switches, some blade fuse holders and some 12 gauge wire in appropriate colors. Wiring it up as Figure 1 shows was easy. A pigtail lead with Anderson Powerpole connections provides the power feed for the radio. (Note that these are the small 45 A Powerpole bodies that many hams are using for their radio dc power connections.) The cigar lighter port could power my laptop or other accessories and both are controlled by the two switches and protected by the fuses in their holders. I mounted all of these components in the battery box lid.

While a deep cycle battery is not the best choice for jump starting a car, I have used it successfully for that purpose in the past. My normal jumper cables connect to my vehicle through a very large Powerpole Connector mounted in the engine compartment of my Chevy Blazer. (I use SB175 connectors, rated at 175 A for this purpose.) This works well and guarantees that the cables are connected correctly, at least at the Blazer end. Since I had an extra connector of this type on hand, and it even had lengths of heavy cable attached, I figured it was worth the effort.

My battery has dual terminals, wing nuts and the standard metal studs. I used a pair of replacement battery cable clamps to secure the jumper leads to the battery directly without disturbing the other wiring. These leads exit the battery box in the normal openings for heavy cables. The connector dangles out the front of the box where it is easy to connect my jumper cables just like I would on the Blazer.

I now have a portable power source with all of the desirable features of the commercial “jumper packs.” Since I had many of the parts on hand already, it only cost about $20 to build. If you have a well stocked “junque box” you can probably do it for even less. Figure 2 illustrates the complete package.

Just a short thought about the weight of this power source. As I indicated, it is permanently mounted on a collapsible luggage cart. My portable station is also on wheels since it is part of the suitcase into which I built the station. Both units can be pulled along just like luggage at an airport or train station. Each package weighs less than 40 lbs. Lifting them into and out of my vehicle may require forethought, but I do not usually have to do that many times during a deployment. Once they are on the ground, they are easy to manage. Update: As I noted above in the caption for the picture, the luggage cart pictured turned out not to be strong enough for the job. I strongly recommend a more beefy luggage cart for use with the weight of the deep cycle battery.