New Pictures: HF Radio added!!!
I've added an Icom 703+ HF/6m rig to the setup -- pictures attached
below. As a QRP rig, the 703+ has an integral autotuner, 10W
output, and minimal power consumption on receive. This makes it
perfect for this application. The depth of the 703+
required swapping the V8000 to the right, with the 703+ going in it's
place. This is due to the fact that there is more headroom
available over the power supply than over the batteries.
DC Power: Battery
Since a primary requirement was
battery powered operation -- and
batteries are heavy and consume lots of space -- a good place to begin
was to determine how much battery capacity would be required.
First, I
had to figure out what the load on the battery would be. The
Icom
V8000 2M mobile which I was planning on using has, according to the
Icom
manual,
the following current draw characteristics:
Well, that's only partially helpful;
while the standby number is
somewhat useful, the other two are not. First, I don't plan on
having the volume knob cranked all the way up during operation; and
second, I tend to think that with a reasonable antenna it would not be
necessary to use the highest RF power output level. The V8000 has
four power level settings; per the manual they are nominally 5W, 10W,
25W, and 75W. In reality these are somewhat conservative
numbers, especially at the lower power levels. With a 13.8Vdc
input, my V8000 outputs 7.5W, 13W, 32W,
and 77W respectively into a 50ohm dummy load. Even when powered
with straight 12.00Vdc, the radio nearly meets its advertised rated
output at
all but the highest power level. To obtain better granularity I
measured the current draw under various conditions:
270mA standby, no
microphone att'd.
300mA standby,
microphone att'd.
300mA scanning, ~10
frequencies.
310mA RX,
normal audio output.
4.7A TX, "low"
5W setting.
7.2A TX,
"mid-low" 10W setting.
~10.0A TX, "mid" 25W
setting.
~15.0A TX,
"high"
75W RF setting.
(aside: The last two values are
approximations, as my multimeter only measures current to 10A.
Lacking an external current shunt to do the measurement, I feared that
the higher power settings would pop the the multimeter's internal 10A
"fast-blow" fuse -- a type and rating of fuse for which I don't have a
spare handy. Should you have actual measurements for the V8000's
input current draw at the "mid" and "high" settings, please let me know
via the email address in the header. This data will provide me
with more accurate operating time calculations in the following
section.)
Using a fairly aggressive 70/20/10
duty cycle (70% standby, 20%
receive, and 10% transmit at the 25W setting) yields the following:
.7 x 0.3A = .21 (42 minutes standby every hour)
.2 x 0.3A = .06 (12 minutes of RX every hour)
.1 x 10A = 1 (6 minutes of TX every hour, at 25W output)
Summing these results in a 1.27A
average current draw. To operate
at this duty cycle for an hour would require 1.27AH of battery
capacity. And, to operate for 24 hours would require
approximately 30AH.
Those of you familiar with current sealed lead-acid battery technology
know that 30AH is getting into "it's getting tough to lug around"
territory.
From a practical standpoint, I had
three constraints. First, the
battery had to be small enough to fit into a modest enclosure; second,
it had to be light enough to be carried around; and third, it had to be
reasonably priced. I discovered that if I relaxed my operating
time requirement just slightly I could concurrently meet all of my
technical criteria and my "it should be low cost" goal. I chose
to use a pair of 12V 12AH SLA/AGM batteries, wired in parallel of
course;
this would provide a total of 24AH of capacity. Moreover, 12V
12AH SLA/AGM batteries are widely used in UPS applications, meaning
that
the economies of scale were on my side. In fact, one of the most
popular sizes of UPS (~1000VA range) is configured to use precisely the
same setup -- a pair of 12V 12AH batteries such as this
APC
model
"RBC6" 12V
12AH x 2 battery pack. High quality batteries of this
type
at very attractive pricing could easily be found by searching on
google
and
Ebay
for RBC6. This battery pack was to be the starting point for my
portable box. The RBC6 weighs in at 17 lbs [7.7 Kg].
AC Power: Samlex 1223
I had a spare
Samlex
1223 switch mode power supply which simultaneously met two
criteria: it was very light (about 3.5 lbs [1.6Kg]) and it had more
than sufficient current output capacity (23A continuous) to supply the
radio at maximum RF output. The headroom also would power some
12Vdc accessories as well. More details on this excellent AC
power supply are in the
user
manual.
The battery pack and power supply fit
nicely together and would be mounted to the bottom of the
enclosure. To do so I thought of using a "carrier" panel which
would mount the two items and prevent the heavy battery pack from
bouncing around. Both the battery pack and the power supply would
be held to the panel via web strapping and simple friction locks.
The panel would then be screwed to the
bottom
of the box. Optimally the carrier panel would be thin,
strong, and easy to machine during construction. My plan to use a
nice, 1/2" thick Delrin panel collapsed when my wife discovered me in
the kitchen measuring her new cutting board. Instead, I
substituted a piece of 1/2" thick plywood -- I figured that it would
allow me to work out the design details and then I could make another
foray into the kitchen. Using my
router,
I plowed a
recessed
area to hold the battery pack, and additionally made cutouts for
the
web
strapping which would be used to
secure
the battery pack and power supply. I then
drilled
holes which would accept T-nuts; these fit flush with the top
surface of the plywood panel and remove the need for hex nuts and
washers inside the box. A total of 4 marine-grade stainless 1/4"
[6mm] dia screws secure the panel to the bottom of the box. Under
the screw heads are stainless fender washers, which are large diameter
to spread the load and prevent pull-through of the screws. In
addition, small flat rubber washers are used to ensure that water can
not get in through the screw holes. I even tested this out by
putting the box in the bathtub overnight, sans any radio equipment of
course. Weighed down with a few bricks, the box sat overnight in
2" [50mm] of water without a drop getting inside.
Once
mounted into the box, the panel securely held the battery pack and
the power supply and maintained water tightness. Time to move on
to installing the rest of the gear.
As you can see from the requirements
listed in the introduction, there were a number of necessary components
that were not yet accounted for. For example, I needed to
implement features such as overcurrent protection, selection of power
supply, battery monitoring, and accessory power outlets. This
would require mounting circuit breakers, switches, a panel meter, and a
number of connectors. I started off by gathering up all of the
piece parts and
laying
them out in the box, placing each where wiring would be optimal
(i.e., shortest path). I went through quite a few
iterations. The problem was that I had too much "stuff", and
mounting all of it was looking problematic. The various component
shapes and sizes could make fabrication of several brackets
necessary. I considered several options, but settled on making a
single large bracket that would mount all of the switches,
instrumentation, and connectors. This mounting bracket would be
located on the box wall opposite the radio, and thus on the bottom when
the box was on it's side in the normal operating position.
Several back-of-the-napkin sketches were made of the layout. As
there were a variety of mounting hole shapes and sizes, it was clear I
was going to be spending quite some time at my drill press and with a
file. The round holes aren't so bad but the square cutouts required for
the switches and panel meter would require a lot of finesse.
Ultimately I decided to call in air support. A friend of mine
runs a small sheet metal fabrication business. He does the design
work in
PTC Pro/Engineer,
a high end CAD tool, and then exports the
design data to a CNC automated turret punch machine. The CNC
punch machine, driven by output from the CAD tool, makes quick work of
knocking precision holes in a flat sheet blank. Subsequently, the
flat blank is formed into a right angle on a bending machine called a
brake. This was exactly what I needed. We spent a few hours
playing with the design in Pro/Engineer, rotating the
3D
model on the
screen and
working
on ensuring proper fit. Then it was off to
the punching and brake machines. And so for the cost of the
aluminum sheet material and some pizza, he fabricated my multiple hole
mounting bracket plus a spare. The result was a professional
component arrangement, one which certainly functions and looks worlds
better than what I could have done with my drill press and vise.
The completed bracket mounts the following, from left to right:
AC power supply output 20A breaker
Battery pack 20A breaker.
DC source select rocker switch, DPDT center off type.
Charging circuit 4A breaker.
Digital Panel Meter (DPM).
Toggle switch, SPDT X 2
(#1 selects power supply or
battery pack voltage; #2 DPM backlight).
Andersen PowerPole panel mount
gang-of-four connector.
BNC connector X 2, panel mount radio RF outputs
(currently one spare)
AC power input receptacle, IEC 320 type with
integral EMI filter
Here is a
PDF
format keynote drawing of the component mounting bracket.
Wiring, Breakers, and Panel
Meter
All of the various components fit perfectly into the bracket and the
process of wiring started. I planned to have the three
subsections (power supply/battery pack panel, radio mounting bracket,
switch/instrumentation/connector bracket) easily separable. I
employed
Andersen
PowerPole connectors (got them from
PowerWerx, also available from
West Mountain Radio) and
12 AWG wire to interconnect
the power source and loads, including the external connectors.
These clever, asexual connectors are easy to assemble, handle up to
45A, and when paired they prevent reverse polarity mating
accidents.
Note that there is a
PowerPole RED/BLACK
orientation convention in widespread use within the amateur radio
community, and adherence to
proper
crimping (see also
here) is
essential. For connection to external loads, I used an Andersen
panel
mount "gang of four" housing. In addition, I made up a short
cable which on one end had PowerPole connectors and at the other end a
cigarette lighter socket. This way, I could power anything that
had a automotive cigarette lighter plug on it.
Under normal operation, the AC power supply is selected to supply
current for the radio. In the event that AC power fails, or for
remote operation, the rocker switch is simply toggled to select the
battery pack. There is a center-off position to the rocker switch
which disconnects all supplies from all the loads; this insures that
the battery isn't inadvertently drained during storage. I also
needed a busbar
for connecting all of the ground wires to; I used a
Square-D
load center grounding bar that I picked up at Home Depot.
In my requirements I noted that I wasn't going to use fuses. My
take is that no matter what fuse style you pick, the specific type you
need to replace a blown one is never handy. This would be very
problematic in the field or in an emergency situation. Clearly
overcurrent protection was needed, so I elected to use
panel mount DC
breakers. These are widely available at marine stores in my
area. The magnetically actuated breakers provide an on/off switch
function along with overcurrent protection. In my circuit, there
is a
pair
of 20A breakers, one each protecting the AC power supply and
the battery pack. In addition, a third 4A breaker protects the battery
charging circuit.
Some time ago I picked up a pair of digital panel meters (DPM) at a
computer show. I didn't actually have a use for them at the time,
and
so they sat in a box for several years before this project came
along. At first, I hadn't thought of using a DPM, in fact I was
preparing to build up a
simple LED
meter using the National Semiconductor
LM3914
device. But while I was looking through my junk boxes for some
other parts, I re-discovered the DPMs that I had stashed long
ago. After a little bit of datasheet inspection, the
Lascar
model DMM939 seemed to be perfectly suited for my task. It is an
autoranging type, has an internal isolated power supply, and requires a
minimum of connections to measure DC voltage. Of the 16 pins on
the back of the DPM, I only had to short two together, connect one to
ground, connect one to the 12V supply, and then two others would
provide the measurement input. These last two I wired through a
SPDT switch so I could select measurement of the AC power supply output
or the battery pack voltage. With the
DPM
in place, I could
monitor battery voltage either during operation or when charging was
underway.
---> Link to basic wiring diagram:
PDF Schematic
