For some time I have wanted to
try powering my ham radio station with solar power and batteries. In May 2010 I
decided to do something about it. As you see on other parts of this website, I
do a lot of low-power operating
using small, simple transceivers (rigs) that put out as little as half-a-watt
and as much as 5 watts, contrasted to “standard” amateur radio transceivers that
run 100 watts. These low-power rigs are simple and use only CW (Morse code).
I decided to do some research
and see what it would take to put together a solar/battery-powered low-power
station. I found that putting together such a station was simple and not at all
This PDF file that I found on
the Internet is an excellent explanation of what is required to use solar and
battery power to provide power to simple radio equipment:
First, let’s look at some of the technical
- Electronic equipment draws
electrical current from a power source of some kind – a power supply that
operates off the electrical power grid, a battery, or a photo-voltaic panel.
- Receiving equipment draws
much less power than transmitting equipment.
- Transmitting equipment
does not draw full power all the time.
- The amount of current that
a piece of equipment draws from a power source is measured in AMPERES (amps,
A) or MILLIAMPERES (milliamps, mA; 1/1,000 of an amp).
- Batteries are rated at XX
Volts at YY AMP-HOURS (AH). An amp-hour is one amp of current drawn
for one hour. So – if a piece of equipment requires 12 volts DC and
draws one amp, and a battery provides one amp-hour of power at 12 volts,
then, that battery will operate that piece of equipment for one hour.
(NOTE: It’s not really that simple because as a battery nears depletion,
the voltage and current available drop at a much faster rate than when the
battery is fully-charged. However, I’m not going to worry about this fact –
I’ll just build into my system a bit of excess capacity.)
Now, let’s see how I decided on the
solar-battery parts I needed.
To calculate that size of
battery and solar panel needed, you need to know to pieces of information: (1)
how much current does your equipment draw when receiving, and, (2) how much
current does the equipment draw when transmitting?
In the case of my
Labs SW-40 rig, it draws 22 milliamperes (22 mA) while receiving and not quite
150 mA when transmitting. So – if I listen for one hour and do not transmit,
the rig will draw 0.022 Amp-hours – because it draws 22 mA (0.022 A) and it will
be drawing that current for one hour = 0.022 A X 1 hour = 0.022 Amp-hours.
By the same token, if I
transmit for one hour, the rig will draw 150 mA for one hour. The math looks
like this: 0.150 A X 1 hour = 0.150 Amp-hours. HOWEVER – when the rig is
transmitting, it is not drawing this 150 mA of current constantly. For example,
when transmitting using Morse code, the transmitter is operating ONLY when the
key is pressed down – when the key is up, the transmitter is not drawing
transmit power. In the case of CW – Morse code – transmission, the transmit
duty cycle is about 60 percent. Thus, if you’re transmitting with CW for an
hour, you really are transmitting only about 60 percent of that hour, or, 36
Reviewing the foregoing, we
come up with these formulas. ASSUME that in the course of one hour, you are
transmitting half the time and receiving half the time; also assume CW operation.
Current drawn while
receiving, expressed in Amp-hours = (current drawn by the receiver) X (0.5
Current drawn while
transmitting, expressed in Amp-hours = ((current drawn by the receiver) X
(0.5 hour)) X 0.6)
capacity of battery in Amp-hours = (Current drawn while receiving) +
(Current drawn while transmitting)
The SmallWonder Labs SW-40
In the case of operating the
SW-40 at 1.5 watts output for one
hour, receiving half the time and transmitting half the time, we get these
(0.022 receive current) X (0.5 hour) = 0.011 Amp-hours for receiving
((0.150 transmit current) X (0.5 Hour)) X (0.6 for 60 percent duty cycle) =
0.045 Amp-hours for transmitting
(0.011 Amp-hours receiving) + (0.045 Amp-hours transmitting) = 0.056
Amp-hours consumed by the SW-40 in one hour.
Thus, a 1-Amp-hour battery will operate the SW-40 for 1/0.056 hours, or,
transceiver, operating CW with 5 watts output, we get the following.
Receive current: 400mA (0.400 A)
Transmit current: 2.0 A
Assume transmit half the time and receive half the time, and, assume a 60
percent transmit duty cycle.
Receive current = 0.400 A X 0.5 hour = 0.200 Amp-hour
Transmit current = (2.0 A X 0.5 hr) X 0.6 duty cycle = 0.600 Amp-hour
Total current capacity required: 0.200 Ah + 0.600 Ah = 0.800 Amp-hours.
12-Ah battery will last 12/0.8 = 15.0 hours.
By comparison, my ICOM IC-729 transceiver that
runs 100 watts output has the following power requirement.
Receive current: 1.3 Amps
Transmit current: 20 Amps
Assume transmit half the time and receive half the time, and, assume a 60
percent transmit duty cycle.
Receive current = 1.3 Amps X 0.5 hour = 0.650 Ah
Transmit current = (20 Amps X 0.5 Hour) X 0.6 duty cycle = 6 Amp-hours
Ah transmit + 0.650 Ah receive = 6.650 Amp-hours per hour
In this case, a 12 Amp-hour battery would last less than 2 hours: 12 Ah/6.65Ah
required = 1.8 hour = 1 hour, 48 minutes.
After reviewing these
calculations, I decided to purchase a 12 Amp-hour, 12 Volt DC sealed gel-cell
battery for use with my several low-power radios.
The Solar-Battery System
A battery stores electrical
power. It’s more complicated than that but that’s all we need to know for this
Any piece of equipment –
radio, MP3 player, LED light, whatever – takes electricity out of a battery.
If electrical power is not put
back into the battery, whatever is drawing power from the battery eventually
will exhaust the battery and you’ll have a dead battery.
A photovoltaic panel – or, a
solar power panel – generates electricity when the cells in the panel are struck
by light. Any kind of light generates electricity but light from the sun is the
most abundant, and, the price for sunlight is right.
A battery charger generates
electricity and puts it into the battery. A solar panel can be used as a
battery charger because it generates electricity that can be put it into the battery
So – how about we use a solar
panel to generate electricity and put that electricity back into the battery,
essentially charging the battery for free from the sun. It’s that simple with
one small complication: We need some kind of circuit between the solar panel
and the battery to control the rate at which electricity flows from the solar
panel into the battery. We need to do this to prevent overcharging and damaging
Thus, a system that would
enable an amateur radio station to run off solar and battery power consists of
SOLAR PANEL to
control rate at which electricity from the solar panel flows into the
battery and the rate at which power flows from the battery to the load (load
= whatever is attached to the battery).
BATTERY to store
electricity so it can be used by radio equipment.
Building My Solar-Battery System
After calculating the Amp-hour
load of my low-power radios, I decided to purchase a 12 Amp-hour battery and a
solar panel that would put out enough current to charge that battery. Because
the big radio -- the IC-729 -- consumes almost 7 Amp-hours per hour, I decided
to wait and purchase a large battery later after I have had some experience with
the low power radios. I shopped around the Internet and finally decided on
the following items:
Photos of the components
This is what the various pieces look like before I wired them.
The solar panel.
Produces 12 volts DC at 500 mA (0.5 Amp). Measures
9.75" x 9.38" x 1.31" and weighs 1.9 pounds. The round
thing sticking out at the top is a can of paint on which I leaned the panel for
the photo. The panel has a 15-foot long cable coming out of the back,
carrying the electrical current generated by the panel. The photovoltaic
cells are mounted on a substrate which is enclosed in an aluminum frame and
covered with glass.
The charge controller. Phocos
CML-V2 controller, Model CML05. The controller has three sets of connections:
INPUT from solar panel, POS and NEG.
OUTPUT to battery, POS and NEG.
OUTPUT to load (in this case, my rig), POS and NEG
The solar controller constantly monitors the voltage coming from the panel,
the state of charge of the battery, and the demand for current coming from
the load. The controller then applies more or less current to the battery
to keep it charged but to prevent overcharging by the solar cell, and, to
prevent the load from pulling too much current from the battery.
As the battery approaches full charge, the controller throttles back the
current coming from the solar panel so the battery is not overcharged. As
the battery charge drops, the controller lets more current from the solar
panel into the battery.
As the load draws current from the battery, the controller monitors the
battery voltage. All batteries have a minimum operational voltage -- if you
draw the battery below that voltage, you can damage the battery. The
controller prevents the battery from being drawn down too far -- if the
battery voltage gets too low, the controller disconnects the load so it
won't damage the battery.
Note the three sets of red/black (POS/NEG) leads attached to the controller:
LEFT -- leads coming FROM the solar panel; CENTER -- leads going TO the battery;
RIGHT -- leads going TO the load.
The battery. 12
volts DC, 15 Ah, sealed. The battery measures L - 6", H - 4", W - 3.8".
Wiring everything together is so simple a
caveman can do it
- The solar panel has
a cable coming out of it with two wires in the cable – positive (white) and negative
- The controller has
- From the solar panel,
one positive, one negative.
- To the battery, one
positive, one negative.
- Connect the radio to the
battery, positive to positive, negative to negative. Note this means
there will be TWO sets of connections to the battery:
- Battery positive to
controller positive and radio positive, and,
- Battery negative to
controller negative and radio negative.
Here’s a photo of the system
wired together. Generally, red wires are positive and black wires are
negative -- however -- color codes may vary depending on the manufacturer, so,
READ THE DATA SHEETS that come with the components before making any
connections. A ground wire will go from the metal frame of the solar panel to
earth ground. (Note: The square white object with the words "SolarGuard"
is a controller that I used for a few weeks after which I replaced it with the
Phocos controller shown above.)
Note that I installed
connectors on the ends of all cables and wires. These connectors
are becoming universal in amateur radio and other services; I used them so I
could take any single component out of the system and insert another component.
The thick black cable from the solar
panel carries the electricity generated by the panel to the controller.
That cable is connected to the yellow and black wires from the controller
(yellow to positive, black to negative).
The output of the controller goes to
the battery terminals where current from the solar panel is applied to
charge the battery.
Connected to the battery terminals
is a second set of leads that take power to the radio -- notice the set of
red-and-black connectors to the right of the meter that is not connected to
anything -- radio connects there.
The long red and black things
clipped to the battery (lower right corner of the photo) are leads for the
meter that is lying next to the solar panel -- shows 13.79 volts DC from the
battery. In full sunlight I measured 16.5 volts DC from the solar
panel. The charge controller reduces the voltage from the panel so the
battery is not overcharged.
Here's the solar panel mounted next to the
house with its power cable running into the window along with the antenna
cables. The panel is mounted onto a couple of strips
of wood which are screwed into a 2X8 which is then screwed into a 4X4 post set
18 inches into the ground. The panel is slanted at a few degrees more than
my latitude and is oriented to true south (not magnetic south ; more or less).
|This is the original 5-watt solar panel
||This is the 20-watt panel installed in late
March, replacing the original 5-watt panel.
Maximum power voltage ( Vpm ) : 17.5V
Maximum Power Current: 1.17A
The light-colored object on
the ground to the right of the panel is our whole-house generator --
propane-powered, comes on when we lose power from the mains (which happens from
time to time out here at the end of the supply line). The red thing is a hummingbird
feeder filled with sugar water and red food coloring.
And here is a photo from
inside the station. (See UPDATE
The controller is mounted to the wall by a
piece of Velcro.
The black object in the bottom center of the
photo is the 12-volt 15-amp-hour battery.
On top of the battery is a multiple outlet
connector for PowerWerx PowerPole connectors. The three radios that
use this battery are connected to this multiple outlet.
The red/black lead from the bottom left of the
controller goes to the solar panel. The center red/black lead goes to the
battery. The red/black lead on the bottom right goes to the PowerPole
multiple outlet connector through which voltage goes to the radios that operate
from solar power.
The two meters in the aluminum box measure
battery voltage and the current being drawn from the battery.
In late March 2014, I re-arranged things and added two meters to monitor
voltage and current from the solar panel to the controller and from the battery
to the rigs. Here are photos.
|Here's a close-up of the solar controller and the digital meters.
The meter on the right measures voltage from the solar panel
and current being drawn by the controller and battery as the battery
is charged. The meter on the left measures voltage,
current and other circuit parameters from the battery to the rigs.
||Here's a photo of my modest station, 1 April 2014. The
solar controller and digital meters are mounted on a small board
attached to the wall next to the main circuit breaker box. (This
photo shows only one of the meters associated with the solar
controller -- made this photo before installing the second meter.)
The solar controller is the Phocos
CML-V2 controller, Model CML05 described above.
This photo was taken at night when there was no voltage coming from the solar
panel. When the panel is supplying voltage, a green LED glows in the hole
that is top-center of the controller. The yellow LED that is glowing shows
the battery is fully charged -- the diagonal row of three yellow LEDS show full,
half, and low charge depending on battery condition.
The digital meters were
purchased from PowerWerx, the same people who make the Anderson PowerPole
connectors. In the photo above showing the controller and the two
The meter on the right is between the
solar panel and the controller; it measures voltage from the panel, current
being drawn by the battery through the controller, and other voltage and current
The meter on the left is between the controller's load terminals
and the rigs that are powered by the battery; it measures the same parameters as
the first meter.
These digital meters are interesting
Here's a link to the PowerWerx page that describes the meter. The
meter measures up to 60 volts and 130 amps. The display shows four items:
Voltage, current, and wattage are always displayed. The fourth section of
the display switches among amp-hours, watt-hours, peak amps, peak watts, and
minimum volts. For example, in this photo (taken from the PowerWerx
website), the meter shows 19.90 amps at 13.01 volts, which is a power
consumption of 275.0 watts. These three parameters are always displayed,
The fourth measurement, in the lower-left corner of the display, shows the
amount of amp-hours currently being drawn from the supply. This number
switches every two seconds to display, in order, amp-hours, watt-hours, peak
amps, peak watts, and minimum volts
My purpose for installing two meters is to allow me to measure the current
performance and state of charge of the system.
- The first meter shows me how much voltage is coming from the solar panel
and how much current the battery is drawing, which gives me an idea of how
much the battery is discharged -- that is, if the controller is drawing a
lot of current from the panel, I know the battery is low on charge because
it's drawing a lot of current to re-charge.
- The second meter shows the voltage being supplied by the battery to the
rig and the current being drawn by the rig. The meter also shows the
cumulative number of amp-hours being used. By knowing this
information, I can tell if I am loading the battery too heavily.
- The minimum voltage for these meters is 4.8 volts. This is
interesting -- when the sun goes down, no voltage is coming from the solar
panel, thus, the meter goes blank. In the morning, as the sun comes up
and as the panel starts to produce voltage, the meter slowly lights up as
the voltage from the panel approaches 4.8 volts. When the panel is
producing 4.8 volts, the meter turns on fully.
How does it work?
This system works just
fine. The 15AH battery provides plenty battery capacity. I power all my QRP rigs with the
battery-solar charger system and I have never run the battery down to a point
where the rigs quit working. In fact, I cannot tell any difference between
running the rigs off the battery and running them off a power supply.
A Portable Power Supply Using Solar Cells
and a Battery
A week after putting together
the solar cell - battery power system described above, I decided to make a
second installation for portable operation.
Follow this link to the page describing my
portable solar cell and battery power supply.