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 expensive.
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 stuff
- 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 SmallWonder 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 minutes.
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 hour)
- Current drawn while transmitting, expressed in Amp-hours = ((current drawn by the receiver) X (0.5 hour)) X 0.6)
- Required current 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 results:
- (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, 17.8 hours.
For my Yaesu FT-817 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.
- A 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
- 6 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 exercise.
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 the battery.
Thus, a system that would enable an amateur radio station to run off solar and battery power consists of three pieces:
- SOLAR PANEL to generate electricity.
- CONTROLLER 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.
|In late March 2014, I replaced the original 5-watt solar
panel with a 20-watt solar panel:
Instapark® NEW All Black 20W High-Efficiency Mono-crystalline
This panel measures 24 inches tall, 11 inches wide, and 3/4 inch thick; weighs about 5 pounds. $68.95 from Amazon Prime.
If this panel is not available on Amazon, search for any 20-watt solar panel — you’ll find lots of sellers, and, prices on solar panels are dropping almost daily.
Patuoxun/Anself 10A 12V/24V Solar Charge Controller
Available from Amazon.com — $10 – $15
|12-volt, 15-amp/hour sealed gel-cell battery
from this supplier.
$47.95. Batteries of different capacities (more or less amp-hours) will cost more or less.
This is what these components do
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. Patuoxun/Anself 10A 12V/24V Solar Charge Controller. 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.
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 (black).
- The controller has four connections:
- 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 “SunGuard” is a controller that I used for a few weeks after which I replaced it with the Patuoxun/Anself controller shown above.)
Note that I installed Anderson PowerPole 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.
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.
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 meters:
- 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 parameters.
- 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.
- The controller is not the one in use now.
These digital meters are interesting devices. 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.
The system described above was installed in 2010 and has been in constant use since installation. I use the battery to power my Yaesu FT-817 and Elecraft K1 low-power CW rigs, each with 5 watts output. I’ve used the rigs for weekend-long contests, day and night, without ever having a problem with voltage supply. I noticed one time, about dawn, after operating all night, the battery voltage had dropped to 11.9 volts, which was still enough to power the FT-817 without a problem.