RENEWABLE POWER FOR AMATEUR RADIO (and other electronic devices)
by Larry D. Barr, K5WLF
About the author: Larry D. Barr is an Amateur Extra class amateur radio operator, first licensed in 1966. He is uniquely qualified to write on this subject, having lived offgrid for 19 months with the majority of his electricity provided by a Wincharger 1222H wind generator. Larry is a journey level electrician, an alternative energy systems designer and the former editor of Energy Self Sufficiency Newsletter. His pickup mounted, solar powered ham radio installation was featured in the American Radio Relay League’s “We Do That” video series and on their website. Currently employed as the Planetarium Manager for Tarleton State University in Texas, Larry continues to be active in renewable energy and looks forward to living offgrid again in the near future.
Because of my interest and involvement in renewable energy, I’m often asked by other amateur radio (ham) operators about the best way to run their stations on renewable energy sources. Most of these queries pertain to solar, or photovoltaic (PV), sources, but we’ll also mention wind and minihydro in addition to PV in this article.
The good news is that modern, solid state ham rigs lend themselves extremely well to renewable power. They draw relatively little current at a nominal 12 VDC, and therefore require fairly modest expenditures in generating devices.
The bad news is that hams who like the old vacuum tube (hollow state) rigs will not be able to power those old “boat anchors” without a serious layout of funds for PV panels or a much larger than usual wind generator. The old rigs simply draw too much current to be practical for operation on a renewable system.
So, let’s look at the practicality of running a modern, 100 watt, solid state transceiver like my Yaesu FT897D on a PV system. It’s easy to do – and at a relatively low cost for the solar setup.
First, let’s consider the power required to operate the radio. There are two distinctly different current requirements for the unit. One is the power required for the radio to receive incoming signals. That’s about one ampere (1A) at a nominal 12 volts direct current (12 VDC). Nominal 12VDC turns out to be somewhere in the vicinity of 12.6 VDC, for a fully charged 12 volt battery, to around 13.8 VDC which is the output of an average vehicle alternator. We’ll mostly stick with 12 VDC for this article just to make the calculations easy.
The other requirement is 22A while transmitting at the full 100 watt output level. Well, you’d think that wouldn’t take long to run down a battery, and you’d be right. But think a minute. We don’t transmit all the time. Actually, the ratio of transmit to receive in normal ham operation is right at 1:9. 10% transmit and 90% receive.
Now, we need to figure out how many Amphours (Ah) we’ll use per clock hour in normal operation. Amphours is the numbers of amps, the current, consumed over a period of one hour. It’s the way the battery capacity is rated. As I said earlier, normal radio operation is generally calculated at 90% receive and 10% transmit.
So, in 1 clock hour we’re consuming:
(1A X 0.9h) + (22A X 0.1h) = (0.9Ah + 2.2Ah) = 3.1 Ah
Figuring our 100Ah battery at 50Ah, because we don’t ever want to take the battery below 50% depth of discharge, we divide:
50Ah / (3.1Ah/hour) = 16.129 hours
Which is about 16 hours and 8 minutes from a fully charged battery. I run two 100 Ah sealed lead acid (SLA) batteries in my battery banks for a rated 200 Ah capacity and a ‘real world’ capacity of 100 Ah. That doubles my run time to about 32 hours and 16 minutes.
There are those who will disagree with me about my advice to never exceed 50% depth of discharge in a deep cycle battery. They are welcome to do so. And I will never loan one of those folks my batteries. Your batteries will last much longer and provide better service to the end of their life if you follow my advice. Each time a battery is drawn below 50% charge, it gives up a small part of its longevity. Personally, I can’t afford to replace batteries before the natural end of their life. So, I treat them well. My shack and pickup batteries are over six years old and still operating at peak efficiency.
I must mention here that manufacturers base the capacity ratings of their batteries on the assumption that the discharge will be made at a constant rate. That rate is assumed to be one twentieth (1/20) of the published Amperehour rating of the battery. In the case of our single 100Ah battery, the rate would be 5A. For our 200 Ah bank, it would be 10A. This relationship is called C (capacity) / 20. You’ll see it published simply as C/20 or ‘the C/20 rate’.
Any deviation from this C/20 rate, especially discharge rates which exceed it, will result in a different amount of power available from the battery. If we exceed the C/20 rate, the capacity of the battery will be less. In many cases, much less. It depends on the extent to which we exceed the C/20 rate of discharge.
In the case of our 100 Ah example, since our calculated rate of discharge was 3.1Ah/hour (or 3.1A), we were below the C/20 rate of 5A and should get at least the run time we calculated. However, if we were to exceed the C/20 rate, our run time would be less. How much less would be proportional to the amount above the C/20 rate that we imposed on the battery. If our discharge rate is below C/20, we may get a bit more. But let’s figure for worst case and not count on it. This phenomenon has been well documented by a gentleman named Peukert and his analysis of the effect is known as Peukert’s Theorem.
We should note, and must accept, that this does not indicate that the battery is faulty. It’s simply reacting in accordance with the laws of physics and chemistry that batteries operate under. To draw an analogy — if you bought a car and the manual stated that you could expect 25 MPG at 50 MPH, it would be unreasonable to expect that same mileage at 120 MPH. You’ve changed one of the variables in the equation and you can’t expect the result to be the same.
Now, let’s look at the PV panels and other gear required to support our FT897D on a solar electric diet.
My system consists of two UniSolar US64 amorphous panels rated at 64 watts each. They’re connected in parallel for a total of 128 watts. With the Xantrex C12 charge controller set at an output voltage of 14.2VDC – it seems high, but it’s right for the SLA batteries – that gives me about 9.01 amps to the batteries. Let’s just call it 9 amps. So, in one clock hour, I’ve put 9 amphours back into the batteries. That’s almost a 3:1 ratio of input to output.
Truth be told, I usually see about 7.4 amps, more or less, from the panels going into the battery bank. But that’s more than twice what I’m using and certainly explains why, on occasion, I’ve gone out on a radio mission with less than fully charged batteries, worked on the air for four hours or so and returned home with a fully charged battery bank. And all free, from Mother Nature.
My UniSolar panels aren’t available anymore. Unisolar has decided to dedicate their manufacturing capability to mainly Building Integrated PhotoVoltaic (BIPV) and has discontinued their line of discrete PV panels. We recently mounted a Kyocera 235 watt panel on our local ham club’s tower trailer, and if I were buying now that’s what I’d get for myself.
Let’s look at the total cost of a PV system to run the radios using the Kyocera panel.
The PV panel will run you about $375, the Schneider/Xantrex C35 controller with the CM digital display (recommended) is about $165, and a pair of PowerSonic 100 Ah SLA batteries will round out the system for $275 each or $550 for the pair. That’s a total of $1090 for the system. With proper care, the panel and the controller will last you for a lifetime. The life span of the batteries depends on you. I’ve been running mine for about six years now, and they’re still doing their job, and doing it well. If you abuse them, by discharging them below 50% capacity, or over or under charging them, their life span will decrease.
Now, let’s talk about wind power for a minute. If I were buying a wind generator today, I’d get an Air 30 turbine made by Southwest Windpower. It’s a 400 watt unit and has all the controller circuitry built in. At peak output, it’ll give you somewhere around 25 amps, and because of the integral controller, it interfaces seamlessly with a PV system. Cost is somewhere in the neighborhood of $600. If you live where wind is one of your most prevalent natural resources, you might get by with just the Air 30, but I really recommend a hybrid system that uses more than one source. Wind and PV is a great combination, for many times when the wind is blowing the most, the sun is obscured.
Minihydro is a wonderful power source if you have a year round watercourse on your property. If you don’t, just forget about it. My dream is to find a property with a year round stream on it, but unless I win the Lotto and maybe leave Texas (not likely), I’ll never find it. Don’t even fret over hydro unless you can provide your system with a reliable and continuous source of water. There aren’t many locations available with that resource and it’s best to not even think about it unless you already own it. If there’s a call for it, I’ll gladly write about minihydro at length in a future article.
OK. let’s summarize. I’ve explained how to calculate the draw of your radio. We’ve discussed the factors that control battery run time and battery life. We have talked about the initial cost of a PV system, and considered adding a wind turbine to the system. It’s easy to add other 12VDC devices, such as lighting or entertainment devices, to the system. Just do your calcs and ensure that you’re not drawing your battery bank below 50% capacity. Be sure to follow all appropriate wiring codes and make damn sure that your wiring is safe and overload protected. Enjoy the free energy that Mother Nature provides. ldb
Off grid info and components available at http://www.green-trust.org/products/
Discuss Amateur radio and alternative energy topics at http://groups.yahoo.com/group/Alt_Energy_Hams/