My solar-powered, Wireless Phone System

(A shorter version of this was published in issue #88, April/May 2002, of Home Power Magazine)

Overview of the project

Because the nearest phone line is a mile away, I wound up installing a wireless phone system at my off-grid house. Not a cordless phone, but a long-range wireless system. I wound up installing a Telemobile PTEL system. This is a 4watt UHF based system with a range of about 20 miles, line of sight. The local phone company gave me some huge number for a quote, and at the same time, I didn't really feel like digging up the street to run a very expensive phone line, when good satellite technology is just around the corner, and their are good wireless solutions available now.

This project actually started months ago when I used some UHF handheld radios to check the signal strength, and find the best areas. This I did by having one person sit on the roof of the house (to simulate the likely height of the antenna mast), while I drove around all the dirt roads within a few miles. Out here in the Rockies, the phone company has little green boxes at each driveway, house, or property where they offer access. One of these would be my landline end. So as I found these boxes driving around, I'd note the signal strength from my UHF radio (a Yaesu FT-51R), the phone box ID, and the GPS coordinates.

Once I had this info, I then plotted the data from the GPS a Garmin Map 12) on my PC using the TopoMap mapping software. This is a collection of 7.5 (1:25000) scale Topo maps that one can plot GPS data on. For me, the main thing I wanted to do was to plot out the line-of-sight between my house, and each phone box. Although I had done signal strength tests with my UHF, the TopoMap software lets one take a route, and then plot the profile, as opposed to a regular map view. This let me see very plainly any obstructing things, like a hill top, rock outcroppings, etc... At this point I had the info distilled down to 3-4 prefered sites, anyone of which would work.

I then contacted the owners of the best location. I couldn't get Qwest permission to install anything on a Qwest pole, so I had to install things on private property. Using a landline on private property saved me from months of arguing with my local phone company about access to one of their poles for my antenna and transceiver.

The owners of the property were very supportive, and then I ordered another phone line at their address, that gets billed to me. Once the phone line was hooked up, Qwest had to spend 7 days fixing the trunk lines, as my location was literally at the end of the phone cable. Then I had to scout out a place on the hillside near the phone box for the underground cable.

At the other end of this connection (my house), I had previously installed a quick & dirty 40 foot antenna mast, and wired the PTEL transceiver directly into my 12VDC breaker box. I cheated on installing the antenna mast, by using a tree to hold it up. Later I'll be taking the tree down (it's too close to the house, and mostly dead), and redo the antenna mast to be properly guy lined and supported. I then used the "goto waypoint" feature of my GPS to orient the antenna towards the landline end.

I finally settled on a small meadow about 85 feet uphill from the box. I then setup my existing portable power system, as I ordered the parts for a permanant power system, but I have to wait for them to arrive. My portable system is a 235AH system I use for a portable UHF backcountry repeater. Once Qwest had fixed the trunk lines to this location, I could pop the cover off the green box where the landline comes out of the ground, and using a telephone handset, modified to work as line tester, I found I had a dial tone! Then I spliced a 100ft, standard phone cable into the wire pair for one one line. Finally I hooked that cable into my power system and transceiver. After I set the antenna up on a short mast, I called the house via a poor cell phone connection, and it worked! Then we discovered "the problem".

The problem was that after a phone call, the line would short out, and no phone calls could be made until it was cleared by Qwest. They kept telling me it was a problem in my system, and all my tests kept showing the problem was on their end. The problem was even worse, because they have no experience with wireless phone systems of this type, so they were convinced the problem was somewhere in my system. Luckily my 25 background as a phone phreak came in handy. After 2 weeks of arguing, with me running many tests, I finally convinced them it was their problem, and suddenly they found a bad circuit board, miles from my house! Once that was replaced, it worked reliably for about 2 weeks.

So back to testing, and it was a similar problem as the first time. Qwest finally found a real engineer someplace to work with me, which was almost a pleasure, after a month of dealing with the their excuse of technical support. So that was another circuit board replacement. Then for whatever reasons, over the next few weeks they disconnected the phone line twice more while doing other "maintainance", but this fix is easy, they just have to go reconnect whereever they screwed up.

The phone actually went down all the way once in my system, when the Lyncom charge controller showed an unexpected problem dealing with cold temperatures. (like about -40F) It had good timing, cause it died in the morning, and that afternoon the new SOLSUM charge controller I had ordered showed up via UPS! It figures that I get this system online, and then get hit with Colorado's coldest fall this century... and my domes are at 8800 feet in the Rockies.

I had another problem on my end, but it didn't bring the system down at all. It turns out the Trojan T-125s I use in my portable repeater power system also weren't dealing well with the cold. I had heard of other folks putting light bulbs in with their Telemobile systems, and even a few of those I'd heard were off the grid. But I couldn't track down any real info, and didn't want to build a huge power system to run a heat source as well. The sub zero temperatures for days on end, combinded with a week of overcast, snowy weather really drained the batteries. When the Deka 280AH Gell Cell I had ordered finally arrived after weeks stuck on a loading dock in Denver, I decided to replace the battery right away, before I lost vehicle access to the spot where my landline is. There is no way I'd be able to carry a 135lbs battery to the site. The Gell Cell was rated to -40F, so I guess we'll see...

Luckily 130lbs of battery adds great traction to the rear end of my Toyota 4x4, so I manged to drive to a spot uphill from the phone system. I then slid the battery down a 2x10 board from the back of my truck directly into a plastic kids sled. My son Abel and I then slid the battery down to the phone system. The hardest part was sliding the old batteries uphill back to the truck! I was glad to finally swap the batteries, cause the Trojan's were down to a dangerous 11.5VDC. I was actually suprised the charge controller hadn't shut the transceiver down at such a low voltage. During the last month, also filled with cold, overcast, and snowy weather, the Gell Cell has performed much better. I snowshoed down to the landline end of the phone today with Abel, and the batteries were at 12.23VDC. Not too bad. I'm going to add another 64Watt Unisolar panel that I happen to have around for the winter. I've discovered the spot my solar panel is gets too much shade during these winter months. Guess it's time to buy a Solar Tracker, but I'll just add more power till I get a chance to move the panels. Doing any major projects is difficult till Spring. (which means late May around here)

The portable Power System

This system produces about 100 watts, powered by a UniSolar unbreakable 64 watt panel and a UniSolar 32 watt flexible panel from Jade Mountain, and 2 - 235 Amp Hour (6 VDC) Trojan T-125 deep cycle batteries, along with a 24 Amp Lyncom charge controller. I didn't use the 32Watt flec panel for the phone though.

This system was configured to run a 4watt UHF Ham radio repeater at Rainbow Gatherings, and gets heavy use during emergencies, and at other times. So it's a bit over powered, but oriented to running a repeater, which draws 300 milliamp during standby, and only 3A during transmit. This system was designed somewhat from a seat of the pants, perspective, but has worked good for both the repeater, and it's temporary use for the phone. It's just oriented for summer use, and the 2 T-125s are used, cause at 60lbs, they're carriable by a human to whereever I set the repeater up. More info on the repeater is on this page I did on Backcountry Radio Systems, in my case, more oriented towards Search and Rescue kinds of activities.

The box was lined with closed cell foam all around, and a 2 inch thick piece of styrofoam for the base. I then cut holes for the phone line input, the antenna coax, and the power line from the solar panel.

The entire system is housed in a PortaPak plastic container, which I found seals the best, and had good handles for the locks. I then chained the box through both the handles to a tree. While this is a remote location, I still wanted to be careful to prevent easy vandalism.

The Permanant Power System

The permanent system is a little different than the portable one. The permanent system has a smaller charge controller, a SOLSUM 5.0, cause the Lyncom I bought in case I needed it to jumpstart the house someday. The SOLSUM only handles 5 Amps. I also got a Deka 280AH Gell Cell battery. The Gell Cell will deal much better with the cold weather (-40F) that we get around here. I also ordered a new Unisolar unbreakable 64 watt panel. I ordered this stuff from Rocky Mountain Solar, a friend who now distributes alternate energy stuff.


Replacing the batteries turned out to be interesting. The old batteries, being a portable system, weight about 65lbs a piece. Heavy, but still hand carriable by one person. The new Gell Cell weights more like 135lbs. The Gell Cell is also rated to about -40F, which is about as cold as it ever gets around here at this altitude, but it was the best I could find.

This system was much more "designed". I used the spreadsheets I wrote for power system sizing, and the correct wire gauge to work out the specs. These spreadsheets are on my software page.

I had several problems with the battery. First, the shipping company refused to come down my road, because the didn't think their truck would make it down the 1 mile long private drive. So I had to met them in town, and the two of us loaded the battery directly into my little Toyota truck. Then it was huge, and I was hoping I got all the measurements right, so I could put it in the same plastic box I'd been using. Abel and I managed to get it from the sled, into the box, and it just barely inside the insulation, but it did. Whew.

Then we had to deal with the problem of not enough sun at our location. During December and January, we were only getting 45 minutes of sunlight a day! While we were't quite ready to revisit our epic with moving the 135lbs battery, we saw no choice. I broke down and bought a Solar Pathfinder. This little device is excellent for figuring out the amount of sunlight you can get at any location, for any time of the year. Using the pathfinder, we found a great spot about 200 feet away (uphill though) were we could get about 5 hours of sun per day. That's plenty enough to keep the phone battery charged.

We then built a cheap frame out of 2x4s to hold the panel, cause it now needed to be self-supporting. We anchored the ends of the 2x4s into the ground, and added a few more braces on the downwind side. Being near the Continental Divide, we get pretty consistant winds, but as the can reach around 130mph sometimes, we felt extra supports were a good thing. Once this was up, we then used another tree to hold the antenna mast up, aimed it towards the house, and were back online.

How it's worked out

So far it's worked worked pretty good. The main problem is my antenna coax at the house end runs too close to the invertor power feed, which causes some 60Hz hum in the phone line. We've also discovered a problem with heavy loads. If I run the large 1400 Watt Miter Saw (I've been laying a floor, and building walls) during the day when there is plenty of excess power, things work OK, althought the saw makes a noise on the phone line. But if I try to do this at night, when running 100% off the batteries, running the saw will disconnect the call. This hasn't been to inconvienient, I just have to make sure I don't saw anything when anyone is on the phone.

For awhile, I've been trying to get my computer modem to successfully connect over the wireless phone. I've discovered several problems. The first problem was my older PCMCIA modems wouldn't recognize the dial tone. This was easy to fix by buying a new modem. As a backup, I got one with cell phone support as well. That solved the dial-tone problem. The I had the problem that I couldn't actually connect. The modem would go through all of it's initialization tones, and then finally give up. This turned out to be a problem with the buzz on the phone line. This buzz is caused by the inverter. I'm about to try putting a noise-limiter on the 12VDC power line, but for now, I just flip the AC disconnect off, and the line is quiet enough to connect at around 14.4 - 19.2 baud. At the least, it sure beats sitting on a rock outcropping with my cell phone in January to check email!

Update March 22, 2003

Well, another Lyncom controller fries... This is the second one I've had problems with. They seem to be sensitive to cold, (like -20F) weather. The problem was I had the PTEL tranceiver hooked up directly to the battery, cause with the now dead Lyncom, it would actually put a buzz on the line when it was connected to the load. It probably needs a noise limiter like I have on the other end. Anyway, we noticed cause one day the phone died, and when I snow-shoed in, the battery was at 6VDC! Ahhh!

On another snow-shoing trip into a few days later, I swapped in my other Lyncom charge controller. This when then failed in a similar way. By now, I was getting tired of snow-shoing in, since I had made several other trips to hook the PV panel directly to the phone, where it would run PV direct. At least that way, we'd have communications when the sun was shining.

I asked around, and finally bought a MorningStar SunSaver 10A charge controller. I snow-shoed back in yet again, and installed it. Unfortunately, it started snowing heavily, and didn't stop will we had literally 6 feet of fresh snow! So it hadn't gotten any sun, and since the battery was low, the phone was dead during the entire blizzard. Once the snow had stoppped, we knew the panel would be buried, so my son snow-shoed in, for a nice change of pace, and dug out the panel so the battery would charge.