Border Fort Manual: Solar Generator

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The solar generator is an important Border Fort topic. In fact, for the new owners (we have now put the place on the market and will be moving to Montana at the end of May, 2017), this might be the most crucial bit of reading in the entire Manual.


A couple of years ago, I read one remark by a veteran of solar system usage that declared every individual inevitably ruined his (or her) first solar setup. The learning curve can be steep…and I sure enough did fit the mold.

In early 2012, after many hours of Internet research on portable solar generators, I called one builder of small 500 watt systems and asked if he could double the size of one of his trailer mounted units, custom manufactured to my requirements. Since he was a retired electrical engineer, his answer was “yes.” In May of 2017, he even delivered the unit personally, willing to do so because he (a) only lived about 400 miles from our place and (b) wouldn’t mind seeing this part of southeastern Arizona. It was an exciting prospect, especially since we’d been living off grid with only gasoline-fired generators to generate electrical power for more than three years by that time.

As a super-brief tutorial for the newcomer to solar power (ignore this part if you’re an old hand), any solar system–portable or stationary–includes four basic essential components:

1. Solar panels. Our new generator’s panels were (and are) capable in theory of producing up to a total of 960 watts of incoming electricity on a nice sunny day. In practice, we’ve never reached that magical limit, but the panels still crank up more than enough juice to recharge the battery bank after a night’s usage.

2. Controller. This unit accepts the incoming voltage from the panels–which can vary from nothing all the way up to around 150 volts–and converts it to the proper voltage for the storage battery bank. In this case that’s 24 volts.

3. Storage battery bank. The generator arrived with a total of four big 12 volt Trojan batteries designed for solar systems, wired to create two 24 volt pairs.

4. Inverter. This device accepts the stored power from the battery bank and “inverts” it from 24 volt DC to 120 volt AC power suitable for household usage.

From the inverter, the lovely clean power flows to eight outlets, regular plug-in types that accept extension cord plugs. Now for some photos to help visualize all this gobbledygook….

The solar panels, gathering sun power.

The device on the right is the controller, converting high incoming voltage to 24 volts before passing the juice on to the storage battery bank.

The storage battery bank, currently eight 6 volt Rolls deep cycle batteries connected to make a 24 volt system. (The original setup included four 12 volt Trojan batteries, also connected to make a 24 volt system.)

The 3000 watt Samlex inverter–a heavy duty industrial model–takes the 24 volt electricity from the battery bank and “inverts” it into clean 120 volt AC power for the household.

The First Disaster

The original system as it was delivered–portable because we weren’t sure exactly where we’d end up wanting to position the generator long term–should have been able to last for ten years or so with minimal routine maintenance…but it was stone cold dead in a mere three years. So what went wrong?


1. The manufacturer made one “electrical mistake.” When the generator was delivered in May, just as heavy Arizona heat was rolling in for the summer, everything worked perfectly. But come October and cooler weather, the controller started acting up. Eventually, it was a TriStar customer service rep who helped me figure it out over the phone. The retired electrical engineer had wired all four solar panels in series. This was fine in warm weather, but it turns out that solar panels kick out higher voltage in colder weather. The TriStar’s upper limit was 150 volts…and during the cooler months, that series-connected setup popped out just enough volts to “bump” that limit. Not quite enough to totally fry the controller, but it surely did turn the thing schizophrenic. Thus, within six months of purchase, we had a funky thing going on there, and had to reset the controller every now and then. Plus, the builder, after he found out the problem was his error, stopped taking my calls!

2. We limped along with the “bruised” system for 2 1/2 more years…but I was unknowingly abusing the poor thing badly, in two ways. (A) I’d use it too hard overnight and think nothing of it. Turns out that, deep cycle or not, these batteries last a lot longer if they’re not discharged beyond a certain point. And (B) I was over filling the batteries. Good intentions, but bad results nonetheless.

Massive Upgrade

By the time I’d thoroughly busted the first setup, I had a much better idea of what I was doing. The solar panels were fine. The inverter was fine. Both the controller and the entire battery bank (boo coo bucks) would have to be replaced.

The New Controller

There were two possible ways to fix the problem of too much voltage. Either the four panels could be wired in two strings, using a combiner box and individual breakers, or–if one existed–a controller capable of handling the higher winter voltage could be installed. The easier option was the stronger controller. Fortunately, Midnite Solar made an extremely good one; the unit now in play will handle up to 200 volts of incoming juice, and the panels will not ever get close to that limit.

In truth, I’m pretty much in love with that Midnite Solar controller. We had one “sideways storm” hit the first summer after it was installed, slammed a bunch of windy rainwater at the controller before I could get the tub lid closed to protect it, and sure enough, knocked the controller out…for about twenty-four hours. After which it had dried itself out and fired right back up again, no harm, no foul. That’s one tough controller.

The New Battery Bank

As fortune would have it, we ended up liking the generator in the exact spot where I’d had the builder park it when it first arrived. Mobility was no longer needed. So the axle was removed and the trailer became nothing but a stationary solar system frame on blocks, fastened to the ground to prevent wind problems. Pam’s son has a welder; he gladly came by and built a side extension to the steel frame to accommodate a much larger battery containment box, which I built.

Then the eight big 6 volt Rolls batteries were installed. I’d studied reports on solar-suitable batteries for hours on end and decided the Rolls were–in my book, anyway–absolute top of the line. The new battery bank has 840 amp hours of storage capacity and, with just a little bit of proper care, should last many more years–fifteen, or even more. New, heavier duty cables were used to make the connections, and we were good to go.

The Rolls batteries are top of the line.

What The User Needs To Know

All of the above is merely preface to the crucial tips for helping the new Border Fort owners to avoid my mistakes. Here are the keys:

KEY 1: Keep an eye on the controller display. Not every second, obviously, but whenever there’s a doubt, this display will help you out. The most crucial number is the voltage number at the top right of the screen.

24.4 volts. If it’s cloudy overhead during the day and you’re seeing that number, it’s a good idea to fire up the gas powered generator and give the solar a rest. 24.4v is a fine number as a minimum after the TV and other devices are shut down for the night, but it’s a warning number if it’s there very long after the sun has come up for the day. (How foolish was I when I ruined the first setup? There were times when I let it run down to 22.9 volts without a thought for the consequences–and I paid the price.)

25.0 volts. This is a good strong number with which to start the night (after the sun goes down and the incoming wattage reads zero). With our setup, averaging one TV and one desktop computer running until midnight or two a.m., 24.8 volts is acceptable. Obviously, 25.1 or 25.2 volts is outstanding (though not necessary).

27.5 volts This is a great daytime “full charge” number when the battery bank has been restored for the day and 300 to 700 watts of power are coming in from the solar panels.

28.5 volts This is getting a hair too high. It’s not at all dangerous to the system, but the inverter feels it’s “pushing” a bit and will start flashing one orange light (with one steady green light) instead of showing two steady, happy green lights. At that point, the inverter is saying, “If this goes on too much longer and gets up around 29.5 volts, I’m going to start flashing a red light. And if that doesn’t help, eventually I may just shut down for a while.” Which is no big thing unless the only person home at the moment is disabled, as my wife is, and then it can be frustrating. However, this only happens during the warmer months (90 degree temperatures or above, usually), and there are simple remedies:

–You can turn on every power using light and appliance in the house, drawing more juice. We did that today (May 1) and made the inverter happy immediately.

–Alternatively, the red breaker to the left of the controller can be opened, cutting off incoming solar power and drawing entirely from the battery bank for a while. This works immediately, and also works if the inverter has actually shut down before anybody noticed a potential problem.

That’s a lot of information from one little number, huh?

The controller display screen. We monitor the battery bank voltage number (top right) most frequently.

The breaker to the left of the controller can always be opened to eliminate “too much” juice from coming into the system for a little while.

Two happy little green lights on the front of the inverter indicate everything is working “just right.”

The other number we watch is the incoming wattage (lower left), which of course is “zero” at night and highly variable during the day. If a few hundred watts are coming in, it’s okay to use a 1250 microwave oven–but if it’s after dark and the incoming wattage is zero, it’s a better idea to fire up the gas generator, move the black cord over, and use that to cook your TV dinner. (If it’s just a one-minute burn to reheat a cup of coffee or some such, the solar system can handle it even after dark. But for longer cooking times…yeah, use the gasoline powered generator.)

KEY 2. Don’t over fill the battery cells. Obviously, letting the water level get too low in a lead-acid battery will destroy the battery in a hurry…but over filling is bad, too. The Rolls battery instructions say to fill to just a hair below the bottom of the fill throat indicator. I still usually violate that just a teensy bit, letting the fill water barely touch the bottom of the throats, because I can be more accurate that way. But with that first set of Trojan batteries, I was filling them halfway up the throats–and then wondering why they boiled over all the time! So, lesson learned.

Corrosion seems to be really simple to remove–just fire up the garden hose and give the terminals a squirt. Note: If you ever decide the cables need to be removed for a thorough cleaning, it’s highly recommended to do them one at a time. Otherwise, hooking them back up in the wrong order would be far too easy, at least for me.

Never fill the batteries above the BOTTOM of the fill throats.

KEY 3. Adjust the tub lid (covering the sensitive electronic controller and inverter) according o the weather. In cooler weather and even during moderate monsoon rainstorms, just placing a 1″ x 4″ board under there is enough to let the electronics breathe sufficiently. But if a storm is really fierce, you may want to pull that board entirely and let the lid close completely until the worst is over. And when it’s clear and hot, defined as ninety degrees or above, the lid needs to be lifted higher. Wide open is good in really hot weather. If there’s not enough lid opening, the inverter will occasionally overheat and shut itself down until things cool a bit. The overheating will not harm the system but will most certainly irritate a wife who was in the middle of watching Days of Our Lives…or so I’ve heard….

Here the lid is propped wide open to let the components air out on a hot day.

And…that’s about it. The solar generator as it stands today is a robust system that should last the new owner for many years without any major component replacement…if these tips are followed.

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