Ones and Zeros

So, the solar-charged camper works well and the 65 AH battery is sufficient. Even on cloudy days we were getting some charge. We were able to charge brother-in-law’s rechargeable blender charged too.

The solar panel was supported by a piece of wood cut to a good length and with a notch at the top. I set it at an angle roughly equal to the latitude. Through the day, I also moved it - rotated it - this kept it pointing directly at the sun. One night during a windstorm I laid it flat on the ground so it wouldn’t blow over. This “maintenance” was a trivial effort.

Some lessons were:

• I probably overestimated our load. No problem there as I didn’t drastically overestimate. And, I’d rather overestimate than underestimate.
• It would have been good to see some measure of charging current and load current and of battery voltage. I have no easy way to see what my battery level is right now.
• Wiring in a popup camper is hard. The up-and-down of the camper is difficult on wires. Nothing broke, but my wire mounts did not hold.

All it all it was a good idea and much quieter and more pleasant-smelling than the generator at the other end of the campground too. My setup probably cost about the same too. And I have no ongoing expenses for fuel or engine maintenance either. Ours wasn’t the only solar system in the campground, it’s an idea catching on.

Later at some point, as requested, I’ll put up my wiring diagram and a component list for anyone interested in doing something similar.

I’ve finished the installation of my solar power system in the popup camper. I think of it as a pilot to a possible house solar system that’s rather more-expensive.

I talked about this a little before, but in short we have a 30 Watt panel feeding a 65 AH battery with a charge controller. This is a larger battery that I think I need, but was a standard size that I could buy. Having more reserve won’t hurt. When I tested it, I propped up the panel as below. (Yes, it still generates power in the shade, but less.)

The battery, in turn feeds several 12 Volt DC uses: LED lighting strips and four 120mm computer fans for ventilation. These are almost silent (I bought them specially for that). Then there’s the 120VAC inverter for AC power. That makes a sound with its vent fans so we’ll only use it when we need AC. That’s for charging a computer, etc.

The first steps to doing a solar installation are to figure out the electrical load you want to supply, and thus the amount of power you’ll need. My load is 200 Watts/day. Pretty minimal. Your house uses much more than that. Read your power meter for your house’s load. Or, for a smaller system like mine, calculate your load. There are online tools for this at places like the www.altestore.com which also has many helpful articles too.

Once you have an idea of the load, then figure the power you’ll get from the panels. Mine is for use in the longer sunny days of summer, so I figured 5-6 hours of sun per day. For a house, you’d need a year-long average of hours of sun/day, and adjust that for shade from nearby trees, hills, etc. The amount of power helps determine the size and number of the panel.

You also will need to know how many days reserve power you’ll need. If you’re an off-grid system, this is more critical since you can’t pull power from the mains. If you’re connected to the grid, you actually don’t need much (or perhaps any) batteries. Your reserve requirements determine the size of your batteries.

Then, you need a charge controller. Overcharging or overusing your batteries can shorten their life drastically. Since they’re expensive, it makes sense to spend a little money on a device that controls that charge level. It has to be sized for the amperage and current your panels provide. Wire this together with wiring for the amperage you’ll be passing through the wires. Put some fuses in place (I have one leading to the battery, and one from the battery.)

Then, you need an inverter, this converts the DC power to 120VAC power. Some systems use 12 VDC like mine, but larger systems will use batteries in series at higher voltages.

My inverter is the small blue device here. This is my battery, the small gray thing is my charge controller. The large black cable and the device it attaches to is a parallel system for plugging the camper into campground-provided AC power that we’re not using. Since I took this photo, I’ve added the outputs from the battery in terminal strips that the LED lights, fans, and USB power converter’s plugged into.

Most of the work was in the wiring and in figuring out the connections. In any real project the minutia of fitting the parts into what’s already there is a big part of things. Most of the connections are soldered, a few are crimped as I trust crimping less.

A less minimal system would have amperage meters to show the charging current and load current.  Some more expensive controllers have a monitor to show power stored, etc.  But this is a vacation-purposed system though, if the power dies it isn’t a big deal.

More planning on my part would have simplified the installation as I would have just ordered all the parts and wiring I needed from DigiKey, Jameco, or Mouser Electronics. But I tried to buy local from Radio Shack. Radio Shack is no longer a parts store and hasn’t been for years; I hereby give up on them. Since I like to see the parts and handle them when planning I really miss a local parts store. If I still lived in Austin TX or Silicon Valley there would be no problem. (I love Fry’s Electronics!) But government is the local industry here and they don’t need local electronics parts stores, just conference rooms.
So, vacation is soon and we’ll test out the system in real life instead of the driveway. And perhaps I’ll get some solar-powered iPhone programming done!

I spent a couple months working long hours recently writing neat new stuff in software. The resulting demo and presentation to the customer went well. So, my reward in that is to get to write more neat new stuff. (Be careful for what you wish.) I’m hoping, probably too optimistically, that this next round of software writing won’t be as schedule driven.

In a second category of neat new stuff, the new airplane battery works very nicely! On my post-maintenance check flight it started the engine swiftly and easily. No more just barely turning over and almost not working. We (the plane owners) are hoping this is near the end of the spate of expensive repairs this last six months. The last one (we hope) being the next item:

The third neat new item is delayed. The directional gyroscope is still on backorder, once again extended. This time we’re hoping we’ll get it near the end of the month. This is annoying as it’s really interrupting my IFR training! It will probably cost me some time to get back into the groove of things once my instructors and I can get going again. I’m considering a sim flight or two with the new sims that the flight school has.

My wife and I have purchased a new pop-up camper. It’s new to us at least. We’re cleaning it up and fixing it up. We’ll be camping where there’s no plug-in power. But, I have a problem. We’d like to run a couple fans, and perhaps have a reading light or two. Then, I will need power to run my laptop for iPhone programming (see below). So, I’m putting together a small (very small) off-the-grid solar power system. Only about 200 W/day, but that’ll be enough for our needs my calculations say. The panel and charge controller are ordered, I can get the battery locally. The fans are quiet 120 mm size computer vent fans, four of them. And the lighting is LED. Most of the wiring will be 12V DC, but I have a small inverter too. I’ll assemble this next week.

I spent last week at Apple’s World-Wide Developer’s Conference (WWDC) in San Francisco. I’m under non-disclosure so there won’t be any really great news here. But rest assured that you’ll hear all about most of the news relatively soon. I’ve been to WWDC before a number of times, but not for a 3-4 years now. It was nice to be back in San Francisco. I like it there, but I’m really glad my wife and I don’t live there. Cities are too busy, too loud, and too concrete for my taste.

But the Bay Area is a real geek paradise. You can buy parts or scrap electronics, find up-to-date technical books in the local library, and have some really good bookstores around. Stanford and Berkeley are nearby and easy access, and your retired neighbor mowing his lawn down the street was probably instrumental in some key technology breakthrough that changed the world. He’ll have great stories, and you’ll be able to learn something there. So while the DC Metro region is a leading user of technology, the Bay Area is a leading generator of technology. It’s a whole different level.

I spent most of my time at WWDC learning how to program the iPhone. This is something I need to do for work, and something I’d like to learn for myself as well. I remember that years ago UNIX geeks would speculate when they’d get a real UNIX laptop. Well, the MacOSX-based MacBook Pros are UNIX laptops. (The most capable new one has a 3 GHz dual-core processor and comes with either 4 GBytes or 8 GBytes of memory.) And, the iPhone is Mach UNIX internally, so is a hand-held UNIX touchscreen computer. The new iPhone model has a compass and video camera too.

One of the things that keeps me going as a technologist, despite bad project schedules and other major annoyances, is the fascination of new ideas and new devices that were science fiction dreams not so long ago. In my career I started programming on a machine that had no boot ROM and only 4 K of memory and could only do 666,000 instructions per second. Now, I can walk into a store and buy a 8 GByte machine that’ll execute six instructions every 1 billionth of a second, about 9000 times faster. Or more if my code uses the graphics processor. The new machine has all sorts of other features like sound, color, and wireless networking for a start. It will last longer, have many fewer problems, doesn’t require a $350/month maintenance charge, and only costs 13% as much. (Prices adjusted for inflation to current values of course, I’m an economist too.) On top of that, these new MacOS laptops have 500 GByte disks, vs paper tape storage for the the DEC PDP-8 I started with.

So truly some neat & new stuff!

At work we’re cleaning out and recycling a number of older computers. In keeping with good data practices, we want to wipe the disks before we do so. We decided we needed a degausser to do this. But they cost a lot of money. So, I decided to make one. No problem, I’ve made them before for various purposes.

It’s just a coil of wire that line current goes through. Since the line current already switches direction 60 times per second, it does a pretty good job of degaussing.

I wrapped the necessary 30 AWG wire around a cardboard form I made that was the same shape as a disk drive and a little larger in size. I checked the maximum current for 30 AWG wire, and de-rated that some for safety sake. Then I figured the necessary resistance for the line voltage to allow the desired current. I wired a 1/4 W resistor in series with the coil and the power cord.

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