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Small-Scale Solar Experiments

While sheltering in place this week, I’ve been tinkering with a small-scale setup for solar power generation. I’ve got a 100 watt solar panel, and access to the sun. What fun things can I do with this? Is it actually useful? Let’s find out.

My first thought was to power some equipment directly from the panel, but that’s not practical for most situations. Even if I could tolerate only having power during daylight hours, the output voltage and available power from a solar panel fluctuates too much from moment to moment. I’d either need a DC-to-DC voltage converter with a wide input range, or some equipment like a pump that can tolerate a wide voltage range and doesn’t mind frequent stopping and starting.

For most purposes it’s better to charge a battery from a solar panel, and then use the battery to power other equipment. I already have a solar generator (a large battery with integrated charger, inverter, and other conveniences) that was ideal for this experiment. I only needed to connect the panel’s MC4 output to the solar generator’s MC4 input adapter cable, stick it in sunlight, and wait.

100 Watts? Not So Much

With a 100 watt panel and something close to 12 hours of daily sunlight, I expected to get something close to 1200 watt-hours of electric production daily. My solar generator has a 150 Wh battery, so it should only take about 1.5 or 2 hours to charge. So I confidently set up the equipment, and after an entire day in the sun I only managed to increase the battery level by about 40%. What?

Maybe 1200 Wh was a little unrealistic. Or a LOT unrealistic. After some reading, I concluded the panel would probably never output 100W unless it was noon on a bright sunny day somewhere near the equator. But I might hope to get about 70W at noon at my latitude, with lower power output during the morning and late afternoon. Factoring in shadows from trees and other buildings, I decided I might expect to get about 400 Wh of average total daily production, with more in summer and less in winter.

OK then, 400 Wh should still be enough to charge my solar generator’s battery almost three times during the course of a day. So why wasn’t I getting that result?

Measuring Solar Panel Output

It’s not so easy to measure the power generated by a solar panel. With a multimeter I could measure the open circuit voltage, and the short circuit current, but multiplying the two figures wouldn’t tell me the power. I need a load to get a useful measurement for power output. But a fixed resistive load won’t work, not even a 100W-rated resistor, because it likely won’t bring the solar panel to the correct voltage for optimum operation. That optimum voltage varies from moment to moment, based on the sunlight hitting the panel. To do this right, I needed a solar charger like the one integrated into my solar generator. Then I needed to measure the current and the voltage simultaneously. I could have built some wiring adapters and used two meters for the measurements, but instead I bought a cheap inline power meter and soldered MC4 connectors to it.

I measured 19.7W in full sun at noon. Huh?! No wonder the solar generator’s 150 Wh battery takes forever to charge. Is there something wrong with my panel? After several days of tinkering with the setup under different lighting conditions, I never saw a continuous output higher than 23W. Most of the time it hovered right around 20W. Hmm.

I began to suspect the solar generator was at fault. Sure enough, buried in the manual were the specs for the solar input: 13V-22V / 2A max. With my solar panel, that means I’m theoretically limited to about 40W max (2A at almost 20V). I’m not sure why I rarely saw more than 20W though, and never saw more than about 1.3A of current. Maybe the integrated solar charger is even more limited than the manual suggests? Maybe I have bad wiring, or another problem?

As an engineer, 20W from this panel is insulting! Even if I have no practical need for this solar panel, losing 80% of its output is unacceptable to me. To save my pride I’ve begun to research plan B, which will involve a stand-alone solar charge controller featuring a much higher maximum charging rate, and a separate battery. More about that soon. Maybe I’ll put together a solar-powered Mac Plus.

Finding the Parts

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Here’s the equipment I used.

Renogy 100W monocrystalline solar panel. You can find slightly cheaper panels, but the Renogy has an extra-sturdy aluminum frame and a strong reputation for quality. This particular panel is also more space-efficient than most other 100W panels, if minimizing area and weight are important to you.

Suaoki 150Wh portable power station. Despite its annoying 2A charge rate limitation, I love this thing and use it all the time. You can charge it from solar, from a car, or from a wall plug. It has a built-in 100W inverter for running small appliances, USB ports (including a Quickcharge 3.0 port) for charging phones and tablets, 12V ports for DC lights and other appliances, and an integrated high-brightness emergency lamp.

200A Inline Watt Meter. I’m not confident it will actually handle 200A, but it works nicely for lower currents involved in small-scale solar. It shows volts, amps, watts, accumulated amp-hours, watt-hours, max watts, and min volts.

MC4 Male/Female Solar Panel Cable Connectors. Solder these to the watt meter.

DROK 12V Battery Meter with adjustable limits. Other cheap battery meters typically have fixed voltages for the 100% and 0% charge state. This one makes it possible to set custom values for the upper and lower bounds. Measured from one of the Suaoki’s 12V ports, I measured 12.33V fully charged and 8.96V just before the low-voltage cutoff disconnected the battery. The discharge curve isn’t linear, so the meter won’t go smoothly from 100% to 0%, but this is still vastly better than the simple built-in 5-bar power gauge on the Suaoki.

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Constant Power Battery Discharge

Recently I’ve been looking at battery datasheets, in preparation for an off-grid solar project. I’ve noticed something strange about the “constant power discharge” numbers in the datasheets of several 12V lead acid batteries. Here’s an example from a 20 Ah Euroglobe sealed lead acid battery.

In the Constant Current Discharge table, if you discharge to a final voltage of 1.80V/cell (10.8V total voltage), the entry circled in yellow shows that you can get a current of 1.00 amps over 20 hours. The voltage will drop from around 13V down to 10.8V during that time. Let’s call it an average of 12V times 1A – that means you can average about 12 watts for 20 hours.

But wait. In the Constant Power Discharge table, if you discharge to a final voltage of 1.80V/cell over 20 hours, the entry circled in yellow shows a power of just 1.98 watts. That’s far less than 12 watts. Why?

Other table entries show something similar. It’s 11.3 amps constant current for 1 hour – that should be an average rate of about 136 watts, but the Constant Power Discharge table shows a measly 21.6 watts. It’s not just this particular battery either. Here’s a 35 Ah lead acid Mighty Max battery that shows the same curious pattern in the Constant Power Discharge table.

So what’s going on here? Am I misunderstanding what these tables mean? Or is there some other factor that limits the power to a much lower number than is suggested by the constant current data? I’ll keep digging for answers.

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Shelter In Place

My family and I have been ordered to shelter at home until at least April 7, to help stop transmission of COVID-19 in the San Francisco area. Many of you may already be living under similar orders, or will be shortly. Travel is restricted to only the “most essential needs” – basically food and health care.

As you can imagine, this will severely impact business shipments. BMOW will still be accepting new orders during this time, but it will likely be impossible to ship anything until April 7 or later. Please be patient, and if you’re not prepared to wait at least 3-4 weeks for delivery, then please hold off until mid-April to place your order.

Stay safe everyone. Remember to wash your hands.

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Backyard Metal Foundry Dreams

Sometimes my brain works in unexpected ways. I haven’t started any new electronics projects lately, but my thoughts have been spinning in other directions.

Last weekend I jokingly told my kids that I was starting a home-based ore smelting business. Because today’s busy families just don’t have time to process their bauxite, taconite, and other ores at home, the way Grandma used to. Keeping up with the household’s demand for antimony and zinc can be such a chore – but now there’s a better way! My friendly staff will pick up your ore, lovingly smelt it, dispose of the slag responsibly, and return the processed metal in 100g nuggets stamped with your choice of fun logo designs. Naturally, this ore smelting business will be named He Who Smelt It Dealt It.

Three things I learned from this groan-worthy joke:

  1. It’s taconite, not taco night
  2. I’ve been pronouncing the word antimony (an·tuh·mow·nee) wrong for my entire life
  3. Melting converts a solid into a liquid. Smelting converts ore to its purest form.

Yet somehow this smelting comedy gradually transformed from a bad joke into a semi-serious idea for a fun backyard project. Actual smelting probably isn’t a great plan, because where the heck would I find ore? And do I really want to process large piles of messy rocks to extract a bit of tin? Instead of smelting, I soon found myself researching designs for a backyard metal foundry.

I was fascinated. This Mini Metal Foundry design looks simple to build and operate, but can easily reach temperatures of 660 C (1221F) – hot enough to melt aluminum, zinc, lead, tin, and pewter. The molten metal can then be poured into steel molds or sand cast to make tools, toys, and trinkets. Sure the quality won’t be great, but if you perked up at hearing the words “molten metal”, then I like your thinking and we should hang out sometime. Check out this video:

Of course I immediately began planning for my backyard metal foundry. My wife, however, was considerably less enthusiastic about my prospects for doing this without making the neighbors call the fire department or outright killing myself. She has an advanced degree in materials science, and actually has real lab experience working with large pools of molten lead, germanium, and other metals, so she probably knows what she’s talking about. I began to pay more attention once I learned about what happens if there’s a metal spill onto outdoor concrete. Moisture held in the concrete can instantly flash into steam, shooting globs of molten metal in all directions at high speed. See the example at time index 7:35 in the video. It looks horrific. So I’ll hold my backyard foundry plans in the “maybe” category for now.

Enter plan B, an inexpensive 500 Watt electric ladle. Designed for small metal casting projects, this little gem can’t melt aluminum, but it’s still hot enough to melt lead and maybe zinc (though I’m not sure exactly what I’d do with molten zinc). For about $50, it could be the perfect tool for DIY-enthusiasts who want to melt some metals without burning down the house.

A few metals that might pair nicely with this tool, ordered by melting point:

zinc (maybe) – 419C, 787F – The tool says it’ll melt lead, but the melting point of zinc is not too much higher. What can you do with zinc? I’ve heard of zinc plating, but don’t think I’ve ever seen a solid zinc object.

lead – 327C, 621F – Lead has a bad reputation these days, but how great is the risk assuming you’re not eating the stuff? Maybe it’s best to avoid it anyway.

pewter – 295C, 563F – In my mind, pewter is what 18th century candlesticks are made from. It’s an alloy of tin, antimony, and copper. It’s also sometimes used for jewelry and can be polished to a shiny finish.

bismuth – 271C, 521F – I have no mental concept of bismuth except as an ingredient of Pepto-Bismol. What does metallic bismuth look like? Is it safe to handle? Is it ever used for metal casting?

babbitt – 249C, 480F – I’m including babbitt on this list because I’d never even heard of it until yesterday. I learned that babbitt is an alloy of tin, lead, copper, and antimony, and is commonly used for making low-friction bearings.

tin – 232C, 449F – In years past, tin was popular for making cups and dishes. It should be cheap and safe, but maybe not very exciting. At this melting point, I wouldn’t even need any special heating tools: I could just melt tin ingots in steel molds with my kitchen oven.

solder – 183C, 361F – Solder wouldn’t normally be used for casting, but why not? Probably because it’s too easily bendable, and there are better alternatives. Lead-free solder has a higher melting point of 217C/422F, but it’s still lower than any other metal on this list.

Why do all the metals with low melting points have a silver/gray color? It would be nice to have more variety. To find a metal that’s a difficult color, I believe you have to climb the temperature scale to about 890C/1630F to melt brass and bronze. Copper and gold have melting points that are even higher. If I were a super chemist, I’d probably have some explanation why metal colors are related to their melting points.

Have you ever experimented with metal casting for making jewelry or tools? Ever built a backyard foundry and melted some aluminum soda cans? Leave a note in the comments and tell us your story.


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Windows 10 External Video Part 5 – Failure

I’m either very persistent or very stupid. After 4+ months, I’m still chasing unexplained problems with external video on the HP EliteBook x360 1030 G2 laptop that I bought in May. Recently I thought I’d finally solved it, but I was wrong, and now the problem is worse than ever. I am slowly going insane.

For the previous chapters of this story, see part 1, part 2, part 3, and part 4. Here’s a short refresher:

  • Windows 10 laptop with an external monitor, ASUS PB258Q 2560 x 1440
  • works OK during normal use
  • problems appear every couple of days, after a few hours of idle time or overnight
  • random crashes in Intel integrated graphics driver igdkmd64.sys (stopped after upgrading the driver)
  • computer periodically locks up with a blank screen and fan running 100%
  • Start menu periodically won’t open, must kill WindowsShellExperienceHost.exe
  • Windows toolbar sometimes disappears
  • Chrome window sometimes gets resized to a tiny size

This might sound like a random collection of symptoms, but I’m 99% sure they’re all somehow related to the external video. I suspect the external video is periodically disconnecting or crashing or entering a bad state, which causes errors for the Start menu, toolbar, and applications, and sometimes causes the computer to freeze.


Here’s a recap of the past month. On August 15, I switched from using an HDMI cable to a USB-C to DisplayPort cable. This did not fix the problems. On August 22, in the Windows advanced power options, I changed the Intel Graphics Settings power plan when plugged in to “maximum performance”, and also changed the minimum processor state when plugged in to 100%. The computer then went seven days without problems. On August 29, I also installed two “critical” HP updates: a BIOS update and an Intel Management Engine Driver update. Neither one mentioned anything about video issues in its release notes. The computer went a further 11 days without problems – 18 total days problem free!

Believing that the issue was resolved, on September 9 I switched back to an HDMI cable, which I prefer over DisplayPort for reasons of convenience. Within a few hours, the problems returned. I swapped the DisplayPort cable back in, and everything seemed OK.

But this morning, I once again experienced a frozen computer with a blank screen and fans running 100%. After forcing a shutdown and restart, the external monitor via DisplayPort no longer works at all. When I connect the cable, the Device Manager shows “Cable Matters USB-C Video Cable” but no external display is detected. I’ve tried rebooting and unplugging/replugging the cable at both ends, and cycling through options in the monitor’s menus, but nothing helps. Maybe the cable is broken? It was working last night, and I didn’t touch it after that.

Where Do We Go From Here?

I’m at wits’ end. Is this is a Window 10 driver problem? Laptop hardware problem? External monitor hardware problem? Cable problem? Multiple such problems at once? The sometimes long delay between problem episodes is frustrating any attempt to find a solution. Typically the problems appear every couple of days, but I recently went 18 days between problem events. That makes it almost impossible to make changes one at a time and draw conclusions about whether they helped.

A few people have suggested I try running Linux, to help determine whether this is a Windows problem or a hardware problem. I have briefly run Linux a few times, and it works OK. But I can’t devote 18+ days to running Linux simply as an experiment. Much of the software that I use is Windows-only, and I’m not interested in switching to Linux as my desktop OS right now.

I could look into repairing or returning the computer, but I’m not interested in that. It was a used/refurb machine, and not terribly expensive. While the money is not insignificant, my time and the disruption to my work are more important. I can’t be without this computer for three weeks while a reseller or PC tech experiments with it. If I need to move everything to another PC anyway, then I’ll simply go with that as the final solution.

I could try another DisplayPort cable. Maybe it simply broke somehow. That would be cheap and easy, and everything did seem OK via DisplayPort up until today.

I could also try switching back to my old 1920 x 1080 external monitor. In earlier testing from June-July, that seemed to work OK, but perhaps I just didn’t test it long enough. Reverting to the smaller and lower-resolution monitor would be a disappointment, but at this point I would be happy with any solution that works.

Finally, I could just replace the whole computer. That’s what I keep threatening to do, but I haven’t yet. Reinstalling and reconfiguring all the software on this PC would be a major pain, and the memory of that experience is still fresh in my mind from May. Several multi-gigabyte packages would need to be downloaded again, and node-locked licenses re-requested and regenerated for several software tools. When I went through the process in May, it took close to a week to get through it all.

Perhaps I could clone the existing hard drive and use it in the new PC, avoiding having to repeat all the software setup. But then I’d also be cloning all the HP-specific drivers and plugins and utilities, while missing out on all the vendor-specific stuff for the new computer. And I’d still need to regenerate the node-locked licenses for some software, even if I didn’t need to download and install them again. Maybe it’s better to start with a clean slate, even if it takes longer.

I know any computer can have hardware problems, and any OS can have bugs. But I can’t escape the feeling that this type of driver/hardware mystery is precisely why so many people dislike Windows. I feel like I’m living in one of those “I’m a Mac, I’m a PC” television commercials. If you have any suggestions for other solutions I could try (short of a sledgehammer), please share them in the comments.

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Windows 10 Crashes Part 4 – 2K Video

I’m still chasing after unexplained errors and crashes with the new Windows 10 powered HP EliteBook x360 1030 G2 laptop that I bought in May. See part 1, part 2, and part 3 for the backstory. The computer crashes, freezes, reboots, or experiences other problems every day or two when I’m not using it – I’ll return to the computer after a few hours and discover that something’s gone wrong. From investigation of event logs and other clues, the problems seem related to the graphics display. I’m using the laptop with an external ASUS PB258Q 2560 x 1440 monitor. On June 15 I uninstalled the HP OEM graphics driver and installed the generic Intel graphics driver, after which I had no more crashes, but I continued to see other problems:

  • computer periodically locks up with a blank screen and fan running 100%
  • computer is unexpectedly off, then hangs during booting
  • Start menu won’t open
  • Windows toolbar is missing
  • Chrome window gets resized to a tiny size

After a few months of testing, I believe I’ve finally isolated the problem: the computer can’t handle 2560 x 1440 graphics on an external monitor. If I use a 1920 x 1080 monitor, or a 2560 x 1440 monitor running at 1920 x 1080 resolution, everything is OK and the computer runs smoothly for weeks at a time. But switch to 2560 x 1440 resolution and problems reappear within a day or two.

What’s going on here? A previous commenter mentioned that for resolutions above 1920 x 1080, HDMI uses a different signalling method with a higher frequency data rate. That’s probably part of the answer, but if there were problems with the faster data rate, I’d expect to see video artifacts rather than Windows errors. I tried two different HDMI cables to see if that might help, but it made no difference. Perhaps the 2560 x 1440 resolution is forcing the integrated graphics hardware to work at a faster rate or in a different mode, exposing some firmware bug or hardware defect, or simply overheating.

As a last-ditch solution, as of today I’m running 2560 x 1440 using a USB-C to DisplayPort cable instead of HDMI. Maybe that will help, maybe not. If it doesn’t eliminate the problems, I’ll have to choose between attempting to RMA the computer or just living with 1920 x 1080 resolution. The lower resolution by itself isn’t so bad, but that solution would leave me with a useless 2K monitor. Anybody interested in some used hardware? 🙂

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