Most people are familiar with the idea of an Uninterruptible Power Supply (UPS), such as used to help keep a computer running throughout power outages. Intended for only seconds to minutes of use, long enough to get past a short power glitch, or to give the user time to save files and shut down before power fails completely, a home or office UPS is typically small and inexpensive. Plus, a typical UPS will be a square wave or modified sine wave (essentially the same thing with gaps), which is fine for a computer, but we would prefer a pure sine wave output. See our previous ground solar inverter article for more details about these different waveforms.
In previous articles, we have been describing the use of LED Christmas lights as emergency off-grid lighting powered directly from a 24 volt battery array. The first article described using strings of cool white lights. Subsequent articles described building a test fixture for these and warm white lights to overcome problems with untested lights, and then constructing arrays with red LED lights, including the use of an external resistor. In this article, we finish the series by describing the use of multi-color lights, some of which are manufactured with a separate resistor embedded in the string. We’ll also describe a useful design procedure for creating off-grid LED strings using any color combination you wish.
In two previous articles, we discussed using LED Christmas lights as emergency lighting powered straight from an off-grid battery array, as well as a test fixture to sort individual lights for making a reliable DC-powered string from the random sampling of LEDs in a typical 110 volt string. Both of those articles focused on cool white and warm white LEDs. In this article, we’ll discuss the use of red LED lights. For some applications, red light is a better choice, and a few red strings sprinkled in with cool white strings can even out the spectrum a little bit if warm whites are not available.
In a previous article, we described the adaptation of LED Christmas lights as emergency solar lighting powered directly from an off-grid battery array. This approach provides many advantages versus running them from an inverter, including useful lighting while trying to fix your inverter. In that article we made some recommendations about string lengths, current and light levels. Immediately after publishing that article, we discovered that some strings burned out although they should not have, and some strings did not burn out when they should.
To figure out what is really going on, we built a test fixture using materials accessible to most people, and tested batches of cool white, warm white and red LED lights. The results are enlightening, and the whole project makes a great homeschool science lesson. Plus, by using this test fixture with your own lights, you can create light strings, emergency or otherwise, which are more reliable, consistent and long-lasting.
As part of our off-grid solar series, we’re looking for bare-bones options for the charger and inverter components to meet the minimum requirements of driving a 70 watt freezer, 24/7 if possible. We recently tested a Bestek 300W Pure Sine 12V Inverter, shown to the right. Although this unit failed to drive the freezer, it is still worth reviewing in detail. Also, review our previous inverter article in the off-grid solar series for important background information regarding inverters in general.
The unit is small, light and fairly rugged, so we wouldn’t think twice about tossing it in the trunk or the tire well and forgetting about it until it is needed. While we wouldn’t chock the wheels with it, it isn’t a glass slipper, either, but rugged enough to be comforting. The small size and light weight caused us to suspect that it wouldn’t be able to handle the promised surges, though. This turned out to be the case.
After a sweltering hiatus due to warm weather on and after Thanksgiving, winter is finally back to the old school, so this means that we can continue our winter chemistry experiments over the wood stove. We like extracting chemicals from things around us, so we’ll start with potash, which is derived from wood ashes (1).
It’s Christmas season at the old school, and it is time to do something with those light strands. These days, LED light strands are cheap and ubiquitous. With a bit of judicious modification, we can use them as emergency lights directly off our off-grid battery array, no inverter required.
Last week, we took our two Duracell 29HM deep cycle marine batteries and the MicroSolar 24v inverter from our hurricane ground solar experiments and added an AC charger, essentially building an oversized UPS for our freezer. We’ll talk about that system more in detail once we’ve run it for a while, but this morning it appeared that this system had failed. Although this turned out to be a false alarm, the steps we went through to verify the continued operation of the freezer and its power system are good to know.
We’re ready to finally wrap up our series on the ground solar installation we used during Hurricane Matthew to keep our freezer and refrigerators cold. We’ll provide links to all the previous articles at the end of this post as a convenient reference. In this post, we talk about the wiring, connectors and tools used for connecting all the components. We’re not done talking about solar, though; future articles will address lead-acid battery alternatives and other solar power options beyond our hurricane experience.
We’ve been discussing our Hurricane Matthew ground solar installation (overview, combiner, charger and inverter), as well as fundamental solar panel principles and off-grid lead acid battery principles. This time, we will discuss the battery array used for this exercise, as well as the automotive DC safety breaker. Refer again to the photo of our inside components below: