Functional and Useful 100W Solar Array

Once the Monoprice PowerCache 220 was connected to the Harbor Freight 100W Solar Kit (Item #63585), we have everything we need to gather a little bit of sun power and make use of it every day. Given the non-optimal solar panel position and the fact we’re close to the winter solstice, this is just about the worst case scenario for solar power. Nevertheless this system has been gathering enough power to keep all the battery-powered electronics in the house charged up. This includes daily use & charge items like cell phones, tablets, and laptop computers. Plus the occasional items like a digital camera.

There is much more we can do to improve performance of this system, but it has met a minimum level of satisfactory performance so we can leave it running as-is for a while and switch gears to other projects. The focus will eventually return to this solar power system and here are two candidate projects for later:

Physical tracking: the panels are currently just sitting indoors vertically set against a south-facing window. It was done as an easy nondestructive way to experiment. When it comes time to improve upon this configuration, we can build a more permanent outdoor installation that angles into the sun. Maybe even motorized sun tracking throughout the day!

Electrical tracking: at the moment, the solar panel output voltage is dictated by the battery being charged. This is convenient and simple to implement but not the most efficient. We can buy (or design and build our own) a “maximum power point tracking” (MPPT) charger that keeps the solar panel voltage at its most efficient level and transform that to the correct battery charging voltage. It costs some power to do this tracking & voltage conversion, but if implemented correctly, the additional power will more than offset the cost.

We’ll add these projects to the bottom of the “to-do” list. For now, behold the glory of electronics being charged by sun power.

PowerCache 220 At Work cropped

Solar Charging Plug for Monoprice PowerCache 220

The product description page for Monoprice PowerCache 220 (Item #15278) had pictures showing its solar charging input as two round ports, but there were no connector specifications. Since it was advertised as a solar power cache, it would make sense for them to be MC4 connectors. This turned out not to be the case – they were actually two identical sockets that are electrically wired in parallel.

The device comes with an AC adapter for the charging port, but using household power would miss the point of the exercise. Neither do we want to lose the option to charge from grid power, so we don’t want to just cut off the charging plug. We should find an identical plug for solar charging.

The calipers indicate this connector has an outside diameter of 7.9mm and an inside diameter of 5.5mm. There is a small pin in the center roughly 0.5 mm in diameter. Putting those dimensions into search returned a few candidates and a large number of Lenovo laptop power adapters. A fortunate association, as there is a Kensington “Universal Laptop Power Supply” already on hand. It came with a set of interchangeable plugs to fit different laptop brands. This one was purchased to power a Dell, so the Lenovo plug has sat unused. But not for long!

Kensington Laptop Power

The Lenovo laptop plug matches all the diameters, and is slightly longer. It appeared to fit in the socket nicely. Since the two charging ports are electrically parallel, we could plug the AC adapter into the other charging port. This allowed us to read the voltage on the pins of the Lenovo plug so we know where to solder the positive and negative wire.

The plastic housing of the Lenovo plug was damaged in the soldering process so this plug will probably never fit on the Kensington laptop adapter again, but that’s fine. It now has a new purpose as solar charging plug for Monoprice PowerCache 220.

Lenovo now Solar plug

Hunt for AC Inverter Finds Monoprice PowerCache 220

Now that we have a 20 amp-hour 12 volt battery, charged by a solar array delivering up to 125 watt-hours daily. To put that power to use, we’ll need an inverter to convert battery power into household 120 volt AC power. This way the collected solar power can be used for more than just charging USB devices.

An old inverter was dug out of the old equipment collection, but it could only sustain about a minute of work before it would stop, reset, and restart. This isn’t great for the electronics, but what made it intolerable to humans were the cascade of noises that devices emit when charging began. Hearing the symphony roughly once a minute was unacceptable so the search begins for a replacement AC inverter.

The Harbor Freight lineup of AC inverters were obvious candidates. Starting from a basic model just under $20 and going up from there. While investigating options outside of Harbor Freight, one stood out: Monoprice #15278  “PowerCache 220”

It is designed exactly for the task we’re building for. It can accept power from a solar array to charge its 18 amp-hour 12 volt battery. That power can be consumed directly as 12 volts DC, as 5 volt USB power, or as 120 volt AC power.

The PowerCache mostly duplicates the components already in the current solar experiment setup. Buying one might be called wasteful, but for the sake of exploration we’ll call it redundancy. This nearly doubles the battery capacity and allows more ways to put solar power to use. It is also more user-friendly than the current maze of wires and connectors. It is an enclosed unit therefore easily portable. This might come in handy if we ever have a reason to take a little portable power source on the go.

So the search that began as a search for a simple AC inverter ended up with purchase of an integrated unit that included the AC inverter and basically everything else short of the solar panels themselves.

PowerCache 220

Initial Results of Solar Generation by 100 Watt Kit

Once the replacement battery arrived, it was possible to use the power captured by the Harbor Freight 100 watt solar kit. (Item #63585) The E-Flite Power Meter tracks the cumulative solar energy pumped back into the battery every day. Over several sunny days with minimal cloud cover, the daily tally ranged from 8 amp-hours to nearly 10 amp-hours. On an overcast day, the daily tally struggled to reach 4 amp-hours. (Reminder: the solar panels are not optimally placed to face the sun in these experiments.)

At the battery voltage range of 12 to 13 volts, this means a sunny day gives us about 125 watt-hours of electricity. (12.5 volt * 10 amp-hour) An overcast day’s output drops to about 50 watt-hours. (12.5 * 4) Since the sunniest and most productive times for solar largely overlaps with the most expensive times of the time-of-use electricity rates, we can try our best to make this solar array look good, by comparing against the highest rate of 35 cents per kilowatt-hour.

Even when using that expensive rate, a sunny day’s generation only works out to a tiny bit over 4 cents of grid electricity. A cloudy day couldn’t quite make up to 2 cents worth. Rough estimates point to a meager 10 dollars a year of savings on the electric bill.

Fortunately, we’re not doing this for money, and there is room for improvement as well. The solar array can be better aligned with the sun which, from earlier experiments, we know will make a huge difference. But a more immediate concern is the fact only a few items around the house can directly use DC power. There aren’t enough cell phones and tablets to consume 125 watt-hours a day.

In order to make solar power more useful, we’ll need an inverter to take the battery’s 12 volt DC power and turn it into household 120 volt AC.

20Ah Battery.jpg

Initial Use of 100 Watt Solar Kit Hampered By Battery

For the initial round of testing, the solar panels of the Harbor Freight kit (item #63585) was set up in a very temporary way: they were leaned against the south-facing windows of the house. To measure the output, we’re enlisting another member of the parts pile, unearthed when we were digging for the lead-acid battery: an E-Flite Power Meter designed to measure electric consumption of remote-controlled aircraft motors. It can handle the expected range of voltage and amperage and as a bonus it also tracks the total power in milliamp-hours.

E Flite Power Meter

Based on experiments with the small 1.5 watt panel, we knew not to expect the advertised 100 watt output with this sub-optimal, non sun-tracking orientation. The power meter gave confirmation: over the sunlight hours of a winter day, the panel generated power ranging from 20 to 30 watts. This is roughly in line with the small 1.5 watt panel experiment indicating sub-optimal placement returned as little as 25% of the power compared to directly facing the sun.

The solar charge controller allowed the battery voltage to rise to 14.4 to top it off, then disconnected the battery from the panel to avoid over-charging. Once the voltage dropped to 13.8 volts the controller kept the battery at this sustained charge level for as long as the solar panel could keep it there. All this fits expectation of a charge controller doing its job properly.

But something was wrong when withdrawing power from this assembly after the sun went down. Trying to charge a cell phone at night, battery voltage quickly dropped below cutoff threshold of 12 volts and the controller halted operations. There seems to be usable battery capacity remaining but the battery should have been able to hold roughly 12.5 to 13 volts for the majority of the power delivery period.

Looks like this battery did suffer some damage when it dropped down to 6 volts while sitting neglected in storage. Time to head over to Amazon and buy a replacement lead-acid battery with a good amp-hour per dollar ratio. The best ratio varies from day to day pricing fluctuation but at the moment meant this 20 Ah unit.

Harbor Freight #63585 100 Watt Solar Kit

Seeking more power than what a 1.5 watt solar panel could provide, it’s time to step up to the 100 watt solar kit, Harbor Freight item #63585. The manual, posted online as a PDF, fails to describe a few useful details which we’ll cover here.

Every product picture showed the four panels lined up in a row. But in fact the four panels are capable of standing separately as each panel is in their own frame and has their own folding stand. Bolting them together is optional. If the panels are to be deployed and stowed frequently, leaving them separate might make sense as the panels are much easier to handle individually.

The package content lists wires but not their length. Each panel has a 3 meter long wire permanently attached. This wire terminates in a connector common to Harbor Freight solar products but its exact type specification is unknown. It is definitely not the MC4 connector common in rooftop solar installations.

(UPDATE: Thanks to a tip in the comments, we now know this is a connector commonly used in the automotive world and can be purchased from auto parts stores. For example it is commonly used to make electric connections to trailers. While this connector follows the pattern of SAE J928 and J1239, it is not explicitly covered by either specification.)

The four panels connect into a 4-to-1 module. The four wire side are half a meter long, and the unified side has a 3 meter long wire towards the controller. A final half-meter long adapter has the unknown HF solar automotive connector on one end and a barrel connector on the other. (~5.5mm OD, ~1.5mm ID, 12mm length) The barrel connector fits into a corresponding jack on the controller.

HF 63585 100W power adapter

Adding it all up: Each of the panels can be up to 3.5 meters from the central 4-to-1 hub, and that hub can be up to 3.5 meters from the controller. The package includes a 1 meter cable to connect controller to battery.

The kit included two LED light bulbs, each of which have a 5 meter long wire. Curiously, the long wire ends in a standard light bulb socket. But instead of the 120V AC household voltage we would expect from such a socket, it carries the battery DC voltage. This is a decidedly nonstandard and confusing way to do things. (UPDATE: An earlier version of this paragraph incorrectly stated 120V AC conversion took place, a bad assumption based on the standard light bulb socket. Voltage meter told the truth and paragraph has been rewritten.)

HF 63585 100W LED bulbs

The simple charge controller covers the basics, guarding against battery overcharging and over-discharging at adjustable voltage thresholds. The manual claims there is over-current protection as well, but there appears to be no way to adjust the current limit, either for charging or for discharging.

Hunt For Larger Solar Panels

Now that the project ambitions have grown beyond a little 1.5 W solar panel from Harbor Freight (Item #62449) the hunt is on for something larger. The 1.5 watt panel is intended to trickle-charge automotive batteries and is sized well for the job. We’re aware of much larger multi-kilowatt installations for household rooftop solar. What kind of market would support solar equipment in between that range?

One answer is the outdoor activities market, where some people desire a bit of electric power while away from civilization. Cell phones won’t work in the wilderness but there are still other reasons to have a power source: LED lanterns, GPS equipment, and cameras to document the adventure. The products designed for this market place focus on size and weight, important for carrying in a backpack. But since those values aren’t important for the current experiments, there’s no reason to pay the corresponding price premium.

Another answer is the market of people who want a less rugged experience away from home: boats and RVs. While these leisure vessels have power generators, supplementing them with solar panels reduce fuel consumption and associated noise and fumes. For this market there isn’t much desire to make trade-offs for size or weight, and so we can get more watts for the dollar.

Which brings us back to Harbor Freight who offers two products for this market. A small single 15 watt panel (item #96418) or a larger package featuring an array of four 25 watt panels plus a controller module (item #63585). The constantly varying world of Harbor Freight coupons means the exact dollar-per-watt changes for any given day. But the general trend is clear: between the 15 watt kit and the 100 watt kit, we pay roughly double the money for over six times the power plus a control module to treat the battery properly. The choice was easy to make.

HF 63585 100W

Old SLA Battery for a 1.5 Watt Solar Panel

The little solar panel (Harbor Freight #62449) has proven itself to be capable of sending out 1.2 W, within reasonable reach of the 1.5 W announced on the box. However, we’ve also learned its actual power output varies tremendously depending on its orientation relative to the sun and the weather. As a result it’s not terribly useful on its own. We’ll need to add a battery in to the mix.

Enercell SLA

An old sealed lead-acid (SLA) battery from the parts pile is thereby enlisted in the project. We can start the experiment by hooking up our solar panel directly to the battery terminals. It’s not ideal, but a big lead acid can tolerate this abuse, at least in the short-term. (Never do this with lithium-ion batteries of any size.)

The volt meter indicated this battery was overly neglected in storage, because its voltage had self-discharged down to 6 volts. This is far below the recommended range for lead-acid batteries and may have caused some damage. Fortunately it was able to handle a charging cycle and held an open-circuit voltage of 12.5 volt. Good enough to continue the experiments.

Once the battery is in place to cache power delivered by the little solar panel, we can now power a 12 volt USB charger and charge a cell phone on solar power. But the small panel does not track the sun throughout the day, so it could deliver only a fraction of its maximum power. As a practical matter this means the panel need to charge the lead-acid battery over several days before enough power is collected to charge a cell phone for a single day of use.

Based on the latest findings, we can take the solar investigation in one of two directions:

  1. Wring more power from the little panel: build a sun tracker so it can face the sun throughout the day.
  2. Throw money at the problem: buy bigger solar panels.

The sun tracker can be a fun project, but it’ll have to wait. The vote was decided by the arrival of a Harbor Freight coupon for their solar kit. So: option #2 it is!

Observing Behavior of 1.5 Watt Solar Panel

Now that we have a power meter for the small solar panel (Harbor Freight #62449) it’s time to take it into the sun and see what it does. The first lesson learned is that a solar panel’s voltage range is far wider than a battery. A charged and rested “12 volt” lead-acid battery’s open-circuit voltage is around 12.5 volts, and the charging voltage should never exceed 14.4 volts. In contrast, the open-circuit voltage of this “12 volt” solar panel sitting in the sun is more than double that nominal rating. Yikes!

Open 27V

While we expect the voltage to drop as soon as a load is put on the circuit, there’s still that momentary spike of voltage which might cause problems until we better understand how to handle it. Digging through the parts pile for a test load found a 24V cooling fan that was retired due to a bad bearing. Since it was designed for 24V operation, a quick spike of 27V (or possibly higher) should not be immediately fatal. The maximum amperage listed on the label is 0.1A, which translates to a maximum power ceiling of 2.4W so it should be able to handle the power of a 1.5W solar panel.

Upon connection to the voltage output, the fan twitched but did not start turning. A tap of the fan started it turning and we can see the solar panel delivering 9.3V * 0.0328A = 0.3W. This is only 20% of the advertised power while the panel is sitting flat on the ground.

Flat 0.3W

This was in the mid winter afternoon, when the sun is already at a fairly shallow angle relative to the ground the panel was sitting on. Now we have this baseline, the next experiment is to prop up the panel so it faces the sun directly. We expect the power output to increase, and the meter will tell us by how much.

Facing 1.2W

The answer: 19.3V * 0.0625A = 1.2W, or roughly quadruple the output, just by finding a better angle into the sun. This reinforces why solar installations prefer to face into the sun and some photo-voltaic solar systems even track the sun’s movement across the sky. Since this is not a rigorous test, there may be other factors involved that may overstate (or understate) the effects. But after this experiment it should be fair to state:

  • The advertised power rating of 1.5W probably represents the most optimistic value under ideal conditions, but we can get reasonably close.
  • Orienting solar panels to face directly into the sun makes a huge difference.

Measure Output of 1.5 Watt Solar Panel for “Free”

Now that we have a small cheap solar panel (Harbor Freight #62449) to play with, we can start exploring solar panel behavior. The initial quick and dirty test was to connect it to a car USB charger and while we were able to light a little power LED, the panel didn’t do much beyond that.

Before we repeat the experiment (and tackle new ones) we’ll need a way to monitor the voltage and amperage output. The multi-meter in the standard tinkerer toolkit can perform these measurements, but not both at the same time. Aside from the obvious problem of having only a single numeric display, there’s also the fact voltage measurement has the meter wired in parallel with the circuit while the amperage measurement requires it to be in series. Constantly changing wires around would get old very quickly.

We can buy instruments that are designed to monitor power output and simultaneously track voltage and amperage. But for the sake of a small side project, we’re going back to the Harbor Freight catalog. They sell some basic digital multi meter as item numbers #69096, #90899, and #92020. These multi-meters are frequently part of the Harbor Freight “free with purchase” coupon offering, so their prices are “free” subsidized by other sales.

Two of these were wired together so one monitors voltage and the other amperage, displaying their readings side-by-side. A few zip-ties to hold the contraption together and now we have a cheap clunky power meter. Here it is, showing that the solar panel has almost 18 volts of open-circuit voltage just sitting under the light of the photo booth.

Solar power monitor

The upside of a super cheap power meter is that we would shed no tears if an experiment accidentally destroys it. The downside is that we have to be realistic about the (in)accuracy of cheap Harbor Freight instruments. For one data point, we can connect a good Fluke multi-meter to compare readings. This difference is not great but acceptable for exploration.

HB and Fluke




Solar Experiments Begin with Small Panel

Solar power can be a part of everyday life in many different ways, from tiny solar-powered calculators to a home rooftop solar power system. There is great potential for interesting solar power projects. But before that: some investigation to get orientated.

The low-power capability of the 8-bit PIC micro controller might make an interesting pairing with calculator-sized solar panels, but let’s not overly constrain ourselves on power budget until we are comfortable dealing with it. Similarly, a home rooftop solar system is well into the realm of power that can kill, and thus a bad idea for beginner experimentation.

Let’s learn with cheap things first by starting with a small solar panel from Harbor Freight. Item #62449 is designed to be placed in a parked car to keep its battery topped off with solar power. With the coupons typical of Harbor Freight, it should be obtainable for less than $10.

The panel is advertised to supply power to a car battery. So our first quick-and-easy experiment is to wire it up to an accessory meant for car power: an USB charger designed to plug into the lighter socket.

Small solar

This particular USB charger has a blue LED to indicate power. When the solar panel is placed in direct sunlight, the blue LED illuminates. Unfortunately it doesn’t do much beyond that – if a USB peripheral is plugged in to charge, the LED goes dark and there is no sign of charging taking place.

Well, we’ve tried the easy thing first. Now we start poking around to better understand what we’re dealing with.

Maytag Top Load Washer (LAT8826AAM) Lid Switch + Fuse Module

Today’s distraction came courtesy of aging appliance. Specifically, the 20+ years-old Maytag top-loading clothes washer stopped working this morning. It has just started doing a load of heavy laundry that was out of balance and shut down when the tub started shaking. This itself has occurred before, we just had to redistribute the load and restart. Except this time pulling the knob failed to restart the machine. There was no sign of life, not even the power “ON” light.

Given that the machine acted as if it had no power, I first checked the house circuit breaker, verified the machine was plugged in, the easy things. After the simple checks were out-of-the-way, I started looking for a circuit breaker or a fuse built into the machine. A web search turned up several mentions of the lid switch which I initially ignored. During normal operation, an open lid would prevent the wash cycle from starting, but the power “ON” light would still be on. Since that light was dark, I had decided the lid switch couldn’t have been the problem.

That was the wrong decision.

The lid switch is actually a module that included the switch and a fuse. This fact didn’t sink in until I found this page, which described how to test continuity with a multimeter and cautioning that improper switch module installation may blow the fuse inside the module.

I removed the lid switch module from my washing machine, tested with my multimeter, and confirmed it was not behaving as it should. I am annoyed that Maytag did not design the fuse to be easily replaced. The whole module had to be replaced as a single unit: it was held together by fasteners that were clearly not intended to be removed. While I had the tools to remove them, it is a permanent removal.

Maytag Lid Switch

Once opened, the fuse was quickly found. The red arrow in the picture below points to a black piece (now broken in two pieces) that looks and feels like plastic but is electrically conductive.

When intact, this piece of fuse material holds the “LINE” terminal always in contact with the “MACHINE” terminal. When the washer lid is open, there is continuity between “NEUT”(RAL) to “MOTOR”. When the washer lid is closed, “NEUT” loses its connection to all other terminals, but “MOTOR” is put in contact with “LINE” and “MACHINE”.

The narrow neck of the fuse material is now broken, which also broke the usually always-on contact between “LINE” and “MACHINE”. When the washer lid is open, none of the terminals have continuity with any other terminal. When the lid is closed, “MACHINE” is in contact with “MOTOR” but that doesn’t do any good as “LINE” is disconnected.

Maytag Lid Switch Fuse

Now that I know how the module incorporates a fuse in addition to the lid switch, it was easy to rig up a quick test to see if the rest of the machine works. A successful test gives me the confidence a replacement module will bring the washing machine back up and running safely.

The next question is why the black piece broke. Was it from old age (innocent) or because there was a problem causing excessive amperage flow (worrisome)? The multimeter found no obvious short on the washing machine. And since the machine has been working for more than two decades, age is a plausible explanation. I’ll try the replacement module first. If the fuse blows again, I’ll have to dig deeper.


Simple Circuit Board On 3D-Printed Plastic

CircuitBoardHere’s a behind-the-scenes follow-up to the LED test fixtures of the previous few posts: when we only need a simple circuit for a 3D-printed project, we can meld the two instead of using a formal circuit board. In this context “meld” is meant literally: the parts of the circuit can be heated up with the soldering iron so they melt into the 3D printer plastic.

When I built the dual-LED acrylic illumination test rig, I wanted the simplest circuit possible. It’s not something I need to be durable long-term and I wanted to be up and running with my tests as quickly as possible. The full length of a resistor and its wires are almost long enough to bridge the gap between the two sides of the fixture, so I tried to make that work.

When I started soldering all the wires together, I had planned to just leave everything dangling. But the close proximity of the soldering gun to the 3D printed PLA plastic started softening the plastic and I realized I can use this to my advantage. A few seconds with the soldering iron was all it took to heat up a wire so it can be melted into and embedded into the plastic. The resistors themselves took a little more effort, but I sunk them into the plastic as well. The LEDs had been held in place by their bent legs, which was sufficiently stable but had a tiny bit of wobble. Melting the plastic around LED legs gave us a much more secure placement.

Components melted into the plastic are no longer subject to flexing and eventually breaking from metal fatigue. Add a strip of electrical tape to guard against short circuiting to complete the quick and simple circuit to light up the test rig LEDs.

Illuminate Acrylic Edge: Test Fixture 2

After running through a few acrylic test pieces looking for the best edge illumination, I decided I need a dual fixture to allow side-by-side comparison as I swap through test pieces.


Another change I made in the text fixture is to remove the aluminum foil at the bottom. While the foil may be useful to direct light, it distracts from the testing. If a particular test piece is losing light to the fixture, I don’t want that light reflected back in. I want to be able to see the failure in the form of illuminated white plastic. When there are no acrylic test pieces in the fixture, the cone of illumination is clearly visible.

Test fixture #2 illuminated without acrylic test pieces.

The two sides aren’t exactly identical. One of the LED is slightly brighter than the other, and the two sides ended up with slightly different textures. But it should be good enough for our comparison purposes.

The first fixture implied that the cavity surround the LED is where we should focus our attention, so let’s try a few shapes. A square and a circle seems to differ only slightly in the brightness of the center top hot spot.

Square LED cavity (left) and circular LED cavity (right)

A triangular cavity was much more interesting – all the light has been diverted from the top center, sending them off to the side. And I tried a teardrop shape just to see what would happen. The important detail to note on the teardrop is that a lot of light was lost to the fixture instead of being sent to the edges. This tells us the cavity edges should be as small as possible to push its surface right up against the LED to reduce light loss.

Triangular (left) and teardrop (right)

The cavity sizes were then minimized for the next set, again testing for different shapes. A flat top to the cavity didn’t work as well as the cavity shape conforming to the LED shape.

Flat top cavity (left) and conforming curve cavity (right)

But the best results came from putting a small curve in front of the point of the LED. This appears to break up the central beam and sends it to the edges like we want.

LED scatter curve

From an cost/benefit ratio perspective, this small curve is a winner. It is a very minor change to the geometry and yet it delivers significant improvement to the resulting light. When put into a larger sheet of acrylic, with greater number of internal reflections, it should do quite well. And for a little extra smoothness in illumination, we can take a piece of sandpaper and lightly roughen up the surface. Adding a frosted edge reduces the reflections somewhat, but it does help even out the overall illumination.

Best illumination to date with the small curve (left) which can be further enhanced by a frosted edge (right)

These experiments have been quite informative. I look forward to applying what was learned here to future acrylic projects.

Illuminate Acrylic Edge: Goals and Test Fixture

After the surprising success of LED illumination in FreeNAS v2 enclosure, I wanted to spend some time experimenting with the concept. When searching for “acrylic edge illumination” on Google, everybody seems to be talking about positioning the LED at the edge of the acrylic sheet and lighting up the pattern of something engraved on the acrylic. My goal is the opposite: I want to place the LED in the middle of the acrylic, and I want the light to shine out to the edge of the acrylic sheet.

We start with the assumption that by default, a LED shining inside a piece of acrylic will only illuminate in the direction it is pointed.


Our ideal goal is to determine how to direct this light so it illuminates all the edges of the acrylic sheet, not just the direction of the LED face.


I 3D printed a small test fixture for these experiments. It has space for a 75mm x 75mm test piece of acrylic and a LED that pokes up in the middle of that space. There’s a 10mm wide border around the test piece so I can observe the pattern of illumination beyond the edge. At the outside edge of the border, a wall to observe the intensity of illumination beyond the edge. A piece of black tape covers the direction of the viewer so the LED doesn’t overwhelm the rest of the observation. A piece of aluminum foil lines the bottom of the test fixture to reflect any light back into the acrylic.


The fixture lights up as expected in the absence of any acrylic.


These two experiments tested cutting grooves in the acrylic. One set had straight grooves, a second set curved. They were successful in breaking up the center top hot spot, sending some of that light elsewhere. But the light seems too concentrated on the bottom third.



Instead of cutting grooves, this piece tested cutting entirely through the acrylic. The circular shape does seem to disperse the light fairly well.


These were interesting, but the most surprising result came from a test piece of acrylic with nothing cut in the middle. I had expected the light pattern to resemble the triangular hot spot of the LED by itself without any acrylic, but we got this:


It has the same basic trend of the other light patterns in this set of experiments, which tells us the majority of the light scattering is not done by the curved/straight grooves or the circle. The feature with the largest impact is actually the small cavity surrounding the LED itself.

The fixture has been informative, but it has one problem: it is difficult to make comparisons between different test acrylic pieces. Before proceeding with investigation, the test fixture will be expanded so there are two test pieces side by side for comparison.

Acrylic Lights: Infinity Mirror

I’ve played with putting lights in my 3D-printed creations for glowing illumination effects. There were limits to what I could do with 3D printing, though, because printing with a clear filament does not result in a clear object. In contrast, acrylic is clear and works as a light guide with a lot of possibilities.

I’ve noticed a few attention-getting light effects in my acrylic projects to date, most of them created by happy accident. The acrylic box with external fixture made good use of external light. The Portable External Monitor version 2.0 was built from stacks of acrylic sheets: its fluorescent back light reflected between the layers like an infinity mirror.


This effect was on my exploration to-do list for the future, but I moved it to the top of the list after seeing surprisingly good results on the FreeNAS Box v2 enclosure.

I had planned for it to have the standard PC status LEDs: one for power, and one for disk activity. The acrylic plate for motherboard mounting spacer also had two cutouts for 3mm LEDs along the center line. The red hard drive activity light is to be mounted high, and the blue power light mounted down low. The idea was for the blue light to illuminate the top edge of the plate. When there is hard drive activity, red LED will light up the center of that edge, and it should blend to purple with the power light. Both LEDs were blocked from direct view by the motherboard, so all we should see is a nice soft glow emitting from behind the motherboard.


That was the plan, the reality was different. The red activity light worked as expected: when there is disk activity, the center of the top edge had a little red glow.

The blue LED decided to ignore my “nice soft glow” plan and put on an extravagant light show. It didn’t just light the top edge, it lit every edge of that acrylic sheet and had plenty of extra light energy to throw on the surrounding shelving.


Here’s a close-up of the sideways illumination.


The many rays visible in the side illumination, as well as the lines making up the top illumination, indicate infinity mirror action going on inside that sheet. It wasn’t directly visible, and probably very difficult to photograph even if so. Without internal reflections, the blue light would have just gone straight up. But with the smooth surfaces and edges of the acrylic reflecting inside the sheet, the light of a single LED bounced around, found different angles, and was emitted in many more directions.

This LED illumination effect warrants further investigation. It is a happy accident that I fully intend to learn from, and put into future acrylic projects.

I want every acrylic project to look this awesome!