DSO 138 Oscilloscope Kit by JYE Tech

An oscilloscope has been on the tool wish list for a while, but good ones are really expensive. But occasionally a simple basic scope would have been better than no scope at all, which is where today’s project comes into the picture.

JYE Tech makes the DSO 138 oscilloscope kit perfect for electronics hobbyists who can make use of a simple scope and also willing to put in the time and effort to assemble one out of a kit. The kit is available at a very low-cost, a fair exchange for making their customers do their own assembly.

This product is popular enough to spawn counterfeit copycats, which was a concern. Not just out of fear of a problematic product, but also the desire to support the original authors. Fortunately JYE Tech offers the option to send in the serial number for authenticity validation. The serial number of this unit purchased from Amazon vendor Kuman checked out as authentic.

There are two versions of the kit that differ by their treatment of surface-mount components: pre-installed or not. This particular example is the variant with surface mount pieces already installed, the customer just has to take care of the remaining through-hole parts. All those parts to be soldered came in a single bag and had to be sorted and identified before assembly could begin.

DSO138 parts sorted

The instructions were straightforward enough for someone already familiar with basic electronics soldering. The only complaint with this kit is that some of the mount points were not designed for easy soldering. They connect directly to large pieces of copper trace that acted as a huge heat sink making it difficult to bring the solder joint up to temperature. It would have been nice if they etched a little more. Leave one contact sufficient to carry the current, and etched around the rest to serve as a thermal break.

Apart from that minor complaint, the soldering was not difficult, only tedious. The electronics hobbyist is reminded why manual assembly of circuit boards is not considered a great career. This particular example took roughly four hours to assemble. Thankfully, when power was connected, everything started running as they should. Here is the assembled DSO 138, showing the built-in square wave test signal.

DSO138 complete

A few simple tests followed the self test, clearly showing some limits of this little oscilloscope. For one thing, the voltage scale is quite unreliable. An AA battery at 1.22 volts (according to the Fluke multi meter) was interpreted by this oscilloscope as 1.67 volts. But we didn’t get this thing to read voltages – we want to use it to graph wave forms that we couldn’t see with a multi meter.

It’s now part of the toolbox. Thanks to its low-cost, it wouldn’t take much data to throw it in either of these two buckets:

  • Positive: “That was so much easier to diagnose with a scope, even a simple one. This was well worth the money.”
  • Negative: “The inaccuracy of the scope led us down the wrong diagnosis path. This was a waste of both time and money.”

While we wait for the verdict to come in, let’s work on an enclosure for this device.


Dell XPS M1330 Battery Pack Teardown

We had an earlier success tearing down a Dell laptop battery pack, where the six salvaged cells still have 70% of original capacity after ten years of service. However, that was from a laptop that could still boot and run from its battery pack. This XPS M1330 battery pack is in far worse shape. How much worse, we were about to find out.

The first critical detail was realizing the battery pack was not the original Dell battery pack. It is an aftermarket type of unknown manufacture. The earlier battery pack tear down yielded Samsung cells, we’re probably not going to get anything nearly as nice this time around.

Once the case was cracked open the suspicion was confirmed: These appear to be generic 18650-sized lithium cells with no manufacturer branding. The nine cells of the battery pack were divided into three modules in series, each module had three cells wired in parallel. The module in the worst shape exhibited severe corrosion and had no voltage across their terminals.

Corroded 18650

The other two modules were in slightly better shape, but they have self-discharged down to approximately 1 volt DC, well under the recommended voltage range. A web search found some details on what happens to overly discharged lithium cells. In short: the chemistry inside the cell starts dissolving itself. If recharged, the dissolved metals may reform in inconvenient ways. Trying to use these cells has three potential outcomes:

  1. Best case: The metals dissolved into the electrolyte will hamper chemical reaction, resulting in reduced capacity.
  2. Medium case: The dissolved metals will reform in a way that damages the cell, causing it to fail as an open-circuit. (As if no battery was present.)
  3. Worst case: The dissolved metals will reform in a way that damages the cell, but causing it to fail as a closed circuit. Short-circuiting the internals will release a lot of energy very quickly, resulting in high-pressure venting and/or fire.

The corroded cells that have discharged down to zero volts have the highest risk and will be discarded. The remaining cells will be slowly (and carefully) charged back up to gauge their behavior.

Dell XPS M1330 Power Port Salvaged Using Desoldering Tool

Recently a dead Dell XPS M1330 came across the workbench. The battery was dead and the machine fails to boot. After some effort at reviving the machine, it was declared hopeless and salvage operations began. Today’s effort focuses on the motherboard port for the AC power adapter.

Dell Octagonal PowerThe power plug on this Dell different from the typical Dell laptop AC adapter: octagonal in shape rather than round. The shape meant it could not be used on other Dell laptops designed for the round plug. However, the dimensions of the octagon are such that an AC power adapter with the typical round Dell plug fits and could be used to charge the laptop. So while the laptop could be charged with any existing Dell-compatible AC adapter, the AC adapter that came with this machine is specific to this Dell.

Once the XPS M1330 died, its octagonal plug power adapter is not useful for other Dell laptops. It still functions as a power supply transforming household AC to ~19V DC so it might be useful for future projects. To preserve this possibility, the octagonal power port will be recovered from the system board.

The solder used in Dell assembly was possibly one of the lead-free types and is definitely reluctant to melt and flow. Trying to desolder the power port using hand tools (desoldering wick and hand suction pump) had no luck. So this project was chosen as a practice run of using a dedicated desoldering tool, in this case a Hakko 808. The tip of this tool heats up to melt the solder, and with a press of the trigger an electric vacuum pump pulls the melted solder through center channel of the heated tip and into a chamber for later disposal.

The desoldering pump was able to remove more solder than hand tools could, but was still not quite enough to free the port. Using a soldering iron, some user-friendly leaded solder was worked back into the joints to mix with the remaining Dell factory solder. Upon second application of the electric desoldering tool, enough solder was removed to free the port from the system board with only minimal damage.

Desoldering Tool

A test with the voltage meter confirmed this port is now ready to be used to provide ~19V DC power to a future project.

Socket Extraction Success


WebAssembly: A High Level Take On Low Level Concepts

webassemblyWebAssembly takes the concepts of low-level assembly language and brings them to web browsers. A likely first question is “Why would anybody want to do that?” And the short answer is: “Because not everybody loves JavaScript.”

People writing service-side “back-end” code have many options on technologies to use. There are multiple web application platforms that are built around different languages. Ruby on Rails and SinatraDjango and Flask, PHP, Node.JS, the list goes on.

In contrast, client-side “front end” code running on the user’s web browser has a far more limited choice in tools and only a single choice for language: JavaScript. The language we know today was not designed with all of its features and capabilities up front. It was a more organic growth that evolved alongside the web.

There have been multiple efforts to tame the tangle that is modern JavaScript and impose some structure. The Ruby school of thought led to CoffeeScript. Microsoft came up with TypeScript. Google invented Dart. What they all had in common was that none have direct browser support like JavaScript. As a result, they all trans-compile into JavaScript for actual execution on the browser.

Such an approach does address problems with JavaScript syntax, by staying within well-defined boundaries. Modern web browsers’ JavaScript engines have learned to look for and take advantage of such structure, enabling the resulting code to run faster. A project focused entirely on this aspect – making JavaScript easy for browsers to run fast – is asm.js. By limiting JavaScript to a very specific subset , sometimes adding hints to the browser it is so, allows JavaScript that can be parsed down to very small and efficient code. Even if it ends up being very difficult for a human to read.

Projects like asm.js make the resulting code run faster than general JavaScript, but that’s only once code starts running. Before it runs, it is still JavaScript transmitted over the network, and JavaScript that needs to be parsed and processed. The only way to reduce this overhead is to describe computation at a very low-level in a manner more compact and concise than JavaScript. This is WebAssembly.

No web developer is expected to hand-write WebAssembly on a regular basis. But once WebAssembly adoption takes hold across the major browsers (and it seems to be making good progress) it opens up the field of front-end code. Google is unlikely to build TypeScript into Chrome. Microsoft is unlikely to build Dart into Edge. Mozilla is not going to bother with CoffeeScript. But if they all agree on supporting WebAssembly, all of those languages – and more – can be built on top of WebAssembly.

The concept can be taken beyond individual programming languages to entire application frameworks. One demonstration of WebAssembly’s potential runs the Unity 3D game engine, purportedly with smaller download size and faster startup than the previous asm.js implementation.

An individual front end web developer has little direct need for WebAssembly today. But if it takes off, it has the potential to enable serious changes in the front end space. Possibly more interesting than anything since… well, JavaScript itself.

Remove Camera From Acer Aspire Switch 10

When the Acer SW5-012 (Aspire Switch 10) was received in a non-functioning state, it had a sticker covering the webcam lens applied by the previous owner. This is a common modification from owners who are concerned about malicious hackers activating the camera at unauthorized times. Some computer makers are finally meeting customer demand by placing physical shutters over webcams, but until that becomes commonplace, we’ll continue to have stickers/tabs/post-it notes covering webcams.

Removing the camera module would be a far more secure solution if the webcam is not to be used anyway. While impractical for some difficult-to-disassemble devices like an Apple iPad, we’ve already cracked open this Acer and test the concept. It turned out to be a straightforward exercise. The camera module is a distinct unit, the ribbon cable detaches from the motherboard easily, and it was only held in place by what felt like double-sided tape.

Acer Aspire Switch 10 Blinded

With five minutes of removing the back panel of the machine, the camera module was removed. The only lettering on it said CIFDF31_A2_MB and a web search on that designation returned several vendors happy to sell a replacement module. Sadly no technical information was found in a cursory search, so we won’t be trying to drive it with a PIC micro controller or anything. It’ll just sit in a zip lock bag for now.

And this intentionally-blinded Acer tablet is now available for use by house guests who are wary of hackers getting into the camera: no hacker in the world can activate a camera that is sitting in a zip lock bag in another room.

FreeNAS Failed Drive Recovery

One of the major reasons to set up a FreeNAS machine with ZFS volume is to ensure that network storage data is always available in a redundant manner to ensure everything will still be OK after a hard drive inevitably fails. But before theory can be put into practice, we had to wait for a drive to actually fail. In that sense, today is our lucky day.

FreeNAS Critical Alert Box

A drive failed to respond to some commands and returned errors in the wee hours of the morning. Although it appears to have since recovered and is functioning, we shouldn’t be comforted by the momentary blip – it is almost certainly a sign of things to come if we continue to use this drive. So we’ll replace it instead of waiting for a catastrophic failure.

The instructions to replace a failing drive is covered in the FreeNAS manual. Following the procedures, the drive was taken offline in the Storage/Volume Status screen.

FreeNAS Volume Status

Then we go to Storage/View Disks screen to retrieve the identifying serial number. This ensures that we remove the correct physical drive from the computer by comparing this serial number against the number on the physical label on the drive.

FreeNAS Storage View Disks

Since this FreeNAS machine does not have hot swap capability, it then had to be shut down for the actual drive replacement. Once the machine restarts, we go back into Storage/Volume Status and select “Replace”. (The button next to “Offline” we clicked earlier.) If there’s any existing data on the replacement drive, FreeNAS will double-check to make sure it’s OK for the replacement drive to be overwritten.

FreeNAS Force Replace

And after that… we wait for the data from the remaining good drive to be replicated to the newly installed replacement drive.

FreeNAS Resilver In Progress

This procedure will take several hours and this time is technically a window of vulnerability – if the remaining good drive fails during this time we’ll lose data. To guard against this, ZFS allows even deeper redundancy by using more than two hard drives. In the case of this server, the data is not critical enough to warrant such protection and we’ll just cross our fingers the remaining drive does not fail during the recovery process.

Duet Display External Monitor: High Resolution and Features to Match High Price

Having multiple monitors is a great luxury. Not everyone appreciates it, but those that get used to it miss it greatly when traveling. It’s the biggest downside of using a MacBook Air as the travel laptop. It is smaller and lighter than the homebuilt external monitor, making it kind of silly to use them together. When light weight and portability is important enough to take the MacBook Air, we’ll also need the external screen to be equally portable.

The search for a thin-and-light external screen companion started with units that receive both power and data via the USB port. Sadly most of them offered only a low 1366×768 resolution at the starting $100 price range. Very few offer 1920×1080 resolution and they are in the $200 range. To get resolution any higher than that, we’ll need an iPad running Duet Display. Which means spending >$300. The good news is, for that price, the system worked very well with only two caveats:

First, Duet uses a proprietary protocol that requires a special driver running on the computer to talk to the app running on the iPad. Installing this driver triggered several warnings from MacOS and required explicit authorization to run non-Apple code signed with the name Rahul Dewan. A web search indicated this was the name of founder and CEO of Duet Display, so that matches, but it’s still a scary action from a security perspective.

Second, application windows could not span the two monitors. They can be dragged from one to the other, but each window will show only on one monitor. If a window is dragged to straddle the divide, only half of the window will show on one monitor, and the other half is not visible anywhere.

Other than that constraint, Duet Display works well to make an iPad (2017, Model A1822) serve as an external monitor for a MacBook Air (13-inch, early 2014). The speed and responsiveness are great. So far, the performance has been indistinguishable from an external monitor connected to the MacBook Air via HDMI.

It even offers something not available on other USB external monitors: the ability to hook into Apple’s Touch Bar feature and show the bar on the iPad. Even for Apple computers that aren’t equipped with the Touch Bar.

Duet+iPad has turned out to be the most expensive of the external MacBook monitor options, but it makes a compelling case to justify its price. High resolution, super lightweight, and naturally the iPad is still a perfectly good tablet when detached from the computer.

Duet in Action


Fusion 360 Lines Created Via API Are Not Limited To Sketch Plane

Cube on Sketch

Today’s performance tip helps avoid creating unnecessary planes and sketches when creating objects using the Fusion 360 API. First, some background: when sketching lines in Fusion 360 must be done in the context of a sketch object. This sketch object is in turn created to be aligned with a plane. It may be one of the default planes that intersect the origin (XZ plane, XY plane, or YZ plane) or a construction plane.

When sketching with the interactive UI, the user’s sketch entities are constrained to the plane of the sketch. For example, if a sketch was created on the XY plane, then all sketch entities would have a Z coordinate of zero. This makes sense to keep the data organized and easy to understand by the human looking at a 2D computer monitor.

When creating entities with the API, though, they are apparently not constrained. The first clue came from looking at the SketchLines.addByTwoPoints API – its two parameters are Point3D objects. A little experimentation confirmed the API would gladly accept 3D coordinates that lie outside the sketch plane. The example screenshot on this page is the result of drawing an one-centimeter cube on a sketch aligned to the XY plane. Only four of the eight corners (and four of the 12 edges) lie on the plane, but the API happily accepted all the information for a 3D cube.

This is very useful when creating geometries via code. Humans need to see points on a sketch stay in a plane for them to be workable on a 2D monitor screen, otherwise things get too confusing. But code doesn’t care about appearance on a screen. So go ahead – let code create complex 3D entities on a single sketch. Skipping the unnecessary planes and sketches will generate fewer API objects. Reducing object management overhead and allowing faster performance.

Accelerate Fusion 360 API Object Creation With DirectDesignType


Exploring the capabilities of the Fusion 360 API will involve experiments creating objects via script. Since it’s all code, it’s easy to repeat a process many times, a natural allure of using scripts to automate repetitive tasks. The downside is that Fusion 360 (as of time of writing) has problems resulting in slow response.

The sample code below creates an array of small cylinders one at a time. (This is not the most efficient method to create an array of cylinders but merely an illustration of the problem.) The size of the array can be adjusted by changing the value of arraySize before running the script. For a 4×4 array, the results are almost instantaneous. On a modern Core i5, slowdowns can be observed in an 8×8 array. The first few cylinders are fast, but as additional cylinders appear, each new cylinder takes longer than the last.

Fusion 360 performs a lot of bookkeeping overhead to track these operations. While the majority are outside our control, we do have control over the most expensive overhead: the timeline. It is useful when we are working with hand-created designs, but unnecessary for script – if we want to change anything, we’d update the script and run it again. In the user interface, we can click on the gear in the lower right hand side and select “Do not capture Design History”. To do the same thing in script, we can set the type of the design object to DirectDesignType. (Uncomment line in sample code below.)

This mitigates but does not solve the problem. While it is now practical to generate far larger number of objects, there is still a noticeable slowdown as the object counts go up. According to this forum post, this issue has been logged as a defect for the development team. Perhaps a future release of Fusion 360 will create the last object as quickly as it created the first.

import adsk.core, adsk.fusion, adsk.cam, traceback

arraySize = 8 # Will extrude arraySize^2 objects

def run(context):
  ui = None
    app = adsk.core.Application.get()
    ui = app.userInterface


    # adsk.fusion.Design.cast(app.activeProduct).designType = adsk.fusion.DesignTypes.DirectDesignType # Uncomment to turn off tracking timeline

    rootComp = adsk.fusion.Design.cast(app.activeProduct).rootComponent
    sketch = rootComp.sketches.add(rootComp.xYConstructionPlane)
    extrudeDistance = adsk.core.ValueInput.createByReal(1)

    rangeX = range(1-arraySize, arraySize, 2)
    rangeY = range(1-arraySize, arraySize, 2)

    for nowX in rangeX:
      for nowY in rangeY:
          adsk.core.Point3D.create(nowX, nowY, 0), 0.5)



  if ui:

This code is also available on Github.

Windows 10 Can Activate With Windows 8 Hardware Key

Our recent project with the Acer Aspire Switch 10 laptop had concluded with one mystery: how did it get the license key? Because we didn’t have the password for the installation of Windows 8 on the machine, the hard drive was wiped clean and Windows 10 installed from scratch. We expected we’d need to purchase a new license of Windows to activate on this computer. Fortunately, Windows 10 proclaimed itself activated without the need for a new license.

At the time we did not understand, but we were also not going to complain.

A second data point came in the form of a Dell laptop, which also shipped with Windows 8 but purchased by someone who decided they did not like it. A Windows 7 license was purchased and installed on this computer, which was then upgraded to Windows 10 during the free upgrade period. The original Windows 8 was lost. Recently a new SSD was installed on this computer and Windows 10 was installed from scratch. And like the Acer, Windows 10 proclaims itself to be activated even though no product license key has been entered.

Curiosity now demands a web search for answers, where we learn both of these computers participated in a new licensing scheme launched with Windows 8. Instead of a counterfeit-resistant license sticker attached to the bottom of the computer, their product license is embedded in the hardware instead. We will never have to worry about the license key becoming illegible, or getting lost and separated from the corresponding hardware.

Windows 8 could access this key and activate itself. Windows 7 installed on the Dell laptop could not. Windows 10 could access this key and, more importantly, are willing to activate on it even though the license was technically for Windows 8. The official free Windows 10 upgrade period has ended but we can still get a free step up under these circumstances.

Windows Key Sticker
The Windows Certificate of Authenticity is now a relic of the past.

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