EBD-USB+ Electronic Load – Testing Power Supplies and Batteries

I watched a video from Andreas Speiss reviewing electronic loads, and identifying one in particular called EBD-USB+ from zketech.com and purchased through Amazon or Banggood or wherever. The software is a little hard to find, but it’s available through this link. It comes as a .rar file, which you might need to unpack with 7-zip or Winzip. You will also need the driver.

The resulting Windows-only software allows one to test two categories of things: batteries, by allowing a set amount of current to flow and recording both current and voltage vs. time, and power supplies, by allowing an increasing amount of current to flow and recording voltage vs. current. The Speiss video explains really well.

Here are a couple of results I got while trying to locate a power supply capable of furnishing 5V at 2.1A to power a Raspberry Pi 3B. None of the five wall-wart power supplies really made the grade.

The worst of them, capable of providing only 4.72V at 2.1A
The best of them, the power supply that Adafruit sells and recommends for the Raspberry Pi. It provided 4.88V at 2.1A

Calculating the Axis of Nutation of my Solar Tracker

Following on the cluster analysis of the last post, I pairwise crossed (as in cross-multiply) the resulting cluster centers, and got three reasonably-close vectors after normalization. These were:

0 x 1: (-0.36, 0.93, -0.10)
0 x 2: (-0.23, 0.97, -0.06)
1 x 2: (-0.20, 0.97, -0.14)

While satisfyingly close, I wanted to do better.

Next I decided to take 1M random pairs of points from the raw data, cross and normalize these pairs, and then look at component-wise statistics. I ignored points within my arbitrary minimum separation of 0.5. The results were not only satisfyingly close, but also close to the values I got above.

N: 367187
M: (0.30, -0.94, 0.11) ( sum = (108760, -345150, 40391) )
S: (0.10, 0.08, 0.04)

I am now satisfied that I have the axis of nutation: (0.30, -0.94, 0.11).

Update…

Of course, I couldn’t leave well enough alone. Looking at the data over time, I found that data taken before 2018-01-14 16:41 was radically different. That was the time I mounted the monitor onto its arm on the solar tracker. <sheepish grin>

So now the cluster analysis yields

0 x 1: (-0.36, 0.93, -0.10)
0 x 2: (-0.42, 0.90, -0.12)
1 x 2: (-0.44, 0.90, -0.08)

and the random pair analysis yields

N: 272251
M: (0.350, -0.927, 0.099) ( sum = (95366, -252300, 26948) )
S: (0.07, 0.05, 0.02)

Finally, my analysis program now yields

Projection of Gravity Vectors...

normalized nutation axis 'mean': (0.352, -0.931, 0.099)
unnormalized rotation_axis (-0.93, -0.35, 0.00)
nutation_axis (0.352, -0.931, 0.099) x z_axis (0.00, 0.00, 1.00) -> rotation_axis (-0.935, -0.354, 0.000)
Sin theta = 0.995 -> Rotation angle 1.47 radians
Test Projection of nutation axis: (0.00, -0.00, 1.00)
Most recent ( 2018-01-29 18:39:45 ) theta: -10.0 degrees

So the panel, while its elevation is as low as it goes, has an elevation theta of -10 degrees. Here is the 3D view of the raw gravity vectors now. (For more about how to see this chart in 3D, see my previous post.)

and the trace of elevation over the length of one day (yesterday):

I’m not yet completely satisfied. The plot shows a range of elevation of about -7 to about -36 degrees, for a range of nutation of 29 degrees. I believe that this accounts for less than half the about 70 degrees I think I see.

More investigation to come!

Instrumenting and Analyzing My Solar Tracker

I’m an instrumentation and data collection geek. I love the challenge of developing ways to monitor the systems of my house and making sure they’re working properly. I’ve had a couple bad experiences where systems failed and not knowing it soon enough caused problems.

I have a solar tracker system, one which follows the sun when it’s up. It failed once with a hydraulic leak, and it was a couple days before I noticed it. Never again!

I’ve built and installed a monitoring system including its own solar panel, battery, 9 degree of freedom MEMS device normally used for inertial navigation of unmanned aerial vehicles, a microcontroller, and a LoRa radio with enough range to cover the distance to my house.

I’ll go into the details in another post. What I want to put into this post is the 3D plot of the first telemetry data.

The solar tracker is on a pillar out in my yard; the whole rotates around the vertical axis of the pillar (azimuth), and the panel tilts up and down (the motion is called nutation, the result is called elevation). The inertial navigation system (INS) device measures linear acceleration, angular acceleration, and magnetic field, all in 3D. My first task is to develop a coordinate system with one axis parallel to the axis of nutation of the solar tracker.

I have collected thousands of data points, taken at 1 minute intervals, and including the 3 linear accelerations. These mostly reflect the gravity vector. I’ve now plotted these in 3D; they should all lie in a plane, perpendicular to the axis of nutation. I can see this in the plot. (Look at the picture with 3D glasses, red filter for left eye, cyan filter for right eye.)

My next step is to calculate cross products for many pairs of vectors. The cross products will be perpendicular to each of the vectors, and so all the cross products should be collinear with each other, and also with the axis of nutation.

With 40,000 data points, there would be n(n-1) pairs, and hence 1.6 billion cross products. That’s a lot of computation. But I reckon that crossing vectors that are close together will yield poor results, and account for a lot of noise. So I’ll cross only those vectors that are farther apart, by some arbitrary distance.