Category Archives: Amateur Radio

MPPT Solar Battery Charging in the Arizona Desert

I’ve got a 125 W solar panel feeding a 12 Vdc 85 Ah deep cycle battery at a comms site in the southwest Arizona desert. I’m using a Rich Solar MPPT-20 solar charge controller (SCC), which so far appears to be doing a great job. The load on the battery is a Raspberry Pi with two NESDR Smart radio dongles, running software called RWMon, and decoding ATCS indication messages being sent from railroad control points along the I-8 corridor, but that functionality isn’t the subject of this article. It’s the battery management that’s the thing!

Figure 1 – 24-Hour Battery Voltage

It’s a tough environment out there in the desert, and determining an appropriate energy storage technology is part of the challenge. I settled on a lead-acid battery, mainly because it tolerates higher working temperatures, and since there are plenty of charge management devices that understand lead-acid chemistry really well.

In Figure 1, battery voltage is shown over a 24-hour period. This particular 24-hour period was dead clear during the daylight hours, so the curve is very clean.

Figure 2 – Manufacturer’s Chart on Battery Charge Management

Figure 2 is the chart right out of the Rich Solar MPPT-20 charge controller manual. From about 0700 (the sun begins to directly illuminate the panel) to around 1130 the SCC is in the fast charge mode. From 1130 to about 1330 the SCC is in the sustained charge mode; from 1130 to 1730 the SCC is in float charge mode. It’s nice to see that the real-world situation replicates the manual pretty accurately.

There are other nice things to discuss about this SCC, including very low RFI generation, that future notes will touch on.


I realized that I also have for the same setup the voltage characteristics for the PWM SCC that I had out there last month before switching to the MPPT unit.

In Figure 3, the units are wrong, but the curve is the important bit.

Figure 3 – PWM SCC Voltage Curve

Here, it’s a much cruder controller, but the same kind of curve is evident. The drop off from boost to float is a very slow ramp, that’s probably not as good as what the MPPT does.

“WINGONEER Wireless Digital DC Voltmeter Ammeter Multimeter 2.4”

Purchased this thing via Amazon.

Received device yesterday, no user manual. Searched on line for “VAC8010F-80V” and found what looks to be a .pdf manual for this product. Got thing hooked up per the schematic in that manual. Battery is 12 Vdc, 2x20Ah SLA cells, on a solar PWM charger. Batteries are fully charged (14.4 Vdc) and in good shape. Disconnected batteries from charger.

Through a 12 V – 5 V dc-dc switching converter, connected 4 RTL-SDR-equipped Raspberry Pis and a DLink gigE Ethernet switch (total of about 1.5 A load at 12 Vdc). Device displays -1.6 A current draw, a little high from what my Fluke meter says at -1.5 A. Not bad!

The wireless function is kind of awesome – it just works. The range is at least good enough for having the sensors at the battery and the display head several meters separated, with some house walls in-between. The device uses the NRF24L01 chip from Nordic, so the transmission is in the 2.4 GHz band. I have multiple 2.4 GHz Wi-Fi units in the house, I can’t see how the link degrades, but it seems to be fine. It appears that one sensor unit can communicate to many display heads, or many sensor units can communicate to a single display head. Haven’t experimented with that.

The display is bright and very readable. The three buttons, from top to bottom, are “up”, “select/change”, and “down”. The function of some of the settings is a little hard to determine from the found manual, but I’ll survive. The temperature sensor is a ~100 cm long cable with temp sensor in a ring lug. I have it in-between the two batteries, and shows 28 C, which is close enough.

So the hardware is nice, but the software sucks. Seriously not good. I have had this running now for about 40 hours; the voltmeter function works fine, the current meter appears to accurately show positive current, and the temp sensor works fine, that’s about it. The running Ah and Wh meters just don’t do anything useful. I have 40Ah of 12 V SLA battery, I programmed in via the BAT function the 40.0 Ah size, I discharged the batteries a while until it reached 38.467 Ah. Then I applied a charge to the battery through the circuit, the battery capacity stayed at 38.467 Ah. The battery voltage has continued to increase to full charge, so that’s working. The BPC value is static at 96%. I tried to reprogram the BPC to 100%, but it won’t accept the value. I’ve tried changing the battery capacity to some other value to get it to reset the counters. It will not show negative current (power flowing into the battery from the solar charger). Not sure what to do about this. Probably will return it unless I get some answers soon. I guess I’ll have to wait until Sunday night (Monday in China).

Summiting Woodchute Mountain 28APR18

7840-7880′ elevation – clean prominence: 2900′ – isolation: 25.7 mi

GPS log available at peakbagger link above.

Woodchute (I keep thinking woodchuck, as in “how much wood could a woodchuck chuck if a woodchuck could chuck wood”) is more of a hummock than a peak; it’s forested with pine and there’s no obvious summit. And when you’re there, it’s hard to tell. As I was wandering around the overgrown forest, GPS in hand, looking for a high reading, I found a very mature tree which had apparently been struck by lightning at one time. This made me think I was at the summit, and subsequently I did find a cairn with glass-jar-enclosed peak register.

The trailhead is an easy access dirt road off the end of the paved forest road that leads northwest from SR-89A at its saddle atop the Black Hills.  Less than 0.3 miles in, there’s a left turn and a paved leading to dirt road to the “Woodchute Trailhead”, complete with toilet. But wait! There’s more! If the gate is open, continue on the dirt road that heads kind of northwest from the so-called trailhead. At least when I drove it, it was nearly a freeway in fine condition for any kind of vehicle. About a 3 minute drive later, there’s another trailhead for Woodchute. Park here to start your adventure.

After the trail register stop (in the rectangle just left of center), pass through the step-over latched-shut gate (the rectangle to the far left of center; latch it closed after you pass). 

The trail is well used and obvious in this portion.

Views of Mingus Mountain (shy of Woodchute by only one contour line), SR-89A headed down to Jerome, and the orange cliffs of Sedona in the distance.

The trail is more or less a ridgewalk for the first mile or two, with an opportunity to get to peak 7396 via a short trail diverging to the east.

After passing the Woodchute Wilderness sign (sun on the wrong side, couldn’t get a good picture), a little ways further there’s this sign. Continue following the TR-102 route up to the right and east of the fenceline. The steepest pitch is about there, from the 7400 to the 7600 contour.

Once above the 7600 contour, it’s time to leave the trail to find the summit. McEntee went up the “ridgeline”, while McClellan took a slightly more flat route. I ended up in between those two.

An interesting thing I found – what looks like a small aircraft plexiglass windshield. Maybe 3/16″ thick, smooth on all edges (no breaks or cracks). No aircraft, however.

Finally, I find the rock cairn and peak register.

Meandering east, downslope, I regain the TR-102 trail and begin the return to the truck.

Along the way I grab a shot of the volcanic peaks from Bill Williams on the west to Elden on the east.

After signing out at the trail register, I head down to Chino Valley to Insurgent Brewing to try their beers!

While cellular coverage can be hit-and-miss on the trail, the repeaters on Mingus Mountain are full-scale whether on 2 m or 440. As well, Elden, Bill Williams, and Mt Union all provide fine coverage.


Summiting Browns Peak 21APR18

7659′ elevation – clean prominence: 3297′ – isolation: 25.6 mi

GPS log available at peakbagger link above.

Time-lapse video of trip from SR87/Cline Cabin Road turnoff, to trailhead, then down to SR188, and return to SR87/Cline Cabin Road intersection via Punkin Center.

Drive time to the trailhead depends only a little on the route taken. Going there, I left SR87 at about 0658 and arrived the trailhead parking lot around 0821, for a distance of around 19 miles and a elapsed time of about 83 minutes. Slow road in parts, but completely 2WD street car quality. Had to compete with mountain bikers on the way up.

On the return to civilization, I left the parking lot at 1251, went down the 10 miles of the dirt road to SR188, then up to regain SR87 and then to the SR87 – Four Peak road / Cline Cabin road. That was a total of 62 miles (11 dirt) and 51 miles at highway speed. The elapsed time for that return path was about 1245 to 1412, or 87 minutes. On this side, had to compete with buggy drivers coming up. Actually longer in distance and time but subjectively, the east side dirt road was less stressful than the west. But enough to justify the extra distance? Meh.

Arrived at upper parking area. Sierra Estrella high point is about center in the distance at around 62 miles.

Looking up at Brown’s Peak from the parking area. This parking lot appears to be an overflow for the main lot immediately at the trailhead. However, I like this one a bit better as the view is much wider.

To the southeast with Roosevelt Lake below.

Up the trail a short bit, and able to look back to the truck parked in the upper lot.

Trail is well defined until getting up to the rock.

Looking north toward Mt Ord (the radio communications site) and Mazatzal Peak, the next major bump to the left and the one I summited two weeks before.

More thorny shrubberies.

Up a little higher, looking down into the Tonto Basin.

The Superstitions and The Flatiron in the left middle ground.

Looking up toward Browns Peak.

Spring has sprung – buds on the trees.

The bottom of the chute. This is quite steep. Fortunately, it’s not on a ridge line so there’s little or no wind, and the only way to fall is down %^)

Looking at the crowd atop Browns from the rise atop the chute.

Toward the Salt River canyon with the Browns slope to the left and Brother/Sister/Amethyst to the right.

Atop Browns looking back toward the lower summit.

Didn’t find a benchmark, but this is interesting. Also, did find the peak register and signed in there.

The other 3 of the Four Peaks, with The Flatiron hidden behind Brother peak.

Looking at Mazatzal about center in the image, and realizing it’s 250′ higher.

Headed down the chute, with folks coming up. There are the two in the foreground and one about 100′ below. It’s hard to perceive the extreme slope in this photo.

Looking back up the chute with some people either climbing up or down (hard to see in the glare).

While not a cakewalk, it was surprisingly straightforward. Definitely was sometimes at the edge of scary in the chute, mostly coming down. Some large rocks are only metastable. Several times while descending I realized that the drop below me was too great, so I had to retreat a bit and find a more doable way down.

Pinal Mountain (and summiting Signal Peak) 15APR18

Drove up to Pinal this morning to swap out some equipment. Getting to/from Pinal from the highway isn’t difficult, just 18 miles, with 12 of them on a really great-condition (at least until the rains come) dirt road.

Once I was finished with my other hobby, I started down the road and parked at the Signal Peak turnoff (651B). As I’d never been to Signal, and I’d never used the mobile PeakBagger app to record a hike, I was able to do both and learn a thing or two or three new things.

The first thing I learned was that Signal was less than 300′ minimum prominence, and that’s what I’d set my PeakBagger filter for, so Signal didn’t show up until I dialed that down to 250′.

7812′ elevation – clean prominence: 252′ – isolation: 1.1 mi

GPS log available at peakbagger link above.

Time-lapse video of trip from US 60 to Pinal and back

Signal Peak benchmark directly under fire lookout tower.

Looking NW toward fire lookout tower and cabin.


Summiting White Tank East (radio site visit) 14APR18

For the White Tank peaks, I’m lazy. I can get the key and drive. This morning I went up to check on the radio site on the east ridge where I have an ADS-B receiver and a railroad data receiver setup. The Windows PC there had apparently died a while back, the ADS-B link failed at the beginning of April, so it was time to fix things.

Time-lapse video of the drive between I-10 Verrado offramp to and from the peak

The cool thing about the White Tank road is it goes through the old Caterpillar proving grounds, where they pitted Caterpillar bulldozers against the mountain. And the White Tank road was part of the testing arena.

Verrado’s north end currently ends at the golf course; the tower road is the wide diagonal that heads northwest into the narrows up-canyon.

While Verrado continues to inch its way up the lower portions of the road, it’s unlikely it’ll ever get up this far. This what I call “the bowl”, where Caterpillar dozers not only moved millions of tons of rock back and forth for test and fun, but also cut the 20%-grade, ~0.6 mile long ramp that climbs north out of the bowl and then descends into the White Tank park boundaries.

On this fine day, there’s plenty of people walking the ramp. It’s windy as heck out, and the temperatures are in the mid-50’s, but the sun is warm.

Hauled out the dead PC. Am rebuilding it now to put back on the hill in the next week or two.


Summiting Mazatzal Peak 08APR18

7903′ elevation – clean prominence: 3943′ – isolation: 27.2 mi

GPS log available at peakbagger link above.

Time-lapse video of trip from Scottsdale to Barnhardt trailhead and back

No comms sites on this peak, but Ord, Pinal, Towers, Greens, White Tank and many more sites were reachable on my FT-60. Handy in case of trouble.

Holy quercus turbinella and manzanita, Batman!

After reviewing my mashup of Arizona 2000′ Prominence and 25 Miles Isolation, and seeing the remaining southwestern Arizona peaks I was not going to get to this spring as it’s gotten too bloody hot already, it looked like Mazatzal Peak might be the next candidate. With a 4100′ trailhead only 75 miles from the house, this 7903′ peak was the next closest on my list.

Friday the 6th I set the alarm for 0345, but somewhere before 0345 I must have deactivated the alarm so I awakened at 0700. Thought about it for a bit, and decided instead to not hike. Later on, I’d live to appreciate that decision.

Saturday afternoon I again set the alarm for 0345, and I was up at 0345 Sunday morning, wondering if I really wanted to get out of bed. Nonetheless, by 0415 I had already collected the first of two supertankers of diet Mountain Dew at the local Circle K, and was headed east on Shea through Fountain Hills and then up AZ-87 to the Mazatzal Wilderness just west of Rye.

I thought I’d carefully researched the challenge of the climb up Mazatzal; I read the postings of Casserly, Gaudet, Kassan, McCann, Nuernberger, Poulin, Rankine, and Sexauer. Some were pretty sparse with description. I downloaded into both the phone and the Garmin the GPS logs of Kassan, Poulin, Rankine and McEntee. It was especially good that McEntee had summited the peak only 4 days before me.

On the drive, I hydrated like hell, with about 3 l of diet Mountain Dew, a half gallon of water, all after 4 bags of instant breakfast oatmeal. My (kook) theory is, the oatmeal slows the intestines down and lets the liquid absorb…

Arrived at Barnhardt trailhead around 0620. Interestingly, it was partly cloudy, smelled humid, and the sun was hidden behind low clouds. The tops of the nearby peaks were shrouded. Temperature around 62° F. Dead calm. Watch the video to see how the weather changed over the day.

My plan was to go in via the Barnhardt, climb the broad ridge followed by Rankine and McEntee, and then decide which way to come down. I had Kassan’s ascent route in the GPS, but I’d be following it backward, and he’d mentioned a severe lack of cairns on the cliff section.

On trail at 0634, 28 minutes after sunrise.

Barnhardt trail wilderness boundary marker.

The Barnhardt was a cakewalk, relatively speaking. Good footing, generally easy grade, and I was in the shadows until the combination of sun position and a break in clouds at 0740.

Almost exactly 2 hours into the walk, I arrived at the point where both Rankine and McEntee left the trail and headed up the side of the mountain. While McEntee had chosen the “creekbed” for his climb, Rankine more or less chose the hump of a ridge immediately west.  I didn’t want to boulder-hop the drainage, I chose the Rankine  path.

From this point, I couldn’t find so much as a goat trail while snagging myself on straggly pine-like bushes/trees, whacked in the face with branches, assaulted by thorny shrubberies, until I got about 500′ south and 200′ higher.

At the above vantage point, if one looks really carefully, the cut containing the Barnhardt trail is visible far below.However, in the foreground, one can see dense copses of burned stumps and grey sticks.

While the slope above was reasonably clear of obstacles, the nasty patchy clumps of what could charitably be described as centimetric extemely pointy thorns, supported by leafless, tall, grey-skinned branches and trunks, would prove to be painful and not without a little blood lost.

Looking at the top of the ridge, a pair of pine trees was beckoning. Between me and them were hundreds of downed trees in various stages of decomposition, with unknown peril in footing. And more of the grey-skinned needle trees.

Nearing the top of the ridge, the two pine trees lied to me that they were near the top of the mountain.

Nearly to the pine trees, the far left distance showed what looked to be Mazatzal, but it, too, was a lie.

By now, and around the 7000′ level, I was completely winded, getting a headache, and feeling a little queasy. Slowly it dawned on me that I hadn’t been above 1400′ AMSL for anything but short periods of time over the past 9 months.

The plateau beyond the pine trees was large and pretty much covered in all sorts of prickly vegetation, manzanita groves, more of the grey-skinned stuff, cacti, or more downed trees. Picking a route through the morass was daunting. Generally, I aimed slightly west of south to pick up the line that Rankine, McEntee and Poulin had used. The good thing about that path was that it was more often on hard rock, so there was less of the nasty shrubberies.

Finally, the prominence of Mazatzal was visible, What a massive pile of layered metamorphosed sedimentary rock, with red rhyolite atop, striking NNW/SSE and dipping steeply to the east.

By now it was around noon, and I was really flagging. I’d stayed hydrated, ate a Stinger gel pack or a Clif bar every hour or so, but the lack of trail and the altitude had really smacked me.

Finally at the summit. While only 3:28 elapsed moving time, it had taken me over 6 hours to get here. It was quite breezy, air temp in mid-60s, and all the clouds had burned away.

Found the peak register. Please, the next person summiting bring a fresh notebook. McEntee improvised with a couple of scraps of cardboard, on which I added my arrival.

The ammo box with peak register is about 15′ south of the benchmark itself. Inside the ammo can is a two-way FRS radio, some spare alkaline batteries, and a disposable lighter. Forgot to try the radio or lighter to see if either still worked.

Views, as others have pointed out, are great, and even on a somewhat windy and hazy day like mine, Pinal, The Flatiron, Four Peaks, the endless Mogollon rim, and the San Franciscos were plainly visible. Two panorama views are this one generally from south through west to north, and the second completing the circle.

Did not spend a lot of time atop the mountain. Already exhausted, I was glad that I’d started early, and that there were five more hours to sunset. After a bit of rumination, I chose to descend via the route that Kassan had taken in his assent; it was  only 4.9 miles to the  trailhead via the Shake Tree trail.

Jumpin’ bejeezus, the south side was tough. Manzanita forests, parsed only by repose-angle rivers of rockfall. Again, from Kassan’s assent notes, cliffs were avoidable; dropping the almost 2000′ to the Shake Tree required no dangerous exposures, no more than maybe a 6′ drop or ten, and sometimes even a cairn would show up, providing tantalizing evidence that other bipeds had been there.

I am really glad that I was wearing my standard hiking costume: long pants, long-sleeved shirt, and the broad-brimmed hat with neck drape.  And I checked every once in a while that I could get into one of the distant amateur radio repeaters in case something bad happen. And really weirdly, the AT&T coverage remained generally ok.

It took three hours to get down the 2000′. I was hammered. I was falling more than I was walking! The manzanita forests were dense, with painful scrub oak undergrowth. And hidden everywhere were cacti and yucca. Oh, and it definitely looked like there was poison oak.

The iPhone’s GPS didn’t have the necessary sensitivity to give me a position fix to know where I was relative to the Shake Tree, but I finally picked a wash to descend, knowing that I’d meet the trail eventually. At 1610, in the pine forest, I arrived at what appeared to be a real trail. The realization that I was on the Shake Tree came, when in a dense canopied area I saw what looked to be a trail, at the right elevation, and especially because someone had left atop a big rock a large plastic bag of Spitz sunflower seeds. I dumped the seeds on the ground, for the gentle woodland creatures, and put the empty bag in my trash pocket.

The rest of the return was on the Shake Tree, and while not as nice as the Barnhardt, it was way better than no trail at all. Made it back to the vehicle at 1812, for a total trip time of 11:43 and total elevation gain of 4840′.

My boots finally blew out on this hike, the tread had just about gone but the outer inner cloth of the left foot, just above the leather, got shredded. Was a combo of 150 – 200 miles on the boots over hard Arizona desert, and the manzanitas, thorns, and rocks on this trip. Have a brand new pair in the back of the truck just waiting to get dirty.

While I did it, and I returned to tell the tale, this is one of those hikes that will take a while before the pain fades and instead I remember fondly.

Summiting Woolsey Peak 10FEB18

4375′ elevation – clean prominence: 2333′ – isolation: 31.3 mi

GPS log available at peakbagger link above.

Time-lapse video of drive off pavement

No radio sites, just a nice, challenging, quiet hike on a somewhat cool and breezy day.

Looking up at Woolsey from the northside trailhead.

There are sheer cliffs and difficult escarpments everywhere.

The way up is to pick the right river of lava boulders and other detritus.

However, it’s not easy a priori to know the best route. Boulders can be loose, and i stepped on one, it rolled, and I crash-landed.

Lava-rock-boulder rivers near or at angle of repose. While a 2′ size boulder appears to weigh a lot, putting one’s weight into it for purchase can cause it to shift or break loose.

This is the true Gila Peak (Woolsey Peak) benchmark.

From the top of the mountain looking due north. The vertical beige strip is the final section of the dirt road with the trailhead at the bottom (south) end. The rivers of lava rock are punctuated with bunch grass.

Another view north.

From the false peak.

Looking to the west from the benchmark.

Somebody disposed of a lead-acid car battery here a long time ago. What it was powering up here on the summit is a mystery.

From that battery, bits of lead plate everywhere.

Another view to the north. The trailhead is at the close end of the road below. The nice thing is one can see the trailhead and their vehicle pretty much all the time during the hike. Of course, if something bad happens down at the trailhead, there’s not much one can do from this vantage other than watch, unless one has a very powerful rifle %^)

View to the east from the benchmark; White Tank to the left and the Sierra Estrella to the right.

Looking SW from the benchmark.

Some kind of spiritual thingee, maybe for Pastafarian get-togethers?

Looking to the SE over many lava-flow ridges. Table Top is on the horizon to the left of center.

The White Tank mountains are way off in the distance.

The back side of the Sierra Estrella range; the characteristic shape of Sierra Estrella high point is quite distinctive.

One of the BM locations, desert varnish and graffiti.

One of the peak registers.

Time to return to the truck. It always seems to me to be harder the do the return than the ascent; here, it was mostly boulder-hopping down the slope, keeping aim on distant horizon features to maintain the right azimuth, and paying attention to the next step to avoid boulders likely to move or the possibility of critters, none of which were seen on this trip.

While one vehicle had arrived at the trailhead, turned around,  and then left during my hike, there were no other signs of folks having been here during my time.

The drive back out to old US 80 was uneventful. Stopped by 8-Bit Ale Works on the way back for a pint.

Summiting Table Top 10MAR18

4375′ elevation – clean prominence: 2333′ – isolation: 31.3 mi

GPS log available at peakbagger link above.

Time-lapse video of drive off pavement

Kind of clandestine wireless communications site – off-grid

From the parking lot, Woolsey’s in-between the two saguaros. There was one other vehicle in the lot.

Trail register.

Timber at the top of the ascent trail. This is the SE end of the mesa.

A solar powered radio facility! And all camo’ed out.

While I do not know its purpose or owning agency, it definitely appears to be some sort of relay site, with the cheesy, wire omni antenna (even with an antenna BNC connector, who’d have thunk?), perhaps monitoring VHF high-band transmitters around the peak and relaying messages/signals from them on some UHF frequency using the directional Yagi antenna in the green radome.

Amazing that the panels are not damaged or missing.

The equipment enclosure. Must have batteries and the two radios inside.

The antenna connector at the bottom of the case. Note the green ground wire, so someone working on this has some fleeting idea of the correct insulation color for ground. However, it’s interesting that no critter has chewed through the insulation.

Honestly, I’d be so embarrassed to hoist an antenna as crappy looking as the VHF high-band omni on the right. And what’s worse, the connector used there is a BNC, definitely not rated for outdoor environments.

From the trail-top timber post, looking at the high point of Table Top. There is a very deep gulley/draw between there and here and the trail to the peak is around the east side of the mesa.

As I get closer to the true peak, a shot back toward the SE end of Table Top – the radio equipment and trail-top timber are at the right side of the ridge.

Finally, the benchmark is achieved. It’s been sprinkling lightly for the past hour.

The peak register is hidden near the benchmark. Signed in.

From the top, came back down retracing the path up.

Arrived at the truck right around sunset, by the time I made it to I-8 it was well after 1900.

No CBP or DEA observed. I’m sure that they were observing me, though %^)

volt/amp/watt/energy meters

Got another two of the inexpensive volt/amp/watt/energy meters from mfreelaa on eBay. These are pretty nice, especially for the $12 each including shipping.

I put two of them in series to see how well each tracked the other. There should be a very small drop in voltage for the second on in series as opposed to the first. That does appear to be the case.

The unit under test is pulling approximately 1-1/4 amps at 12 volts. Assuming these ammeters use 100 A/75 mV shunts (since the meters without built in shunts do the same and it’d be easier to keep them all the same) this would imply that the second meter should read about 0.001 volts lower than the first. However, the display precision is only 0.01 A so it’s not practical to see the difference with this small load.

After two hours now, both meters are showing 50 w-h, I’ll have to wait longer to see if they diverge from one another at all. The voltage (refreshed once per second) is generally within 0.02 volts, which is 0.15% agreement. The current reading is looser, maybe 0.2%. The power reading is quite close, but one would expect that the power reading comes from the multiplication of the v and i values. The energy reading is the time cumulative sum of all the power measurements.

Next project is to measure the efficiency of my new MPPT solar battery charger. Just need to have a sunny day!


Here it is the next morning and the DUT has now pulled a total of either 261 or 262 W-h, depending on the meter read. That’s still pretty good internal consistency between meters, well under 1% difference.

So, relatively speaking, these meters are pretty consistent in their performance. Perhaps one of these days I’ll set up a calibrated load to get a better handle on the absolute accuracy. But for now, just knowing that the meters are consistent allows me to do the solar MPPT charger testing.