The thermometer scale on the right shows 30% remaining battery capacity after 48.3 miles of riding, with the 11.6 A·h battery at 47.3 V.
For our type of riding, each 10% increment of battery charge delivers about 7 miles of range. Although we could probably get 70 miles between charges, recharging the battery at 20 to 30% makes more sense; the bike is in the garage, so why not?
Our typical 10 to 15 mile rides now average 12+ mph, with some level sections ticking along at 18 mph (giving me some serious exercise), which isn’t much by pro rider standards.
Computing the lithium battery charge state by measuring its voltage isn’t particularly accurate, but it’s about as good as you’re going to get.
This being the season of lights, I deployed some outlet timers to turn them on at dusk and off at bedtime. The timers spend much of the rest of their lives plugged into outlets in the Basement Laboratory to keep their internal NiMH backup batteries charged, although they’re not controlling anything:
This one is labeled ENOVER, but it’s essentially identical to all the others sporting random alphabetic names; I have a few more labeled UKOKE in the same plastic case. The current crop uses a different case and has one fewer button, but don’t expect any real difference.
One of the timers had a blank display and didn’t respond to button pushes or a pin punch poked in the RESET hole, so I dismantled it to see what was inside.
Both the hot and neutral terminals had stray wire strands:
The power board had the usual missing components, suggesting it had been cheapnified after passing whatever regulatory inspection it might have endured to get a CE mark on its dataplate:
The alert reader may have already noticed the mmmmm smoking gun:
Incredibly, Z1 has a part number wrapped around it! A quick lookup shows a 1N4749A is a 24 V 1 W Zener diode, neatly matching the 24 V relay. The datasheet gives a 10.5 mA test current and a 38 mA maximum regulator current, with a caveat: “Valid provided that electrodes at a distance of 10mm from case are kept at ambient temperature”
The relay datasheet says 8.3 mA nominal coil current, a mere 200 mW, which is much easier to dissipate in wire wrapped around a steel core than in a little diode.
Evidently the poor diode ran rather hot before becoming a dead short, because a phenolic PCB (definitely not at ambient temperature) ought not discolor like that.
Indeed, measuring Z1 in another, still functional, Enover timer showed 25 V and a similarly discolored patch around Z1, suggesting the circuit design requires a bit more disspation from the diode than it can comfortably deliver.
I replaced it with a 1N970B from the Basement Laboratory Warehouse, rated for only 0.5 W in a seemingly identical case, buttoned the whole thing up, and left it in the middle of the concrete basement floor overnight. It wasn’t smoking and continued working in the morning, so I defined things to be no worse than before and declared victory.
Should when the next one fails the same way, I’ll epoxy a small heatsink to that poor diode and its leads to reduce its overall temperature.
For future reference, the underside of the PCB shows a distinct lack of post-soldering flux cleanup:
I swabbed it with denatured alcohol, although doing so certainly didn’t make any change to its behavior.
Memo to Self: no-clean flux is a thing.
It’s worth noting no other components show signs of overheating, despite the diode becoming a short circuit, so R1 (a big power resistor) is most likely the shunt regulator’s dropping resistor and can survive the additional power.
Should the diode fail open, the rest of the circuitry will be toast.
Five years later, the digits I painted with Rust-Oleum Rusty Metal Primer have weathered pretty well, while the original ink has fallen off the retroreflective sticker:
As before, I wiped off the crud with denatured alcohol and painted neatly inside the lines. The other digits on both sides still look as good as the day I painted them, with only a few bubbles and nicks.
A bit of continuity testing shows the green and white data wires are also reversed, so whoever assembled the cable simply soldered the proper wire color sequence backwards onto both connectors. As long as you don’t cut the cable to reuse the connectors, it’s all good.
When you have one tester, you know the USB current. When you have two testers, you’re … uncertain.
The upper tester is completely anonymous, helpfully displaying USB Tester while starting up. The lower one is labeled “Keweisi” to distinguish it from the myriad others on eBay with identical hardware; its display doesn’t provide any identifying information.
The back sides reveal the current sense resistors:
Even the 25 mΩ resistor drops enough voltage that the charger’s blue LED dims appreciably during each current pulse. The 50 mΩ resistor seems somewhat worse in that regard, but eyeballs are notoriously uncalibrated optical sensors.
The upper line (from the anonymous tester) has a slope of 11.8 mA·h/minute of discharge time, the lower (from the Keweisi tester) works out to 8.5 mA·h/minute. There’s no way to reconcile the difference, so at some point I should measure the actual current and compare it with their displays.
Earlier testing suggested the camera uses 2.2 W = 600 mA at 3.7 V. Each minute of runtime consumes 10 mA·h of charge:
10 mA·h = 600 mA × 60 s / (3600 s/hour)
Which is in pretty good agreement with neither of the testers, but at least it’s in the right ballpark. If you boldly average the two slopes, it’s dead on at 10.1 mA·h/min; numerology can produce any answer you need if you try hard enough.
Actually, I’d believe the anonymous meter’s results are closer to the truth, because recharging a lithium battery requires 10% to 20% more energy than the battery delivered to the device, so 11.8 mA·h/min sounds about right.
The current recommendation: remain home unless and until you develop COVID-19 symptoms requiring urgent medical attention. Should that happen to me, I fully expect there will be no medical attention to be found and, certainly, all available medical equipment will be oversubscribed.
Speaking strictly as an Olde Farte looking at the data, the future looks downright grim.
On the upside, it’s amazing how little an order to remain home changed my daily routine: so many projects, so little time.