The Smell of Molten Projects in the Morning
Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
If you measure something often enough, it becomes science
Mary found another tree frog while picking Savoy lettuce for breakfast:
They’re much better camouflaged in their (more or less) natural surroundings, so I didn’t spot it at first, either.
They really are cute little gadgets:
This is only the fourth tree frog she’s seen in the last two decades, but the second one in a month. It may be the same frog as before, although the garden now has a rather husky resident snake who seems to be eating well.
After a few days of riding, the Bafang 500C display on Mary’s bike gives the battery status:
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.
Canada Geese seem primed to travel in a straight line, whether in the air, on water, along a rail trail, or even on a sidewalk:
They proceed around corners in an orderly manner:
But they completely ignore crosswalk markings:
We think two goose families joined forces for this outing: four large geese and seven goslings by our count.
The sidewalks sport a rich assortment of goose poop, so the geese obviously enjoy their hikes.
The truck side marker lights I’m thinking of using as daytime running lights have a pentagonal lens, so they should have a pattern with a bright central beam surrounded by five lobes. The one on Mary’s Tour Easy produced an oddly shaped blotch on the garage wall, so I ran the others though a simple test setup:
The lights sit horizontally in a small vise to keep them level and in the same position, although in no particular rotational orientation, and 100 mm from the graph paper. It’s running at 6 v to keep the brightness down enough to avoid blowing out the image. All of the images were exposed based on the central spot, so the surrounding paper gives some idea of the relative brightness: darker paper = brighter LED spot.
The front view of the lights comes from the stereo zoom microscope, with the wires gripped in a Third Hand and rotated to put the (inverted) TOP label where you’d expect it. They’re all roughly at the same position and pretty nearly lined up with the lens axis. The bubble-looking thing behind the central pentagon is the lens on the Piranha LED package, which should be centered but rarely is. You can see the dark orange square of the amber LED chip in some of the pictures.
Without further ado, the nine truck side marker lights that aren’t on her bike:
Side Marker E has a blob that looks like a cataract atop the LED lens, but it might be a mold imperfection.
Obviously, paying a buck a light doesn’t get you much in the way of build quality these days.
Plotting current against voltage for the amber truck side marker lights produces the expected straight-ish line:
The slope suggests a 330 Ω resistor, but the internal PCB sports a pair of 150 Ω SMD resistors.
I don’t believe the X-axis intercept for a moment, but 1.5 V seems about right for an amber LED.
Oh, and the DMM fuse doesn’t have a ceramic body. You’re seeing the vaporized remains of a 315 mA fuse neatly deposited over the inside of the glass tube after being shorted across a 3 A bench supply.
I hate it when that happens. Replacing it emptied the little bag of those meter fuses; next time it’ll get a half amp fuse.
Although Gee’s Terry Symmetry is sized for female bodies, I managed to ride it up and down the driveway while watching the power display:
| Voltage | 52.5 | ||||
| Rated Current | 24 | ||||
| Max current | 18 | ||||
| Power | Power | ||||
| PAS | Assist | Amp | Calc | Observed | Ratio |
| 0 | 0% | 0.0 | 0 | 0 | ~ |
| 1 | 4% | 0.7 | 38 | 26 | 69% |
| 2 | 6% | 1.1 | 57 | 52 | 92% |
| 3 | 9% | 1.6 | 85 | 78 | 92% |
| 4 | 13% | 2.3 | 123 | 104 | 85% |
| 5 | 20% | 3.6 | 189 | 182 | 96% |
| 6 | 30% | 5.4 | 284 | 258 | 91% |
| 7 | 50% | 9.0 | 473 | 453 | 96% |
| 8 | 85% | 15.3 | 803 | 675 | 84% |
| 9 | 100% | 18.0 | 945 | 900 | 95% |
The variations in the last column suggest my data-taking is … wobbly, at best.
I think the displayed power does not come from actual current and voltage measurements, because recalculating the power using the nominal 48 V battery value produces an unnatural agreement:
| Voltage | 48 | ||||
| Rated Current | 24 | ||||
| Max current | 18 | ||||
| Power | Power | ||||
| PAS | Assist | Amp | Calc | Observed | Ratio |
| 0 | 0% | 0.0 | 0 | 0 | ~ |
| 1 | 4% | 0.7 | 35 | 26 | 75% |
| 2 | 6% | 1.1 | 52 | 52 | 100% |
| 3 | 9% | 1.6 | 78 | 78 | 100% |
| 4 | 13% | 2.3 | 112 | 104 | 93% |
| 5 | 20% | 3.6 | 173 | 182 | 105% |
| 6 | 30% | 5.4 | 259 | 258 | 100% |
| 7 | 50% | 9.0 | 432 | 453 | 105% |
| 8 | 85% | 15.3 | 734 | 675 | 92% |
| 9 | 100% | 18.0 | 864 | 900 | 104% |
The motor controller may measure the actual winding currents while generating the BLDC waveforms, but the values may not be available to the display at the end of the cable. If Bafang documented the commands & responses, we’d know for sure, but they don’t.
Those assist values come from Mary’s Tour Easy, a much heavier bike than the Symmetry, but the first few levels work well in my limited tests. The highest levels may be too peppy for Gee’s normal routes, but having some serious boost in reserve can defang (hah) the worst hills.
IMO, the bike would burn rubber at the motor’s full 24 A current …
These two discrete LM3909 circuits recently stopped blinking:
The green LED (on the left) took six months to wear its pair of not-dead-yet AA alkalines from 2.7 V down to nearly zero.
The blue LED in the radome took two months to go from 1.0 V (!) to nearly zero. It didn’t start very bright and went decidedly dim along the way, but the LM3909 circuitry still managed to jam a few microamps through the LED.
In both cases, one of the cells was reverse-charged by a few hundred millivolts, although neither leaked.
Both got another set of not-quite-dead AA cells and they’re back in action.
The Smell of Molten Projects in the Morning 