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
Spiders know how to handle much larger prey:
Apparently the stink bug’s armor doesn’t count for much when the spider has the luxury of attacking through a weak spot in the underbelly after the critter stops struggling.
Stink bugs cause considerable damage to crops (notably apples) in the Hudson Valley, but they haven’t been the existential catastrophe we all expected when they first arrived.
The UPS coddling the M2 printer began complaining about a bad battery, so I ran (nearly) all the UPS batteries through the tester:
The two blue flubs in the lower left come from the failed battery, with the dotted trace after charging to 13.7 V and letting the current drop to 20 mA.
The red and green traces come from two other UPS batteries installed in 2016, with the dotted traces after charging similarly. The orange-ish trace is from the battery in a Cyberpower UPS bought in 2016, so it looks like all batteries of that vintage fade equally.
Except for another pair of batteries in another UPS that had discharged stone cold dead; it may have been shut down and unplugged during a power outage and they never quite recovered.
After five years, it’s time to refresh the fleet …
The Sony HDR-AX30V helmet camera puts far more demands on its battery than the Planet Bike Superflash:
The four traces on the right show the BatMax NP-BX1 lithium batteries (cells, really) originally stored about 3 W·h when they arrived in March 2020. The four solid traces to their left show the capacity dropped to a little over 2 W·h after two riding seasons. Batteries B and C started out above average and are now below, for whatever that means.
The red dotted trace shows the effect of not using the NP-BX1 test holder for that length of time; those homebrew contact pins apparently needed some exercise.
Having replaced the Planet Bike Superflash on Mary’s Tour Easy with a 1 W red LED, testing the eight Panasonic Eneloop AAA cells that have been powering it (and the one on my bike) for the last four years seemed useful:
The sheaf of curves over on the right came from the first full charge, with the untidy collection below them show the current state after a full charge. This is at an unreasonably high 500 mA discharge.
The overall capacity has dropped by 10%, which isn’t all that bad, but the 10% voltage reduction toward the end of the curves is a Bad Thing for an LED flasher intended to run from 1.5 V alkaline cells. In practice, I recharge the batteries once a week while they are still going strong, but the difference between alkalines and NiMH cells is obvious even at full charge.
Now I can run four pairs through the aging Superflash on my bike …
There’s just enough slack in the LED wiring to clip a Tek current probe in there:
Which reveals the LED current waveform:
The LED is on continuously, except for the two 75 ms Morse code dits in the upper trace.
The lower trace shows the current ramping up at the end of the first dit, from zero to 400 mA in 1.5 ms.
Clamping the probe around the 6.3 V power supply lead:
The supply current includes maybe 20 mA for the Arduino running the Morse code program and the current ramps up from there to about 250 mA when the LED is on.
The LED drops 2.6 V at 400 mA, so it dissipates a smidge over 1 W. The 2.0 Ω current sense resistor (3.3 Ω in parallel with 5.1 Ω) dissipates 800 mV × 400 mA = 320 mW.
The dissipation from the Bafang headlight output, including the Arduino, is 1.6 W.
The running light ticks along at the hot side of comfortably warm on the Electronics Workbench and runs barely warm in free air out on the bike, so I’ll define it to be Good Enough™.
I passed another dead deer on New Hackensack Rd while hauling groceries home:
The next day I walked past the other side of the collision at the corner gas station’s dead car collection:
A closer look at that nice rounded dent links the two contestants:
The impact didn’t blow the airbags, so maybe the car isn’t a total loss, despite extensive front end damage and some scrap metal inside the engine compartment.
As far as I can tell, Vassar College has been holding a deer cull every January, but taking out a few dozen deer definitely hasn’t eliminated the road hazard. If the folks objecting to the cull set up a fund to help drivers damaged by the objects of their affection, it’d demonstrate their understanding of the problem.
With the amber daytime running light connected to the Bafang’s headlight output and the Anker flashlight on the other side of the fairing getting fewer power-on hours, it’s a good time to see how those four Tenergy lithium 18650 cells are doing:
The overall capacity is down by 10%, with the voltage depressed by 120 mV over most of the curve.
Although I don’t keep daily records, the back of the envelope reveals 150 to 200 hour-long rides per year during the last four years, so call it 700 charging cycles:
High brightness draws 1.5 A and low is 50% duty cycle, so a typical ride requires 750 mA·h = 2.5 W·h. Each cell lives for three or four rides with the LED set to low brightness and the numbers work out close enough.
