Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Just before Tropical Storm Isaias rolled through, my hygrometer reached a new high:
Pre-Isaias humidity
The National Weather Service reported 99% at the airport a few miles away, so the meter’s calibration seems about right.
Shortly thereafter, the humidity dropped to the mid-70s as the wind picked up and, over the next few hours, falling branches took out vast swaths of Central Hudson’s electrical infrastructure. My little generator saved our refrigerator & freezer during 15 hours of outage; three days later, thousands of folks around us still have no power.
A confluence of other events, none nearly so dramatic, will throttle my posting over the next two weeks.
Being the type of guy who uses metal bits & pieces, I thought this might be a useful aluminum rod:
EonSmoke vape stick
It turns out to be an aluminum tube holding a lithium cell and a reservoir of oily brown juice:
EonSmoke – peeled open
The black plastic cap read “EonSmoke”, which led to a defunct website at the obvious URL. Apparently, EonSmoke went toes-up earlier this year after ten years of poisoning their customers, most likely due to “competitor litigation”.
The black cap held what looks like a pressure switch:
EonSmoke – switch
Suck on the icky end of the tube to activate the switch, pull air past the battery (?), pick up some toxic vapor around the heater, and carry it into your lungs:
EonSmoke – reservoir heater
Maybe there’s a missing mouthpiece letting you suck on the icky end, activate the switch, pull vapor through the heater, and plate your lungs with toxic compounds. I admit certain aspects of my education have been sadly neglected.
The lithium cell was down to 1.0 V, with no overdischarge protection and no provision for charging, so it’s a single-use item. I’m sure the instructions tell you to recycle the lithium cell according to local and state regulations, not toss it out the window of your car.
Back in the beginning of July, I replaced the NP-BX1 battery in the RGB Piranha astable multivibrator with a 18650 lithium cell and a USB charge controller, then watched it blink for the next two weeks on the first charge:
Astable – 10 11 12 uF tweak – 027
However, the blinks looked … odd and some poking around with a Tek current probe showed the red and blue astables had locked together, so they blinked in quick succession. Alas, I don’t have a scope shot to prove it.
I built all three astables with the same parts, figuring the normal tolerance of electrolytic caps would make the astables run at slightly different rates, which they did at first.
This being a prototype, I just soldered a 1 µF cap onto the blue channel’s existing 10 µF cap:
Astable – 11 uF cap – detail
You can barely make out the top of the additional 2.2 µF cap on the red channel, through the maze of components; now, they definitely have different periods.
Aaaand the scope shot to prove it:
Astable NPN – 10 11 12 uF tweak – 10 mA-div
The bottom trace shows the battery current at 10 mA/div. The first pulse, over on the left, has the red and blue LEDs firing in quick succession with some overlap, but they separate cleanly for their next pulses.
You don’t want to build a battery-powered astable from NPN transistors, because the 8 mA current between blinks is murderously high. In round numbers, each of the three LEDs blinks twice a second for 30 ms at 20 mA, so they average 3.6 mA, less than half the current required to keep the astables running between blinks. Over the course of 14 days, the circuit drew 11.6 mA × 336 hr = 3900 mA·h until the protection circuit shut it down.
I must conjure a holder with contacts for an 18650 cell, support for a trio of 2N7000 MOSFET astables, and some kind of weird spider with the RGB Piranha LED on the top. Even a harvested 18650 cell should last a couple of months with a much longer blink period (500 ms is much too fast), less LED current (this one is shatteringly bright), and a lower average current.
And, yeah, I’ve been misspelling “Piranha” for a while.
The pile of 18650 3P blocks over on the right are some obviously corroded deaders and the lowest performers from these tests:
Harvested 3P 18650 Packs
I doubt they’ll get recycled, as there’s entirely too much overhead involved in dismantling boxes full of cells like these, but I hope they’ll get a decent burial somewhere.
A recent email conversation may prove relevant to someone else …
I have a pole barn which has approximately 100′ run of 10 gauge copper supplying power to the building. I … did not care to pay … $12,000 for a new 200′ line from the road … [with] only lights and 2 door openers for demand.
I … put a 30 gallon air compressor in […]. When I first put it in, it struggled to start @<40 F. They called it a 1.6 running h.p. (whatever that means) motor. Nameplate shows 15/7.5 F.L.A. I switched it to 240v and the problem went away.
Aren’t I likely to get the same problem as I had before or do 240 volt motors start easier?
I screwed up when they buried the wire – in retrospect I would have buried 6ga to the barn to lessen the voltage drop.
After running a few numbers, here’s what I came up with …
do 240 volt motors start easier?
The trouble with motors is they draw far more current while starting than they do while running. A factor of ten more is a good rule of thumb.
So a “1.6 running HP” motor draws 1.2 kW while running at full load: – 10 A at 120 V – 5 A at 240 V
The “full load amps” will be higher than that, because the motor isn’t 100% efficient. You can plug the FLA values into the calculation for an even more depressing result.
During the fraction of a second when it’s starting, however, it will (try to!) draw 100 A or 50 A, depending on which line voltage you’ve wired it for.
100′ run of 10 gauge copper
That’s 200 feet of wire out-and-back.
Look up the resistance per foot in a wire table, finding 10 AWG wire has a (convenient!) resistance of 1 mΩ/ft, so a 200 ft length has 0.2 Ω of resistance:
– A 10 A load drops 2 V – A 5 A load drops 1 V
Both of which are survivable in normal operation at their respective line voltages.
However, the motor starting currents will be completely different. A 100 A current will (try to!) drop 20 V, reducing the line voltage to 100 V and stalling the motor. Running the motor from 240 V means the 50 A starting current drops only 10 V and the remaining 230 V can get the motor up to speed.
Now, 240 V service isn’t a complete solution. The new compressor draws 15 “full load amps”, so it’ll drop 3 V while it’s running and 30 V while starting. It’ll probably start at 210 V, but it may grunt for a bit longer than you like as the speed comes up and the current goes down.
in retrospect I would have buried 6ga to the barn
There’s a Pennsylvania Dutch saying: “We grow too soon old and too late smart.” [grin]
The voltage (yellow) and current (green, 100 mA/div) waveforms look downright tame compared to some of the other chargers!
I made a cursory attempt to crack the case open, but gave up before doing any permanent damage. Hey, that UL listing (and, presumably, the interior details) means they’re three times the price of those Anonymous chargers!
The Smell of Molten Projects in the Morning 