Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
This story begins years ago, as mentioned there. I’d retrieved the offending outlet expander / extension cord from my mother’s apartment and tossed it in my big box of Extension Cords.
I recently plugged it in and was rewarded with a flash-bang inside the box. Taking it apart reveals two more blackened outlet compartments (in the lower right), but no more missing contact blades.
It turns out that the black (hot) wire got caught between a stiffening rib on the back plate and the edge of the box supporting the brass plate connecting the white (neutral) wire to the contacts. Here’s reconstructed view after I cut off the extension cord.
Crushed wire
Flipping the wire over shows the spot where the copper conductor eventually poked through the insulation.
Exposed conductor
It touched the sharp corner of the brass strip just to the left of the divider in this view. The notch in the divider channeled the jet of burning debris across the far wall of the right-hand compartment. The left-hand compartment is completely smudged.
Short-circuit point and debris jets
Looks like I get credit for this one… but even seeing how I did it, I’m not sure there’s any way to know none of the wires got crushed while reassembling the box.
It’s safely in the trash and the cord is in my big box of Random Power Cords.
Memo to Self: Make sure the box fits together smoothly?
Here’s the status of the AA NiMH packs I’ve been using with the radios on our bikes, plus three packs I made up last year and have been keeping on the desk to measure their long-term storage characteristics. Click for more detail.
Bike Radio Pack Status – 2010-03
The “Tenergy 09 x” packs are new & unused with, frankly, disappointing capacity of about half their 2.6 Ah rating. That’s not much better than the used Tenergy packs (T9x and RTU x), which is either a Good Thing (they have good long-term stability) or a Bad Thing (they’re grossly over-rated to begin with).
The two Duracell packs are far better than any of the Tenergy packs.
The three 6-cell packs along the bottom are fading fast.
The previous test runs are there, albeit with a 1 A discharge.
This season I’ll use some Li-Ion packs that weigh twice as much with three times the capacity… plus a built-in charge gauge, pessimistic though it may be.
A comment on yesterday’s post about quartz crystal measurements prompted me to destroy a crystal in the name of science…
The question is, what effect does exposing a crystal to the air have on its performance? I would have sworn it would never work right again, because it’s normally running in an inert atmosphere and maybe a partial vacuum. One measurement being worth a kilo-opinion, here’s what happened.
I picked random crystal from the bottom of the crystal box, based on it having a solder seal that I could dismantle without deploying an abrasive cutoff wheel or writing some G-Code to slice the can off with a slitting saw. The crystal was labeled HCI-1800 18.000 MHz and probably older than most of the folks who will eventually read this… younger than some of us, though.
The center frequency is 18.0050 MHz (at this rather broad span) and it has some ugly spurs out there to the right.
A closeup of the series-resonant peak:
HCI-1800 18 MHz – Baseline BW
The bandwidth is 1.50 kHz at 17.99950 MHz at this span.
Naked HCI-1800 18.0 MHz Crystal
Then I applied a soldering iron around the seal and yanked the case off. I think that didn’t involve whacking the crystal with the case en passant, but I can’t be sure. In any event, it looks undamaged and seems to operate properly.
A pair of spring clips attach to the electrodes and hold the quartz disk in position. They’re just the cutest little things and quite unlike the other holders I’ve seen. I think the solder blobs fasten the spring ends together and don’t bond to the electrodes, but what do I know?
HCI-1800 Crystal Overview
The quartz disk has a few small chips near the edge:
HCI-1800 Crystal Edge Chips
I think those are Inherent Vice… simply because:
They’re not in a position where I could have whacked the disk and
I doubt I could whack it that delicately
Anyhow, with the can off, here’s what the series resonant peak looks like:
HCI-1800 18 MHz – Opened BW
The resonant frequency is now 17.99968, 180 Hz higher, which may be due to instability in the HP8591 spectrum analyzer’s not-stabilized-for-ten-hours ovenized oscillator. The bandwidth is 1.55 kHz, 50 Hz wider, although I think that’s one resolution quantum of difference.
Here are the two bandwidth traces overlaid.
HCI-1800 18 MHz – Overlaid BW
The peak has been centered in both, so you can’t tell they’re slightly different. The interesting point is the difference in the slope to the low-frequency side of the peak, which is slightly higher for the open-case condition. Seeing as how the missing case completely changes the usual stray capacitance situation, I’m not surprised.
Anyhow, I admit to being surprised: there’s not that much difference after opening the case. I’ll put the naked crystal in a small container in a nominally safe place for a while, then retest it to see what’s happening.
Memo to Self: A “safe place” is nowhere near the Electronics Workbench!
Here are some other naked crystals:
Naked Crystals
Notice the tarnished (presumably) silver electrodes on the crystal in the lower left. That one’s been sitting on my monitor and in other hazardous locations for a few years. I can’t find these anywhere right now, but if they turn up I’ll test them, too.
Spent some Quality Shop Time measuring an assortment of crystals, some data from which will make up a Circuit Cellar column.
And the raw numbers will come in handy one of these days, so here they are…
12 MHz Asst
HC-49/U
Co+Cc/2
2Cc
Fs
BW
Rs
ECS
1
4.85
1.47
12.000162
787.5
40.1
ECS
2
4.50
1.42
12.000150
725.0
40.1
ECS
3
4.70
1.42
12.000325
1100.0
50.0
Rs out of range
HC1
4
4.34
1.11
11.999000
600.0
36.0
HC1
5
4.24
1.06
12.000137
537.5
36.9
Sentry
6
5.14
0.96
12.000250
625.0
31.8
many spurs
11.0592 MHz
HC-49/U
1
4.90
1.42
11.059275
562.5
9.3
2
4.99
1.46
11.059112
575.0
14.7
3
4.87
1.42
11.059275
512.5
9.6
4
4.87
1.41
11.059125
550.0
10.0
5
4.29
1.43
11.058935
750.0
18.1
6
4.93
1.47
11.059000
537.5
10.7
7
4.95
1.47
11.059200
525.0
8.1
8
5.03
1.45
11.059037
575.0
11.1
10 MHz
HC-49/U
spur +150 kHz
1
2.57
1.36
9.997888
200.0
14.2
2
2.61
1.30
9.997738
225.0
16.7
3
2.75
1.30
9.997788
225.0
20.0
4
2.67
1.30
9.997750
225.0
16.1
5
2.75
1.26
9.997725
250.0
22.7
6
2.69
1.27
9.997788
225.0
21.0
7
2.69
1.26
9.997825
212.5
16.5
Circuit Cellar example
8
2.69
1.22
9.997832
212.5
18.4
9
2.72
1.24
9.997788
250.0
23.4
10
2.68
1.20
9.997738
225.0
18.0
18.43 MHz
HC-49/US
many spurs +10 +76 kHz
1
3.86
1.33
18.432425
1.56
24.1
2
3.79
1.22
18.432987
1.21
10.9
3
3.93
1.39
18.432050
2.44
46.3
4
3.97
1.40
18.431175
1.90
27.7
5
3.89
1.33
18.431888
2.11
32.2
6
3.92
1.39
18.430888
1.39
16.5
7
3.99
1.35
18.431500
1.36
11.8
8
3.97
1.35
18.431675
2.18
38.4
9
3.95
1.31
18.430512
1.30
10.1
10
4.04
1.50
18.431427
1.36
11.8
The 18.43 MHz crystals are in the short /US cans with surprisingly high stray capacitance. Their bandwidths are in kHz and all over the map, as are the series resistances. Weird. Bad crystals? Bad technique?
Frequency & bandwidth from HP8591 spectrum analyzer with a fixture similar to the K8IQY design; the bandwidths seem to come in 12.5 Hz increments despite a (very narrow) 2 kHz span. The general process is there. Resistance measured from a cermet trimpot using a multimeter good for 0.1 Ω around 10 Ω.
Crystal Test Fixture
Useful equations, with column headings in boldface:
Lead-to-can capacitance for each lead: Cc = 2Cc / 2
Lead-to-lead capacitance: Co = Co+Cc/2 – Cc/2
Circuit Q: Q = Fs/BW
Circuit resistance: R = Rs + 25 (assuming 4:1 transformers)
Herewith, the discharge test results for all the generic Sony NP-FS11 battery packs I have (click for a bigger image).
Sony NP-FS11 Status – 2010-04
The five mostly overlapping upper traces consist of:
Three packs (H, K, and L) rebuilt from the eBay junkers
F rebuilt from a deader in my collection
E is an older, no-name pack that just continues to work
The rebuilt packs now have cells from batteryspace.com that are working fine: nominal capacity 600 mAh, actual around 1200 to 1400 for a parallel pair. It’s surprising to see a cell producing its rated capacity…
The two lowest traces (G & I), plus the purple trace (J) are from the eBay source. The first two are obvious junk, but pack J is actually pretty good. The fact that it’s the best of six packs from that vendor tells you all you need to know about their QC.
For those of you joining us via search engines, the rest of the story:
Finally got around to hacking PowerPoles into the coily cable from those Li-Ion packs, suitable for powering the amateur radio HT on my Tour Easy. The cable has surprisingly fat conductors, on the order of 22 AWG, that (when doubled over) half-filled the 30 A PowerPole terminals. I remembered to use the blue-and-black color code for 9 volt power on the second and third cables…
The right-angle connector activates a switch that turns on the pack’s voltage regulator, which means that leaving the cable plugged in slowly discharges the battery. They self-discharge by about half in two weeks, which means that it’s not absolutely urgent to unplug the battery at every stop, but … I’d rather have an actual power switch.
I also want to bypass that regulator, so as to get more voltage out of the pack. That may not be feasible, as I suspect they’re using the pass transistor as part of the over-current shutdown circuit, but it’ll be interesting to find out. So this is in the nature of a test to find out how well the lashup works before cracking the case.
This view of the installed pack is looking down on the butt end of the bike, which is leaning against the Shelf O’ Crap in the garage.
Battery on Tour Easy Rack
A four-inch length of adhesive-backed Genuine Velcro mates the battery to the rack, although I stuck both Velcro strips to some carpet tape in the hopes that’ll stick better than the OEM goo. Hooks on the bike and loops on the battery, which means the battery won’t affix itself to everything else in the universe while off the bike.
So I dismantled the three junk packs I got from halfway around the world and rebuilt them with better-quality cells. Search for NP-FS11 and you’ll find the rest of the story.
Some observations…
These cases are the thinnest plastic that doesn’t actually break when you pick it up: to crack the case seam, you must push firmly. Two of the three packs were already cracked and the third yielded to a slight squeeze.
The cells are labeled Sony Energytec, which ought to be a reputable brand name. Some possibilities:
Counterfeit cells
Quality test rejects
I don’t know why you’d bother putting counterfeit cells inside a generic case; it’d be more profitable to sell a completely counterfeit battery with a fancy Sony label. So I’m guessing these came from a batch of cells that failed inspection and were miraculously saved from destruction.
Battery Protection Circuit Board
They have the usual protection circuit board on the top. What’s a bit tricky is that you must unsolder the three leads connecting to the case terminals before you can extract the cells. I unsoldered the strap from the negative terminal while I was at it; the positive lead is inaccessible beyond the black IC on the left.
The Smell of Molten Projects in the Morning 