Archive for category Home Ec
2015 Subaru Forester Battery
Posted by Ed in Electronics Workbench, Home Ec on 2019-02-17
With the intent of being able to find a picture of the battery in our 2015 Subaru Forester when I need it:
The manual says the “battery type” is 55D23L, with a 48 A·h capacity.
Here in the US, we measure a battery’s physical size with “Group Size” numbers which have no relation with JIS numbers, despite some overlapping or similar numeric values. The money quote:
Definition of Group Size: The Battery Council International (BCI) assigns numbers and letters to common battery types. These numbers and letters are standards for maximum container size, location and type of terminal and special container features.
So, it’s random. Choose a retailer, feed in the automobile year / make / model, and discover I need a Group 35 battery.
The label includes “390 CCA”, which is the Cold Cranking Amps rating:
The rating refers to the number of amps a 12-volt battery can deliver at 0°F for 30 seconds while maintaining a voltage of at least 7.2 volts
So, if you’re building an automotive gadget and expect the battery to deliver something like 12 V, you’re wrong. Bonus protip: look up “load dump” to get an idea of the highest voltage.
The “20 HR 48 Ah” specifies the Reserve Capacity:
Amp Hour or C20 is an indicator of how much energy is stored in a battery. It is the energy a battery can deliver continuously for 20 hours at 80°F without falling below 10.5 volts.
So a constant load of 2.4 A would do the trick, should you leave a few lights on overnight during the summer. In wintertime, you’re on your own.
Because hell hath no fury like that of an unjustified assumption, the terminals are on the top surface toward the rear, with the positive lug on the left when you’re standing at the front bumper. That may be the “L” in “D23L”.
Long ago, I ran afoul of an automotive battery which required knowing the terminal chirality and, of course, I bought the wrong one. Now I have a picture!
Encrypted Email: What Could Possibly Go Wrong?
So this arrived from an email address similar to, yet not quite the same as, the URL of a physician’s office where I had an appointment a few days hence:
My email client is set to prefer plain text, disallow remote content, and not open attachments, so that’s as far as it got. Donning asbestos work gloves and face mask, I pried open the message and its attached HTML file with the appropriate tools and found, as expected, scripts doing who-know-what.
Called the office and, also as expected, was told my appointment time had been changed.
Showed up, mentioned it to the doctor, and was told the office must check off many boxes to demonstrate its HIPAA compliance.
Bottom line: HIPAA now requires patients (a.k.a., us) to open random attachments from random senders, all in the name of privacy.
Banks do that, too.
Tea Strainer: Tare Weight
Being a responsible consumer, I carefully measure my daily green tea dosage. A laser-cut stainless steel strainer and silicone steam cap recently arrived, with a most auspicious tare weight:
Before my Genuine IBM 5160 PC XT with an 8088 CPU, I scratch-built a Z80 “personal computer” and wrote a primitive multitasking OS. Plenty of electrons have flowed through the transistors since those days.
A great way to start the day; ya can’t make this stuff up!
Stink Bug Haven
We hung a pine-cone wreath beside the back door (a.k.a. the only door we use), replacing a Welcome sign painted on a slate tile. Of course, the tile had long provided a sheltered spot against the house siding:
Marmorated Stink Bugs and Spiders
Reports from the garden suggest Brown Marmorated Stink Bugs aren’t as damaging as they once were, perhaps because something has developed a taste for them.
We hope whatever it might be eats well this year.
Cable Ports vs. Foot Traffic
Spotted this under a counter at Panera Bread:
Power and network cables – floor plates
You’re looking downward from the edge of the communal meal countertop at the power and network cable ports in the floor. The cables snake into the counter legs and emerge at the countertop to provide AC power, USB charging, and wired network ports in addition to ubiquitous WiFi: all the conveniences of modern dining.
Alas, down at floor level, the poor cables get kicked against the edge of their cover plates, bent with no strain relief, and seem jammed under the sharp edges of the leg extrusions. I expect the connectors below the hatches also endure a nightly bath of gritty water, with bonus salt during the winter months.
And, yes, the AC power plug sits halfway out of its socket, with the blades exposed.
Multimeter Probe Cable: FAIL
Posted by Ed in Electronics Workbench, Home Ec, Machine Shop on 2019-01-04
A reasonably good silicone-wire multimeter probe set arrived last spring and has worked well enough (I thought, anyhow) for the usual voltage measurements, but recently failed while measuring a small current. We all know how this will turn out, but the details may be of some interest.
Measuring the resistance from tip to plug located the fault to the black probe, after which I poked a pin through the insulation near the plug:
Multimeter probe – diagnosis
The two leads near the bottom go to my shiny Siglent bench multimeter. Despite their similarity to the failed probes, I’m pretty sure Siglent has better QC (well, mostly).
The probe’s resistance was near zero from the tip (offscreen to the left) to the pin and megohms from pin to plug (on the right). Figuring the wire worked loose, I pulled it away from the plug:
Multimeter probe – disassembly 1
Huh.
Although I wouldn’t have trusted those probes anywhere near their alleged 1 kV rating, seeing that exposed copper-like substance was disconcerting.
Hacking off the strain relief bushing around the wire got closer to the fault:
Multimeter probe – disassembly 2
And, finally, the problem becomes obvious:
Multimeter probe – disassembly 3
Yet Another Cold Solder Joint:
Multimeter probe – cold solder joint
Pulling a black banana plug from the heap, I decided to drill a proper hole to anchor the wire:
Multimeter probe – drilling plug
Which looked like this afterward:
Multimeter probe – soldered plug
And produced a strongly mismatched pair:
Multimeter probe – repaired
Ain’t it amazing how much fun you can have for a few bucks, all delivered by eBay? [sigh]
Transistor Pricing
Posted by Ed in Electronics Workbench, Home Ec, Oddities on 2018-12-30
You can find anything on eBay (clicky for more dots):
ZVNL110A MOSFET – kilobuck eBay pricing
The key information:
ZVNL110A MOSFET – kilobuck eBay pricing – detail
For that price, I’d expect in-person hand delivery.
Stipulated: ZVNL110A MOSFETs aren’t in production and we’re buying from diminishing inventory, but (as of late December 2018) they’re still available for under a buck apiece in small quantities.
It could be a pricing algorithm corner case, a money laundering scheme, or just a typo that could happen to anyone. As the news sites put it, the seller did not respond in time for this posting …
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