Is that because of internal resistance of the battery, or some other effect?
Yes, it's due to internal resistance.
Readit Newsinvalidator commented on Why your outdoorsy friend suddenly has a gummy bear power bank theverge.com/tech/781387/... · Posted by u/arnon
invalidator commented on Why your outdoorsy friend suddenly has a gummy bear power bank theverge.com/tech/781387/... · Posted by u/arnon
That's a bit cursed mental model tbf... The voltages of batteries, in the first place, is function of state of charge. 100% = 4.2V, 0% = ~2.7V, 50% is 3.7V(by volume or something. 2.7 is also technical absolute minimums, cutoff voltage is usually more like 3.2V. Please don't abuse the battery in the ranges between 3.2 to 2.7V, let alone below).
Charge/discharge current capacity is constant throughout, at least so battery manufacturers say, at 1-20x the amp-hour capacity depending on the cell. Usually 5x or less.
Since energy = voltage x current, instantaneous W capacity is higher at first, reducing as it becomes supply side limited rather than load side limited.
But all those is irrelevant to why everyone uses mAh, it's because products with biggest numbers sell fastest. Marking capacity in Wh is noble, but it's a clearance worthy sin if you ask the shelves.
> The voltages of batteries, in the first place, is function of state of charge.
It's also a function of the rate of discharge. Have a look at this:
https://marsen.com.au/wp-content/uploads/2021/08/Panasonic-N...
All that space between the black and green curves is energy being lost to internal resistance.
invalidator commented on Why your outdoorsy friend suddenly has a gummy bear power bank theverge.com/tech/781387/... · Posted by u/arnon
Man it drives me crazy when people/products use Ah instead of Wh as a way to specify battery "capability".
Without knowing more details about the battery, "20Ah" alone does not convey enough information to determine how long the battery could power a given load for. If I need to power a 100 watt lightbulb, will a 20Ah battery power it for an hour? 10 hours? 10 days? No way to know.
Wh is the unit of stored energy, Wh is what I want to see. Even the official Amazon product page for it doesn't list a Wh figure.
There's a technical reason for it: the voltage sags when the battery is discharged quickly. Ah is relatively constant, but Wh decreases significantly with faster discharge rates, so it can't specified as a single figure.
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invalidator commented on Preliminary report into Air India crash released bbc.co.uk/news/live/cx20p... · Posted by u/cjr
The one thing automatic system failure theory can't explain is whether there is a reverse connect from the machine back to the switches where if the machine decides to cut off fuel, would the physical switches toggle to cut-off or stay in run position while the fuel is actually cut off, this would require an actuator setup to flip the switches from inside the system which there is no documentation of if that is even support let alone reported?
They are simple toggle switches without actuators. The switches are Honeywell P/N 4TL837-3D. Source[1]. Data sheet[2].
[1] https://ad.easa.europa.eu/blob/NM-18-33.pdf
[2] https://www.mouser.com/datasheet/2/187/honeywell_hwscs06627_...
invalidator commented on Preliminary report into Air India crash released bbc.co.uk/news/live/cx20p... · Posted by u/cjr
Are we not in agreement?
MCAS overrode the inputs and the thumb switches could override MCAS?
MCAS autonomously adjusts trim downward. The trim switches override MCAS, but when released, MCAS can resume trimming down again. The trim adjustments don't "override" the pilot's elevator inputs (MCAS has no direct control over the elevators), but they can make the controls so heavy that it's impossible to pull up.
I went Yak shaving.
For my 3D audio project I need an affordable way to make plastic cases. I felt like injection molding services are way overpriced, so I decided to make the molds in-house. Turns out, CNC milling is overpriced, too. As are 5 axis CNC mills. So in the end, we built our own CNC machine.
And like these things always go, I found an EMI issue with my power supply and a USB compliance bug in the off-the-shelf stepper control board. But it all turned out OK in the end so we now have the first mold tool that was designed and machined fully in-house. And I learned so much about tool paths and drill bits. Plus it feels like now that everyone has experienced hands-on how stuff is milled, my team got a lot better at designing things for cheap manufacturing.
That's a pretty big yak to shave! Building a 5 axis that gives good results a big task. How long did it take you to get that working?
Why do you need to make so many molds?
invalidator commented on Programmers Guide to the AMIBIOS (1993) [pdf] bitsavers.org/pdf/america... · Posted by u/1vuio0pswjnm7
I should know the answer to this, but was using the BIOS the only way to interact with hardware like disks, mice, and keyboard?
I remember copying code to make wrappers for those in C from books but can't remember if that was the only option or...
I know with VGA you had to use the BIOS to set modes but you could just write to the memory which was mapped at a certain address
The BIOS was an abstraction layer. In the old days, not everything was 100% IBM PC compatible. There were lots of weird graphics cards. Some systems had incompatible disk and keyboard controllers.
There was no memory protection in Real Mode, so you could always poke the hardware yourself, but something written on a Tandy wasn't going to work on a Zenith unless you supported both, or ran everything through the BIOS.
Over time, the OS took over the HAL role, with the BIOS only being used until the OS could load native drivers. Now it's UEFI... same idea with a higher greater level of abstraction and modularity.
invalidator commented on Legendary Bose Magic Carpet Suspension Is Finally Going Global thedrive.com/news/legenda... · Posted by u/PaulHoule
It's really smart though: Why spend a lot of energy moving the wheel up and down, when you can just control the damper and rely the spring to store energy.
It's not the same.
For a simple example, let's say you are simply driving in a circle. The car wants to lean toward the outside. The linear motors can provide a countering force, lifting the outside, lowering the inside, so the car stays level. Variable damping can only control the rate that it rolls. It will still roll in sub-second timescales, unless it completely locks down the suspension, which is terrible for both handling and comfort.
For another simple example: going over a speed bump. Linear motors can lift the front wheels over the bump, and then the rear wheels, so the body stays level the whole time. An active damper can go full-soft the moment the wheel hits the bump, but the compressed spring will still start lifting the front of the car. An active damper can do a better job managing the rebound on the far side so it doesn't oscillate, but it can't entirely prevent the bump from pitching the body up and down in the first place.
That's not to say it's worthless. Very fast active dampers can improve both handling and comfort. It's just nowhere near the level which is possible with linear motors.
I don't think you can reliably fix a specific version of a package though, meaning things will still break here the same way they did before containers.
If you want to lock down versions on a system, Apt Pinning: https://wiki.debian.org/AptConfiguration#Using_pinning
If you have a herd of systems - prod environments, VMs for CI, lots of dev workstations, and especially if your product is an appliance VM: you might want to run your own apt mirror, creating known-good snapshots of your packages. I use https://www.aptly.info/
Containers can also be a great solution though.