Why don't resistors show their power rating on the package, always? Or at least more often.
The package is the power rating ;)
That could be an internet game: given a picture of a resistor, guess its power rating.
Why do electronic components have such odd values? (2021)
131–140 of 168 posts
Re: Why do electronic components have such odd values? (2021)
#132Earlier quoted context omitted.
In 2024, if your resistor vendor has even 5% tolerance, you need to find another vendor.
AFAIK, it used to be that parts binning was used to sort parts by tolerance. So the 5% bin wouldn't include <1% parts because those were already selected into the 1% bin in the factory and so on. Is it still like this?
you can't always bin a ±5% resistor as a ±1% resistor if its value tests within ±1%, because, as i understand it, a ±1% resistor often needs to be ±1% over its temperature range, working voltage range, and lifetime, so it has to be made differently than a ±5% resistor
if your temperature range is -40° to 85° and your resistance is +0.9% off nominal when measured at 22°, your temperature coefficient of resistance would need to be under +16 ppm/° to ensure that it was still below 1% even at 85°. a more typical tcr for ±5% thick-film resistors is +250ppm/° (see, e.g., https://www.vishay.com/docs/51058/d2to35.pdf) and so there is no hope of binning such a resistor as a 1% one
aging is another source of component value error that can prevent binning (the component value drifts over time, usually proportional to the square root of its age), and some kinds of resistors also have a significant voltage coefficient of resistance (mostly semiconductor types like carbon-film and the antediluvian carbon composition)
these phenomena sometimes lead designers to use expensive tight-tolerance resistors (±0.01% nowadays, 50¢–250¢ each) even in circuits that can easily be calibrated to handle component value error, just to keep the calibration from going off due to temperature or aging and to improve linearity
disclaimer: i'm not an electrical engineer, i just play one in ngspice
Re: Why do electronic components have such odd values? (2021)
#133This part is the thing that made me understand the numbering series: > […] Continuing this trend, rounding as needed, and we end up with the series 10, 15, 22, 33, 47, and 68. Components built to the E6 standard have a 20% relative error tolerance, and if we look at the values again we’ll see a trend. Starting with 10 again and adding 20% error we end up with 12. Moving to 15 and subtracting 20% we get… wait for it……
Seems easier to me to say they are logarithmically distributed, rounded to 2 digits. Like yes, this means that if your manufacturing tolerances are typically some percentage of the amount (more natural than an additive error) then the overlaps are nicely spaced. But a log scale means that's true for any relative allowance (manufacturing or otherwise), which is the much more natural sort. It doesn't matter if your 100…
> Seems easier to me to say they are logarithmically distributed, rounded to 2 digits.
Except that it is the tolerance overlap that allows for that specific distribution to work.
Re: Why do electronic components have such odd values? (2021)
#134Earlier quoted context omitted.
As both a sound and electrical engineer I think most high end audio electronics is bullshit. If you know what you're doing a 50 cent opamp will give you results that are beyond what a human could identify in a double-randomized blind test. Same goes for comparing two rusty pieces of wire against highly pure copper speaker cables. For some reason audiophiles will use darn massive gold (or silver) RCA connectors instea…
> For some reason audiophiles will use darn massive gold (or silver) RCA connectors instead of something like a balanced connection that would actually make sense. It's hard to find XLR (or even TRS) balanced connectors on most non-professional (=TV studios, expensive conference room setups, DJs/clubs/similar venues) equipment.
We're talking audiophiles, it's not like they're trying to cheap out.
Re: Why do electronic components have such odd values? (2021)
#135Earlier quoted context omitted.
Because there's basically no design downside to having a higher power rating than needed, aside from BOM cost. If you're ordering a bunch to have on hand, you should just order the highest power rating you're likely to need in that size. For me, that means that my 0402s are all 1/16W, 0805 are 1/8W, 1206 1/4W, etc. And all of my through-hole resistors are 1/4, because the wire stock plays well with breadboards better…
I'd be surprised to find a 1/4W 0402, you'd just about melt the solder off. Yageo claims this one is good to 3W, do you think it glows cherry red? What trace width and pad geometry do you need to push 3W into a 0.0025 ohm resistor? https://www.digikey.com/en/products/detail/yageo/PA0402CRF5P... But to your point, Digikey has >70,000 0402s in 1/16W. There are 900 rated for 0.05W, and they're all exotic high-frequency/…
> I'd be surprised to find a 1/4W 0402
Something close to this is pretty common these days; for example Vishay's CRCW-HP series are good to 1/5W in 0402 size: https://www.mouser.co.uk/ProductDetail/Vishay-Dale/CRCW04021...
Re: Why do electronic components have such odd values? (2021)
#136Earlier quoted context omitted.
Seems easier to me to say they are logarithmically distributed, rounded to 2 digits. Like yes, this means that if your manufacturing tolerances are typically some percentage of the amount (more natural than an additive error) then the overlaps are nicely spaced. But a log scale means that's true for any relative allowance (manufacturing or otherwise), which is the much more natural sort. It doesn't matter if your 100…
> Seems easier to me to say they are logarithmically distributed, rounded to 2 digits. Except that it is the tolerance overlap that allows for that specific distribution to work.
I can’t tell what you mean.
Re: Why do electronic components have such odd values? (2021)
#137Earlier quoted context omitted.
Mostly, no. Nobody except for expensive precision resistor companies are actually measuring resistors more than statistically. The resistors are manufactured so that they are "guaranteed by manufacturing" such that the outliers are 1%, 5%, 10%, etc. And they do statistical checks on batches, but not really looking for the 10% outlier (which is stupendously rare and very difficult to catch) but looking for slight drif…
They should still bin, so that each individual resistor gets the highest price possible by the virtue of its classification, even if the binning is costly.
Not if the additional cost is more than the additional revenue.
Let's assume that without binning you get 20% over cost of manufacturing. If it costs 5% more to bin-check all resistors, and you wind up selling 1% of them for an additional 100% mark-up:
No bin Bin
Cost to mfg: $ 1.00 $ 1.00
Cost to bin: .05
------ ------
Total cost $ 1.00 $ 1.05
Base price $ 1.20 $ 1.188 (99% sold at base)
Premium price 0.00 $ 0.022 (1% sold at un-binned cost x 2.2)
------ ------
Total revenue $ 1.20 $ 1.21
====== ======
Profit $ 0.20 $ 0.16Re: Why do electronic components have such odd values? (2021)
#138Slight sidetrack: > We have to go back a few years to 1877 France. The French military used balloons for various purposes and of various sizes, and they had to be anchored using cables. Over time, they ended up with 425 different sizes of mooring cables that had to be individually ordered and inventoried. Talk about a nightmare. > > Enter Charles Renard. He was tasked with improving the balloons, but discovered this…
Think about tethering a zeppelin with a curved body shape, where you need to attach in multiple places. Combine that with needing to tether at different elevations and it will get out of hand pretty quick.
You're thinking that shorter lines can be thicker without tearing under their own weight, so the optimal mix is a few heavy lines supported by a larger number of light ones? And/or heavy lines for safety, many light lines for stability?
I suppose that makes sense, though it still seems weird that they needed that many types.
Re: Why do electronic components have such odd values? (2021)
#139Earlier quoted context omitted.
As both a sound and electrical engineer I think most high end audio electronics is bullshit. If you know what you're doing a 50 cent opamp will give you results that are beyond what a human could identify in a double-randomized blind test. Same goes for comparing two rusty pieces of wire against highly pure copper speaker cables. For some reason audiophiles will use darn massive gold (or silver) RCA connectors instea…
> For some reason audiophiles will use darn massive gold (or silver) RCA connectors instead of something like a balanced connection that would actually make sense. It's hard to find XLR (or even TRS) balanced connectors on most non-professional (=TV studios, expensive conference room setups, DJs/clubs/similar venues) equipment.
It's on all music studio equipment except the cheapest or small form factors.
Re: Why do electronic components have such odd values? (2021)
#140Wikipedia has a nice table of these values that I actually have printed out and hanging above my bench. https://en.wikipedia.org/wiki/E_series_of_preferred_numbers#... The fact of the matter is that nowadays, E96 series resistors are readily available and dirt cheap. And if you need more precision than that, you either don't know much about electronics or you know a whole lot about electronics, heh.
There’s also part of, good designs don’t depend on high precision components. I think TAoE emphasized that. For high precision one can use trim potentiometers or maybe even digital potentiometer with an ADC at the other side to measure and get as close as possible, but otherwise depending on resistors for high precision is kinda rough (I’m think like an RC circuit that need a very specific resistance to meet some spe…
> There’s also part of, good designs don’t depend on high precision components. I think TAoE emphasized that.
If I call correctly, TAoE said engineering calculations should never keep too many significant digits, since no real-world components are that accurate, and all good designs should keep component tolerance in mind - they should not have an unrealistic expectation of precision. It also mentioned that designing a circuit for absolute worst-case tolerance is often a waste of time.
But I don't think TAoE told you to "avoid precision components in your design, use trimmers instead" (Do you have a page number?) when the application calls for it. For example, 0.1% feedback resistors in precision voltage references are often reasonable.
> For high precision one can use trim potentiometers
From what I've read (from other sources), mechanical trimmer used to be extremely popular, but they went out of favor in recent decades because tuning could not be automated and that increased assembly cost. Using a 0.1% resistor is favorable if it allows trim-free production.
> or maybe even digital potentiometer with an ADC at the other side to measure and get as close as possible
Yes, digital trimming and calibrations is today's go-to solution.