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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Thu, 13 Jun 2024 19:27:51 -0700
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On 6/13/2024 7:02 PM, KevinJ93 wrote:
>>> I've never heard of lower level software being compromised at high 
>>> temperatures so basic phone calls would be ok but action video games would 
>>> run slower.
>>
>> The fact that the phone (and other exemplars) operates outside of its
>> "operating range" confirms there is margin in the design.  We know that. > 
>> But, no one seems to know *what* this margin is.  (It's not just 
> phones but
>> almost all consumer kit -- excepting those for which NO operating/storage
>> conditions are specified!)
>>
>> This suggests that it is NOT a part of the design process but, rather,
>> "whatever it is, it is".
>>
>> If I tried to make a call and the phone was 160F -- because it sat in my
>> car for three hours in the sun -- would it work?  Is there ANYONE at Apple
>> who could answer that question?
> 
> 160F is 71C so the the circuitry I was involved with could be guaranteed to 
> work provided the internal temperature of the phone was not significantly 
> higher than that 160F.
> 
> I believe similar limits would apply to other parts of the phone.
> 
> However if the internal temperature had been raised significantly by any 
> internal power dissipation then all bets are off.
> 
> CPUs are especially challenging as they can dissipate 5-10 Watts at extremes - 
> there is no room for anything in the way of heat sinks or fans etc. The best 
> they can do is to thermally couple them to the case.
> 
> The power amplifiers in the RF section are also significant heat generating items.
> 
> Your question has a multi-dimensional answer, it depends upon a host of other 
> things including the recent usage of the phone.

Of course!  And, I am just using phones as an example as they are ubiquitous.
If you wander around your home, there are undoubtedly countless items that
all have real limits on their operation -- yet DETERMINING those would be
difficult (especially if you wanted to know REAL limits and not just
PUBLISHED limits)

> A phone could be designed to guarantee operation at the temperatures you state 
> but that phone would certainly cost more, be physically larger, heavier etc. 
> The current specifications have been accepted as adequate by the majority of 
> customers. Probably there do exist ones with extended environmental specs for 
> specialized applications such as the military where that is more important than 
> cost, weight, size etc.

But that's exactly my point!  The phone, AS DOCUMENTED, is considerably less
capable than it is, in reality!  If it adhered to its published specifications,
I suspect a good many people would not use it -- because they routinely
encounter conditions that exceed those published for the phone.

SOMEONE (at Apple) knows this to be the case as they wouldn't market
a product that had millions of users complaining that their phones stopped
working in the summer (winter?) months.

> If you want to improve the likelihood that your phone works when you need it - 
> don't leave it lying in sun. Even in a hot car some places are cooler than others.

Of course.  I've used this as an example of how WIDE the margin is in
the phone's design (*my* phone isn't an iPhone).  I doubt many people
worry that the car interior may get too hot for their phones -- because
most people have never had a phone refuse to operate due to temperature
extremes!

>>>> We expect cars to continue to operate in those temperatures.  What's the
>>>> criteria that we use to determine what should and shouldn't be expected
>>>> to remain operational?
>>>
>>> Automotive devices that expect to be in the engine compartment are designed 
>>> for -40C to +125C or +150C.
>>
>> The devices I mentioned are located in the *passenger* compartment.
>> What value an engine compartment that can't be *controlled* by devices
>> in the passenger compartment?  :>
> 
> I've also worked in some aspects of automobile design and there were multiple 
> environmental zones defined - the cabin being the most benign.
> 
> Probably parts there are specified to 105C. Although it can get pretty toasty 
> at the top of the dashboard.

Dash gets up above 160.  I've been amused that the ambient temperature
sensor is so acurate -- yet "sees" the heat reflected off the (180F)
pavement!  Clearly some "engineering" at play, there.

>> Will the GPS operate when the vehicle's interior reaches 160F?  What about
>> the roadside assistance feature?  Backup camera?  Will the electronics that
>> govern the cycling of the air conditioning compressor function?  Do you recall
>> ever hearing someone complain of the electronics in their vehicles NOT working
>> when they returned to their parked vehicle after work?  ("margin")
> 
> The temperature is not uniform in the car and often electronics are placed in 
> areas where they won't reach the high temperatures you mention - in some of my 
> cars for example the electronics were under the seats or behind the glovebox.

Yes, but over the course of an 8 hour "work day" (baking in the sun), I
suspect there are no "refuges" in the vehicle's interior.  If the air
temperature is 113, then the car *will* climb to 113, over time.

(It will *drop* to 90 degrees after 10PM, tonight -- and today was relatively
cool -- just barely 100F)

>> The fact that the car manufacturers recognized these some devices WOULD fail
>> (and added a variety of idiot lights on the dash to signify those failures)
>> suggests they either couldn't make them operate over these extremes *or*
>> couldn't AFFORD to make them operate over these extremes.
>>
>> But, as a buyer looking to drop $50+K on a vehicle, what assurances do
>> you have that those systems (for which you are paying additional monies)
>> WILL operate when you are the vehicle's owner?  If they won't operate
>> when the vehicle is sitting on the *dealer's* lot, will they operate when
>> the vehicle is sitting in the grocery store's lot?  Your employer's lot?
>> Your driveway?  On the highway?  (etc)
> 
> Modern cars are impressively reliable but they may not be guaranteed to operate 
> over the full gamut of environmental conditions and usage. They just have meet 
> the great majority of the customers' expectations.

If you are charging a premium for certain technology features, it seems
like you would take steps to ensure that they *worked* in every market
in which they were offered.

As I said, I stepped behind the wheel of certain vehicles and watched
failure indicators illuminate in rapid succession:  "That's because
the car is in the sun..."  "Ah, OK.  So, if I want those features, I
should keep the car in the shade?  How do I do that on the roadways?"

>> Vendors seem to treat *consumers* as ignorant dweebs; the same sorts of
>> hand-waving wouldn't be tolerated by an industrial/commercial customer!
> 
> The market decides. Price is a dominant factor in vehicle sales.

Price is a dominant factor in *many* decisions.  Until performance
problems capture headlines.  I'm sure the airlines that bought
Boeing products did so largely on price/performance/reputation issues...

Consumers tend to be largely ignorant of product capabilities and
limitations.  They buy *features* -- without even guarantees that
those features work!  And, because they often don't understand
what they have bought, they are never quite sure that a problem
is "theirs" or the *device's*