[time-nuts] HP Stories: Battery Chargers, and a fading idolization of HP

[Luca]

Thanks Hugh for the story, and thanks for the schematic!
Quite interesting.
There is a little strangeness: the wave clipper darlington transistor Q1 is
marked as 1854-0611, equivalent to the standard darlington 2N6055. But why
there is a simple 2N3055 in the picture? Some sort of version update fail?
Thanks
Cheers
Luca
iw2lje

Il giorno sabato 9 febbraio 2019, Rice, Hugh (IPH Writing Systems) <
hugh.rice at hp.com> ha scritto:

> I grew up on Silicon Valley (Santa Clara Valley, California), graduating
> from High School in 1980.   My home town is Cupertino, also the home of
> Apple Computer.    During my formative teen years in the 1970s, HP was THE
> company in the valley, the elder statesmen of Hi-Tech.   (Apple was just a
> small upstart business for computer geeks, and their headquarters were just
> down Bubb Road from my HS.)   The reputation of HP as a great company was
> untouchable.   Both in the quality of the products, and as a the best place
> to work.     Being from Silicon Valley, I choose to study electrical
> engineering (rather than my natural inclination towards mechanical
> engineering, having done a lot of work on cars and bicycles), hoping to
> come back to the area to work when I graduated.    I had fantasies of
> working for HP in my college summers as a “SEED” student, but was never
> able to make the right connections.    A HP job upon graduation with a BSEE
> was like winning the lottery, especially for a Silicon Valley Kid.
>
> Home for Christmas during my senior year, I was visiting a friend from
> church, and her dad (Charles Adams) asked me how my job search was going,
> and if I had considered working for HP.   “I’d LOVE to work for HP.  I just
> can’t crack in and get an interview.”    He said they had an opening for a
> new grad EE, and asked if I would be interested in considering it.   “Uh,
> yes!”   A few days later, I was in the Precision Frequency Sources
> Production Engineering area, doing the all day rounds of a classic HP
> interview.   I did well enough that they offered me a job the next day, and
> I went back to school for my final semester with a HP job in hand.   A
> certifiable miracle.    It didn’t get any better than this.
>
> I asked Charles what I could do to prepare for the job, and he mailed me a
> 5061A Operating and Service Manual to review.   It was incomprehensible.
>  But I could tell that the 5061A was something pretty special, because all
> the circuit diagrams and theory of operation descriptions had things in
> them that even the grad students I knew couldn’t understand.   And I had a
> job at HP!   Working on Atomic Clocks!    (Whatever they were.)
>
> As you know from past postings, my job was part of the 5061A to 5061B
> development team.  The first task I was assigned to was to freshen up A2
> Battery Charger Assembly.   The purpose of this circuit was to keep the 20
> cell NiCad backup battery ready to supply power in emergencies.   The must
> fix issue was a gigantic mica capacitor used in a RC timing circuit, which
> was both expensive and unprocurable.    I think my mentor, Roberto,
> encouraged me to look over the whole circuit, and sift out all the other
> old parts that would a problem in the near future.   (All that code 4 part
> stuff.)
>
> So I studied the circuit like only a new grad can do.   Brand new
> engineers are nearly worthless, and no one has any reason to talk to them
> or distract them.  This was before the internet, cell phones, email (at my
> location), and any other distraction.   I had hours and hours of
> uninterrupted time.    The circuit was strikingly complex for a battery
> charger.    But you have to remember by frame of reference.  HP was the
> best electrical engineering company in the world.   Their products were
> awesome.   Surely every circuit in every product was the result of deep
> expertise from brilliant engineers, and every resistor, capacitor and
> transistor had a sacred purpose.    So I kept digging until I understood
> every aspect of the circuit.
>
> The “brilliant” designer had decided that the battery charger needed to be
> a two-level system.   A fast charge to replenish the battery quickly after
> a power failure, and then a lower “trickle” charge to keep it topped off
> long term.   But how long to do the fast charge?    Well, if we time the
> discharge time, we can then use that to set the fast charge time.   Battery
> power for 20 minutes?   Fast charge 20 minutes at a similar rate.    In
> addition, the charger assembly had a drop-out  relay circuit, so if the
> battery voltage got too low, the relay would trip to disconnect the battery
> protect it from over discharge.   (Oh yes, the relay used was also
> impossible to procure, being some ridiculous double pole, double throw,
> part unique to the 5061A).   Add another circuit to flash the front panel
> light when the  back-up battery was supplying power.  And then the charge
> current regulator itself, which of course was a transistor level fully
> discrete design with dozens of components.
>
> But it gets better:  The discharge, recharge timing circuit used the most
> complex counter IC available from the TI TTL catalog.   A pre-settable,
> programable, up-down counter.   There may have been two counters, for 8
> bits of resolution.    To make it better, the counters were pre-set to a
> specific but obscure number,  that had them exactly count down to zero
> after about 90 minutes, when using the timing rate set by the RC circuit
> with the aforementioned giant unprocurable Mica capacitor.
>
>  I wish I could find a circuit diagram of the 5061A, to fully relive the
> experience and share it with  you all.
>
> OK, now that I finally had the circuit figured out, what do I do?    I
> think Roberto recommended that I read the “GE Battery Book”, since GE was
> the supplier of the Ni-CAD battery pack, to give me background on
> rechargeable batteries.    I bought a new copy, and read the whole thing
> cover to cover in a couple of days.   All kinds of information on charging
> at the “C” rate (a 1Amp Hour battery “C” factor is 1 Amp) for fast
> charging, and 0.1C for trickle charging (full charge in 10 hours), and how
> trickle charging is best for the batteries, and so forth.
>
> As I’m reading the GE book, I’m slowing realizing that the 5061A battery
> charger is pretty complicated, for what appears to be a fairly simple
> task.   As I chat with Roberto more about it, it becomes clear that the
> circuit is perhaps a bit over complicated.    But wait, aren’t HP engineers
> the best in the world, and every circuit they design the best possible
> implementation known to man?   The idolization I had developed from my
> Silicon Valley roots, and all the praise from my university professors and
> peers is starting to loose its luster.   This battery charger wasn’t a
> great design.  I wasn’t even a good design.  It was a ridiculously
> complicated, expensive, idiotic design that never should have made it
> through any sensible design review.   I never did learn who did the work.
> I don’t think they worked at Santa Clara Division any more.   Probably a
> good thing.
>
> This was actually a blessing in disguise.   Only a few months into my HP
> career I learned the priceless lesson that inherited work isn’t always good
> work.  I also learned to really understand the task that needed to be done,
> before you set out to do it.   Like learn how batteries work before
> designing chargers.   And then I had the opportunity to design a completely
> new circuit from scratch.
>
> I had a new goal:  Make a good, simple, reliable battery charger, but it
> had to be backwards compatible to the 5061A.   HP didn’t want to support
> the old design any more (huge mica capacitors and crazy relays), and the
> new circuit needed to be a replacement assembly too.     This presented
> another priceless lesson:  real work design is often constrained, and not
> clean sheet like those university projects.
>
> I’m still proud of the final battery charger design.   So proud that
> attached the 5061B circuit diagram if you want to be impressed.  😊   I
> ditched the timing circuits altogether, and just went a simple trickle
> charger.   If a 5061B application has a power outage of 30+ minutes, how
> likely are they going to have another long power outage within the next few
> hours?   Not very.    The new circuit used standard, inexpensive, robust
> components in the whole design.    There are other clever (to me) aspects,
> and you can discover them on your own if you are interested.
>
> One last story on this.   My first prototype of the circuit was hand
> soldered together on proto-board material.  That generic PCB with grids of
> 0.10” pitch holes all over it.    Roberto told me to go to the 5061A
> production line tech’s, and have them try out the new circuit.   Picture a
> brand new engineer who looks about 17 years old, with this rats nest of a
> proto circuit for them to test.   I recall one of the Tech’s, Ray, putting
> on safety glasses before he put it in a test 5061A and powered it up.  They
> never wore safety glasses.    I don’t think it worked on the first try.
>  But I recall that the problem was something simple to resolve.
>
> Over the next few years, HPs iconic reputation would continue to loose
> it’s luster in my eyes, as I learned that mortal people worked there, and
> that real business had real problems.    But there were also a lot of
> really good engineers and technicians there, and they would help you if you
> asked.
>
> It was a fantastic start to a 35 year (and counting) career at HP.
>
> Happy Chinese New Year from Singapore,
>
> Hugh Rice
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