[Info-vax] OT: the Daily WTF for today is a VAX/VMS story

[William Pechter]

In article <n9ps0p$fue$1 at Iltempo.Update.UU.SE>,
Johnny Billquist  <bqt at softjar.se> wrote:
>On 2016-02-14 10:48, already5chosen at yahoo.com wrote:
>> On Wednesday, February 10, 2016 at 10:03:18 PM UTC+2, rdpi... at gmail.com wrote:
>>> See
>>>
>>> http://thedailywtf.com/articles/overpowered
>>>
>>> for a nostalgic trip down memory lane.
>>>
>>> RDP
>>
>> There is one technical detail that I didn't understand: how did hard
>drives get their three-phase AC power when operating from battery ?
>>
>> Also something sounds wrong with rpm. 3000 rpm is a correct AC
>frequency in the most of the world, but this particular story happened
>in USA, right? Isn't it 3600 rpm there?
>>
>> More I think about it, more the story of VAX hard drive with
>three-phase AC motor (in early 90s, non-the-less) appears apocryphal.
>
>The story was fun, but it is indeed not based on facts.
>Yes, there are drives that run from 3-phase power, such as the RP06, 
>which could have been a base for the story.
>
>However, no hard drive uses a 3-phase AC motor to drive the disk. Anyone 
>with half a brain should realize this. 3 phase AC motors always follows 
>the phases of the supply like slaves. There is no spinup time. You go 
>from standstill to full speed immediately, always. That is not how you 
>want to spin up a disk drive.
>
>The RP06 uses two phases actually, but it does it to extract more power. 
>The actual motor is still a DC thing. And yes, it spins at 3000 rpm (I 
>think that is correct) both in 50 Hz and 60 Hz countries.
>
>I do not know for sure how they dealt with battery backup for such 
>drives. Maybe someone else can tell?
>
>	Johnny
>
>-- 
>Johnny Billquist                  || "I'm on a bus
>                                   ||  on a psychedelic trip
>email: bqt at softjar.se             ||  Reading murder books
>pdp is alive!                     ||  tryin' to stay hip" - B. Idol

Actually I've seen RP04's spin backwards banging their brushes (which were
ECO's out on service contract sites)against the stops... Happened
at New Jersey Bell Telephone when they electricians didn't check the phases
sent to the three phase RP04s.  RP05's and RP06s only used two phases.

This was in New Brunswick New Jersey around 1984-85 or so.

This was when the Telco's were buying up used and surplus pdp11's for 
internal use as line maintenance macines...for SCAMOS etc -- before they
moved to Vax systems and AT&T 3B boxes.

This was just when DEC was discontinuing the 11/70's due to FCC RF noise
spec issues.

I guess they never figured on checking the phase to phase before we tried to
power up the drive.  All drives immediately blinked and went unsafe doing a
full head against stop retract due to the packs spinning backwards.

IIRC the Sperry/Itel RP04's were completely three phases where the RP06's used
two for the drive and 1 for the DCL (IIRC).  Could've been just two with
the DCL and one drive motor set up on the same phase and the second DCL
and the first one's drive motor on the other when they were connected together
sharing the power.

It could have been that there were old RP04's on the site when a PDP11 was
replaced by a VAX... The RP07, IIRC was also a three phase drive with a 
semi-sealed HDA.  If those 400+mb platters blew out... boom.

The RP06's were more than 85 lbs.  The platters weren't.  Perhaps the HDA
on the RP07 was about 85 lbs.  

RA drives weren't three phase.


Bill

-- 
-- 
Digital had it then.  Don't you wish you could buy it now!
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