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

[Johnny Billquist]

On 2016-02-14 14:31, Scott Dorsey wrote:
> Johnny Billquist  <bqt at softjar.se> wrote:
>> 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.
>
> If the motor is designed to have some slip, you can bring it up to speed
> without too much trouble.  Synchronous motors in general always follow
> the supply like slaves, no matter how many phases they have.

"Slip"? An AC motor cannot have slip. It is controlled by the phases of 
power. It has to follow the phases.

>> 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 don't know of any DEC drives that use a motor attached directly to the
> AC line.  That's not to say that they don't exist, but I have never used
> one.  IBM had some.

Me neither. I've worked on most DEC drives since the mid 70s, and none 
have had an AC motor.
The one AC motor I've seen in any DEC stuff is the fan motor in the VAX 
86x0 machines. The source of the hurricane behind the cabinet. And a 
very bad ju-ju if you write it up backwards, as there is a lot of ECL in 
there that requires cooling... But you got airflow sensors that will 
detect this quickly and power the cabinet down.

>> I do not know for sure how they dealt with battery backup for such
>> drives. Maybe someone else can tell?
>
> Same way you deal with battery backup for everything, you have a big UPS
> in the basement.  Power goes into the UPS, it's turned into DC, and then
> the DC is regenerated into three phases by an oscillator and three big
> electronic switches.

Sounds like it could have a lot of loss involved in conversions. But I'm 
not got at batteries.

	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