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

[Johnny Billquist]

On 2016-02-15 00:21, Scott Dorsey wrote:
> Johnny Billquist  <bqt at softjar.se> wrote:
>> On 2016-02-14 21:28, JF Mezei wrote:
>>> On 2016-02-14 04:48, already5chosen at yahoo.com wrote:
>>>
>>>> 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.
>>>
>>> RA82 drive motors were 1/3 horsepower motors. They were not 3 phase, but
>>> required 3 wires in. There was one used to start the motor in the right
>>> direction as I recall.  There was some capacitor that would discharge to
>>> get motor going. I don't recall the exact details.
>>
>> RA81/RA82 do not, as far as I can recall, have any large capacitors to
>> get them running. And they draw a hell of a lot of power when spinning
>> up, which is why you have the power sequence cable on them, so that they
>> do not all try to spin up at the same time, as that would blow fuses.
>
> No, RA81 drives are single phase induction motors.  They have a capacitor
> which provides phase shift to power a second winding, so that during
> starting the motor is a "two-phase" motor with the second phase shifted
> 90 degrees.  That second winding is disconnected once the motor gets up
> to speed.  There are other motors which use a "run winding" so that they
> always are running with the second winding, but those motors tend to have
> more slip.

Ok. Checked the manuals, and three wires to the motor. Two different 
windings, one marked "RUN" and one marked "START". So that seems to add up.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
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