Yes its true, but before you let a disk spin backwards, you checked the
fans in the logic gate, they were 3 ph too. Depending on how they spun
(clockwise or counterclockwise), you had the phases corrected. I never
spun up a drive that went backward using that technique.
And if it was say a 2365, or a 2860 or 70, it would power up just fine,
then get a thermal since the fans were spinning in the wrong direction.
Doug Fuerst
d...@bkassociates.net
------ Original Message ------
From: "Paul Gilmartin" <0000000433f07816-dmarc-requ...@listserv.ua.edu>
To: IBM-MAIN@listserv.ua.edu
Sent: 22-Jun-20 12:03:59
Subject: Re: 3 phase power question for the gray hair group. :-)
On Mon, 22 Jun 2020 15:34:37 +0000, Pommier, Rex wrote:
I have a light - probably trivia by now - question for those of you who have
been around a while. My earliest experience with IBM disk was 3380s. They ran
3 phase power, and if the phases weren't cabled correctly, the machine wouldn't
power up. I seem to recall hearing stories of (older than 3380) disk drives
that would start up, but the drives would spin backwards if the power phasing
was cabled incorrectly. Is there any truth to this story or was somebody
feeding me a line?
Not quite definitive, but:
https://en.wikipedia.org/wiki/Three-phase#Revolving_magnetic_field
https://en.wikipedia.org/wiki/Three-phase_electric_power#Phase_sequence
I knew a man who had worked in hardware field support for CDC. He
told of his site's encountering such a problem. He summoned the
union electrician required by shop contract. Electrician measured
voltage pairwise between phases: "208v-208v-208v -- no problem!"
My friend sneaked in after dark and rewired the motor-generator.
-- gil
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