Re: FREE TO A GOOD HOME

From: Eric Smith (eric-no-spam-for-me_at_brouhaha.com)
Date: 05/26/03 

Date: 25 May 2003 17:28:39 -0700

Chris Olive <nospam@raytheon.com> writes:
> Huh... could have sworn a 750 ran on 3-phase... 8-/

moroney@world.std.spaamtrap.com (Michael Moroney) writes:
> Not the 750 itself, but some old disk drives of that era apparently did.
> A long-time Deccie was telling me just today about these drives with
> three phase drive motors.. wouldn't even spin on single phase.

The common DEC drives that used large packs, such as the RP02 through
RP06, and the RMxx drives did not use three-phase motors. I'm not sure
about the RP07, but it seems unlikely that it would have had a three-
phase motor either. Perhaps the RP20 might have, but I've never seen
one. It was a rare beast with two separate spindles and an IBM channel
interface; it needed a DX20 to attach it to the Massbus.

Of course, the drives that took small packs (RK02-07, RL01-02, RC25)
didn't need three-phase for the motors or otherwise.

The RP05, RP06 and similar drives came wired for 120/208V three-phase
wye, but they simply wired the single-phase drive motor between two
phases, and the electronics between one of those phases and neutral.
The manual for the drive says that the motor is rated for a fairly wide
range of voltages, from under 208 to over 240. (I don't have it handy
to check the exact numbers.) So it should be entirely possible to run
an RP06 without three-phase power, if you have single-phase 240V. If
your 240V receptacle doesn't have a neutral, you might have to use a
step-down transformer to power the electronics.

The only parts of any DEC machines that actually *required* three-phase,
AFAIK, were the ECL power supply of the KL10 and the blower motors on
some VAXen. The KL10's ECL supply ran the three-phase through three
ferroresonant transformers with approximately 12V secondaries, and
fed the secondaries into a three-phase full-wave bridge rectifier.
This allowed them to reduce the amount of filter capacitance needed
as compared to a single-phase design.

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