RP05/RP06 drive power (was Re: PDP11/0x in my apartment?)
Bob Hoffman wrote:[color=blue]
> RP0x drives in the USA had their power daisy-chained from one drive to the
> next in groups of three. That is, the first drive plugged into a 30
> amp, 3-phase outlet (NEMA L21-30), the second drive plugged into the
> first and the third drive plugged into the second. If there was a 4th
> drive, it was plugged into a separate 3-phase circuit.[/color]
The manuals for the RP05/RP06 specifically state that only one drive
should be daisy-chained from a second (i.e., no more than two on one
receptacle). Depending on how your receptacles are wired, that doesn't
necessarily mean that three or four drives require two circuits.
The RP05/RP06 spindle motor is a single phase motor wired across two
phases of the three-phase power (208 VAC phase-to-phase), and a DC logic
supply wired between one phase and neutral (120 VAC). The daisy chain
receptacle is wired with the phases rotated, to distribute the load.
If you did daisy chain a third drive (despite the manual saying not to
do so), the power load would be fairly evenly loaded if all three drives
were spinning. Otherwise, if the third drive is plugged into a separate
receptacle, it would be wise to make sure that the phases to that
receptacle are rotated.
The RP06/RP06 motor is actually rated by the manufacturer (Memorex) for
a fairly wide voltage range, so if three-phase is not available, it is
possible to wire an RP05/RP06 for use on a 240VAC split-phase with
neutral circuit (four-contact NEMA 14-15R, 14-20R, 14-30R, etc.
receptacles), If the neutral is not available, the spindle motor can
be wired across the 240VAC and a step-down transformer used to power
the logic supply.
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