3 Jun
2011
3 Jun
'11
12:13 a.m.
On 03/06/2011 02:29, Jerome H. Fine wrote:
I got the 4.5A from the microPDP-11 Systems Maintenance Guide, which
happened to be the nearest to hand when I wrote that. It might not be
correct; it does seem a lot even for such an old drive. I've just
looked hrough some other manuals
Incidentally, that Maintenance Guide is the same manual which (on page
8-14) tells how to set the drive select jumpers for DU0: and DU1: in a
BA23. Although it also says (on page 5-6) only to install one RD52 in a
BA23 :-)
Pete Turnbull
wrote:
What I do know is that the docs say you must draw
no more than 7A from
the 12V supply in a BA23, and one RD51 takes 4.5A. So 2 x RD51 would
overload it. I believe that's the only restriction, because putting a
second RD5x in a BA23C expansion box, connected via an RQDXE, was
supported -- and AFAIR the RQDXE doesn't do anything clever with the
control or status signals.
I checked the drive specs in the BA23 manual.
I don't know if the values are correct, however,
the manual lists 2.5 Amp on the 12 volt. However, in any case, from my point of view,
it is far better to use an additional PC power
supply (for just the hard drives) when there
are two hard drives used in a BA23 box.
This take the load off the internal power supply.
I don't bother doing that, but...
And if you want to use an RX50 and a TK70
as well, then you would almost certainly exceed
the 7 Amp available on the 12 volt internal
power supply. As I mentioned, always use
the internal power supply for the TK50 / TK70.
Whereas I leave the RX50 outside the BA23
box if there is no TK70, with a TK70 I usually
place the RX50 and TK70 inside the BA23
box and the 2 hard drives outside the BA23
box.
...my 11/83 has two RD drives in the BA23 running off the internal
supply, and (when I got it) had an external RX50 which had its own PSU.
--
Pete Peter Turnbull
Network Manager
University of York