Don North wrote:
Wolfe, Julian
wrote:
I got a UNIBUS ESDI controller and I'm
currently shopping for a disk
drive
for it. What I was thinking of doing is mounting a bracket inside the
BA11-K and powering the disk drive from the BA11-K power supply, just
using
a molex connector to one of the unused harness connectors on the power
distribution board that supplies the correct voltages.
Would doing this pose any sort of problem? i.e. violating amperage
limits
etc? It would probably be something like a Maxtor XT-4170.
The biggest problem is the BA11K box does not produce +12V, but rather
+15V,
and it is limited to +4A max (the Maxtor is rated for 1.5A typ but
4.5A max
at +12v, and up to 3A for the first 15sec or so at startup).
So you'd have to regulate +15V to +12V at something like
5A(max)/2A(typ) which
is straightforward, but I think you'd be hosing your BA11K +15V supply
either
quickly (fuse blow) or slowly (overtemp death).
I'd recommend an external 5V/12V supply for the disk drive.
Jerome Fine replies:
NOTE: My experience is ONLY with Qbus PDP-11 Systems,
so if my comments do not apply, please disregard!
About ten years ago, I acquired a number of 5 1/4"
ESDI disc drives of 600 MBytes which were being used
in groups of 4 as an emulation of some kind. Each box
had its own 300 Watt PC power supply with 5v/12v along
with 2 fans for internal cooling. I also acquired a
number of Sigma RQD11-EC ESDI Qbus disk controllers.
I removed the raw ESDI disk drives, the PC power supply
and the fans from each box and ran the drives as they
were without an enclosure just sitting on top of a cardboard
carton to ensure both electrical isolation and perhaps a
bit of vibration isolation. I ALSO placed a fan beside
EACH ESDI disk drive for cooling. As an additional
precaution, I also attached a ground wire to the frame
of the Qbus (BA-123 in my case) and the PC power supply.
Since the fastest backup is disk drive to disk drive,
I suggest that you use an extra drive just for backup
if you have enough ESDI disk drives - if you have a
backup requirement.
I suggest you take Don's advice and power the ESDI disk
drives from a separate PC power supply. Since the BA11-K
has no drive bays, this seems like a good solution in
any case. Unless many non-computer people are using
the system, there is no need to enclose the disk drives.
As I mentioned above, assuming that the XT-4170 generates
enough heat, it is probably best to use a fan for cooling!
ALSO - for anyone doing this with a Qbus system and using
TK50 or TK70 tape drives, the use of the external PC power
supply was NEVER successful. Never found out why, just
always had to used to internal power form the BA-23 or the
BA-123.
As for slowly cooking the power supply for the BA-123, I
found out the hard way after about 2 years when I was still
using RD53 hard drives.
Sincerely yours,
Jerome Fine
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