Curiosity about power supplies (BA11) - test-drb@ccmp.vtda.org

27 Mar 2006

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  -----Original Message-----
 From: cctalk-bounces at classiccmp.org 
 [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Don North
 Sent: Monday, March 27, 2006 3:04 PM
 To: General Discussion: On-Topic and Off-Topic Posts
 Subject: Re: Curiosity about power supplies (BA11)

 Wolfe, Julian wrote:
  Okay, so I was thinking, would it be possible to
replace the 
 regulators and whatnot in a BA11 with several standard PC power 
 supplies?  Obviously there would be adjustments that need   to be made, 
  but considering the DEC units are now 20+ years
old and the 
 out-of-service modules may have dried up caps, would this   not be a possible
option?
 Certainly possible, with either OTS PC style or switcher PS modules.

 For the 'classic' DEC brick-style regulator modules as in the 
 BA11-K box:

    H744 ....... +5V @ 25A
    H7441 ...... +5V @ 32A   (upgrade to the H744)
    H745 ...... -15V @ 10A
    H754 ...... +20V @ 8A & -5V @ 1-8A
    54-11086 .. +15V @ 4A

 A standard BA11-K box has 2xH744 (or later 2xH7441), 1xH745, 
 1x54-11086, and usually a spot for 1xH754 (for core memory, 
 not req'd if no core).

 Each of the backplanes (DD11-D/C) has one or two AMP MateNLok 
 connectors that handle the power distribution to the various 
 slots, typically a pair of 14ga wires for +5V, and one wire 
 each for the other voltages. Each 9slot SU is nominally 
 10-15A max at +5V, easily handled by a small switcher.

 The main problem I see with OTS PC supplies is they are +12V 
 and not +15V.
 Older DEC cards expect +15V input and do on-board regulation 
 to +12V. Only some of the later MOS memory cards (like 
 MS11-PB 1MB for the 11/44) expect
 +12V on the backplane (which is supplied directly from the 
 BA11-A supply).

 I have built a benchtop debug station that uses a DD11-CK 4 
 slot SU with an inexpensive +5V at 10A, +15V at 2A, -15V at -2A 
 modular supply. I suppose it would be fairly straightforward 
 to rip out the rear end of a BA11-K box an lineup 5 or 6 of 
 these and completely replace the power subsystem.

 I'm just curious, I'm no electrician, nor have I looked   over the leads
yet.

 Secondly, if I have less than half the BA11 box full of cards, do I 
 need both of the fans plugged in?
  For the BA11-K box remember the fans not only cool the boards 
 but also the power regulators and internal power supply 
 transformer. I would not disable one of the fans even if the 
 box were lightly populated. Power supplies want to be in a 
 cool environment, heat is your biggest enemy (besides time, I guess).
 > Julian 
I pretty much counted on this being the answer, and again it was more of a
curiosity thing. Thanks :)

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