info-vax@ucbvax.UUCP (12/06/85)
Here's the scoop on Maximum backplane amps in a Vax 11/750. Virtually
everyone agrees it is 32 amps. Unfortunately the disagreements come
from Digital publications!
Read on!
Thanks to everyone who responded!
umn-cs our link to the outside world was down for a week so I apologize
if I missed anyone.
-steve
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From: Alan Wu <umn-cs!ihnp4!seismo!mit-eddie.MIT.EDU!ALW@MIT-EECS>
DEC Systems + Options catalog says 11/750 Unibus has 32 amps at 5 volts.
This limit is easy to reach with some power-hungry options. The limit can
be "stretched" a bit, but at the expense of reliability (data integrity and
system integrity) and longevity (power supply is under stress).
--Alan
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From: umn-cs!ihnp4!seismo!uwvax!uwslh!dem (a)
On page 466 of the VAX Hardware Handbook (1982-83 edition) in appendix K
It says that the power available is:
25.0 amps at +5 v
2.0 amps at +15 v
3.5 amps at -15 v
However, when we were installing our vax750 I somewhere got the figure of
32.0 amps at + 5v (probably from a salesman).
You probably can figure that there is some margin available over the 25 amps
at plus 5 volts, but it is anyones guess how much.
David Miran
Wisconsin State Hygiene Lab
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From stolaf!ihnp4!cbosgd!ucbvax!info-vax
>From VAX Systems and Options Catalog page 2.2
Expansion power available in the DD11-DK (in 750 UNIBUS...GAR) is:
32.0 @+5V, 2.0 @+15V, and 3.5 @-15V.
Gerard A. Robinson
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From stolaf!ihnp4!ucbvax!info-vax
The maximum amps that one DD11-DK (one nine slot backplane) can handle is
32.
Check your configuration. There are limits to some devices on one unibus
Brad (font of useless knowledge) Foss
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From: Milo S. Medin (NASA ARC Code ED) <umn-cs!ihnp4!seismo!orion.ARPA!medin>
32 Amps standard. Just like a BA11 box. You could go more than that, but
I would avoid it if I were you...
Milo
--------------------------------------------------------------------------------rick@NGP.UTEXAS.EDU (Rick Watson) (12/10/85)
Older BA11's have 25 amp power supplies, not 32. Be sure to check yours. If I remember correctly, you call pull out the BA11, crawl underneath and look at what's written on the supply. Rick Watson University of Texas Computation Center arpa: rick@ngp.UTEXAS.EDU rick@ngp.ARPA uucp: ...seismo!ut-sally!ut-ngp!rick rick@ut-ngp.UUCP bitnet: ccaw001@utadnx phone: 512/471-3241
info-vax@ucbvax.UUCP (12/10/85)
The discrepancy in documentation probably arises because of their age differences. DEC's standard five volt regulators have increased from 25 amps to 32 amps sometime in the last two years. Gerard A. Robinson
info-vax@ucbvax.UUCP (12/14/85)
> Older BA11's have 25 amp power supplies, not 32. Be sure to check yours. > If I remember correctly, you call pull out the BA11, crawl underneath > and look at what's written on the supply. > > Rick Watson > University of Texas Computation Center Rick is pretty close to right with his assessment of this situation. The amperage capabilities of the BA11 boxes (any UNIBUS i.e VAX and non-VAX) is determined by the model number of the +5V regulator inserted in the power system. The "normal" BA11 can hold two +5V regulators, which can be either/or/or both: 1.) H741 = +5V @25 AMPS 2.) H7441 = +5V @32 AMPS. The configuration is determined by the model number of the BA11 box itself at order time. The H765 Power System (which is mounted in the BA11-K box and contains these regulators) is the real determining factor, for example: 1.) H765-A has two H744 regulators. 2.) H765-H has two H7441 regulators. and: 1.) BA11-KE has an H765-A. 2.) BA11-KA can be ordered with either a H765 -A or -H. 3.) ad nauseum. To make this even more fun, DEC Field Circus can change any of these configurations at repair, install, or PM time depending on parts availability or the power requirements of the UNIBUS devices being installed or serviced within a particular DD11 (SPC) or device unique backplane being powered by THAT +5V regulator. (Do you think DEC does all this to confuse the Russians?) Getting back to Rick's observation: To determine what the power capability of your BA11 box is currently: 1.) Look at Regulator 2 & 3 (numbered from right to left) 2.) If both are H744, then BA11 box = +5V @25 AMPS. 3.) If both are H7441, then BA11 box = +5V @32 AMPS. 4.) If there is one of each; a.) The backplanes plugged into J9 and J11 have the power rating of Regulator 2. b.) The backplanes plugged in J3, J5, and J7 have the power rating of Regulator 3. Note: These regulator types may be determined by pulling out BA11 box and viewing from the bottom or swinging up the box to the maintenance position. WARNING 1: This procedure can bring down the operating system, so is preferably done with the system down and the system powered down. WARNING 2: This prodcedure can also result in damage to UNUBUS and communications cables, unless done properly. CONCLUSION: If you really have a need to know the power capabilities of your UNIBUS boxes, have your maintenance personnel do the checking for you!! From the bottle of Wine, Ronald J. Wine AT&T Communications 4200 Commerce Court Lisle, Ill. 60532 N.T.S.C. (1st Flr) ll1!wine