Hardware reference guide

Pwr. & Grnding. Guide
790
35013379 02 October 2007
Another important difference from the summable system is the total available
system backplane loading. If there are N redundant power supplies installed in a
backplane, the total backplane load must not exceed the capability of N – 1 supplies.
For example:
z If three 8 A redundant power supplies are installed (N = 3), the maximum
backplane load available for redundant operation is the current sourced by N – 1
( = 2) supplies, which is 16 A.
z if two 8 A power supplies are installed in the backplane (N = 2), the maximum
backplane load available for redundant operation is the current sourced by N – 1
( = 1) supplies, which is 8 A.
If these constraints are observed, then in a system of two or three redundant
supplies, one supply (it doesn’t matter which one) is hot-swappable. This is possible
because there is excess capacity in the N – 1 remaining supplies to source the
backplane current while the Nth supply is being swapped.
An obvious extension to this argument is that a single redundant power supply may
be used as a standalone supply (but the lowest cost solution will be achieved by
using a summable or standalone supply for this application).
Limits to Backplane Load
z If two 140CPS12420 power supplies are installed in the backplane, the
maximum backplane load available for redundant operation is 10 A.
z If three 140CPS12420 power supplies are installed in the backplane, the
maximum backplane load available for redundant operation is 20 A.
CAUTION
Use only like redundant power supplies except for 140CPS12420 which can be
mixed with one 140CPS22400 or one 140CPS42400.
z If one CPS12420 is installed with one 140CPS22400 or one 140CPS42400 in
the backplane, the maximum backplane load available for redundant operation
is 8 A.
z If one 140CPS12420 is installed with two 140CPS22400 or two 140CPS42400
in the backplane, the maximum backplane load available for redundant
operation is 16 A.
z If two 140CPS12420 are installed with one 140CPS22400 or one 140CPS42400
in the backplane, the maximum backplane load available for redundant
operation is 16 A.
Failure to follow this instruction can result in injury or equipment damage.
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com