ISS Technology Focus, Number 14

Table 1-1. The application recommendations in the table are based on the differences in the
performance, cost, and endurance of the HP solid-state solutions. Follow these
recommendations to ensure that you choose the correct product.
Table 1-1: Enterprise solid-state storage device classes
Efficiency of DC vs. AC power supplies
HP offers 1200 W -48 V DC Common Slot Power Supplies with 90% efficiency for our
ProLiant DL360 G7, DL380 G6 and G7, and DL385 G6 and G7 servers. We also offer self-
cooled 2250 W -48 V DC power supplies with 90% efficiency specifically designed for the
HP BladeSystem c7000 Enclosure. Each c7000 enclosure can contain up to six 2250 W -
48 V DC power supplies for a maximum of 13500 W output capacity. This article will answer
some frequently asked questions from our customers about the origin of -48 V DC power
supplies and about their efficiency compared with that of today‟s AC power supplies.
Origins of the -48 V standard
The -48 V DC standard has existed for many years in the telecommunications industry
because the telecoms use large banks of -48 V DC batteries as their primary power source
(Figure 2-1). They continually charge these batteries using either AC power from the grid or
from generators if the grid fails. If the generators fail, the batteries allow the telephone
system to run until power returns.
Figure 2-1: -480 V AC to -48 V DC power distribution
The advantages of -48 V power
Interest has increased in distributing DC power in the data center because of power losses
that occur whenever conventional UPS and server power supplies convert incoming AC