An EPRI White Paper
DC Power Production, Delivery and Utilization
Powering Equipment and Appliances with DC
Many energy-consuming devices and appliances operate in- ternally on DC power, in part because DC can be precisely regulated for sensitive components. An increasing number of devices consume DC, including computers, lighting ballasts, televisions, and set top boxes. Moreover, if motors for heat- ing, ventilating, and air conditioning (HVAC) are operated by variable frequency drives (VFD), which have internal DC buses, then HVAC systems that use VFDs could operate on DC power. Numerous portable devices like cell phones and PDAs also require an AC-DC adapter. As discussed above, by some estimates the AC-DC conversions for these devices waste up to 20% of the total power consumed.
Many opportunities exist to use DC power with SMPS- equipped equipment since SMPS technology is found in many electronic devices including desktop computers, laptop com- puters with power adapters (see Figure 5), fluorescent lighting ballasts, television sets, fax machines, photocopiers, and vid- eo equipment. Although AC input voltage is specified for most of the electronic devices that have SMPS, in some cases, this equipment can operate with DC power without any modifica- tion whatsoever. Also, in many instances, the location on the SMPS where AC is normally fed could be replaced with DC.
Power supplies for desktop and laptop units
EPRI Solutions examined the compatibility of some common devices with DC power delivery in 2002:6
According to research on power supply efficiency sponsored by the U.S. Environmental Protection Agency and the Cali- fornia Energy Commission,7 as of 2004, there were nearly 2.5 billion electrical products containing power supplies in use in the U.S., with about 400 to 500 million new power sup- plies sold each year.
switched mode power supplies, including those for computers (lab test)
fluorescent lighting with electronic ballasts compact fluorescent lamps (lab test) electric baseboard and water heating units uninterruptible power supplies (UPS) adjustable speed motor drives
The total amount of electricity that flowed through these pow- er supplies in 2004 was more than 207 billion kWh, or about 6% of the national electric bill. Researchers determined that more efficient designs could save an expected 15 to 20% of
Figure 5. SMPS unit for Dell laptop
These devices represent a large percentage of the electric load, and EPRI Solutions’ preliminary assessments show that each could be potentially powered by a DC supply. Although addi- tional testing is needed to determine the effect of DC power on the long-term operation of such equipment, results do indi- cate the feasibility of delivering DC power to these devices.
Switched-mode power supply (SMPS)
Switched-mode power supply (SMPS) technology is used to convert AC 120 V/60 Hz into the DC power used internally by many electronic devices. At the most basic level, an SMPS is a high frequency DC-DC converter.