* See Volt-Amp to Watt conversion below
† Microwave input watts = 1.5 - 1.7 x output watts
(1) Dell 2350 - 200W, Dell 4550 & 8300 - 250W continuous, iMac 15" 130W
(2) Dell Precision 650 - 460 W, Mac G4 460W 6A

See Also: Charging Volts and Amps for consumer electronics.

UPS - Uninterruptible Power Supplies:
The most common are Battery Backup units which switch from direct power to battey in in 4-8 ms. A "True" UPS runs off batteries constantly so there is no switchover time. The 4-8 ms. switchover does not affect most computers. Battery life is typically 3-6 yrs.

Battery RunTime

Conext Battery Backup
300VA/180 Watts - 170 Watts 4 min 100 Watts 11 min.
500VA/300 Watts - 201 Watts 4 min/ 100 Watts 15 min

Volt-Amp to Watt conversion

True Power (watts) = Volts (RMS) x Amps (RMS) x Power Factor

where V = Volts, A = Amps pf = the power factor of the load, applies to all electrical loads.

A standard 120 V household current swings between +170 V and -170 V in a sine wave pattern. the RMS value (root-mean-square) is 1/SQRT(2), or about 0.707 times the peak. This despite the fact that the average value of a sine wave is about 0.637 times the peak.
See:
Teaching RMS from L. B. Cebik, W4RNL.
Introduction to Signals at Bucknell

In the case where the load acts purely resistive, such as that of an incandescent light bulb, heater or a PFC (Power Factor Corrected) switching power supply, the pf will equal 1 or nearly 1. For all other cases, the pf will vary between 0 and 1, and for a typical capacitor input switching type computer power supply, a power factor of about 0.714 is usually exhibited.

Typically 100 watts of supplied UPS power will run 100 watts of incandescent lightbulbs, but only 71.4 watts of a typical capacitor input switching type computer power supply, and nearly 100 watts of a PFC computer power supply.

Example:

A typical capacitor input switching computer power supply is 200 watts. The VA output equivalent can be calculated as follows:

watts = VA * pf, or, VA = watts / pf
VA = 200 Watts / 0.714(pf) = 280 VA

so 280 VA of the UPS supplied power will be needed by the 200 watt computer power supply at full draw.

Another faster way to express this, is

Computer Power Supply in Watts * 1.4 = UPS VA
200 Watts * 1.4 = 280 VA

AC Watts to DC Amps AC Watts divided by 12 x 1.1 = DC Amps

Some appliances or tools, such as ones with a motor, require an initial surge of power to start up ("starting load" or "peak load"). Once started, the tool or appliance requires less power to continue to operate ("continuous load"). So, power inverters (DC battery to AC) and generators are sometimes rated by peak and continuous load. Source: The Volt-Amp to Watt conversion information above came from a web site named Sutton Designs (www.suttondesigns.com/doctext/pf.html) which is no longer available.

DC Inverter:
12 volt inverters require approximately ten (10) amps DC input for each 100 watts output power used to operate an AC load.

e.g. It will require 10 amp hours of battery to operate a 100 watt bulb for 1 hour. The battery rating should be twice this (i.e. 20 amp-hours for maximum battery life and performance.

See: Solar Tutorial See Also:
Charging in technology here
Hand Crank flashlights and Mobil Phone Chargers and Solar Panels in products here.
www.donrowe.com/inverters/inverter_faq.html
Wire Size