A volt-ampere (VA) is a measure of perceived electrical power, whereas an amp (A) is a measure of electrical current. One volt applied to a "load" such as a lamp will result in one amp flowing through that load.
Thus, one may say that a VA source provides enough voltage for a given amount of current, while an amp source must provide sufficient current for a given amount of voltage.
In other words, VA sources are good for driving loads that require more than 1 amp of current, while amp sources are required for high-current applications like motor drives and power tools.
The term "voltage source" can be used to describe either type of supply. A VA voltage source provides DC voltage from an AC power line via two connections: V and A. The letter V means "volts," so this connection must be between zero and 110 volts. The letter A means "amps," so this connection can be any value up to about 500 milliamps. A resistor can be used to limit the current drawn by a VA source to an acceptable level for a particular application.
An amp voltage source has only one connection: A. It provides a constant voltage no matter what current is drawn from it.
So, at 120 volts, a circuit with 1,800 volt-amps of perceived power has a current rating of 15 amps. Voltage is always measured between two points on a circuit, so to determine how much current is flowing through a part of the circuit, you need to know where it is located in relation to those two points.
Because electricity always takes the path of least resistance, current will flow through any part of the circuit where the resistance is lowest. The voltage across a resistor is defined as the applied voltage divided by the total resistance of the circuit. In other words, if 100 volts are applied to a 10 ohm resistor, 20 milliamps will flow through it. If the resistor changes to one with a resistance of 1 ohm, then the current will increase to 20 amps and the voltage will remain at 100 volts.
The amount of current flowing through a circuit is called its load current. Current ratings are usually expressed as a maximum load current, such as 15 amps, which means that the device can be expected to carry this current continuously for some time without damage occurring. However, since most loads do not draw their full capacity all the time, it is important to also look at the minimum load current listed on the product data sheet.
The perceived power in an electrical circuit is measured in volt-amperes (VA). Volt-amperes are only helpful in alternating current (AC) circuits. This calculator converts volt-amperes to watts and vice versa. 1 watt is equivalent to 1 volt-ampere. Therefore, 1 va is equal to 1 w. 1 va can also be written as 0.001 w.
Note that one volt-ampere is not the same as one milliwatt; they are different measures of electric current flow. One milliwatt is equal to one thousandth of a watt. You can think of the mnemonic "one milli = one thousandths" to remember this distinction. When referring to voltage sources we always mean volts, but when referring to current sources we use amperes. There are 120 milliamperes in a volt, but there are only 10 milliwatts in a volt!
This tool gives you accurate results for any combination of values from 0 to 100 in increments of 1. Simply enter your numbers in the boxes below and click Calculate: