K said:

What is the difference between "volt amps" and watts?

Ken

watts are joules per second, so they represent average energy flow in

a given direction. If the case involves DC, you can solve for watts

by just multiplying volts across some circuit by the current passing

through it, But energy can pass in either direction, so if the

current is changing direction, the energy flow can be positive or

negative, depending on the signs of both voltage and current.

In an AC circuit, watts are the average power flow in a given

direction, which may actually include parts of the cycle when power is

positive and parts when it is negative. In the parts of the cycle

where current and voltage have the same sign (as would be the case if

the load were pure resistance) the power is positive, but when the

current and voltage have opposite signs, it means that energy stored

in the load is being returned to the AC source, so this lowers the

average power being delivered to the load. Watts takes all this into

account. To measure AC watts you need to average the product of the

instantaneous volts and the instantaneous amps (including signs) over

an AC cycle.

Volt amps measures the movement of energy, regardless of which way it

is going. It is the RMS voltage times the RMS amperes. The RMS deals

only with magnitude (RMS stands for Root Mean Squared, or square root

of the average of the instantaneously squared magnitude), and amps or

volts squared looses information about whether the sign was positive

or negative). Volt amps is easier to measure in an AC circuit, (just

takes a volt meter and an ammeter, and you to multiply their readings)

and is a useful measurement if you are dealing with power

transformers. The volts are mostly what cause core losses. The

amperes are mostly what cause copper losses. Transformers get hot

even if they drive purely reactive loads that consume no average

watts.

But if you are producing power watts are a better measure of what you

are making.