kVA is not kWatts... More or less. They are two different measurements for different uses.
The "real" equation for power is:
Watts = Volts * Amps (DC)
Watts = Volts * Amps * Cosine of the angle between Volts and Amps (current)
Watts = Volts * Amps * Power Factor
Power Factor can equal Cosine of the V/A angle for linear circuits (motors, inductors, capacitive circuits, etc.).
Or Power Factor is a measured/mathematical term used to describe the V/A relationship for non-linear circuits (typically computer power supplies, lamp dimmers, battery chargers, etc.).
Looking at the picture I posted earlier:
You see that the blue line (current) is not a sine wave at all...
Why is this important--Volts*Amps (or amps directly) better describes the current carrying capacity of wiring, how generator windings/magnetics behave, waste heat from I^2*R heating, etc. can be modeled/defined/designed...
Watts or Power is the amount of energy the system is using...
So, it is very possible to have a circuit that pulls 1 amps at 120 VAC, but with a Power Factor of 0.6 (motor, CFL lamp, etc.) and you get:
1 amp * 120 VAC = 120 VA (wiring design, generator/inverter maximum VA rating, etc.).
1 amp * 120 VAC * 0.6 PF = 72 Watts (amount of heat/energy the load is taking, how much fuel the genset will use, how much energy an inverter will pull from the battery bank).
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Comments
Interesting... it's rated .78KVa - I used an online converter to convert that to watts.
kVA is not kWatts... More or less. They are two different measurements for different uses.
The "real" equation for power is:
- Watts = Volts * Amps (DC)
- Watts = Volts * Amps * Cosine of the angle between Volts and Amps (current)
- Watts = Volts * Amps * Power Factor
Power Factor can equal Cosine of the V/A angle for linear circuits (motors, inductors, capacitive circuits, etc.).Or Power Factor is a measured/mathematical term used to describe the V/A relationship for non-linear circuits (typically computer power supplies, lamp dimmers, battery chargers, etc.).
Looking at the picture I posted earlier:
You see that the blue line (current) is not a sine wave at all...
Why is this important--Volts*Amps (or amps directly) better describes the current carrying capacity of wiring, how generator windings/magnetics behave, waste heat from I^2*R heating, etc. can be modeled/defined/designed...
Watts or Power is the amount of energy the system is using...
So, it is very possible to have a circuit that pulls 1 amps at 120 VAC, but with a Power Factor of 0.6 (motor, CFL lamp, etc.) and you get:
- 1 amp * 120 VAC = 120 VA (wiring design, generator/inverter maximum VA rating, etc.).
- 1 amp * 120 VAC * 0.6 PF = 72 Watts (amount of heat/energy the load is taking, how much fuel the genset will use, how much energy an inverter will pull from the battery bank).
-Billtaint quite right as a watt is about 3.4btu.
Blame Josh, not me!
http://joshmadison.com/convert-for-windows/
I use Convert.exe, because it can convert a lot of different 'factors'..
An engineer at MIT told me it was pretty good, and I've been using it for many years.
Cheers,
Rich