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How to convert VA to Watts and KVA to Kilowatts
Basics
Since watts is volts times amps, what is VA? VA (or volt-amps) is
also volts times amps, the concept however has been extended to AC power. For DC current
VA = Watts (DC current).
In AC if the volts and amps are in phase (for example a resistive
load) then the equation is also
VA=Watts (resistive load)
where V is the RMS voltage and A the RMS amperage.
In AC the volts and amps are not always in phase (meaning that
the peak of the voltage curve is does not happen at the peak of the current curve). So in AC, if the volts and amps are not
precisely in phase you have to calculate the watts by multiplying the volts times the amps at each moment in time and take the
average over time. The ratio between the VA (i.e. rms volts time rms amps) and Watts is called the power factor PF.
VA·PF = Watts (any load, including
inductive loads)
In other words, volt-amps x power factor = watts. Similarly, KVA*PF = KW,
Or
kilovolt-amps times power factor equals kilowatts.
When you want to know how much the electricity is costing you,
you use watts. When you are specifying equipment loads, fuses, and wiring sizes you use the VA, or the rms voltage and rms
amperage. This is because VA considers the peak of both current and voltage, without taking into account if they happen at the
same time or not
Finding the Power Factor
How do you find the power factor? This isn’t easy. For
computer power supplies and other supplies that are power factor corrected the power factor is usually over 90%. For
high power motors under heavy load the power factor can be as low as 35%.
Industry standard rule-of-thumb is that you plan for a power
factor of 60%, which somebody came up with as a kind of average power factor. Converting VA to Amps
How to convert VA to amps? Use the following formula:
Where A stands for the RMS amps, VA stands for volt-amps, V
stands for RMS volts and PF stands for the power factor.
Converting VA to Volts
How to convert VA to volts? Use the following formula:
Where V stands for RMS volts, A stands for the RMS amps, VA
stands for volt-amps, and PF stands for the power factor.
What is KVA?
KVA is just kilovolt-amps, or volts times amps divided by
1000:
KVA·PF = KW (any load, including inductive
loads)
Where KVA stands for kilovolt-amps, KW stands for kilowatts, and
PF stands for the power factor.
Keep the factor of 1000 straight when dealing with mixed units:
KVA·PF = W/1000 (any load, including
inductive loads)
VA·PF = 1000·KW (Kilowatts to
VA)
The Following equations can be used to convert beween amps, volts, and VA. To convert between
kilovolt-amps, kilowatts, and kiloamps, keep track of the factor of 1000.
Convert VA to Amps (at a fixed voltage)
Convert KVA to KW (kilovolt-amps to kilowatts)
Convert KVA to Amps (at a fixed voltage)
Converting Watts to KVA (watts to kilovolt-amps)
Convert Amps to VA (at a fixed voltage)
Convert VA to Volts (at a fixed current)
Convert Volts to VA (at a fixed current)
Convert Volts to Amps (at a fixed VA)
Convert
Amps to Volts (at a fixed VA)
Converting VA to Amps (voltage fixed)
The conversion of VA to Amps is governed by the equation Amps = VA·PF/Volts)
For example 12
VA·0.6/(12 volts) = 0.6 amp
Converting KVA to KW
(Kilovolt-amps to Kilowatts)
The conversion of KVA to KW is governed by the equation KVA = KW/PF)
For example, if the power factor
is 0.6
120 KVA·0.6 = 72 Kilowatts
Converting Watts to KVA (watts to kilovolt-amps)
The conversion of W to KVA is governed by the equation KVA=W/(1000*PF)
For example 1500W/(1000*0.83) =
1.8 kVA (assuming a power factor of 0.83)
F
Converting Amps to VA (voltage
fixed)
The conversion of Amps to VA is governed by the equation VA = Amps · Volts/PF
For example 1
amp * 110 volts/0.6 = 183 VA
Converting Amps to
KVA (voltage fixed)
The conversion of Amps to KVA is governed by the equation KVA = Amps ·
Volts/(1000·PF)
For example 100 amp * 110 volts/(1000*0.6) = 18.3 KVA
Converting VA to Volts (current fixed)
The conversion of VA to Volts is governed by the equation Volts = VA·PF/Amps
For example 100
VA · 0.6/10 amps = 6 volts
Converting Volts to VA
(current fixed)
The conversion of Volts to VA is governed by the equation VA = Amps · Volts/PF
For example 1.5
amps * 12 volts/0.6 = 30 VA
Converting
Volts to Amps at fixed VA
The conversion of Volts to Amps is governed by the equation Amps = VA·PF/Volts
For example 120
VA* 0.6 /110 volts = 0.65 amps
Converting Amps to Volts at fixed VA
The conversion of Amps to Volts is governed by the equation Volts = VA·PF/Amps
For Example, 48 VA
· 0.6 / 12 Amps = 2.4 Volts
Explanation
Amps are how many electrons
flow past a certain point per second. Volts is a measure of how much force that each electron is under. Think of water in a
hose. A gallon a minute (think amps) just dribbles out if it is under low pressure (think voltage). But if you restrict the end
of the hose, letting the pressure build up, the water can have more power (like watts), even though it is still only one gallon
a minute. In fact the power can grow enormous as the pressure builds, to the point that a water knife can cut a sheet of glass.
In the same manner as the voltage is increased a small amount of current can turn into a lot of watts. |
