Volts to Watts (V to W) Conversion Calculator

What is Volts?

Volts – short form of voltage – is the S.I unit of electromotive force, which may also be thought of as electrical pressure. We may also represent it with V.

Volts is a measure of the amount of electromotive force that drives electric charge around a closed circuit through a certain amount of resistance. We can also say volts is the energy per unit charge in a closed circuit.

What is Watts?

Watts – short form of wattage – is the S.I unit of power, typically electrical power. We may also represent it with W.

Watts is a measure of the time rate of energy production or consumption within an electrical circuit.

Why We Convert Volts to Watts?

In some cases, electrical devices come with their power rating written on them. At such times, we wouldn’t have to convert volts to watts to know how much power the devices will consume.

In some other cases, electrical devices do not come with their power rating inscribed on them. At such times, we’d have to depend on their volts (voltage rating) and the current in amps to calculate the watts of such devices. This is where converting volts to watts comes in.

When building a solar system, we need to know the total power consumption of the devices to run on solar power. With this knowledge, we can size the the system properly. We can choose the best battery bank capacity, inverter, and charge controller. We can also estimate the number of solar panels to get for the system.

Besides helping us size solar panels and solar systems, we can convert volts to watts to know how much energy our devices are consuming.

Choosing a Battery Bank

When we know the total power our devices will consume, we can choose a battery bank with sufficient capacity to power them.

Battery bank capacity is typically represented in Ah, Wh, or kWh. When capacity is in Wh or kWh, we can readily estimate the ideal battery capacity for our use case.

For instance, if all your devices have a total wattage of 250W, their total energy consumption in a day would be 250 x 24 = 6000 Wh. This calculation demonstrates how you can estimate how much energy your devices are consuming.

Going by this, if you want a battery bank that can power all your devices for a day, you need a battery capacity of at least 6000 Wh. Then, if you’d prefer that the battery bank powers all the devices for up to 4 days, you’ll need a battery capacity of 6000 Wh x 4 = 24,000 Wh.

Estimate the Number of Solar Panels

Battery bank size is one of many factors that determines the number/size of solar panels you get for your solar system. With larger battery banks, you’ll most likely need more solar panels. But with smaller battery banks, you may make do with small solar panels.

So, when you know the total wattage of your devices, you can estimate the number of solar panels you’ll need.

Choosing Inverter

Since inverters are sized in watts, you need to know the total wattage of your devices to get the correct inverter for your system. Basically, the capacity of your inverter must be higher than the total wattage of your devices.

So, if your devices have a total wattage of 300W, your inverter’s capacity must be higher than 300W.

Choosing Solar Charge Controller

Solar panel charge controllers have two main types of charge controllers based on technology type: PWM (Pulse Width Modulation) controllers and MPPT (Maximum Power Point Tracking) controllers.

Of both options, MPPT controllers are preferred for large solar systems because they can operate at a voltage that exceeds battery voltage. On the flip side, PWM controllers are better used for small solar power systems.

How to Convert Volts to Watts

Volts to Watts Formula for DC Circuit

To converts volts to watts for a DC system, we’ll multiply voltage by current:

watts = volts x amps

We can use this same formula to convert amps to watts.

We should point out that the amperage of an electrical circuit or device is typically its maximum current. So, when multiplying voltage rating by current rating, we are calculating maximum wattage/maximum power.

Volts to Watts Formula for AC Circuits

Converting volts to watts in an alternating current (AC) system is not as straightforward as a DC circuit.

We could use the same formula for both types of circuits, but the result for the AC system would not be accurate.

To accurately convert volts to watts in AC circuit, we must introduce a variable called power factor into our calculation.

Power Factor

Power factor (pf) is the portion of the apparent power an electrical circuit uses. Basically, power factor is the ratio of the power used by the circuit (real power, rp) to the total power available to the circuit (apparent power).

Going by the above, here’s the formula for power factor:

pf = real power ÷ apparent power (1)

since:

apparent power = r.m.s current x r.m.s voltage x c (2)

where c is a constant.

For a single-phase circuit, c = 1. For a three-phase circuit, when using line to line voltage, c = √3. Then when using line to neutral voltage, c = 3.

we can rewrite (1) as:

pf = rp ÷ (amps x volts x c) (3)

Going by (3), the pf of a single-phase AC circuit equals the real power divided by the product of volts, amps, and a constant.

For a three-phase circuit, when calculating with the line to line rms voltage, c = √3, so the pf is:

pf = rp ÷ (amps x volts x √3) (4)

When working with the line to neutral r.m.s voltage of a three-phase, c = 3, so the power factor would be:

pf = rp ÷ (amps x volts x 3) (5)

Conversion for AC Single Phase

To convert volts to watts in a single phase system, we’ll make rp the subject of formula (3):

rp = pf x amps x volts

Basically, to convert volts to watts in a single-phase, multiply voltage by phase current and pf.

Conversion for ac three-phase (line to neutral)

To convert volts to watts in a single-phase system using line to neutral voltage, we’ll make rp the subject of formula (5):

rp = pf x amps x volts x 3

Conversion for ac three-phase (line to line)

To convert volts to watts in a single-phase system using line to line voltage, we’ll make rp the subject of formula (4):

rp = pf x amps x volts x √3

We can convert amps to watts using all three volts to watts formulas for AC systems.

DC Volts to Watts Conversion Examples

Example 1

A solar-powered car fan has a rating of 3.6 volts and 0.6 amps. How many watts can it consume?

To convert the voltage of this solar fan to watts, all we have to do is multiply the voltage by the amperage:

= 3.6 x 0.6 = 2.16 watts

This means the maximum wattage of the car fan is 2.16 watts.

Example 2

A 12 volts solar battery has a current rating of 60A. How many watts can this battery discharge at its peak?

We can calculate how much power the battery can give off by multiplying its electrical pressure (voltage) by its current:

= 12 x 60 = 720 watts

AC Volts to Watts Conversion Examples

Example 1

A 220-volt single-phase outlet has a pf of 0.85 and current of 12 amps. How many watts can it produce?

Since we know the pf, voltage, and amperage of , we can solve the question in one step:

The formula for single-phase AC circuits is watts = pf x amps x volts

So, the maximum power the outlet can produce is:

= 0.85 x 12 x 220 = 2,244 watts

Example 2

What’s the maximum wattage of a three-phase AC circuit with a 240-volt line to neutral voltage, pf of 0.8, and current of 15 amps?

watts = pf x amps x volts x 3

= 0.8 x 15 x 240 x 3 = 8,640 watts

Example 3

If a three-phase AC system whose line to line volt is 350 volts has a pf of 0.88 and a current of 30 amps, what is the maximum wattage it can produce?

watts = pf x amps x volts x √3

= 0.88 x 30 x 350 x 1.73 = 15,985.2 watts

Volts Conversion Chart for Common DC Voltages

How to Convert Volts to Watts Using Resistance

We can also convert watts from volts using resistance instead of current.

For a DC system, the conversion formula would be:

watts = volts² ÷ resistance

For a single-phase AC, the formula would be:

rp = pf x volts² ÷ resistance

For a three-phase AC system using line to line voltage, the formula would be:

rp = pf x volts² x √3 ÷ resistance

For a three-phase AC system using line to neutral voltage, the formula would be:

rp = pf x volts² x 3 ÷ resistance

How to Convert Watts to Volts (W to V)

We can easily convert watts to volts by adjusting the formulas for volts to watts conversion. So, for a DC system, the watts-volts conversion formula would be:

volts = watts/amps

For a single-phase AC system, the formula would be:

volts = rp ÷ (pf x amps)

To convert watts to line to line volt of a three-phase system:

volts = rp ÷ (pf x amps x √3)

To convert watts to line to neutral volt:

volts = rp ÷ (pf x amps x 3)

So, whenever you have no access to a watts-volts calculator, you can work with these formulas.

How to Convert Watts to Amps (W to A)

To calculate amps from watts, we can adjust the volts to watts formulas.

For a DC system:

amps = watts/volts

For a single-phase AC system:

amps = rp ÷ (pf x volts)

To convert watts to amps using line to line volt in a three-phase system:

amps = rp ÷ (pf x volts x √3)

To convert watts to amps using line to neutral volt:

amps = rp ÷ (pf x volts x 3)

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