Plugging a 250-watt equipment like a sound bar with other appliances into a single outlet might overload the circuit. You will risk damaging the appliances or even burning down your home if you don’t know the current draw of your 250-watt equipment.
How many amps is 250 watts? It can be 20.8 amps at 12V and 10.4 amps at 24V DC, at least 2.08 amps at 120V, and least 1.04 amps at 240V single-phase AC, and at least 0.69 amps at 208V three-phase AC.
Table of Contents
250-watt Conversion to Amps at Different Voltages
We prepared a conversion table from 250w to amps for you at various voltages.
The current ratings from DC and single-phase AC supplies are given below. We did the conversion for 250 watts as well as other power ratings.
For AC supplies, we computed the current based on the power factors 1, 0.85, and 0.5.
|Power (watts)||DC||single phase AC|
|12 volts||24 volts||120 volts||240 volts|
|1 PF||0.85 PF||0.5 PF||1 PF||0.85 PF||0.5 PF|
Comparison of 250 Watts at Different Current Supplies
Homes in the US are commonly supplied with single phase AC at 120 volts / 240 volts. However, commercial establishments are supplied with three-phase AC at 120 volts / 208 volts.
We also prepared a conversion table for 250 watts to amps at three-phase AC. We also include the three power factors just like single phase AC:
|Power (watts)||AC three phase|
|Line to neutral 120 volts||Line to line 208 volts|
|1 PF||0.85 PF||0.5 PF||1 PF||0.85 PF||0.5 PF|
How to Convert 250 Watts to Amps
Let us start with direct current or DC. This kind of supply is common in vehicles and can be described using the basic equation of electric power:
Where P = power in watts
I = current in amps
V = voltage in volts
We derive the equation for current as:
If we solve for the current drawn by a 250-watt amp from a 24-volt battery in a vehicle, then we can estimate the current as:
I=P/V=(250 watts)/(24 volts)=10.42 amps
Now let us talk about alternating current, or AC. Unlike DC which continuously allows current to flow in one direction, AC flips from one direction to another as the voltage changes in a cycle.
Homes serviced with AC are usually single-phase at 240 volts with two hot wires and one neutral wire. If you connect to both hot wires, you get 240 volts, but if you connect to one hot wire and the neutral, you get 120 volts.
In an ideal situation, the cycling of voltage and current have the same phase. In a lot of cases, though, the current cycling may be out of phase with the voltage cycling and decreases the amount of usable power.
Thus, when we determine the current draw of a single-phase AC supply from the outlet, we account for the power factor. It is a unitless quantity between 1 and 0 that represents the amount of power needed to reach its rated power output:
Where PF = power factor
P = actual or rated power in watts
S = apparent or outlet-supplied power in volt•amps
If you will notice, apparent power is expressed in volt•amps, not the usual watts. This can be seen from 1 amp = watts/volts.
If we account for the power factor when determining the current drawn from an AC supply, then we need to derive the current from the apparent power. The expression will look like this:
Let us say we want to convert 250 watts to amps 240V single phase AC supply with a power factor of 0.95 (which is a very good power factor, by the way). We use the expression above to get:
I=P/(PF∙V)=(250 watts)/(0.95∙240 volts)=1.10 amps
This equation can be used for both the 240V and 120V AC supply. You can even use this at 220V when the 240-volt supply fluctuates.
Lastly, let’s talk about three-phase supply. Instead of two live wires, three-phase AC uses three live wires, with each wire carrying a current with phase variations 120 degrees apart.
In the US, the most common three-phase AC supply for establishments is the 120-volt/208-volt supply. This means, if you connect one live wire to neutral, you get 120 volts. But if you connect to two live wires, you get 208 volts.
If we want to convert watts to amps when the device is connected to one live wire and neutral, we solve it just like how we solve for single phase AC. Thus, the expression for one line in three-phase AC will be:
Where VL-N = voltage from line to neutral
However, if we convert when the device is connected to two live wires, account for the 120-degree phase difference between the two. The expression will be:
I=P/(√3 PF∙V_(L-L) )
Where VL-L = voltage from line to line
√3 = constant seen in three-phase connections
So if we convert 250 watts to amps in a 208 volt three phase AC supply with a power factor of 0.95, then:
I=P/(√3 PF∙V_(L-L) )=(250 watts)/(√3∙0.95∙208 volts)=0.73 amps
If we want to know how many amps is 250 watts, then we have to see if it’s DC, single phase AC, or three-phase AC. This way, we will not have any overloading issues when we try to connect our 250-watt appliance to an almost-full circuit.
The current can go as low as 0.69 in a three-phase 208-volt supply, or as high as 20.83 volts in a DC 12-volt supply. So make sure you look at our tables to prevent any mistakes.
I am Edwin Jones, in charge of designing content for Galvinpower. I aspire to use my experiences in marketing to create reliable and necessary information to help our readers. It has been fun to work with Andrew and apply his incredible knowledge to our content.