The amount of current (Amps) that a 1500 Watt inverter draws will mainly depend on the voltage of the battery bank (12V, 24V, or 48V), and the power usage (Watts) of the AC load.
However, the wires and over-current protection devices (fuses and circuit breakers) used for the DC side of the inverter (between the battery and the inverter), should be sized based on the maximum amount of current (Amps) that the inverter is capable of drawing from the battery bank.
In this article, I’ll show you how to calculate the maximum amount of current (in Amps) that your 1500 Watt inverter is capable of pulling from your battery bank.
I’ll then discuss the proper wire and fuse (or circuit breaker) sizes necessary to connect your 1500W inverter to the battery bank.
How many amps does a 1500 watt inverter draw?
The maximum amount of current that a 1500 Watt inverter draws will mainly depend on 2 factors: The voltage of the battery bank, and the efficiency of the inverter.
In general, a 1500 Watt inverter running on a 12V battery bank can draw as much as 175 Amps of current. A 1500W inverter running on a 24V battery bank can draw up to 90 Amps of current. If the battery bank is rated at 48 Volts, the inverter will not exceed a 45 Amp draw.
This is assuming the 1500W inverter’s efficiency (at maximum load) is around 85%. Inverters with a higher DC-to-AC conversion efficiency (90-95%) will draw fewer amps and less efficient inverters (75-80% efficiency) will draw more current.
To calculate the maximum amp draw of your 1500 Watt inverter, use the following formula:
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
The 2 variables in our formula are the Inverter’s Efficiency and the Lowest Battery Voltage.
The Efficiency of the inverter:
Inverters convert DC (Direct Current) Power into the AC (Alternating Current) Power that your appliances require. However, some of the power drawn from the battery bank will be lost due to the fact that this conversion process is never 100% efficient.
In other words, in order for a 1500 Watt inverter to put out 1500 watts of power, it will have to draw more than 1500 watts from the battery. Exactly how much more power will depend on how efficient the inverter is.
In general, Pure Sine Wave (PSW) inverters are around 90% efficient at maximum load, and Modified Sine Wave (MSW) inverters are around 80% efficient.
You can refer to the documentation of your inverter to determine its efficiency, if the documentation doesn’t specify the efficiency of the inverter, you can use an efficiency of 85% as a rule of thumb in these calculations.
Lowest Battery Voltage:
The voltage of a battery decreases relative to its State Of Charge (SOC). For example, a battery bank that’s rated at 12 Volts, will have a voltage of around 14 Volts across its terminals when it’s fully charged (100% SOC).
However, the same battery bank will have a voltage of about 10 Volts across its terminals when it’s depleted (0% SOC).
The following table gives you an idea about the actual voltages of battery banks with different voltage ratings, at different States Of Charge:
| State Of Charge\Battery Bank’s Voltage rating | 12V | 24V | 48V |
| 100% | 14.4V | 28.8V | 57.6V |
| 100% | 13.6V | 27.2V | 54.4V |
| 90% | 13.3V | 26.6V | 53.2V |
| 70% | 13.2V | 26.4V | 52.8V |
| 40% | 13.1V | 26.2V | 52.4V |
| 30% | 13V | 26V | 52V |
| 20% | 12.9V | 25.8V | 51.6V |
| 15% | 12.5V | 25V | 50V |
| 10% | 12V | 24V | 48V |
| 0% | 10V | 20V | 40V |
If our 1500 Watt inverter is required to put out 1500 Watts of power, it will continue to do so until the battery’s voltage is low enough for it to be disconnected.
Since Current is Power divided by Voltage (Current = Power ÷ Voltage), at a steady power output of 1500 Watts, the amount of current that our 1500W inverter pulls from the battery will be at its maximum when the voltage of the battery is at its lowest.
In other words, given that you allow the battery to fully discharge (100% Depth Of Discharge), the 1500 Watt inverter will pull the most amount of current (Amps) at:
- 10 Volts if the battery is rated at 12V
- 20 Volts if the battery is rated at 24V
- 40 Volts if the battery is rated at 48V
For example, let’s say our 1500 Watt inverter is 90% efficient and is running on a 12V battery bank. Let’s also assume that the batteries in our battery bank are Lithium and are allowed to discharge fully.
This means that the lowest voltage at which our inverter is going to pull current from the battery is 10 Volts.
The Maximum Amp Draw of our 1500W inverter can be calculated as such:
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ 90%) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ 0.9) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1666.7 Watts) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = 166.7 Amps
Now, to give another example, let’s assume our 1500 Watt inverter is only 85% efficient and is running on a 24V battery bank. And let’s assume that the batteries in our battery bank are AGM batteries, which we only allow to discharge to about 50% (50% Depth Of Discharge).
The voltage of a single 12V AGM battery at 50% State Of Charge is about 12 Volts. Since our AGM battery bank is rated at 24V, it should not go below 24 Volts.
Assuming the inverter has a programmable Low Voltage Disconnect (LVD), or an LVD device (such as Victron’s BatteryProtect) is used, the lowest voltage at which our inverter is going to pull current is 24 Volts.
The Max. Amp Draw of our 1500W inverter is:
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ 85%) ÷ 24 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ 0.85) ÷ 24 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1764.7 Watts) ÷ 24 Volts
Inverter’s Maximum Amp Draw (in Amps) = 73.5 Amps
Now that we know how to determine the maximum amp draw of our inverter, we can use that to find the proper wire size.
What gauge wire for 1500 watt inverter?
In general, if your 1500 Watt inverter is going to run on a 12V battery bank, you’ll need 4/0 AWG copper wires. If the 1500W inverter is going to run on a 24V battery bank, you’ll need 1/0 AWG copper wires. If the battery bank is rated at 48V, you’ll need 4 AWG copper wires.
As there are other variables that might affect the size of the wires that you need, such as maximum room temperature and voltage drop, I recommend using our Inverter wire size calculator to properly size your wires.
In any case, you’re also going to need an over-current protection device (OCPD) such as a fuse or a circuit breaker to protect your wires and equipment if an over-current occurs.
What size fuse (or circuit breaker) for a 1500 watt inverter?
A fuse or a circuit breaker should be placed on the positive side between your battery bank and inverter to protect your wires and equipment. These devices are rated in Amps, and the proper Amp rating will mainly depend on the maximum amp draw of your 1500W inverter.
Generally, if your 1500 Watt inverter is going to run on a 12V battery bank, the fuse or circuit breaker that you need should be rated at 200 or 225 Amps. If the battery bank is rated at 24V, the fuse or circuit breaker should be rated at 100 or 110 Amps.
If your 1500W inverter is going to run on a 48V battery bank, the fuse or circuit breaker should be rated at 50 or 60 Amps.
To size the fuse or circuit breaker properly, multiply the Maximum Amp Draw (previously calculated) by a factor of 1.25 and then round up to the next standard fuse or circuit breaker ratings.
The standard fuse or circuit breaker ratings are: 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000 5000, and 6000 Amps.
For example, let’s say our 1500 Watt inverter is 85% efficient and is running on a 12V battery bank which is allowed to discharge fully.
The lowest voltage at which our inverter is going to pull current from the battery bank is 10 Volts. The Maximum Amp Draw of our inverter is then calculated as such:
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ Inverter’s Efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ 85%) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1500 Watts ÷ 0.85) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1764.7 Watts) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = 176.5 Amps
We then multiply this value by 1.25 to determine the fuse or circuit breaker amp rating:
Fuse or Circuit Breaker’s Amp Rating = Maximum Amp Draw (Amps) x 1.25
Fuse or Circuit Breaker’s Amp Rating = 176.5 Amps x 1.25
Fuse or Circuit Breaker’s Amp Rating = 220.6 Amps
Since they don’t make 220.6 Amp fuses or circuit breakers, we’ll round up to the next standard amp rating: 225 Amps.
However, another important thing to note is that the Amp rating of the fuse or circuit breaker that you use should not exceed the ampacity of the wires you’ll be using.
Since our 1500W inverter is going to run on a 12V battery bank, we’ll be using 4/0 AWG copper wires. Copper wires of this size can handle up to 230 Amps of current. A 225 Amp fuse or circuit breaker should be able to protect our wires and terminals from overheating in an over-current situation.
