In this article, I discuss the amount of Current (Amps) that a 1000 Watt inverter is capable of pulling from the battery and explain how to use the voltage of your battery bank and the efficiency of your inverter to determine this amount of current.
I also discuss the size of wires and circuit breaker that you’ll need to connect your 1000W inverter to the battery bank.
How many amps does a 1000 watt inverter draw?
The maximum amount of Current (Amps) that a 1000 Watt inverter draws will mainly depend on the voltage rating of the battery bank (12V, 24V, or 48V), and on the efficiency of the inverter (75-95%).
Generally, a 1000 Watt inverter can draw up to 120 Amps if the battery bank is rated at 12 Volts, or up to 60 Amps if the battery bank is rated at 24 Volts. If the battery bank is rated at 48 Volts, the 1000 Watt inverter will not draw more than 30 Amps.
This is assuming the 1000W inverter is about 85% efficient. Inverters that are more efficient (90-95% efficient) will draw fewer Amps, and inverters that are less efficient (75-80% efficient) will draw more Amps.
You can calculate the maximum amount of current (Amps) that your inverter is capable of drawing from the battery by using the following formula:
Inverter’s Maximum Amp Draw (in Amps) = (Inverter’s Continuous Power rating (in Watts) ÷ Inverter’s efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
For example, let’s say our 1000 Watt inverter is 85% efficient and is running on a 24 Volt battery bank.
Although our battery bank is rated at 24 Volts, the actual voltage across the terminals of the battery is going to increase above or decrease below 24 Volts depending on the State of Charge (SOC) of the battery bank.
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 |
The voltage across the terminals of the battery bank is going to be at its lowest when the battery bank is depleted (0% SOC), but if required, our 1000 Watt inverter will still deliver 1000 Watts at its output.
So, the amount of Current (Amps) that our inverter is going to pull, will be at its maximum when the voltage of the battery bank is at its lowest.
Following our example, our battery bank is rated at 24V. If we look at the table above, we can see that the lowest voltage for this battery bank is going to be 20 Volts.
We’ve also made the assumption that our 1000 Watt inverter is 85% efficient. We can then calculate the Maximum amount of current that the inverter is expected to draw:
Inverter’s Maximum Amp Draw (in Amps) = (Inverter’s Continuous Power rating (in Watts) ÷ Inverter’s efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
Inverter’s Maximum Amp Draw (in Amps) = (1000 Watts ÷ 85%) ÷ 20 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1000 Watts ÷ 0.85) ÷ 20 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1176.5 Watts) ÷ 20 Volts
Inverter’s Maximum Amp Draw (in Amps) = 58.8 Amps
Now, let’s say that for example, our 1000 Watt inverter is 90% efficient, and is running on a 12 Volt battery bank.
The lowest battery voltage is going to be 10 Volts, let’s calculate the Maximum Amp Draw:
Inverter’s Maximum Amp Draw (in Amps) = (Inverter’s Continuous Power rating (in Watts) ÷ Inverter’s efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
Inverter’s Maximum Amp Draw (in Amps) = (1000 Watts ÷ 90%) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1000 Watts ÷ 0.9) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1111 Watts) ÷ 10 Volts
Inverter’s Maximum Amp Draw (in Amps) = 111 Amps
Now that we know how to calculate the maximum amp draw of a 1000 Watt inverter, we can use that to size our wires.
What gauge wire for a 1000 watt inverter?
The required wire size for a 1000 Watt inverter will mainly depend on the Voltage of the battery bank.
Generally, you’ll need a 1/0 AWG copper wire if the 1000 Watt inverter is running on a 12V battery bank, or a 3 AWG copper wire if the 1000W inverter is running on a 24V battery bank. If the battery bank is rated at 48V, an 8 AWG copper wire will be sufficient.
However, there are other variables that may influence the size of the wire that you need for your 1000 Watt inverter. Such as the distance between the battery bank and the inverter, and the maximum room temperature.
To size the wire properly, I recommend using our Inverter wire size calculator.
In any case, once you’ve determined the size of the wire that you need, you’ll also need an Over-Current Protection Device (Circuit Breaker or Fuse) to protect your wires and equipment.
What size circuit breaker (or fuse) for 1000 watt inverter?
A fuse or a circuit breaker placed on the positive conductor between your battery bank and inverter will protect the wires from overheating and potentially melting.
If your 1000 Watt inverter is running on a 12V battery, the circuit breaker (or fuse) should be rated at 150 Amps. If your 1000W inverter is running on a 24V battery, the circuit breaker should be rated at 80 Amps.
If the battery bank is rated at 48V, the circuit breaker or fuse should be rated at 40 Amps.
To determine the size of the circuit breaker properly, simply multiply the Maximum Amp Draw calculated in the first section of this article, by a factor of 1.25:
Circuit Breaker (or Fuse) Amp Rating = Maximum Amp Draw (Amps) x 1.25
For example, if our 1000 Watt inverter is 85% efficient, and is running on a 24V battery bank, the Maximum Amp Draw is:
Inverter’s Maximum Amp Draw (in Amps) = (Inverter’s Continuous Power rating (in Watts) ÷ Inverter’s efficiency (%)) ÷ Lowest Battery Voltage (in Volts)
Inverter’s Maximum Amp Draw (in Amps) = (1000 Watts ÷ 85%) ÷ 20 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1000 Watts ÷ 0.85) ÷ 20 Volts
Inverter’s Maximum Amp Draw (in Amps) = (1176.5 Watts) ÷ 20 Volts
Inverter’s Maximum Amp Draw (in Amps) = 58.8 Amps
We then multiply by 1.25:
Circuit Breaker Amp Rating = Maximum Amp Draw (Amps) x 1.25
Circuit Breaker Amp Rating = 58.8 Amps x 1.25
Circuit Breaker Amp Rating = 73.5 Amps
Now, there are no circuit breakers or fuses rated at 73.5 Amps. However, all we have to do is find the next larger Standard Amp Rating.
The Standard Amp Ratings of Over-Current Protection Devices 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.
An 80 Amp Circuit Breaker such as this one, or an 80 Amp Fuse such as this one, would both be a good fit for our system.
