How Many Amps Does a 1000 Watt Inverter Draw?

1000 Watt inverters are a very popular class of power inverters suitable for use even with car batteries, at least for shorter periods of time.

With 1000 continuous watts and often 1500-2000 surge watts, 1000 watt inverters are suitable for powering smaller devices, tools, gadgets, and appliances. However, many people wonder what is the actual load on the battery in terms of the current draw.

Published: January 22, 2022.

Inverter Current (Amps) and Power (Watts) Draw

When calculating the required current and power of the inverters one must know output power (watts), energy efficiency of the power inverter, and input voltage.

Input Voltage: Most 1000W power inverters are 12V units with some models accepting a broader range, including 24V, 36V, and even 48V.

Energy Efficiency varies depending on the model, but on average power inverters feature energy efficiency in the 80-95% range - of course, models with higher energy efficiency tend to be more expensive.

Surge vs Continuous Power: 1000W power inverters feature continuous power of 1000W, although some models support up to 1100-1200 watts. Surge power is usually double the continuous power and is usually in the 1500-2500W range - this is output power that the inverter can provide for a very short period of time and is required when tools and appliances with electric motors and similar loads are powered using inverters.

In order to calculate the inverter current draw, first, we must calculate input power - the power that the battery must provide to the inverter in order for the inverter to provide 1000 output Watts.

P_Bat (W) = P_Inv (W) / Energy Efficiency (%)

In order to calculate battery current draw, we use the following formula:

I_Bat (A) = P_Bat (W) / U_Bat (V)

The following table lists required battery power and current in order for the inverter to provide 1000W, depending on the inverter energy efficiency and the battery voltage:

Energy Efficiency (%)	80%	85%	90%	95%
Battery Power (W)	1250W	1177W	1112W	1053W
12V	104.2A	98.1A	92.7A	87.8A
24V	52.1A	49.1A	46.4A	43.9A
36V	34.8A	32.7A	30.9A	29.3A
48V	26.1A	24.6A	23.2A	22.0A

As one can see, input power varies significantly depending on the energy efficiency of the power inverter. Also, as the battery voltage is increased, required currents are significantly decreased. Also, smaller currents mean less heat loss in the wires, increasing the overall energy efficiency of the system.

Note: most power inverters feature energy efficiency in the 85-90% range, with 85% being more common - this must be checked for each inverter model.

1000 Watts Inverter Battery Sizing

Battery size in terms of voltage and capacity depends on the actual load and required runtime of the battery-inverter system.

Basically, there are two types of deep cycle batteries suitable as inverter batteries - lead-acid batteries and lithium batteries, each one with its own pros and cons.

Lead-acid batteries are heavy and support up to 200-300 charging/discharging cycles down to 100% DoD and up to 400-500 charging/discharging cycles down to 80%.

Also, lead-acid batteries are cheap and reliable - after all, they are used for centuries!

But, the biggest issue with lead-acid batteries is the capacity loss when they are discharged with strong currents - for example, 1.0C current causes capacity loss down to 55-72% of the battery's nominal capacity.

So, if You have a brand new, fully charged 12V 100Ah lead-acid deep cycle battery and You want to power a 1000 Watt inverter with an energy efficiency of 85%, You can expect a runtime of ~30-35 minutes.

Reasons:

- capacity loss due to the strong discharge current: 98.1A @12V is very close to the 1.0C current,

- as the battery voltage drops over time (below 12V!), the inverter must draw even more current in order to provide 1000 output watts.

For short: if You intend to power a 12V 1000W inverter, go for a 100Ah or a larger 12V lead-acid battery, or the overall energy efficiency of the battery/inverter system will be rather low.

Lithium Iron Phosphate (LiFePO₄) batteries are rather lightweight, maintenance-free batteries that support up to 2000-4000 charging/discharging cycles down to 100% DoD and up to 4000-5000 charging/discharging cycles down to 80%.

Also, they can be recharged quickly, and they don't suffer from the capacity loss when being discharged with 1.0C or similar currents, at least not as much as lead-acid batteries.

However, lithium batteries feature a built-in Battery Management System (BMS) that limits their continuous output current usually down to 1.0C, with surge current usually around 2.0C for 3 to 30 seconds, models dependent.

When the lithium batteries are being discharged with smaller currents, for example, 0.1C, their output voltage is usually around 12.8V most of the discharge time (90+%). When their discharge current is around 1.0C, their output voltage is usually around or slightly above 12V most of the discharge time (90%+) leading to much better energy efficiency when compared with lead-acid batteries.

Thus, if You have a fully charged 12V 100Ah LiFePO₄ battery powering a 12V 1000W inverter with 85% energy efficiency, You can expect a runtime of almost 55-60 minutes, which is a much better result when compared with lead-acid batteries.

Note: lithium batteries also cost more than lead-acid batteries and require dedicated lithium battery chargers or advanced AGM battery chargers with dedicated lithium battery charging modes. Also, if the inverter tries to draw more current than the BMS supports, BMS will shut off the battery in order to protect it - in that case, the inverter loses power and also shuts down.

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Long Story Short: Depending on the voltage and the energy efficiency, 1000W 12V inverter draws ~88-105 Amps, 1000W 24V inverter draws 44-52 Amps, 1000W 36V inverter draws 30-35 Amps and 1000W 48V inverter draws 22-26 Amps.

The inverter battery sizing must be done according to the battery chemistry (lead-acid or lithium) and a required runtime.

For safety reasons, it is always recommended to go for a somewhat larger battery - generally, regardless of the battery chemistry 12V 100Ah battery is the smallest battery recommended for the 12V 1000W power inverter.