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How much current will an

inverter draw from my


This depends on the equipment

connected to the inverter. There is a

simple method to calculate how much

power your inverter is using: For 12-volt

inverters, divide the connected load by

10; for 24-volt inverters, divide by 20.


How much does an inverter consume

with a 400 W load connected?

For a 12 V inverter such as a Mass Sine

12/1200, consumption will be 400/10 =

approx. 40 amps. For a 24 V inverter,

say a Mass 24/1500, the corresponding

figure is 400/20 = approx. 20 amps.

It is important to remember that this is

only an approximation: The actual

consumption will tend to be some 5 to

15 % less, depending on the load type.


How thick should my battery

cables be?

Using the method described above,

calculate how much power your inverter

will be drawing at maximum capacity (120

amps in the case of a Mass Sine 12/1200,

for example). Then count 3 amps per

mm². In the above example this is 120

divided by 3 = 40 mm². The standard

cable thickness closest to that is 35 mm².

This rule applies to cables up to three

metres in length. If the inverter is further

away from the battery, choose the next

size up (50 mm² for instance).


Does an inverter need

a lot of ventilation?

An inverter needs very little ventilation -

two approx. 60 cm² ventilation openings

are usually enough. Larger inverters,

from 1500 W upwards, need twice that

size. Inverters used in high ambient

temperatures, and those expected to

be operating at full capacity for a long

period, require openings that are four

times as large.


Can an inverter be used in

parallel with the generator or

the grid?

No, stand-alone inverters cannot function

in parallel with a generator or grid

connection. A Mastervolt Mass Combi

is the solution if you need more power

than is available from the grid connection

or the generator. These models can

compensate for the lack of grid or

generator power using the batteries.

A Masterswitch or Systemswitch needs

to be installed when grid or generator

power is connected to the onboard grid

simultaneously with an inverter. The

main function of the Masterswitch is the

automatic and safe switching between

grid, generator and inverter power.


What is no-load?

No-load is the amount of current used by

the inverter when no loads are switched

on, while the inverter is switched on



What is efficiency?

An inverter uses a small amount of

energy during the conversion process.

The difference between the input power

and the output power is expressed in

percentages. The efficiency of modern

inverters is more than 92 %. This means

that a maximum of 8 % of the power

consumption is used to convert battery

voltage to 230V/50Hz. A connected load

of 250 watt, for instance, requires less

than 270 watt to be supplied by the


Efficiency versus output power:


What are trapezoidal or

square wave inverters?

Square wave and trapezium inverters

are often available in DIY shops and

supermarkets at low prices. These

cheap inverters are not suitable for

all loads, however, and therefore

not safe to use. Modern inverters

generate a sine wave-shaped

output current similar to or even

better than that of the public grid

and perfectly suited to powering

sensitive equipment. Trapezoidal

inverters, also called modified sine

wave, are the ancestors of the

modern sine wave inverters. As

the name suggests, they generate

an output voltage in the shape of

a trapezium. This type of voltage

is inappropriate for sensitive

equipment. The square wave

inverter is the predecessor of the

trapezoidal inverter and represents

the first generation of inverters. It

is also very unsuitable for delicate



Square wave

Trapezoidal or modified sine wave

Sine wave



input voltage 12/24 V