Owner`s manual

General Information
TruSine 4.5 kW Inverter Page 24 Owners Manual
are obtained by multiplying volts times amps produced or used by a device
To properly determine an inverter size (in watts) for your application decide which AC loads you plan to operate.
Inverter size is the sum of the wattages of the AC loads that you wish to run at the same time, plus a safety
factor, say 10 to 20 percent.
Continuous Output Power - Continuous power is defined as the AC power in watts (or voltamps) an inverter can
produce on a continuous basis. The ambient temperature can affect the continuous rating of the inverter, and is
normally specified, e.g., 25° C. or 40°C.
Surge Output Power - Inverter power can also be rated in terms of surge power. Surge power is the short term
duration of AC power that the inverter can produce. It is often specified as the watts (or voltamps) that can
operate a resistive load for two or three seconds. Sometimes this is specified in AC amps because the inverter
may allow output voltage to drop (which would reduce is wattage). Like continuous power, the surge rating is
affected by ambient temperature.
Note - Regardless of an inverter’s power ratings, an inverter’s AC output capability is only as strong as the DC
source. To achieve optimum performance an inverter must be installed with properly sized cable and have an
ample DC supply. Recommended cable sizes are listed in the DC Cable and Fuse Chart. The following
sections in this manual will cover the basic information required to properly size the inverter battery and the
vehicle alternator. Keep in mind that if information in this manual directly conflicts with instructions from a
specific battery or other equipment manufacturer, Vanner recommends that those manufacturer's
recommendations be followed.
6.3 DC Power Consumption
An inverter takes in DC power, and produces AC power to operate AC loads. In general, we can see a direct
relationship between DC input power and AC output power. This allows us to establish the following rule of
thumb:
For 12 volt DC inverters: Output Watts ÷ 10 = DC Input Amps.
For 24 volt DC inverters: Output Watts ÷ 20 = DC Input Amps.
This rule of thumb can be used to estimate the minimum alternator size required for your application. It may
also be used in calculating the minimum size battery required when operating from an alternator and battery
combination; a photovoltaic panel and battery combination; or when operating from battery alone. The following
examples should help to clarify the use of this rule of thumb.
Example A
What is the DC current draw of a 12 volt DC input inverter when it is operating a vacuum cleaner with a
name plate rating of 6 amps at 120 volts AC?
The appliance rating is given in amperes, so we must first calculate the power it consumes. Then the
rule of thumb can be used to find the DC input current of the inverter.
Output power = 120 volts x 6 amps = 720 watts, and
DC input current = 720 ÷ 10 = 72 amps DC.
Example B
What is the DC current draw of a 24 volt DC input inverter when it is operating a toaster with a name
plate rating of 1050 watts at 120 volts AC?
Since the appliance is rated in watts, the rule of thumb can be applied directly:
DC input current = 1050 ÷ 20 = 52.5 amps DC.
This information on estimating the DC input current requirement for an inverter will allow you to size an
alternator or charging system to supply an inverter for continuous operation. This rule of thumb will be used
later in the discussions on battery sizing.