Vanner SRC12-1200L Owner's Manual - Owner'S Manual - D913482
Owner's Manual - D913482
SRC12-1200L/S INVERTER/CHARGER
10/31/08 - 10:20 AM
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I N C O R P O R A T E D
12.6 DC POWER CONSUMPTION
An inverter takes in DC power, and produces AC power to operate attached 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:
For every 10 watts of AC output power, an inverter requires one amp of DC input power on a 12 volt
input inverter.
Example:
An inverter powering a 1,000-watt AC load requires 100 amps DC.
1000 watts/10 = 100 amps
Using our rule, we can determine the requirements for an electrical system needed to power our
inverter (typically, an alternator and battery combination, or a photovoltaic panel and battery
combination).
12.7
INVERTER DC INPUT CURRENT REQUIREMENTS
A DC to AC inverter converts DC power into AC power. For the purposes of this discussion, power (watts)
is equal to the supply voltage (volts) multiplied by the current draw (amps) from the supply for both AC and
DC circuits. For example, 2,400 watts = 12 volts DC x 200 amps, and 2,400 watts = 120 volts AC x 20
amps. From these two examples of 2,400 watts at 12 volts and 2,400 watts at 120 volts, it is easy to see
that since there is a 1 to 10 voltage conversion (12 to 120), there is a 10 to 1 amp conversion (200 to 20). A
more accurate relationship between the input power and output power is:
(DC Input Power) x (Efficiency) = (AC Output Power)
This formal relationship has lead to the following rule of thumb for estimating the DC input amps for an
inverter:
For 12 volt DC inverters: output watts ÷ 10 = DC input current
This rule of thumb can be used to estimate the minimum alternator size required for your application and is
also used later in calculating the minimum size battery required when operating from battery only. 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 nameplate rating of six 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.
This information on estimating the DC input current requirement for an inverter would allow you to
size an alternator or charging system to supply an inverter for continuous operation.