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VANNER POWER GROUP
VANNER POWER GROUP
IQ SERIES
IQ SERIES
IQ SERIES OWNERS MANUAL
- 39 -
the basic information required to properly size your vehicle alternator and inverter battery, as well as give some
examples of AC power distribution systems which are commonly used. Keep in mind that if information in this
manual directly conflicts with instructions from a specific battery or other equipment manufacturer, you should
follow that manufacturer's recommendations.
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, 2400 watts = 12 volts DC x 200 amps, and 2400 watts = 120 volts AC x 20 amps. From
these two examples of 2400 watts at 12 volts and 2400 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
For 24 volt DC inverters: output watts ÷ 20 = 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
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.
Sizing the Inverter Battery
Sizing a battery system for an inverter application can be a very tedious task if all the different variables, such as
discharge rate, depth of discharge, and operating life time are included in the calculations. To simplify these
calculations and get a reasonably correct battery size, we will assume: 1) A 50% depth of discharge for the
purpose of obtaining a reasonable life time for a reasonable battery system cost, 2) there is no charge current into
the battery system, 3) the batteries are in a fully charged state at the beginning of the discharge cycle, and 4) the
DC current draw from the battery does not exceed 1/3 the battery C rate for any length of time.
Follow the steps listed below to find the A-H capacity required for your application.
Steps
1.
Make a list of each appliance, its power requirement in watts, and the amount of time in hours it will be
operating between charging cycles.
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