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QuietPower 1800 Inverter Owner’s Manual Rev 15 OCT 01 Page 16
Table 5. Sample Operating Time Calculation.
Load Power
Consumption
Operating time (cumulative
usage between recharges)
Watt-hours (power
consumption * operating time)
TV & VCR 115 watts 3 hours (1 hour per day) 345
Coffee Maker 750 watts 1 hour (20 min per day) 750
Microwave Oven 800 watts 0.5 hour(10 min per day) 400
TOTAL 1495
Convert the watt-hours to amp-hours by dividing total watt-hours by 10: 30°C (86°F)
1495 watt hours / 10 = 149.5 amp-hours
A 150 amp-hour battery is required to supply enough power for the above loads, and become completely
discharged. Ideally, you normally want to discharge your battery to only 50% capacity, so for the above
loads, you would require 300 amp-hours of battery capacity.
When sizing your battery, be generous. More capacity is better since you will have more reserve
capacity, and your battery won’t be discharged as deeply. Battery life is directly dependent on how
deeply the battery is discharged. The deeper the discharge, the shorter the battery life.
As your power requirements increase, to obtain sufficient battery capacity, you may need to use more
than one battery. Two identical batteries can be connected positive to positive and negative to negative
in a parallel system that doubles the capacity and maintains the voltage of a single battery. It is not
recommended to connect batteries from different manufacturers or with different amp-hour ratings or with
different battery electrolytes in parallel. Decreased battery life may result.
10. Performance Graphs and Specifications
10.1. Power Derating Curve
As with all inverters, the amount of continuous power that the QuietPower Inverters can deliver without
overheating is limited by ambient (surrounding air) temperature. The nominal temperature for the power
ratings specified for the QuietPower Inverters is 25°C (77°F). They will operate and deliver their
continuous power ratings at higher temperatures, but the extent to which they can do this is limited by the
ambient temperature as well as the input voltage from battery. The following “Power Derating Curve vs.
Temperature” illustrates the relationship between power output and ambient temperature.
The rated power output of the QP-1800 inverter is 1800W up to 25°C ( 77°F). Operating the unit above
this temperature will result in thermal shutdown or decreased performance. At input voltages less than
24V, the unit runs warmer which will cause thermal shutdowns at temperatures below these ambient
temperature guidelines.
Operating the unit in conditions outside the power and temperature limits (“above” and “to-the-right” of the
derating curves) will result in thermal shutdown and/or significantly decreased performance. In addition,
operation in this range is outside of the ratings covered by the product’s regulatory approvals.
These curves are published for information purposes only to let you know what may happen while
operating in high ambient temperature conditions. Under normal battery voltage conditions and non-
extreme temperatures, inverter operation will be within the derating curve.