Subject: Inverters 4 of 5



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(3584)   Mon 29 Jul 91 12:51                             
By: Don Kulha
To: all

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Average Consumption Put a star beside all appliances that are 
required to operate at the same time. Include in this starred 
list all appliances with automatic controls, for example 
refrigerators and freezers. Add the total wattage of all the 
appliances on the starred list. This wattage figure is the 
smallest amount of power that will do the job. The inverter must 
be sized larger than this figure if the system is to work as 
planned. If the inverter is undersized, it may shut itself off 
due to overloading and leave you in the dark. The wattage of each 
appliance multiplied by the number of hours per day it is 
operational gives an estimate of energy consumption in watt-hours 
per day. This figure is used to determine the capacity of the 
battery pack necessary to do the job. Surge Consumption 
Appliances which use electric motors require more power to start 
themselves than they require to run. This high starting power 
consumption is called starting surge. Many motorized appliances 
require over 3 times as much power to start than to run. These 
starting surges must be considered in sizing the inverter's 
wattage. If these surges are not allowed for then the 
refrigerator starting up may overload the already loaded inverter 
and shut it off. Most power inverters worth having are capable of 
delivering 3 to 5 times their rated wattage for surges. If there 
are several large motors in the system that may start themselves, 
then the situation becomes more complex. For example, consider a 
system where both the deep well pump and a refrigerator are being 
used. Both the pump and the refrigerator may turn themselves on 
at the same time. The resulting surge demand may be high enough 
to shut down the inverter. It is best to assume that all 
appliances on automatic control are starting at the same time. 

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