Page 5
Loads that require “surge power” to start
Resistive types of loads (like incandescent lamps, toaster, coffee maker, electric range,
iron etc) do not require extra power to start. Their starting power is the same as their
running power.
Some loads like induction motors and high inertia motor driven devices will initially
require a very large starting or
“surge”
power to start from rest. Once they have started
moving and have attained their rated speed, their power requirement reduces to their
normal running power. The
surge
may last up to 5 seconds.
TVs and microwave ovens also require surge power for starting. The manufacturers’
specification of the appliances and devices indicates only the running power required.
The surge power required has to be guessed at best. See below under
“Sizing of inverter
for loads that require starting surge”
If an inverter cannot efficiently feed the surge power, it may simply shut down instead of
starting the device. If the inverter’s surge capacity is marginal, its output voltage will dip
during the surge. This can cause a dimming of the lights in the house, and will sometimes
crash a computer.
Any weakness in the battery and cabling to the inverter will further limit its ability to start
a motor. A battery bank that is undersized, in poor condition, or has corroded connec-
tions, can be a weak link in the power chain. The inverter cables and the battery intercon-
nect cables must be sized properly. The spike of DC current through these cables is many
hundreds of amps at the instant of motor starting. Please follow the instructions under
“Installation - DC side connections" on pages 23 & 24
Sizing of inverter for loads that require starting surge
Observe the following guideline to determine the continuous wattage of the inverter for
powering loads that require starting surge.(Multiply the running watts of the device /
appliance by the surge factor)
*NOTE:
The surge power rating specified for the inverter is valid for duration
of less than 2 seconds. This very short duration may not be sufficient
to start motor based loads which may require up to 5 seconds to
complete the starting process. Hence, for purposes of sizing the
inverter, use only the continuous power rating of the inverter.
Type of Device or Appliance
Surge Factor for Determining the Continuous *Wattage of the Inverter
(No. of times the running power rating of the device/appliance)
Refrigerator / Freezer
5
Air Compressors
4
Dishwasher
3
Automatic Washer
3
Sump pump
3
Furnace fans
3
Industrial motors
3
Portable kerosene / diesel fuel heater
2
Circular saw
3
Bench Grinder
3
