DIY Manual

11 | P a g e 10-543-1 REV A
DIY Manual
Step 5 INVERTER SIZING
The final step in our system design is to size the inverter to power all your loads. Let’s look again
at the Load Analysis Example.
If you want to power all the loads at the same time, then you will need an inverter capable of
continuously providing at least 2395W, which is the total wattage of the appliances: 75W + 20W
+ 500W + 1800W = 2395W.
Of all the appliances in our example, the refrigerator is the only one with a motor or compressor,
which will draw more current upon start-up. Thus, we must factor in surge capacity. General
rule of thumb is 3X the rated wattage. For the refrigerator, that means 1500W (3 x 500W).
For continuous duty and to power all the appliances listed above, we need at a minimum a 2500W
inverter that can surge momentarily to 3500W (which is the extra 1000W for the refrigerator at
start-up). Most inverters will surge to at least twice the continuous duty wattage.
Appliance / # Watts Hours Watt-Hours (Wh)
TV / 1 75W 4 Hrs 300Wh
LED Lights / 3 20W 5 Hrs 300Wh
Refrigerator / 1 500W Cyclical 1500Wh
Toaster Oven / 1 1800W 0.5 Hrs 900Wh
Total Watts 2395W Total Watt-hours 3000Wh
Well Pump
A well pump can surge to 3x the normal running current. This surge will be short in duration and
will momentarily lower the battery voltage due to the initial surge. If the pump runs during the
early morning hours when the batt voltage is low, this may trigger the inverter to shutoff. When
sizing a system, ensure the batt bank is of sufficient Ah to accommodate the surge and size the
batt bank in terms of Wh, as mentioned in the Load Analysis, for the repeated cycling of the pump
over a 24-hour period.