Inverter Sizing For Submersible Pump Applications
Minimum continuous power rating of an inverter to start an AC submersible well pump (with no additional loads)
|HP of Pump||Min. Rating of Modified-Sine Wave Inverter (KW)||Min. Rating of Sine Wave Inverter (KW)||KW Max. Running Power (Watts)|
* Typical running power is 10-20% less, but add 10% for typical inverter loss. For "modified sine wave" add another 15%, due to loss of efficiency in the motor.
Minimum inverter sizing is based on field experience with Xantrax inverters, allowing ~25% voltage drop during startup. To eliminate noticeable voltage dip, add 50% to the minimum size. Other brands of inverters differ in their surge capacity relative to continuous rating. Exact starting capacity is difficult to predict and inverter manufacturers are hesitant to specify it. Dankoff Solar welcomes your feedback and will publish more information as a result.
If a "modified sine wave" inverter is to be used and pump's control box is labeled "solid state", then it must be changed. Obtain a relay-type control box or a relay conversion kit, from any pump supplier.
If the pump is a "two-wire" type (having no control box), oversize the inverter by an additional 50%. A two-wire pump may not always work on a modified sine inverter.
Most well pumps require 230 VAC. Either two stacked inverters, or an inverter with 230V output, or a transformer must be used. (The Trace T-240 transformer will handle 2 HP max.). If all of this is too expensive for your situation, consider replacing it with a lower power pump, carefully selected for the best efficiency (watts per gallon). You can also consider an intermediary storage tank with a DC pressurizing pump. The use of a storage tank will relieve your well pump from the need to start every time the pressure runs low (many times per day). You can pump into the storage tank just once or twice per week, and then use a DC pump to supply the water pressure as needed (or use gravity flow, if feasible). See DC Pressurizing Pumps for Domestic Water Supply and Irrigation. You may also be able to change to a lower power well pump, even a DC well pump, after this step is taken because less pressure and less flow will be required from the well pump.
At Wholesale Solar, we will be happy to help find the products that are right for you. For pricing and product information give us a call. We'll also answer any questions you might have about your system. 1-800-472-1142