Can I run a sump pump with an inverter?

Using an inverter to run a sump pump is certainly possible, but there are some important factors to consider before choosing this setup. In this article, we’ll go over everything you need to know about running a sump pump with an inverter.

What is a Sump Pump?

A sump pump is a pump used to remove water that has accumulated in a water-collecting sump basin, usually located in the basement of homes. The water may enter via the perimeter drains of a basement waterproofing system, funneling into the basin or crock. The pump activates when a certain water level is reached, automatically pumping water away from the home to prevent flooding.

Sump pumps are extremely important for preventing water damage in basements. They are commonly used in areas with high groundwater tables or in flood-prone regions. While most sump pumps run on standard household electrical power, battery backup sump pumps and inverter-powered sump pumps provide protection against power outages.

How Do Sump Pumps Work?

A sump pump system consists of a basin, pump, discharge piping, and power source. The basin is a hole or container installed in the lowest part of the basement floor where water naturally collects. A sump pump usually sits at the bottom of the basin, immersed in water. It turns on when the water reaches a certain level and pumps the water away from the home.

Most sump pumps are electric and plug into a standard 120V household outlet. A float or switch activates the pump when water rises. The pump motor spins an impeller to push water out of the discharge pipe. Check valves or flap valves prevent backflow. The water is pumped away from the house to a storm drain, ditch, dry well, or the yard area.

Why Use an Inverter for a Sump Pump?

During power outages, a standard electric sump pump will not operate unless it has a battery backup system. An inverter allows you to power the sump pump using a standalone battery or renewable energy source, such as solar panels. There are a few main reasons to use an inverter with a sump pump:

Provides power backup – Keeps the sump pump running during blackouts
Off-grid operation – Allows using the pump completely independent of the grid
Use renewable energy – Can connect the inverter to a solar panel or wind turbine

Grid-tie with battery backup – Remains operational if the main grid fails

An inverter maintains consistent AC power suitable for pumps even when powered from DC sources like batteries or solar panels. This makes inverters ideal for use with sump pumps so they can keep working during emergencies.

What to Look for in an Inverter

There are several important factors to consider when selecting an inverter intended to power a sump pump:

Continuous power rating – Select an inverter that can provide adequate continuous power for the pump motor size. Most sump pumps require 500W to 1500W.
Surge capability – Inverters need sufficient surge capacity to start pumps without problems. 2-3x the pump power is recommended.
Pure sine wave output – For pump motors, a pure sine wave inverter is strongly advised instead of a modified sine wave.

Automatic transfer switch – For grid-tied setups, get an inverter with an automatic transfer switch to seamlessly switch to battery power when the grid is down.
Enclosure type – Choose an inverter suitable for damp basement environments – NEMA type 3R or 4X enclosures are best.
Battery voltage – Select an inverter that matches the DC voltage of the batteries you plan to use.

How to Size the Inverter

Choosing an inverter requires matching its power output to the power demand of the sump pump. Here are the key steps in properly sizing an inverter for a sump pump application:

Check the pump motor nameplate for its rated power in watts or horsepower. A 1/3 HP pump runs around 500W. 1/2 HP is around 1000W.
Factor in the surge power needed for motor startup. Multiply the rated pump power by 2 or 3.

Select an inverter that provides more than the required continuous and surge wattage.
For off-grid systems, choose an inverter with at least double the capacity to allow for future expansion.
Consider the AC voltage – 120VAC or 240VAC inverter output to match the pump.

Always oversize the inverter slightly to account for losses and avoid running the inverter at full capacity. For example, a 1000W sump pump would need an inverter rated for 2000 – 3000W minimum.

DC Power Options for Inverters

There are two main options for powering an inverter that runs a sump pump – batteries or solar panels. Here is an overview:

Batteries

Deep cycle lead-acid batteries are commonly used given their affordability.

Lithium-ion batteries provide longer lifetimes and higher performance but have higher upfront costs.
The battery bank must offer adequate capacity to power the pumps during outages. Typically require 200-400 Ah.
A minimum of two 12V batteries wired in parallel at 24V works well for most home setups.

The inverter monitors battery state of charge and stops pumping if the battery is depleted to prevent damage.

Solar Panels

Photovoltaic solar panels can directly convert sunlight into electricity to run the inverter and pumps.
Solar panels typically produce 12V or 24V DC output matched to the battery voltages.

A charge controller regulates the power from panels to safely charge batteries throughout the day.
Batteries buffer the solar energy to run pumps when there is no sunshine.
Need a large enough solar array to provide adequate power even on cloudy days.

Inverter System Design Tips

Here are some recommendations when designing an inverter system to run your sump pump efficiently and reliably:

Install the inverter near the sump pump for shorter cable runs.
Size the batteries to provide power autonomy for several days if needed.

Allow the inverter to automatically control the pump based on water levels.
Use wiring rated for a minimum 30A for safety and to reduce voltage drops.
Include blade type fuse holders or DC breakers to properly protect wiring.

Enable battery level alarms on the inverter for early warning of issues.
Consider an offshore sump pump switch for improved reliability in flooded conditions.

Common Mistakes to Avoid

While using an inverter to power a sump pump can work well, there are some potential mistakes that should be avoided:

Getting an undersized inverter that can’t provide enough starting surge for the pump motor.
Not having enough battery capacity to run pumps for extended outages.
Failing to account for flooded or debris-filled sump conditions that increase pump cycling.

Connecting the inverter incorrectly without proper fuses or circuit breakers.
Installing the inverter in a wet location without a proper protective enclosure.
Using the wrong capacity wiring that causes excessive voltage drop.

Forgetting to check that the pump actually runs and moves water when powered by the inverter system.

Taking time to properly design and test the inverter system for the sump pump will help identify and prevent issues that could affect operation during outages.

Best Practices

Follow these best practices when setting up an inverter system for a sump pump installation:

Consult a qualified electrician or installer for proper design and setup.
Use only listed, UL approved inverter rated for wet locations.
Ensure the inverter has adequate power capacity for both continuous load and surge.

Select suitable batteries sized appropriately for runtime needs.
Include appropriate disconnects, fuses, wiring gauge and surge suppression.
Enable battery level monitoring and external alarm capabilities on the inverter.

Test the system under load to confirm proper pump operation and check float switch function.
Develop a maintenance plan to check inverter, batteries, cabling and pump condition.

Example Inverter Sump Pump Systems

Here are two sample inverter sump pump setups that utilize different power sources:

Battery Backup Example

1/3 HP cast iron sump pump (500W rated power)
Pure sine wave inverter rated 3000W continuous
Two 6V 225Ah golf cart batteries in series for 12V operation

Xantrex automatic transfer switch
Battery cables, fuses, enclosures included

This system uses two typical golf cart batteries connected to a 120VAC inverter with enough capacity to run the 1/3 horsepower sump pump. The transfer switch enables switching to battery backup power when the grid power is interrupted. Approximately 18 hours of runtime is provided.

Solar Powered Example

1/2 HP cast iron sump pump (1000W rated)
4000W 24VDC pure sine wave inverter
Four 230W solar panels for 920W total solar array

MPPT solar charge controller
Four 6V 260Ah batteries for 24V

This solar powered setup uses a larger 24V inverter and battery bank to operate the higher capacity 1/2 HP pump. Four 6 volt batteries wired for 24 volts provides adequate capacity, charged by the solar panels during the day. The system could provide over a week of backup runtime if needed.

Cost Considerations

Installing an inverter system for a sump pump represents a significant investment, but provides protection against costly flooding damage. Here are some typical pricing estimates for component costs:

Inverter for sump pump: $250 – $800
Batteries: $200 – $1000

Solar panels: $400 – $1500
Misc parts, wiring, enclosures: $200 – $500
Installation labor: $500 – $2000

The total installed cost for an inverter system to run a sump pump ranges from around $1500 on the low end for a basic battery backup setup to $5000 or more for an off-grid solar powered system. Get multiple quotes to find the best value installation.

Key Considerations

Here is a summary of the main considerations when using an inverter to power a sump pump:

Inverter sizing – Properly size for continuous and surge capacity.

Battery capacity – Have sufficient capacity for runtime during outages.
Monitoring – Enable battery alerts and monitoring capabilities.
Enclosure rating – Use inverter rated for damp environments.

Wiring – Use proper gauge wires protected by fuses/breakers.
Installation – Install in dry location for reliable operation.
Testing – Confirm pump operation on battery/inverter power.

Paying attention to these key factors will ensure your inverter sump pump system performs reliably when you need it most.

Frequently Asked Questions

Can I run my sump pump off a car battery?

Technically you can connect a sump pump to run off a standard 12V car battery, but it is not recommended. Car batteries are not designed for deep discharge cycles so would only power the pump for a short time. Purpose-built deep cycle batteries provide much longer runtimes for the pump and withstand repeated discharge cycles.

What size inverter do I need for a 1/3 HP sump pump?

For a 1/3 HP sump pump that runs around 500 watts, the minimum size inverter would be a 1000W unit. However, 2000-3000W models are recommended to provide enough surge capacity to start the motor without problems.

Can I run two sump pumps off one inverter?

You can connect two sump pumps to a single larger inverter provided it has the capacity to run both pumps simultaneously. The startup surge when both pumps cycle on will require a much larger inverter size compared to running a single pump. A 4000-5000W inverter would be advisable.

How long will my sump pump run on a fully charged battery?

Runtime from a fully charged battery bank depends on the pump size, vertical lift, and battery capacity. For example, two 100Ah batteries could run a small 1/3 HP pump for 12-15 hours. Batteries around 200-400Ah will provide 1-3 days of runtime for a typical home sump pump.

Can the sump pump charge the battery when not in use?

No, the sump pump itself does not have any charging capabilities – it can only draw power from the battery bank when running. The batteries need to be charged by another source such as solar panels, an AC-powered battery charger, or an engine-driven generator when available.

Conclusion

Using an inverter to power a sump pump from batteries or solar panels provides a reliable backup option to keep water pumped out of a basement during grid power outages. With proper sizing of the inverter and batteries, plus smart system design, an inverter sump pump setup can provide real peace of mind against flooding damage for your home.

The key is working with qualified experts to select suitable components and install the system correctly. While requiring some upfront investment, an inverter sump pump system delivers invaluable protection to your most valuable asset, your home.