Inverter trips when looms or motors start

Our guide to running a home water pump on solar covers sizing a system for a pump. This page is for when the pump already will not start.

Safety box. If the motor hums but does not turn, switch it off within a few seconds; a stalled motor overheats fast and can burn its winding. Switch off and keep away if you smell burning, see smoke, or there is water around the motor, its switch or its cable joints. Do not touch the motor terminals or open the capacitor box, and never bypass a breaker or the motor's overload protection. Pumps sit near water, so the motor body must be properly earthed; see our earthing guide.

Water motor not starting on inverter: what it means

A household pump is an induction motor. From standstill it draws several times its running current until it gets up to speed, helped by a start capacitor. On grid power, that burst is easy to supply. On an inverter in backup, the inverter and battery must deliver all of it, on top of whatever else is running. Each inverter has a short-term surge limit. If the motor's start pushes past it, the inverter cuts the output, beeps or shuts down. If the start is weak, the motor hums and stalls.

Quick-check table: motor not running on solar

Inverter overload on motor start

This is the most common solar-side cause, and it usually happens during load-shedding or at night on battery.

• Other loads running. A pump starting while an AC compressor, fridge or iron is on can tip the inverter over. Two motors starting together, such as the pump and a fixed-speed AC, is the classic trip. See inverter AC vs non-inverter AC.
• Inverter too small for the motor. A 1 HP motor needs real surge headroom; a small inverter may manage it alone but not with the house running.
• Low battery. As the battery voltage falls, the inverter cannot deliver as much surge, and the battery's own protection may cut out on the current spike. See battery low voltage alarm.

If the overload alarm appears with other loads too, read inverter overload and beeping.

Motor and pump causes

These show up whatever the power source, so they are not solar faults:

• Weak or failed capacitor. The classic sign is a motor that hums but does not turn, sometimes tripping its breaker. It gets worse on any supply with less surge margin, so a pump with a tired capacitor may still start on grid but fail on the inverter first.
• Seized pump. A pump left unused, or with sand or scale inside, can jam.
• Dry running or air lock. The motor may run but deliver no water, then overheat. Most suction (donkey) pumps need a primed suction pipe and a working foot valve.
• Long or thin cable, which drops voltage at the moment of start.
• A stuck float switch or failed automatic controller.

Pressure pumps, home lifts and gate motors have the same starting behaviour; see home lift, pressure pump and gate motor on solar.

Pump not working on UPS

Many homes still use a separate battery UPS. Two problems are common:

1. The UPS is too small. Many home UPS units are sized for fans and lights; a motor's starting surge exceeds their limit.
2. The output waveform. Some UPS units produce a stepped or modified sine wave rather than a pure sine wave. Induction motors on such a supply can hum, run hot or struggle to start.

A modern hybrid solar inverter produces a pure sine wave and is usually sized with motors in mind. If you are deciding between keeping a UPS and moving to solar, see UPS vs solar for load-shedding.

Safe owner checks, step by step

1. Note when it fails. On grid, on battery, at night, or only with other loads on?
2. Read the inverter screen or app at the moment of failure: load percentage, battery level, any alarm. Photograph it.
3. Try the motor alone. Switch off ACs, irons, kettles and other motors. Wait a minute, then start the pump.
4. Try once on grid, if available. If it hums and stalls on grid too, the motor or pump is the problem.
5. Switch off a humming motor within seconds. Do not keep trying.
6. Check the water side. Is the tank or bore supplying water? Are valves open? Is the float moving freely?
7. Check the breakers. Note any that tripped; reset once only.
8. Send your notes, photos and the inverter model to your installer, and the motor's nameplate photo too.

What an engineer will check

• Inverter and battery ratings against the motor's running and starting current plus the other loads.
• Battery settings and health: discharge current limits, cut-off voltage and communication with the inverter.
• Supply voltage at the motor during start, cable size and connections.
• Breaker type and size for a motor circuit. See breakers and protection and solar breaker tripping.
• Motor health, including the capacitor, winding insulation and earthing. This may be for a motor electrician.
• Load arrangement: whether the pump should be on the backup output, on a timer for sunny hours, or on a grid-only circuit.

For borewell and agricultural pumps on a dedicated solar pump drive (VFD), the causes are different, such as low sunlight in the morning or dry-run protection. See solar tubewell with VFD.

How to prevent it

• Run the pump in sunny hours and fill the tank fully around midday.
• Start the pump with other heavy loads off, and do not start it at the same moment as an AC.
• Use a float switch or timer so the pump never runs dry.
• Size the inverter with surge headroom for the motors you actually run. Dips in lights when the pump starts are a warning sign; see lights flickering with solar.

How Solar Works Pakistan handles pump complaints

For systems we install, WhatsApp 0336 666 4321 with a photo of the inverter screen or app at the moment the pump fails, the inverter model, and the motor's nameplate. Our own engineering staff handle the complaint, and we target sending service personnel within 48 hours of a registered complaint to begin diagnosis. Our 1-year service warranty applies under the applicable project terms; faults in the motor or pump itself are for a motor or pump mechanic. See how after-sales service works.

We can also check motor-starting problems on systems installed by other companies, as a chargeable service, across Punjab.

Frequently asked questions

Why is my water motor not starting on inverter but works on WAPDA?

The grid supplies the motor's starting surge easily; the inverter and battery may not, especially with other loads on or a low battery. Try starting the motor alone, and ask your installer to check the inverter's surge rating.

Why is my motor not running on solar during load-shedding?

On battery, the inverter must supply the full starting surge alone. An AC or iron running at the same time, or a low battery, is usually the reason. If your inverter is on-grid only, nothing runs in load-shedding.

How to fix inverter overload on motor start?

Switch off other heavy loads before starting the pump, run it in sunny hours, and have the motor's capacitor checked. If it still overloads with the motor alone, the inverter may be too small for that motor.

Why does my water motor hum but not start?

Usually a weak capacitor, a jammed pump or a motor fault. Switch it off within seconds to avoid burning the winding, and call a motor electrician.

Why is my pump not working on UPS?

Many home UPS units are too small for a motor's starting surge, and some produce a stepped waveform that motors do not like. Check the UPS rating and output type.

Does a pressure pump or booster have the same problem?

Yes. Pressure pumps, boosters and home lifts are motors too, with the same starting surge. They also start automatically, so they can kick in while an AC or iron is running and trip the inverter without warning.

Sources

1. InspectAPedia, electric motor starting capacitor FAQs (symptoms of a failed start capacitor: humming, not starting, breaker tripping): https://inspectapedia.com/electric/Electric-motor-starting-capacitor-FAQs.php