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Regency Generators Knowledge Base

Three phase generator Under Voltage On Starting - Diagnosis and How To Fix it

he solution to generator under voltage depends on the actual symptoms experienced. Carefully looking at the generators output can help you effectively diagnose the fault and hopefully correct it quickly. Electricity is dangerous, so ensure you are suitably qualified to work on this equipment before attempting any procedure below.

You can also refer to the Stamford Fault Finding Manual

This article assumes your generator is 3 phase and your control panel will show you all three phase readings. Welland generators come with a digital controller as standard to monitor most functions. You should also ensure you have a multimeter ready to measure the actual output voltages.

There are two broad types of under-voltage faults we see. There are genuine alternator faults, where the voltage is low at the alternator and there are panel / wiring issues that cause low voltage alarms.

Reading / Verifying the Panel Voltage

Follow these steps:

  1. Ensure the generator is off.
  2. Make sure the generators breaker is also tripped (i.e. off).
  3. Run the generator, monitor the voltages on all three phases.
  4. Turn the generator off.


Generator Voltage is 0V on one phase or more phases

Normally, even when the alternator has failed a small voltage would be present. This indicates that the controller cannot read the voltage on the phase where it is 0.

  • Check the control module plugs are fitted tightly.
  • Check the fuses / breakers between the alternator and the control panel on the phase(s) where the voltage is 0, install a new phase or put the breaker to the on position.
  • Test for open circuits in the voltage sensing circuits.

Check the actual reading using a multimeter, at the generator terminals. If that shows normal, you could have blown the voltage sensing in the control module. Check the control module on another unit to confirm.

If the multimeter shows 0V on one phase also, further investigation of the alternator may be required.

Generator voltage is low on all three phases

See the article on Generator Voltage Low on all three phases.

Generator Voltage Low on One Phase, Other Phases Normal or High

If the voltage is low on one phase (not 0, if it is zero see above!) then continue to the alternator voltage low on on phase, normal / high on other phases.