Frequency
Generator Low Frequency & Frequency Faults
Frequency is the hertz reading, and on a generator it normally follows how fast the engine is turning. A low or wandering Hz reading still has to be confirmed. Possible causes include the engine not reaching speed, a governor problem, fuel restriction, overload, a controller or sensing fault, or an alternator signal the display is misreading. The governor is not a screw to turn until the number looks right.
- Hz follows speed until proved otherwise
- Fuel and load included
- No unsafe governor adjustment
- Onsite across Gauteng
The hertz reading
What does low generator frequency mean?
It means the displayed frequency is below what that set should hold, often near 50 Hz on a South African standby machine. Because frequency is tied to engine speed, a low reading often means the engine is slow. The diagnosis still confirms that, because a sensing or controller fault can show a low number while the engine is not.
A reading that is fine with no load and falls when equipment connects is a different job from a reading that is low all the time. Under load, fuel delivery and whether the set is simply too small for the start current sit beside the governor.
A zero on the frequency display, with the engine clearly running, is not the same as a low number. That can be sensing. It is recorded as what the screen shows, and then checked against the engine.
Speed, fuel and the display
Why is my generator showing low Hz?
Frequency drops under load
The engine cannot hold speed once current is demanded. Overload, fuel and the governor are separated while the load is on.
Engine speed and governor problems
A sticky or maladjusted governor can leave the speed low or hunting. Adjustment is done against a reading, not by ear, and not as a customer step.
Fuel supply and frequency
A restriction can let the engine idle and then pull the speed down as soon as it is asked to work. Filters come before pump replacement.
Controller frequency readings
The module displays what its sensing tells it. A wrong pickup or a configuration mismatch is checked before the engine is rebuilt around a bad number.
Low frequency with low voltage
The two often travel together when speed is down. Voltage is not raised on the AVR to compensate for an engine that is slow.
How frequency faults are diagnosed
Hz, engine behaviour and load are recorded together. A trip under that same load is followed on the trips-under-load page.
Google reviews of ProService Generator Repairs
Google Review
They serviced my Ryobi portable unit beautifully. The technician cleaned out the old fuel and adjusted the governor so it runs much smoother under load.
Google Review
Excellent local servicing in Florida, Roodepoort. Our home unit runs flawlessly now after they fixed a sticky mechanical governor on our business generator very quickly.
Common Questions
Questions about low generator frequency
What does low frequency on a generator mean?
The hertz reading is below the speed the set should hold. It often means the engine is turning too slowly, and that is confirmed rather than assumed.
Is frequency the same as voltage?
No. Frequency follows speed. Voltage is the electrical output. They can fail together, and they can fail apart.
The Hz falls only when I connect equipment. Why?
The engine is not holding speed under that load. Possible causes include fuel restriction, overload and the governor.
Can I adjust the governor myself?
No. Speed adjustments made without a proper reading can leave the set fast or still unstable, and some linkages are not safe to move while it is running.
The display shows zero Hz but the engine is running. Is it stopped?
Not if the engine is clearly running. A zero reading can be sensing or the controller input, which is a different test from a genuinely slow engine.
Low frequency and low voltage arrived together. Which do you fix first?
Speed is checked first. Raising voltage on the AVR while the engine is slow does not correct the frequency.
The set shuts down when the Hz drops. Is that a frequency fault or a trip?
It can be both. Protection that stops the engine because speed collapsed is diagnosed with the reason the speed fell.
What should I send with a low frequency reading?
The Hz figure if you can see it, whether the engine sounds slow, and whether it only happens under load.
Still unsure what the fault is? Call or WhatsApp 082 057 4605 for onsite diagnosis.
Service Areas
Onsite visits across Gauteng
Technicians travel to the generator. These are the main Gauteng areas. Suburb pages sit under each region.
What to send before we attend
ProService Generator Repairs confirms an onsite visit from these details. Send what you have. A missing model number does not stop the booking.
- Location
- The suburb or site, so the visit can be booked in the right area.
- Make and model
- The generator brand and model, if they are known.
- kVA
- The size printed on the data plate.
- Fuel type
- Diesel, petrol, LPG, natural gas, or dual-fuel.
- Controller model
- The module name on the panel, when it is visible.
- Fault or alarm
- What the set does, and any text on the screen.
- Photos
- The generator, the data plate, and the controller or alarm. Send these on WhatsApp.
Book a Visit
Send the Hz reading if you have it
Say whether the engine sounds slow, and whether the number only drops after equipment is connected.
- Call
- 082 057 4605
- Message us on WhatsApp