Good day.
Had an interesting one yesterday. A client with an off-grid house was trying to charge the batteries with a generator.
When running the gen as grid-supply the inverter didn't sync with the generator, a frequency problem. The generator was running at 53hz according to the inverter.
Running the gen as gen/aux I can load the batteries at 40A, no problem but the gen-supply trip in the inverter after a spike due to something switching off like a hairdryer, pressure pump, or some other heavy user.
The mechanic will be setting the idling of the gen lower today, hoping that this will sort the frequency problem out. Will go back after the mechanic had worked on the generator.

What meter is best for measuring frequency? I'm also thinking of putting a pilot light in the db that indicates the frequency.