I have 4 x 3Kw Synerjy inverters. Each have 2 x 120Ah Gel batteries. The inverters are installed in 4 separate locations. One of these are used to power led tube lights. There are 10 x tube lights connected. For some odd reason there is a soft or low level buzzing sound on this inverter. The other 3 are dead quiet.

This sound is only when on utility.  Switching to battery, the inverter is quiet.

 

Any ideas please?

Perhaps a fault with the "safety" relays? One for live, one for neutral. They are about the only hardware thing active in line mode and not in battery mode.

If so, that seems serious, potentially even a fire risk. But that's pure speculation on my part. 

Edit: Or perhaps some utility power supply component is acoustically active, usually a film capacitor or inductor. In the latter case, silicone might quiet it down. You really need to open it up to find out what is going on. I understand the reluctance to do this. 

Edited June 22, 20233 yr by Coulomb