I just powered on three Quattro's (DC only, building a 3 phase system). The Quattro's are only connected to DC (same battery bank) and come straight out of the box. I updated the firmware and I noticed a big difference in 50Hz humming noise level between the 3 devices while doing so (to be clear not any programming yet, three separate devices with default settings running the latest firmware).
- Device 1 has a really load hum.
- Device 2 two is almost quiet, you can't almost hear anything.
- Device 3 is somewhere in-between.
I was just wondering, is this normal behavior? I would expect that the noise level of all three devices should be about the same. And where is the noise coming from? There is no AC input so there isn't anything to charge. There also isn't any load connected to the AC output.