Midnite Classic 150 buzzing

Saipro

It's a Classic at a friend's place. It began making unusual noises this morning thus I was called to see it. It's kinda weird. With loads beyond 400W in the dawn sunlight, the Classic starts humming (this low transformer hum). No, it's not the fans. And it goes off if he specifically switches of the fridge. It's puzzling because insolation at that time is minimal. Also because the DC aspect is totally isolated from the AC side - unless there's a bridge somewhere in the inverter (the only device where AC and DC coexist in a housing). Anyone had this problem before? What is it? How does one get rid of it?

Hill_Country

Hi Saipro,

I'm guessing it's the LoMax tweak setting that is causing (or "allowing") the sound you're hearing.  If you have the MidNite Solar Classic 150 user's manual handy (or you can download it at http://www.midnitesolar.com/pdfs/Classic_manual_REV_2056.pdf) and go to page 78 you'll see a FAQ that addresses your observation, especially since the PV array is probably at a relative low voltage given the dawn sunlight.  According to the MidNite manual the reason for the sound is...

MidNite Solar Classic User Manual Rev_2056 Page 78:  "*This is the inductors "Singing" when the Input voltage is really low. This is
normal and is no cause for concern, however if it bothers you then you can
disable it by going to the main menu and entering into tweaks. Look for
LoMax and set it to off and press enter.
Note: If the PV array is real low voltage and its max power point is close to the
battery voltage disabling LoMax will cause a slight loss in power as the Classic
will not be able to track all the way to the battery voltage looking for the
MPPT voltage"

Hope this helps!

Saipro

You're the greatest! Thanks!