How MPPT works - video

Here is a MT50 display connected to a 4215BN mppt controller.  The controller is holding Float voltage (Vfloat).  Note that the screen we see here is stats on power coming from the panels into the controller.  No down-conversion or charging/load amps are shown here.

So little power is required to hold Vfloat that the controller has driven panel voltage (Vpanel) up to nearly Voc.  In the summer heat Voc of these mono panels is a little under 40v.

I apply the load (dust devil – turn down your audio!) and the controller drives Vpanel  down toward Vmp (around 36v), thus increasing panel output.

I remove the load and Vpanel rises back toward Voc and output drops.

It would be neat if this evidence convinced the “MPPT only works in Bulk mode” people, but I am not holding my breath.