question

Hi @MissBliss,

It’s to be sure there is enough voltage differential to operate.

The MPPT needs a panel voltage higher than the battery voltage to operate. It’s a buck circuit and cannot boost.

Open circuit voltage is higher than operating voltage in a solar panel.

So when a load is put on a panel, the voltage will drop.

If the MPPT starts up, and the panel voltage drops to where it is so low that it is not producing any power, then the MPPT is actually consuming power, and likely cycling on and off.

The 5V minimum acts as a hysteresis, to make sure there is enough solar production once the MPPT has started and the panel is loaded.

If panel voltage is so low that this is an issue, then a PWM charge controller, or alternative panel, or alternative panel wiring configuration is the solution.

Update - @Johannes Boonstra (Victron Energy Staff) from Victron has made a short video that explains this in further detail - Q&A: Why does the Victron Energy MPPT starts 5Vdc above the battery voltage?

A votronic mppt with a +2V wake up will actually consume more power than produce for a little while after start up. It's not much but it's there. Probably not that different with any other brand.