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missbliss avatar image
missbliss asked

Reason for +5v wake-up?

Further to earlier discussions on this forum about the +5V wake-up setting of the Victron SmartSolar: does anyone know why this feature has been included in the programming? Is there a good reason why a charger should not switch on with a voltage difference between battery and solar panel of less than 5V?

Asking this because I am inclined to buy Victron, but supplier suggests to buy other charge controller stating this downside of the Victron as the reason. Was wondering if there is a battery life upside to this feature, or that maybe the 5V has been arbitrarily chosen.

smart solar charging behaviour
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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

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?

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spirou avatar image
spirou answered ·

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.

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