question

andrew.g avatar image

Can +5v wake-up be changed?

We have a 75/15 Blue solar charge controller that requires the usual PV>Batt+5v before it will wake up and start charging. Can this behaviour be changed either via a command or via configuration? It would be very useful for situations where we reboot the unit and the wake-up behaviour becomes reset.


Blue Smart Charger
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3 Answers
Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@andrew.g, the +5v is a direct measurement; that is, the actual measurement of the battery voltage compared to a direct measurement of the voltage coming in off the PV side... rebooting will not affect this behavior at all. Thus, if your batteries have been discharged overnight and you're sitting at 11.8v, your controller will turn on when it sees 16.8v from the panels... if your battery is sitting relatively full at 12.8v, your controller will turn on when it sees 17.8v from the panels. Rebooting will not affect this, as it's a calculation based on direct measurement of the actual voltage difference between the two sets of terminals at any given time.

If you have low-voltage panels and are having difficulty with the controller not turning on, the easiest way to boost your voltage is of course to wire your panels in series, as series connections are voltage-additive while parallel connections are amperage-additive.


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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Some of us do not have the option to rewire the panels, as there is room for only 1 panel. I've had to junk the Victron 75/10 and go with another solution due to this bug/bad design. They need to address this as I've had to steer a large customer away from Victron due to this issue as well.

The VBatt+5V "issue" is not just a Victron 'design' and it's certainly not a 'Bug/Bad Design@ - quite the opposite. It's common with other quality brands. At the cheap end of the spectrum such as ePever, there are much bigger 'issues' such as locking to battery voltage, locking to poor MPP curves etc. If space is an issue, then it's just a case of selecting a panel that has a Voc of at least 17.5V/18V. Any less than that and you'd be better off specifying a PWM PRO.

andrew.g avatar image
andrew.g answered ·

thanks @Justin Cook


The PV voltage in question, would this be the open circuit voltage? Or the voltage measured when the unit is connected?

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You need a panel with a vmp of about 18v. 36 cells, not 32/33 cell.

It's Voc vs Vbat at the time, nothing to do with anything historical. Rebooting shouldn't do anything either.

Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@andrew.g, for better or for worse the +5v over batt voltage is a hard-coded parameter.

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