mcs avatar image
mcs asked

Smart solar MPPT 100/20 48V

Our VW camper has leisure battery, solar panel, electric hookup setup. Following installation of the leisure electrics, everything worked as expected for about a year. For the last 6 months, I noticed on the Victron app that the MPPT charger is "off" almost all the time. I assumed during the UK winter that this was due to low light and short days. We're now in Spain. The charger seems to come on for about an hour at sunrise, and the panel voltage gets up to about 18-19v. However, the leisure battery state of charge continues to diminish, and then the MPPT switches off as the sun gets higher. There is bright sunshine in the middle of the day, but the app shows no solar voltage generated. This pattern seems the same whether we're plugged in to a campsite EHU or not. Can anyone suggest what might be happening?

MPPT ControllersSolar Panel
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Alexandra avatar image Alexandra ♦ commented ·

Likely your panels or wiring to the panels has a problem

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mcs avatar image mcs Alexandra ♦ commented ·
Hi Alexandra

Yes, that's my feeling. I wasn't sure if a failed solar panel could still generate some power, but if so, that seems a likely suspect

Thank you

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Alexandra avatar image Alexandra ♦ mcs commented ·

It would need the voltage to be 5v above the battery. At 19v you would barely get there.on a 12v system.

When panels get hotter their voltage drops, so charging would stop. With a slightly higher battery voltage then you wont have the 5v start voltage again.

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Andrew Ford avatar image Andrew Ford Alexandra ♦ commented ·
I second this. Check your panel voltage at the CC point to make sure it's more than 5v over your battery volts. Open circuit is enough to start the cc, I believe.

I had this problem with a panel that only had voc of 18v, if batteries were at 13.8v then the cc wouldn't start.

It is weird that your cc is turning off though.

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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

The input voltage to the MPPT needs to be 5V more than the battery voltage for it to start. If you panel is only 18V, and the battery at 13, then you are marginal for getting the charger to start. Once it has started, the volt difference can drop as low as 1v for sustained operation. (as mentioned above). In this case, a PWM controller would work better. Best move is to add a second module in series, or replace the 18V module with a higher voltage type.

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mcs avatar image mcs commented ·
Hi Mike

Thanks for that info. Am I right in thinking the 5v diff between panel and battery is needed to switch the MPPT on, but once started, it should stay on, even if the voltage diff was around 1v? In which case, if my MPPT keeps switching off, could that be a faulty MPPT?

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