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bruceo avatar image
bruceo asked

Solar charger exceeding float voltage

I just replaced my batteries with a bank of FireFly AGM's. I'm paranoid about blowing them up, since I just ruined a bank of FLA batteries. FireFly wants a 14.4V charge, with a 13.4 float. I set up my Victron MPPT solar controller with those values - 14.4V absorption, 13.4 float.

When I checked today, my batteries were reporting a voltage of 13.64. The solar controller reported the max voltage applied as 14.7.

I expected that the max voltage applied would be 14.4, and that the float voltage would be 13.4. There are no other charge sources applied to that batteries.

What am I missing?

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MPPT SmartSolar
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2 Answers
JohnC avatar image
JohnC answered ·

Hi @bruceo

Look to your Temperature Compensation as the likely reason. It's quite normal.

But I'd look really hard at the value you have set there. It's surprisingly high, and suspiciously like a degC to F conversion of the Victron default value made the wrong way..

The actual results don't reflect how high it is, and maybe? Victron has a default max that it applies?

That said, don't get too excited about the daily max reported, as this can happen from a spike from load changes, which is just fleeting, but recorded.

It's good you have a temp from the BMV to network in the mppt, but if you watch the appropriate Trends graph while in genuine Absorb. you can see where it's targetting V. And even do the calcs manually to see if it's doing what it should.

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bruceo avatar image
bruceo answered ·

Thanks! I just added a temperature sensor (which I hadn't had before) and didn't even think of setting the Temperature Compensation. FireFly says 13mV/F° so it looks like I am off. I assume I enter that as -13mV/F?

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JohnC avatar image JohnC ♦ commented ·

@bruceo

That's better. Don't forget the "-", as it tells it which way to compensate.

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