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lorettaboy avatar image
lorettaboy asked

Watts drop down to zero...

I had my camper trailer dealership install my rooftop solar panels, battery monitor, and MPPT controller (100/50). It seemed to be working fine yesterday (cloudy day, pulling in about 60 watts).

Today (sunny day) i checked and the controller was showing 0 watts but about 70 volts. If i reset the controller it'll jump up to about 200 watts, fall back to about 80 and then gradually go down to zero given about 2 minutes time. All the while the voltage seems to remain fairly constant. Any idea what the issue is here? I'm thinking maybe it's been wired up incorrectly.solar-1.jpgsolar-2.jpg

MPPT Controllers
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5 Answers
netrange avatar image
netrange answered ·

What Type of Battery is connected to the system ??? Maybe with a bms System ???

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lorettaboy avatar image lorettaboy commented ·

System is 6 100watt panels wired in 3S2P, with 2 6v golf cart batteries.

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netrange avatar image
netrange answered ·

Temperature is about 2 degrees ... Maybe your bms save your batteries ...

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Maybe the batteries are just full?!

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lorettaboy avatar image lorettaboy commented ·

BMS shows batteries are at 89% capacity.

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Kevin Windrem avatar image
Kevin Windrem answered ·

This seems like the expected behavior when your batteries are at 100% state of charge:

When initially turned on, the charger will enter bulk mode briefly because the battery voltage is below the float threshold. But the float voltage will be reached quickly.

The charger will then enter absorption mode briefly, then switch to float.

The battery monitor will provide you with the battery's SOC and if it is at or near 100% there is simply no where for the solar energy to go.

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lorettaboy avatar image lorettaboy commented ·

yes, you nailed it; thank you. I went back, turned a few things on, and the charger fired back up. The odd part is that my BMV is showing the battery at only 89% charged.

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tozz avatar image tozz lorettaboy commented ·

The SoC percentage is calculated by the BMS using some math, some figures from the battery (eg voltage) and some guessing. It's not always accurate, especially in new systems it might be doing a lot of guessing. Your charger / MPTT doesn't use the SoC percentage. it uses the voltage thresholds to determine which charge phase it should be doing.

For example, lets assume you have a 12V battery that is fully charged when voltage is 14V and empty at 10V. If your MPTT is configured to go into absortion at 13V it'll never reach the 14V / 100%.

If you believe the SoC is correct, you might need to adjust your voltage thresholds for absortion/float in the charger settings.

Another thing you might look at is if your settings have the correct battery Ah value. If you have 'dumb batteries', you need to manually configure this setting. Perhaps its incorrect now?


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Kevin Windrem avatar image
Kevin Windrem answered ·

The BMV has its own voltage calibration that triggers SOC calibration. This should be set to a tiny bit lower than the absorption voltage so that when the battery reaches that voltage the BMV is reset to 100%.

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lorettaboy avatar image lorettaboy commented ·

thanks again Kevin; i'll take a look tomorrow and see if i can figure it out.

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