12v system suddenly not reaching full charge

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amarine asked Oct 7, '19

12v system suddenly not reaching full charge

Hello. I have the MPPT 100/30 controller and a BMV-712 monitor. I'm running 2 x 12v 125 amp/hour batteries for a total capacity of 250 ah. About 11 days ago, according to my app, my battery voltage started dropping and has not reached absorb or float voltages. Before this happened, I was able to go several days in my van/RV with my average daily loads. Now, the batteries never get above about 12.6 volts, even after great sun all day on my 200W solar system. I'm not sure what happened or why. Does anyone have any ideas? Thanks in advance!

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Answer 1 · 2019-10-08T00:19:34Z

Justin Cook answered · Oct 08, 2019 at 12:19 AM

@amarine, obviously in a complex system there are a whole lot of things to check... but first and foremost, two things:

1: Using a multimeter, check the battery voltage at the controller (easiest to check at the top of the terminal screws)

2: Using the same method, check your PV voltage.

Whichever one is different from what you would expect tells you which direction to proceed with your multimeter... if PV voltage is lower than what you would expect to see under given circumstances, then move up the line toward the panels, checking all connections and fuses/breakers/wire connections. Sometimes an MC4 connector gets loose and burns out, sometimes a panel goes bad, sometimes a squirrel eats through the insulation and half the conductor from your PV and you get enough voltage loss that the MPPT doesn't initialize to start charging (seriously, I've seen it...)

If your PV voltage looks good but your battery voltage at the terminals isn't what you expect, then work toward your battery with your multimeter... again, check every fuse, breaker, and connection to make sure you don't have a blown fuse/popped breaker/loose connection somewhere along the string. ALSO check the terminal screws on the controller and make sure they're tight and actually tightened down on bare cable instead of (as I've also seen) being tightened onto cable sheathing, leaving a gap between the actual cable and the terminal connection.

The last time someone on this forum reported this happening, it ended up being a blown fuse between the controller and the battery: https://community.victronenergy.com/questions/30466/my-battery-was-on-137-in-uk-now-in-spain-it-only-o.html?childToView=30726#answer-30726

After you've eliminated all connections, fuses, breakers, wire runs, and PV malfunctions... then it's time to start troubleshooting your MPPT, in which case we need screenshots from the app if at all possible. I'm reasonably confident, however, that you'll find a loose connection or blown fuse somewhere along the way before we get to that point.

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amarine commented · Oct 08, 2019 at 06:47 PM

Thanks for your response. I have done some testing and all seems to be as expected, except for the batteries. I even have my system connected to my alternator to charge while the van is on. Despite this, the batteries won't seem to reach an adequate voltage. I suspect I may need to replace my batteries. It's possible I discharged them too much and now they are damaged or degraded in some way. I hate to do that, since it will be costly, but I can't think of any other reason after testing my entire system.

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