Trying to troubleshoot my solar charging setup, discrepancy voltage reading between MPPT and BMV

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simonmtl asked May 6, '23

Trying to troubleshoot my solar charging setup, discrepancy voltage reading between MPPT and BMV

So, I have a Victron solar system on my van since 2019, everything has been fine since last summer, when for some obscure reasons my batteries stopped being charged.

I'm trying to figured why my mppt smartSolar is reading 6.62V for my battery voltage while my BMV reads 12.05V

My system was doing that kind of free game last summer, my system would be working perfectly and then one day it would stop charging

like this now, everything is fine for some days, minimum voltage is around 11.6V, and then one day it start reading a minimum voltage of around 6v and it stop charging the battery, as you can see:

MPPT SmartSolar

img-3636.png (191.3 KiB)

img-3637.png (191.5 KiB)

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Answer 1 · 2023-05-06T07:24:30Z

pwfarnell answered · May 06, 2023 at 07:24 AM

If the voltage is too low I do not believe that the MPPT will start its charge cycle.

The clue I think is in the low voltage, this should be a minimum of the battery voltage, not 6.6V that you have. To me this suggests that you have a poor connection somewhere in your wiring between the MPPT and the battery, perhaps a loose connection, failing fuse, poor termination, crimp or a faulty isolator. You need to turn get your multimeter out and check where the voltage difference is in both the positive and negative wiring. The fact it is a van installation means the wiring is subject to vibration. Put the multimeter between battery positive and MPPT positive. If the volt drop is zero do the same for negative. If the volt drop is not zero do the same from battery positive to the next closest terminal, fuse switch etc until you find the problem.

Are you using the cheap isolators / breakers shown below, these are well known for poor connections and are commonly found to cause the trouble your are having.

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simonmtl commented · May 06, 2023 at 02:05 PM

thanks for helping me sorting this out.

I do think the low voltage is a clue here

you might be right, maybe it is a loose connection, I will check and double check with multimeter my connections and see if I can spot a voltage drop. But when I built the system I knew about the effect of vibration so I made sure nothing is crimped but soldered, I think I have used quality component, I'm trying not to use Chinese knockoff. still I will double check all my connections

but see when I say this viltron system is doing free game on me, the screenshot are from yesterday at night, and now this morning I didn't move the van and still the reading is funky :/

now it's 10 am sun is shinning, I have charged computer during the night, used some lights, fan etc so SOC is now down to 88%. and the reading on the MPPT for the battery voltage is 13.39V and the charger is fliking between bulk/float/abs

it is acting very weird:

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img-3638.png (195.5 KiB)

pwfarnell simonmtl commented · May 06, 2023 at 03:42 PM

Soldering is not the best solution for vibration, crimping is best as the cable can flex a little with vibration. If you solder you can end up with solder making a solid wire which then becomes flexible at the end of the solder so the cable can not flex and cracks as it vibrates. Check all your connections and the wire for breaks near the connections. The fact that it is flicking between states suggests a variable resistance in the wiring.

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Answer 2 · 2023-05-08T15:35:45Z

simonmtl answered · May 08, 2023 at 03:35 PM

problem solved!

I had a cable that was busted/burned, probably from when they boosted my van after long term winter storage and I didn't took care of isolating the van batterie/alternator from the house battery bank before storing it....

good luck everybody staying off the grid !!

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