On my mppt during the day it will over read by about 6 volts and at nights time it will read zero volts. I have changed the MPPT, I have renewed the wiring from the MPPT to the battery, I have renewed the fuse and I have also renewed the battery. I have taken all other connections off the battery so just my MPPT is connected. I have tried everything even all the cabling from the solar panels. Any ideas I would be so grateful. The first picture is now and as you can see although the battery never went below 13 volts you can see at night it went to zero volts and as soon as there is any sun on the solar it jumps up to the correct voltage or just above. The second picture is from a few weeks ago when everything was fine.
New everything apart from the solar panels. What panels do you have. Could there be a panel fault. Do you have more shading now, are you in southern hemisphere. It is hard to tell with the info provided. Are you using more power than you are harvesting and the battery BMS is shutting down on low voltage.
I have disconnected all the solar panels and connected them up singularly. They all seem ok all the readings are correct not showing any faults. I have had to turn most of my power off so I am only running one small fridge. The BMS won’t shut down as the battery is around 13 volts. If I disconnect the cable from the MPPT to the battery the MPPT will still show 14 volts I just dont understand where it is getting this figure from. My battery has now gone into absorption as the MPPT shows 14.2 but my battery is only 13.3. Thanks for any help I really appreciate it
Sorry a bit more about the solar panels. We are actually in Turkey at the moment so plenty of sun. I have 3 solar panels they are in parallel total of 560 watts. The solar panels are under 2 years old. The only thing I have not changed are the solar panels.
If the MPPT shows 14.2V and the battery 13.3V then either your mppt to battery cable is undersized causing a lot of voltage drop or you have a poor connection. Use a multimeter to trace the voltage drop, could be positive or negative.
On testing panels just a voltage check will.not pick.up a poor connection, if you have a multimeter that reads amps try a short circuit current test on each panel, that sorts out a problem.
Thanks very much, I will try the solar panels again, do you know where the mppt is getting the battery voltage from?
Forgot that answer.
Even without a battery it will go to absorption voltage then float if the panels are connected. That is normal behaviour.
The odd one is dropping to 0V overnight, this suggests a poor connection to the battery. Do you have a breaker or isolator switch that could be giving an intermittent fault.
I have a voltage drop on the fuse of 0.07 which is slightly high, I have also run a short cable from the MPPT to the battery without a fuse just to see and no difference. Ihave just retested all the solar panels individually, short circuit test and all good. I still can’t make out where the battery voltage on the mppt gets is voltage from? Thanks for helping really appreciate it
It’s possible the internal fuse of the MPPT is blown. This can cause a discrepancy between the measured battery voltage and the reported battery voltage by the MPPT.
At first I thought it was the MPPT so I went out and purchased a new one and it was the same. Yesterday I did run another live and neutral from the MPPT to the battery the result was a lot better although not great so tomorrow I will go out and purchase the best cable and fuse I can and re crimp everything and try that. I have also put the absorption time on zero hopefully this may help.
Thanks for your help
Mike
Rather you should put the absorption time to 4 hours, as this is the delay before the MPPT drops to float. Depends on your battery type too.
I have a lithium battery..
If that’s LiFePO4, then you look like you have a 4 cell battery.
If the voltage rating of your MPPT is higher than 3 times the open circuit voltage of your panels, you will be better connecting these in series not parallel.
For lithium batteries, the float voltage should be 50 - 100mV below the Abs/Bulk voltage. Abs time still wants to be 2-4 hours, depending on dc loads and battery size.
did you fix the drop to 0V on the mppt overnight battery voltage?
Thanks for your reply, my solar panels are just over 9 amps each, the reason they are in parallel because they are different sizes. The last couple of nights they have shown the correct voltage all through the night. So today I have rewired the MPPT back to the battery, fitting all new cable lugs, fitting new busbars and new fuses, I also fitted a victron battery sence. Before I set up the battery sence the mppt was over reading about .5v, I then set up the battery sence and bingo the battery, the mppt, the dc to dc and the battery sence all had the same voltage, then my battery went into Float mode and the battery and battery sence were reading different to the mppt and dc to dc.
I will monitor them and see what’s happening, this fault.did happen overnight, for 4 years everything was perfect.