question

andzei avatar image

Why MPPT is overcharging

MPPT 75/15 overcharging


It was working all fine for 3+ months but then I saw that it charges the battery in 16v+ range. Few days before that I used the same controller to charge another battery and then switched back to the main battery. I don’t know if that triggered some problems because it was cloudy on those days.


But now, if it’s sunny, it goes to 16v range and always stays in a BULK mode (flashing fast), never going into Absorbtion or Float. I tried disconnecting everything and connecting to another Victron battery and the same thing, as if the charger thinks that the batteries are 24v, but they are 12v. Could that be a problem? I don’t have a dongle to check it out, can’t buy one because shops are closed. Is there anything else I can do to find the cause of the problem or temporarly fix it?


My set up:

2x 120w solar panels connected in series.

MPPt 75/15

130ah battery.


As I said before, it was working perfectly for few months and then suddenly the problem occured. Currently my solution is to disconnect the panels if its a sunny day, but my campervan fridge drains it quite fast. I tried partially covering the panels but strong wind blows anything off the roof…


Thanks for help.

charging batteryovervoltageovercharging
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4 Answers
elf avatar image
elf answered ·

To reset the usual thing to do is disconnect all and reconnect in order. a) battery, b) PV c) load

Disconnect in reverse order of above.


If that doesn't work at least reconnect with only one PV or connect in parrallel to reduce the MPPT input voltage - you don't say what the output voltage of the panels are.

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told36 avatar image
told36 answered ·

If you disconnect all power the MPPT and leave it for few days it will return auto detect mode and set the voltage you connect to 12 or 24. Thats an option if you dont have the kit to connect.

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Oh thats great! Do you know whats the actual amount of time needed, is it 48h? Nothing on this in manual. Need to finish food and fast so i can disconnect the fridge...

andzei avatar image
andzei answered ·

Thank you for your replies!

1. Don’t have papers anymore but i assume panels are 12v.

2. I tried disconnecting the battery and solar panels, but i didnt disconnect the actual wires from controller. I just made sure that no voltage goes in (from panels) or out (to battery) of it and that nothing blinks on it. Do you think pulling out the cables would make any difference? My controller is just hidden and very hard to reach, possible but troublesome.

3. I cant do the re-wiring of panels because shops are closed and i dont have stuff, but i could connect my second battery (back up one which i dont normally use) to the main battery. My main battery is 130ah and the backup one is 170ah. Different brands but both deep cycle. Is charging 2 batteries too much for 2 panels?

Thanks for your help, really appreciate it!

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@Andzei

https://www.victronenergy.com/upload/documents/Manual-BlueSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20,-100-20-48V-EN-NL-FR-DE-ES-SE-.pdf

Here is documentation for your MPPT, pg12 gives some info on panel sizing and charge voltages

But spirou is correct you need to program it now. When it first auto selects it does not usually do it again but depending on how you connected your other battery it may have done so.

If you use the two batteries that are different in both type and capacity in AH (not recommended) and they have different float and absorption voltages there may be an issue. Also you no longer know what voltage it is charging at (from the settings) but you can check it with a multi meter.

If you panels were done with mc4 connections rewiring is as easy as unplugging them from one another and then plugging the cables into one only. this can be done near the panels.

To be honest if you are able to make sure they are not being over charged using the multi meter you could as a stop gap use it as 24v to keep them charged, until you are able to get it sorted properly. But if your van has a 12v system this will be a juggle.

My cables are too short and can’t te-wire panels unfortunatety...Thanks for suggestions!

spirou avatar image
spirou answered ·

As you guessed it is quite likely it switched itself to 24V mode. It has happened to me in much the same situation and a few others if you search the forum.

How to change back without BT or USB dongle I don't know. Find someone near you that has the necessary equipment perhaps?

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