question

andzei avatar image
andzei asked

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.

battery chargingovervoltage
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5 Answers
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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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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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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Alexandra avatar image Alexandra ♦ commented ·

@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.

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andzei avatar image andzei Alexandra ♦ commented ·

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

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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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andzei avatar image andzei commented ·

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...

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eltgeorg avatar image
eltgeorg answered ·

Hi andzei, I can also confirm your overcharging behavior.

My Blue Solar MPPT7515 has switched itself from 12V to 24V charging setup after 20month faultless operation on a 12V 80Ah Gel Battery. PV Module has 200Wpeak and 34V open circuit voltage.

The battery voltage charging range has been from 11.8V to 14.5V when the Blue Solar MPPT 75/15 was in operation for over 1.5 years.

The Jumper was between Pin2 and Pin3.


Since commissioning, there has been no modification to the system.

Without intervention the MPPT 75/15 suddenly charges the 12V battery to >17V when PV Power is available.

It seems that the unit loses its initial configuration and switches to dangerous 24V Setup although using still a 12V battery.

The analysis with the dongle showed that the unit has set itself to 24V.

Without the dongle, it is not possible to check the correct voltage setting.

The status LEDs cannot indicate whether the MPPT7515 is in 12V charging mode or 24V charging mode.


The overcharging due to the MPPT 7515 has heated the battery up. It has lost capacity due to constant overcharging and has now a high internal resistance.

Victron could not confirm if it is even allowed to operate the Blue Solar without supervision.

It would be beneficial to contact the insurance company to see if any damage triggered by blue solar MPPT7515 would be covered.


This dangerous condition for battery and surrounding can only be interrupted by manually disconnecting the battery or PV system.


The blue solar MPPT7515 unit shows no error and charges at full power, as the 12V battery for the solar controller appears as an empty 24V battery.

It´s interesting that Victron got the CERTIFIED ELECTRICAL SAFETY Standard from UL and CSA with the behavior, that the MPPT 75/15 switches itself to a higher battery voltage without any reason.


Without the dongle it is not possible to determine, whether the blue solar is in 12V or 24V mode.

A disconnection of PV Module and Battery and a restart after 48h did not lead to any improvement.


It is already a matter of several concerned systems, as various forums are pointing out the overcharging topic with statements like “MPPT7515 stuck in Bulk Charge Mode”.

To reset the unit to 12V operation, a chargeable 60Dollar Dongle and an update to V1.56 is necessary.

Device safety in the delivery condition is apparently not guaranteed.

@Dave van Dongen

@Steve


picture1

dangerous-battery-level.jpg







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klim8skeptic avatar image klim8skeptic ♦ commented ·
Please confirm what firmware your mppt is running.
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eltgeorg avatar image eltgeorg klim8skeptic ♦ commented ·

The firmware history cannot be displayed after the update. The blue solar MPPT7515 was purchased in 2019, it depends on which firmware the Blue Solar devices were delivered with. After the update with the dongle, firmware V1.56 was displayed. The unit is now back in 12V setup. According to the manual it should not be possible for the blue solar to reconfigure itself a second time without manual intervention. I cannot judge how much lover the probability with V1.56 is, to switch again itself to wrong 24V setup after long period of operation on 12V.

one-time-only-automatic-battery-voltage-recognitio.jpg

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