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sintesis asked

MPPT shows wrong voltage

I have a 48V system with a Blue Solar Charger MPPT 150/60 and MultiPlus 48/5000/70-100. The system voltage that my MPPT is showing is totally different than the real one (more that 6 volts above) measured at different point of the system. The MPPT then wrongly thinks the batteries are fully loaded and goes into float mode. This leads to the batteries not being fully loaded and the system voltage showing a slow descent. I sent the MPPT in for service and got it back after they tested it, saying that it is working correctly.

Even at night with no solar input, the MutliPlus can show 48,02V and the MPPT 54,34V. Suspecting some kind of resistance issue I have measured on the terminals of the MPPT, directly over the batteries and closer to the MultiPlus, including a 200A fuse. I always get very similar values, which more or less correspond to the value from the MultiPlus. So what can be the issue here?

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MPPT Controllersvoltagebattery system voltage
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Is this the same system / problem?

Time to grab a multimeter and measure the battery voltage at the battery terminals,

the battery voltage at the BMV shunt ~ B1 terminal,

the battery voltage at the mppt's battery terminals,

the battery voltage at the multiplus battery terminals..

Make a note of the voltage, and how much current each device is handling.


Do you have DVCC and SVS enabled?

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Mike Dorsett avatar image Mike Dorsett commented ·
do you get any charge from the mppt at all? This looks like a blown fuse inside the mppt.....
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4 Answers
sintesis avatar image
sintesis answered ·

When the MPPT came back from the service shop and was reconnected to the system it started loading the batteries perfectly well, showing it was charging 30A/102V on a multimeter. Right now there is no shunt or BMV connected as the screen broke and have to be replaced. As I said before measuring the voltage at the MPPT, on the batteries and after the fuse, I get very similar values, close to the value given by the MultiPlus. When the MPPT goes into bulk mode in the morning it does start to load, just not long enough before it considers the job done. So I don't think there is a blown fuse in the MPPT, perhaps it could be one circuit of many that is not responding or a software bug, I don't know.

The service shop said it could be some problem with the cables, but according to the installer, they are fine.

It just seems like the voltage the MPPT thinks the system has over time starts to divert from reality, which creates the slowly descending real voltage curve of the system.

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klim8skeptic avatar image klim8skeptic ♦ commented ·
Could we please see 2 days of the mppt's work.

Mppt PV voltage and current.

Mppt battery voltage and current.

VE Bus Voltage and current.

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sintesis answered ·

Thank you for helping out. This system sits at a rural location with just some domotics connected when no-one is around so the typical consumption is around 40W.


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klim8skeptic avatar image klim8skeptic ♦ commented ·
1 more graph please.

MPPT STATE-

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klim8skeptic answered ·

The recommended course of action appears to be to shut down the mppt for some time (overnight?). Disconnect the PV array, then the battery, to fully power down the mppt.

Reconnect the battery first, then the PV array.

Report back if things improve, or go down hill...

It is probably worth mentioning what firmware version the mppt is running. View in Remote Console > mppt > device > firmware version.

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sintesis avatar image
sintesis answered ·

This course of action was taken in July when the system was disconnected in the above described way and the MPPT was sent off to the service shop. It came back tested in august, without having found any anomaly, and was connected again. The VE.Bus DC Voltage picture I sent shows the development from the moment of reconnection in August until today. The MPPT starts charging in a normal way but then the real voltage slowly descends, and the MPPT´s own voltage value slowly ascends. The firmware version is 1.59 (the latest version).

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Related Resources

MPPT Product Page

MPPT Error codes

MPPT 150/60 up to 250/70 Manual

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