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vendu avatar image
vendu asked

New smart solar MPPT 100/20 disagrees with BMV-501 readings.

Hi everyone,

I have a narrowboat and have fitted a solar panel. It's been on for about a week and a half.
My setup is a single 250W, 48V Voc, panel connected to a Victron 100/20 smart solar MPPT which in turn is connected to my 3 service batteries.


The MPPT updated firmware a couple of times before I turned the system on and the battery values are Victron default.

The MPPT is in the engine bay about 8 inches from the battery box so no temperature sensor is needed. The original installation includes a Victron Phoenix multiplus 3kW inverter, currently switched off, and a BMV-501 battery monitor.
When I first switched the panel on it was facing slightly away from the sun and it showed 125W and 9 amps into the batteries which I thought was quite good.
I left the fridge on for a couple of days to load the batteries and see how much the solar helped. After the 2 days the battery monitor showed the batteries at 82.4% and the overcast weather had just started so I switched the fridge and all other loads off expecting the panel to charge the battery.
However for the last 4 or 5 days the BMV501 has shown a constant 82.4% and the solar shows something like 3W and virtually no current into the batteries. I know there won't be much power produced with it overcast but yesterday whilst the solar showed 3W the sun came out but the panel showed no increase in power. It did show an increase in panel voltage so it registered a change.


All the time the panel is on it is producing 13.67 Volts across the batteries and is showing float mode. The load output is set to 'always off' since I have no load to connect. The BMV-501 battery voltage agrees with the smart solar app.
Today was much sunnier so I checked the panel but it was showing much the same values. I then turned the panel off and the BMV-501 showed a battery voltage of 13.32 Volts but still 82.4% charged.
I have a picture of the BMV-501 before solar installation showing a battery voltage of 12.88 Volts when it is indicating 100% charged.
So it looks like the MPPT thinks the battery is fully charged and refuses to put any charge into
the battery but my BMV-501 thinks it is only 82.4% charged.

Does anyone have any advice please?

BMV Battery MonitorMPPT SmartSolar
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2 Answers
Pieter Boomsma avatar image
Pieter Boomsma answered ·

Hi,

You should look into the settings of the BMV since it doesn't seem to reset properly. Please check with your charging voltages what the maximum charge voltage is you are going to. If it is 13,7v the BMV now should reset to 100%. You can do this with the setting 2: Charged Voltage. Also look into the first 7 settings of your BMV and check paragraph 3.2 of the manual about charging with solar.



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vendu avatar image vendu commented ·

Hi Pieter,

Thanks. Checking the manual now.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Where is the MPPT connected?
The negative of the MPPT has to be connected to the "Load/Charger" side of the Shunt, not directly to the battery.

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vendu avatar image vendu commented ·

Hi Matthias,

It's connected directly to the battery. Where would I find the shunt? Is it part of the BMV-501? I hope it's not on the Phoenix inverter as that is buried behind my shower :-)

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ vendu commented ·

The BMV-501 is pretty old (over 15 years) but the shunt looks like this:

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bmv-shunt.jpg (191.9 KiB)
vendu avatar image vendu Matthias Lange - DE ♦ commented ·

Thanks Matthias.

I have found the shunt and moved the MPPT negative to the right place. I then manually syncronised the SOC to 100% and it looks like it is working now.

Should I change the MPPT battery settings to match the BMV or are the Victron defaults sufficient?

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