question

toonpuissant avatar image
toonpuissant asked

MPPT 100/50 suddenly stops charging (SOLVED but still a MYSTERY)

Context:

- on a boat, in sunny circumstances

- 4x 170Wp solar panel array (2x2 in series then parallel)

- 400Ah LifePO4 battery (70% state of charge)

- 1 100/50 MPPT

Without any warning, the Victron MPPT 100/50 between the solar panels and battery stops charging. The app is showing 0W and only 13V on the solar side. When I measure the disconnected solar cables, I get +/-50V; when I measure after I connect them to MPPT, I get 13V.

Tried the following without any success:

- use the bluetooth app to disable and enable the charger

- disconnect all MPPT cables and re-connected in the right order

- I have carefully checked and re-done all the wiring


I looked in the previous topics, but could not find any immediate answer. My guess is the unit must be faulty, right? Any suggestions for other things I could try to remedy this would be very welcome.


Thanks!

MPPT SmartSolar
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4 Answers
pwfarnell avatar image
pwfarnell answered ·

The data suggests that you have a poor connection in your cabling between the MPPT inducing a high resistance and voltage drop so the MPPT tries to draw power but the poor connection restricts the flow of electricity and all you see on the MPPT input terminals is battery voltage. Check all your MC4 connectors, all wiring terminations and any fuses, switches or breakers. What is very common is people using cheap circuit breakers of the type shown on the PV to MPPT and these are well known for poor connections. If you have this type of breaker use one from high quality manufacturers such as Blue Sea and make sure it is from them not a clone.

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toonpuissant avatar image toonpuissant commented ·

Thanks for your quick response and suggestion. I did check all the cables, replaced the MC4 connectors, all seems to be in very good shape, I see not loose connection that could cause the issue. The MPPT keeps giving the same result. I do not expect my solar panels to be the issue but I am unsure what I should measure to exclude that possibility. My guess it is the mppt itself, although it is not showing any error message (only blue/bulk blinking light which indicates too low PV power).

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pwfarnell avatar image pwfarnell toonpuissant commented ·

@toonpuissant If the MPPT was broken and not allowing any charge into the battery then the voltage at the terminals would be 50V, the same as you measure with no load on. If the MPPT is broken and short circuited then you should see no voltage from the panels. If the MPPT is broken and allowing solar power through but not to the battery then it will be very very hot.

One test is with your MPPT running with sun on the panels and 13V displayed for the PV input, go into the VictronConnect app, select settings, battery and turn the charger off. If I am correct, the PV voltage will now increase to 50V as the MPPT stops drawing current.

Measuring the voltage will not tell you if you have a poor contact somewhere, especially if you test a 2x2 series parallel set. You need to test each panel individually for voltage. Then you need to test each panel individually for short circuit current. This will show up if any panel has an issue. This means using your multimeter on the DC current setting, but make sure your multimeter DC current range is larger than the Isc listed on the panels. If all the panels turn out OK then add one onto your cables with the MPPT disconnected and again measure the short circuit cu to see if the current can get through.

Another way is to have the panels running with the MPPT on and then use your multimeter to check the voltage at each junction in the circuit. The trouble is with MC4 connectors you can not get into measure them during use.

Just take care doing this as panels in series can create high DC voltage.

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toonpuissant avatar image
toonpuissant answered ·

And just like that, after 5 hours without any changes, when the sun is almost down, the MPPT decides to wake up again??? Now showing 50V on PV side and charging 58W so 4A at 13V. Still a mystery though, would be interested if anyone has experienced similar and knows a remedy.

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pwfarnell avatar image pwfarnell commented ·

Intermittent loose / poor connection.

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Alexandra avatar image
Alexandra answered ·

@toonpuissant

Rebulk offset.

Pv voltage is not 5v above battery voltage. (Usually seen in why is my mppt not charging reason)

Bad/damaged panels.

Reverse polarity is another reason - although not likely as you say they intermittently start charging.

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Alexandra avatar image Alexandra ♦ commented ·

From the manual

Re-bulk voltage offset


This setting sets the re-bulk voltage offset. This offset voltage is used to determine when a charge stage stops and the bulk stage starts again, i.e. the charge cycle resets and starts at the first charge stage again.


The re-bulk voltage is calculated by adding the re-bulk voltage offset to the lowest voltage setting (normally this is the float stage).


An example: If the re-bulk offset is set at 0.1V and the float voltage at 13.8V, the charge cycle will restart once the battery voltage drops below 13.7V (13.8 minus 0.1) for one minute.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

HI @toonpuissant,

Thanks for the report, even though it appears to have resolved itself now please follow up with any more changes.

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