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jessluvs2romp avatar image
jessluvs2romp asked

MPPT Smart 100/50 suddenly dropped voltage/performance

Hello. I have 720W of solar on the roof of my truck. 3x 180W in series with 2x 100w in parallel.

When I first hooked them up, the MPPT was reading 90V, and supplying a good amount of wattage. Then, the next day it basically stopped working. When I disconnect the solar +/- wires and read the voltage, it is still 90v in direct sun. When I plug them back into the MPPT and switch on the breaker, it for a moment reads 90V then drops down to ~40V or less.

I tried taking out the breaker switch to see if that was the issue, same behavior.

Again - this is all in direct sunlight. The highest it gets now is 120W, and all at the same ambient temperature.

I updated the firmware before the installation.


What am I missing? Did the MPPT just go bad?

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MPPT SmartSolar
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5 Answers
jessluvs2romp avatar image
jessluvs2romp answered ·

edit - i realized my float/absorption voltages were swapped, but I do not think that's the source of my issue. corrected them and still see the same issue.

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jessluvs2romp avatar image
jessluvs2romp answered ·

also, if it matters but probably doesnt much, 8x weize lifepo4 100ah 12v in parallel

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Scott avatar image
Scott answered ·

Provide a drawing of how the PV modules are connected, and the specs of the PV modules.

In general,

all PV modules in a series string need to have the same IV curve (easiest to use identical PV modules in a series string); Max voltage at minimum temperature needs to be within the MPPT's ratings.

and any parallel connected strings need to have the same Vmp as other strings (easiest to use an identical number of PV modules of the same type as the other strings); There are ways to use other PV modules in a parallel string if you're careful to match the Vmp at their actual operating temperature, but mismatch can cause problems with the MPPT trying to find Vmp.

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mvas avatar image mvas commented ·

One string ...

3 panels @ 180 Watt all in series and

Then ( 2 x 100 watts in parallel ) acting like a single 200 watt "4th panel" , also in series with the above 3 panels.

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mvas avatar image
mvas answered ·

Very important that the total sum of all Voc ( Voltage Open Circuit ) is not too high.

Is it possible the parallel connection has come undone / failed? That would explain 90 Voc no-load and significant loss of watts under-load.

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Scott avatar image
Scott answered ·

Please provide the specs of the PV modules. Voc, Vmp, Isc, Imp. ?

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