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xrsprint avatar image
xrsprint asked

Over Current on MPPT 100/50

Hi There Everyone,

i have read a few posts with some differing answers, but would love to see that you guys think on this subject

I currently have two 400w Panels feeding a 100/50 controller running 12v charging two 200AH AGM batteries in Series. the specs of the panels are open circuit voltage at 49.1V, and short circuit current at 10.10 Amps


the load is 10amps constant at night, and during the day goes back to grid using a ATS, so the batteries have no load charging during the day.


now that winter is here if finding after two days my batteries are drained, due to no sun, clouds and also a tree in the way for 2-3 hours of sun.


I'm thinking of adding another two of the same panels to the system, and wiring them series-parallel, so i keep the voltage under 100v but increase the amps. now i know this should be ok in winter as it wont get to the 50 amp limit of the controller, but summer would be a different story.


i can see on the 100/50 datasheet that nominal power is 700w, (i currently have max 800) but if i do this the system will be at 1600w. i can see that is says Max. PV short circuit current is 60 amps, so i know i will be under this value, and i don't mind if i am not using the panels full capacity in the summer, but i know ill have more power being generated in the winter


what are all your thoughts on this? as getting another 100/50 would be costly, and if needed i would go to this direction, but seeing that I'm not going over the specs of the controller, i can see an issue why this would not work, unless people have other experiences


Thanks again for you time to read this and welcome and input



MPPT Controllers
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4 Answers
bossrox avatar image
bossrox answered ·

I don't see you needing another charger. You have 2 400 watt panels that make 10 amps each & adding another 2 would be 40 amps so you're within tolerance with 10 amps to spare for what you're describing & if the max open circuit voltage is 49v you're still within tolerance but just by a hair.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·
10A at PV are not 10A at the battery!

P = U x I
(lower voltage means higher current for the same Power)

And 98V are to close to the max of 100V because the 49Voc are at 25°C and with each degree below 25°C the Voc will rise.

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

@xrsprint

Use the online calculator to see if your setup will work and what MPPT you will need.

https://www.victronenergy.com/mppt-calculator

You have to enter ALL data from the datasheet.

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JohnC avatar image
JohnC answered ·

Hi @xrsprint

Charging 12V, I'd run all panels in parallel (up to a max of 5x to avoid exceeding the 60 Isc limit on that mppt). That may also help with the shade you mention. And avoid the high Voc issue ML points out.

The mppt can only provide it's 50A rating, and will curtail at that. But into 400Ah of battery that's a pretty good design level.


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xrsprint avatar image
xrsprint answered ·

Thanks for the advice everyone @JohnC and @Matthias Lange - DE thanks i didnt think of going completely Parallel, however i do have MPPT logging and the most its ever gone to is 95 Volts, which is close to the limit, so i agree bringing it to Parallel it will sit about 50V, or is 95 ok to work with (i assume there is some voltage drop). to confirm however i understand the MPPT is 50 amps charging to the battery at 12 volts, and its stated that 60amps max short circuit current at the PV, so i should be ok, obviously i will be not using the panels to their potential at summer time, but winter should at least get me from 10-15 amps charging at the battery to 20-30 amps which will do the job


Thanks again

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klim8skeptic avatar image klim8skeptic ♦ commented ·

i do have MPPT logging and the most its ever gone to is 95 Volts, which is close to the limit, so i agree bringing it to Parallel it will sit about 50V, or is 95 ok to work with (i assume there is some voltage drop)

The most realistic scenario would be for the mppt to go into FLOAT while the pv array is cooler than STC.

When the mppt goes into FLOAT, it will disconnect the PV array from the batteries, ie the PV array goes into Voc...

Should the PV array actually cooler than STC calculations, the array Voc will spike upwards..

It only takes a moment when the array is colder than STC due to colder conditions, or even a passing rain event cooling the array..

Keep the magic smoke inside your controller..

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