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silviu avatar image
silviu asked

Victron mppt 250/100

Hi.please can someone help with an setup that I want to mount on the ground?I have the victron 250/100,100/30 and 100/20 but I would like to use the 250/100.i have for the moment 4x280amp lifepo4 battery and an victron 12v/1200va inverter so yes its an 12v setup(I haven't bought yet an bms and balancer as I'm still trying to find out which should I use not very expensive)and I want to buy some panels and it will be a lot of cloudy days from November to March.so my question is?what is the best option as panel size and of course they will be in series.how many can I use in series or maybe series parallel but I'm interested that the setup to start charge as early as possible.waiting for some answers and thank you

MPPT SmartSolar
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4 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Take a look at the MPPT calculator:

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

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silviu answered ·

I know that page but its not easy to understand.how is that Canadian solar 470w/44v cs3y/470mb 4 panels are all ready 130% oversized value for the 250v/100a mppt?44v x4 is 176v and multiplied by 10.74amp per panel so this is 44V×4(panels)=176v and multiplied by 10.74a=1.9kw but the mppt in theory is 250V×100A=25kw(this is what the mppt should handle) this is what I don't understand so on the page at the calculator it shows at temperature max 70° and lowest -20° and 10m cable length of 6mm thickness that for 4 panels in series it says PV max V@min temperature 234.6v and PV min V @max temperature 150v and that my mppt 250/100 it will be 130% oversized(wich in theory should be ok).why it can take only 4 panels?its an 250v and 100a charger so it should handle few more strings in parallel.this is very confusing.i want to connect panels 5 panels in series to have an very early charging start-up but 5 it shows in victron page that there is no mppt that can handle this.hmmmm....

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gazza avatar image
gazza answered ·

I think you are mis-understanding the model numbering system for the MPPT.
"250/100" equates to a max input voltage of 250V (after temperature corrections) and a max output current of 100A. As you have a 12V system the nominal PV power (from the data sheet) is 1450W, (ie battery charge power of 14.5x100), so the "oversizing" is based on that value.
According to the MPPT calculator you could do 2 parallel strings of 4 in series (with that 470W panel), ie 8 panels? This would be 259% oversized... you would need to consider cooling of the MPPT in the summer as it would be working hard for much of the daylight hours?

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silviu answered ·

My friend "gazza" wouldn't 259% be to much doesn't matter how much you are trying to cool it down?in my country in the summer we reach 40° most of the day's(of course the mppt won't stay out in direct sunlight i will build an shed with sandwich panel wals to try to keep the temperature as stable as possible)Will it be better smaller panel watt for example 400w so 4 in series and the 2 strings in parallel?thank you for taking the time and answering

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Alexandra avatar image Alexandra ♦ commented ·
As long as you do not exceed the input current and voltage limit you can put what you want onto the mppt.

Oversizing is good for cloudy days and you mentioned that you are expecting quite a few upcoming.

For a 12v system 1200w is what you can install to be at 100% loaded.

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kevgermany avatar image kevgermany ♦♦ Alexandra ♦ commented ·
@Silviu

By input current, it's the Isc value.

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silviu avatar image silviu Alexandra ♦ commented ·
Thank you for the comment.yes is good for cloudy days but then when the summer comes what do I do then?the panels will produce a lot more so I suppose to disconnect one?I'm trying to find the best ballance without destroying the mppt actually after reading so many comments in other pages there is nothing that indicates what panels(as max watt per panel) are the best to push it over the 250v/100amp but without destroying it as it cost me a nice sum of money.i can buy any panels but the victron calculator is very complicated to understand it.for example this mppt all ready for 5 Canadian solar 340w/33v/cs3l/340p at minimum -20° and max 70° all ready shows me PV max V at min temperature 222.9v and PV min V at max temperature 137.4 and victron says this is 117% oversized.i have for the moment 4x280a lifepo4 soon I'll buy another 4 im interested to mount 12v setup as its easier in the cloudy days to get charge otherwise for 24v you need double as the nr of panels and I'll be using for lighting only 12v e27 led bulbs.i know it needs thick wires but I have some 0 gauge ones and I will mount the mppt and the victron inverter very close to the battery' s.by my location victron calculator it shows for November and December like 2.6kw daily yield which isn't much.im interested to have as much as possible max input voltage in the mppt so I'll mount the panels only in series and no parallel string
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