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rupes avatar image
rupes asked

Multiple MPPT's

Hi,

Searched and found many previous questions about this but none that answer this specific one.

I have a motorhome with 4 x 550w panels. I have a 5000/48 multiplus, 16 x 314amp EVE cells forming a battery with a JK 200 BMS. Now the panels dont fit on the roof. I have them overlapping in frames and when parked they spread apart with actuators. The panels are 2400mm x 1100mm. When overlapped each pair is 2400mm long x 1600mm wide so only 500mm of the lower panel is exposed. I was originaly running 1700mm long panels sideways with no overlap through a 150/35 wired 2s2p

My thinking led me to buy a second 150/35 so the lower panels would be on their own MPPT and in addition I have a 2 position (3 if you include off) rotary 8 pole switch suitably rated. The idea was this can switch between 2 wiring configs, one with the upper panels on one MPPT and the lower panels on the other MPPT ... or.... Front panels on one MPPT, rear on the second incase I'm parking the front or rear under shade. Now I'm questioning whether I need the second MPPT. How does it deal with parallel input from 2 strings that are produceing different power levels?. Does the lower one drag down the higher? Secondly if I stick to my plan of using 2 MPPT's how does the system deal with the outputs from these given they are going to be very different especially in the overlapped configuration. You wouldn't want them to be synced? I guess this would be the same as 2 arrays on a house with very different yields.

MPPT Controllers
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2 Answers
Duivert NL avatar image
Duivert NL answered ·

Best is to use multiple mppts, like on house situations with shadings or diff orientation you will get max production that way

different power levels from mppts is no problem, both will support/charge on there own

Different power level from panels with shading combined in serial/parallel will lower overall performance

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rupes avatar image rupes commented ·

@Duivert NL

Perfect. Just wanted to confirm that. I will have a GX soon. I'm assuming when it comes time to fit the second MPPT and set it up the system will figure out what to do with the controllers and how to send to the battery.

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Alexandra avatar image
Alexandra answered ·

@Rupes

If you want to track two different power points for arrays then either an mppt with multiple trackers is used or a second mppt. That is best practice.

Just FYI your input current limit on the 150/35 you need to watch that if you are going to add more strings.

If you connect different facing panels onto one mppt, but you will see that the lower array (particularly if it is voltage lower) will mees with overall performance. It will work and produce, but if you dont want to waste anything then go all in.


Also switching live DC can create its own issues. (Arcing and the like not a good thing so mostly related to safety and switchgear life.) If you want to switch you have to stop the mppt producing, then switch over.

Do you have a GX? If you do you will be fine with more than one mppt. They handle themselves if you don't. And your battery can definitely take 70A of charge since you are running a 5kVa with that BMS. So no issues from that end.

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rupes avatar image rupes commented ·

@Alexandra


Thanks for that. I've got most of the gear except the GX but need to work out which one. Was looking at the Ekrano and Touch but I'll be using Home Assistant and there are some integration possibilities there so maybe just the Cerbo, does have 1 extra tank sender that I could use. Won't be adding any more panels. Roof is full. I do have DC switchgear on the outputs of the MPPT so will just flick it off, change wiring config and switch back on. Only issue that has just come up was 2s2p was working just fine with old 380w Longi panels, they're nominal voltage was in the high 30's I think. These new ones are Risen 540's. Just looked up the spec and voltage is 29.3. I don't know if these are high enough in a series pair for charging 48v batteries. I've only hooked up the top 2 and I did notice it was only putting out 700-800 (rated for 1080) watts in full sun mid morning where as the Longi's always got pretty close to rated power in full sun. Wonder if the low voltage is the issue. I mistakenly assumed being bigger panels they would be at least the same voltage if not higher. Can't believe I didnt check that first.

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