question

gianmarco avatar image
gianmarco asked

MPPT String Overcurrent/Overpaneling - RS450|200

Good evening everybody.

As for the title, I'm asking you if is possible to exceed the current limit (Isc/Imp) on the single trackers in the RS450|200.


As I read on the datasheet, the only problem with exceeding the 20A Isc limit is that over 20A the reverse polarity protection doesn't work, so I risk to fry the regulator if I wire the solar string in reverse polarity.


For more details:

I'd like to parallel 4 strings (2+2) in order to use only 2 trackers of the RS, and on the panel datasheet I read that the Isc on STC conditions is 14.22A.

Paralleling the 2 strings implies that the tracker could reach 28.44A of current.

I read around that in this condition the regulator simply "clips the power".

Is that true or I risk to fry the regulator?

Note that the Voc limit would be strictly respected.


Thank you for your time and sorry for my broken English.

MPPT ControllersMPPT SmartSolarcurrent limitinput currentrs450
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Alexandra avatar image
Alexandra answered ·

@gianmarco

The question from my side is - why would you do that when you have the use of all the trackers?

You you can over panel to the absolute max of 30A short circuit, but you void the warranty immediately. (And still have the 4000W limit of each tracker so wasting the solar as well)


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gianmarco avatar image gianmarco commented ·
It's not an absolute need, but I'd like to leave 2 trackers free because I have in mind to install more panels.

Btw It wouldn't be a complete waste of power, since in summer I have more light hours and in winter the panels will never produce all the power.

Anyway, thank you for your answer.

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Alexandra avatar image Alexandra ♦ gianmarco commented ·
BTW the reverse polarity not working means components could possibly self destruct trying to short the PV input.


It will produce the same power using all four trackers as it will in parallel. Rewiring is easy anyway when you do add more.

It does/ should not reduce switchgear to parrallel the strings anyway.

In low light you want the max voltage, so run the voltage for each string as high as you can for your battery float.
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Craig Chamberlain avatar image Craig Chamberlain commented ·

@Alexandra Unless I'm mistaken, it only voids the warranty if you DO connect your panels in reverse polarity at more than 20A Isc. I don't think it voids your warranty just by running at between 20A and 30A if correct polarity is ensured.


I have a pair of MPPT 250/60 controllers running where each is attached to a 4s2p string of Trina Vertex S 425w panels with Voc of 50.2V each and Isc of 10.74A each. So the 4s2p combined strings yield just over 200V Voc and 21.48A Isc at standard conditions. That means I can't rely on built in reverse polarity protection, although I doubt the extra 1.48A would be decisive, but since I'm under the 30A ultimate limit and have polarity correct, my warranty should be good.

Edit: Correction, it's 35A absolute max Isc for the 250/60 MPPT.

Further Edit: The data sheet says 35A but the MPPT manual (HTML & PDF) says 60A . I very much doubt that it can take a 60A reverse current so I shall assume the 35A is correct. I also can't find the bit where it says 20A max reverse current. I'm sure that was there previously.

Anyway, my comments are related to the 250/60 not the RS450/200 so feel free to ignore.

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Alexandra avatar image Alexandra ♦ Craig Chamberlain commented ·
Hmm ok.


I will re phrase, going out of recommended nominal boudaries means the warranty is not likely to be given, or will make the process of explaining create alot of hurt feelings when dealing with sales and distribution. Even if there is a different problem not reverse polarity related.
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Alexandra avatar image Alexandra ♦ Alexandra ♦ commented ·
The 250/60 is 35A. must be a typo in the live manual.

The calculator spreadsheet will tell you three strings is higher than max input current. With a big red NOT accepted at the bottom

Same will be true for the 450 series.


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Craig Chamberlain avatar image Craig Chamberlain Alexandra ♦ commented ·
Yeah, I agree, I certainly wouldn't go beyond the Isc max figure. What I'm confused about is that I was almost certain that the 250/60 had a reverse current protection figure of 20A with a max Isc (correct polarity) of 35A whereby if you connect it correctly then it's good to 35A but will only protect itself against reverse PV current to 20A. Either I'm mistaken or the documentation has been updated to drop the 20A limit for reverse PV current. Anyway, sorry to take things off at a tangent. :)
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