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secz avatar image
secz asked

12*Axitec 405W per String on SmartSolar RS450/100

Hello all,

unfortunately I have not found the answer to my question in my search.

I would like to know if the following setup which I bought works:


2 strings with 12* Axitecmodule 405W each.

37,3 Voc, 13,81 Isc

31,4 Vmpp, 12,9 Impp

All this on SmartSolar RS450/100


Batteries Pylontech US3000c

FloatVoltage 51V according to Victron:
Victron & Pylontech UP2500, US2000, US3000, US2000C, US3000C, US5000, US5000B, UP5000, Phantom-S, Force-L1 & L2 [Victron Energy]

Charging voltage according to Pylontech 52,5-53,5V
us3000c-anleitung-deutsch.pdf (solar-autark.com)

1668979228293.pngAccording to the MPPT Calculator, you can't put the 12 modules in series because the open circuit voltage would be too high:
MPPT Calculator - Victron Energy

But now I also want to feed in and thus consumption is always present and open circuit theoretically never present.

If I raise the float voltage slightly and replace the open circuit voltage (which should not exist) with the nominal voltage, it would fit.

Now my question would be, whether this also works in practice?

Or does the MPPT switch me or even perhaps damage?


1668979205994.png

rs450
1668979205994.png (157.2 KiB)
1668979228293.png (184.1 KiB)
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5 Answers
klim8skeptic avatar image
klim8skeptic answered ·

Now my question would be, whether this also works in practice?

In practice 12 x 405w Axitec panels at 0c will have an array Voc of 479 volts.

The maximum PV voltage input for the mppt is 450v.

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sharpener avatar image
sharpener answered ·

12 * 405W is 4.86kW per string.

The 450/100 is rated at 100A * 48V = 4.8 kW in total

So unless the two strings point in different directions and so don't generate at the same time you will need more than one MPPT this size.

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solarmax-canarias avatar image
solarmax-canarias answered ·

Just put 6+6 in parallel per string and everything solved

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klim8skeptic avatar image klim8skeptic ♦ commented ·
That is over the 20a Isc limit for the mppt.
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secz avatar image
secz answered ·

You are all rigth Voc of 479 volts is over spec.!
But I do want to be preped for winter. So is there a way to oversize the MPPT?

Maybe 6*2 on one string. But then I will overdrive the Isc (2*13,81= 27,62A) (20A is max.)


The max. power isn´t the problem.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

The max. power isn´t the problem.

Well it is a bit. The mppt can charge your Pylontech US3000 52v battery # @ 100a. The max output of the mppt would be limited to 5200w.

Now looking at your MPPT RS 450/100 your array Voc is limited to 8 x battery float voltage. 408 Voc. An array of 9 series panels would be 376v @ -15c (10 series = 418Voc).

Now your mppt has 2 trackers, so 18 panels total. 7290w of panels, for a max output of 5200w. If you really need to use all 24 panels, you will need 2 x MPPT RS 450/100, op a single MPPT RS 450/200.

# Take note of the recommended charge current per battery module.


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klim8skeptic avatar image klim8skeptic ♦ klim8skeptic ♦ commented ·

@SeCz Maybe 6*2 on one string. But then I will overdrive the Isc (2*13,81= 27,62A) (20A is max.)

You really should not have an array with an Isc of more than 20a.

1. The mppt is designed to withstand/survive an array reverse polarity connect of 20a. At 26a input the mppt/cabling might just catch fire.

2. The mppt is designed to short out the pv array, should something go wrong, and the batteries are being subjected to higher than programmed charge voltages (to prevent battery damage, and fire). We dont want the batteries to catch fire, or the mppt.

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secz avatar image secz klim8skeptic ♦ commented ·

I found the solution to my question:

In German the specifications is not in the manual...

1669318934871.png


But in english I found what I was looking for: So I´m allowed to put 27,62A on on tracker.

Isolated SmartSolar MPPT RS (victronenergy.com)
1669319072728.png

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secz avatar image secz klim8skeptic ♦ commented ·
The Battery charging I can set up in software, so I´m fine with my bigger battery arrey. Thanks!
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klim8skeptic avatar image klim8skeptic ♦ secz commented ·
It pays to read the whole manual :).

I have requested clarification regarding Isc limits. Fingers crossed.

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secz avatar image secz klim8skeptic ♦ commented ·
@klim8skeptic : Any news about the Isc?
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klim8skeptic avatar image klim8skeptic ♦ secz commented ·

Excerpt from RS 450-100 manual.

3.4. Solar array configuration

The MPPT RS must keep the individual tracker inputs isolated from each other. That means one solar PV array per input, do not attempt to connect the same array to multiple tracker inputs.

The maximum operational input current for each tracker is 18 A.

MPPT PV inputs are protected against reverse polarity, to a maximum short circuit current of 20 A for each tracker.

Connecting PV arrays with a higher short circuit current is possible, up to an absolute maximum of 30A, as long as connected with correct polarity. This outside of specification potential allows for system designers to connect larger arrays, and can be useful to understand in case a certain panel configuration results in a short circuit current just slightly above the maximum of the reverse polarity protection circuit.

The technical gurus have affirmed the 30a absolute maximum, tracker input current limit.

20a is the mppt's reverse current protection limit per tracker. Arrays with an Isc of more than 20a, will potentially damage the mppt, should reverse polarity connection to the mppt occur.

18a is the working current limit of the mppt. That will limit the maximum output of each tracker to 3,300w. Array Vmp x 18a limit.

Array Isc goes up with increasing temperature. Factor that in.

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klim8skeptic avatar image klim8skeptic ♦ klim8skeptic ♦ commented ·
bump.
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secz avatar image
secz answered ·

So it will work but isn’t the favorite.

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