ukxan avatar image
ukxan asked

Add 6 panels to MPPT RS 450/100

Good evening everyone,

I have 2 strings of 7 panels each on the MPPT RS 450/100

Im planning to add more ,should I make it 2x9 panels or 2x10?

What margin of safety to keep regarding max Voc?

Panels are canadian solar 410w -Voc 37.2,Isc 14.01


mppt rs
2 |3000

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klim8skeptic avatar image klim8skeptic ♦ commented ·

@ukXan As per the manual re note 1, what is your battery float voltage?

Voc goes up with lower temperatures. What is the lowest temp your array will experience?

Perhaps use the mppt calculator?

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ukxan avatar image ukxan klim8skeptic ♦ commented ·
Well,given Im in East Anglia,in spite of global warming the temp did drop to -6 I believe on 1 day this winter.

Pylontech battery float as per victron documentation is 51 V

Many thanks,

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nesswill avatar image nesswill ukxan commented ·

I too have the RS 450/100 (well x2) and x9 panels on each tracker and live in the same area as you. Over the coldest sunny day when on float i was still well within spec of the 450/100 a and my voc is a bit higher than yours so i would say x10 on each tracker but as suggested check the calculator first.

The only other thing to consider is shading if x10 have one shaded you might be better off with x9.


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nesswill avatar image nesswill nesswill commented ·
You can always bypass one panel if you find it get close to the limit and reconnect when cloudy.
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dbainbridge avatar image dbainbridge commented ·
It would be fine since the highest Voc even at -6C would be 402V with 10 of those panels in series. The issue you would have is with 2 strings of 10 panels in series would result in rated power of 8200W. Each tracker on the MPPT RS can only handle max of 4000W so you'd potentially lose over half the power. It would be much better to keep it to single string of 10 for both trackers. Even then you will run into the maximum amperage of MPPT RS of 100A since that 8200W would be well over 100A charging capability. Everything would still work you will just be losing a lot of potential power if you need it.
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nesswill avatar image nesswill dbainbridge commented ·
410 x 10 = 4100 each tracker but realistically you wont get near that in the winter only in the summer (what i have seen) but in the summer you won't use so much battery so bulk charge wont last to long before you go on absorption and the mppt wont try to pull full power from the panels.

This is just what i have seen and not a recommendation or suggestion you need to make up your own mind.

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kevgermany avatar image kevgermany ♦♦ dbainbridge commented ·
Don't mix PV power with MPPT output power. If there's excess available it's lost. It's advantageous to add more PV capacity than the controller output to give adequate output in poor light. The thing to watch is Isc ratings. Determining the cost effectiveness of the approach is a different issue.
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ukxan avatar image ukxan kevgermany ♦♦ commented ·

So in summary would 9 panels on each tracker be safer then given Voc 37.2,Isc 14.01?

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kevgermany avatar image kevgermany ♦♦ ukxan commented ·
Isc is not affected by the panel count in a string. So as your panels are 14.01V, the controller is 20V per tracker, no issue.

VOC of 10 panels in series is 372V at 25C. Temp coefficient for voltage is 0.26%/C.

You have a voltage margin of 450-372=78V. To make the maths clearer, let's take a ridiculous case - temp drops to -25C or 50C below the reference standard. So voltage increase will be 50*.0026*372=48.36V. This still leave a margin of almost 30V.

That's safe in my book. Unless the beast from the east comes in really really cold... ;-)

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