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jimmi5645 asked

75/15 mppt newbie question

Hello, newbie question here.

I have a blue solar 75/15 Bluetooth, 2 x 170w 12v panels and 3 x 12v lifep04 30AH batteries.


Can I wire the panels in series for 24v volts, connected to mppt, and wire batteries in parallel for 12v 90AH?


Will the mppt step the voltage down to safely to charge the batteries and is this the most efficient way of charging with the above kit?


Many thanks

MPPT SmartSolar
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Fideri avatar image Fideri commented ·

What is your VOC on the solar panel label? The total can't be exceeded however you connect. There's a Victron calculator for that.

F.

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prein avatar image
prein answered ·

yes. That's the 75 in the product number. Solar can go to 75V input

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jimmi5645 avatar image
jimmi5645 answered ·

Thanks for your replies guys


Voc says 23v on solar panel website

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Fideri avatar image
Fideri answered ·

In that case, you are safe with a 75/15 any way you wire them, even allowing for temperature fluctuations.

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frankhe avatar image
frankhe answered ·

The total open-circuit voltage of your three panels is indeed below the maximum of the MPPT charger. 23 V per panel, 3 panels in series makes 69 V in total which is below the 75 V of the charger.

You can wire the batteries in series to get 24 Volt or keep them in parallel for 12 Volt.

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kevgermany avatar image kevgermany ♦♦ commented ·
It's 2 panels, 3 batteries.

If it was 3 panels, then voltage change/ temperature checks would be needed.


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frankhe avatar image frankhe kevgermany ♦♦ commented ·
You are indeed correct. Two PV panels in series and three batteries in parallel. @Jimmi5645 could even add a third (same) panel in series.
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kevgermany avatar image kevgermany ♦♦ frankhe commented ·
Only after voltage/temperature checks are carried out. 69V may rise enough to kill the MPPT in colder areas.
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frankhe avatar image frankhe kevgermany ♦♦ commented ·
It is indeed a tight margin of <10%, is the 75 V an absolute value without any tolerance?
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jimmi5645 avatar image
jimmi5645 answered ·

Thanks guys!


Much appreciated

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