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robublind avatar image
robublind asked

Newbie question using Victron MPPT 100/30

So I want to use these cells

  • Rated Power: 250W
  • Open circuit voltage (VOC): 37.6 V
  • Max power voltage (VMP): 30.3 V
  • Short circuit current (ISC): 8.85 A
  • Max power current: 8.27 A
  • Power Tolerance 0/+3%
  • Maximum system voltage: 600V (UL)
  • Fuse Rating: 15 A
  • IP65 Junction Box w/ standard solar connectors

with a 12 volt battery system (I will be upgrading to a 24volt system next year)

How many panels can I use if any and what would be the best config. It will be on a RV so I would like to get three panels, do I have to upgrade my charge controller?

MPPT Controllers
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3 Answers
Erik Sporns avatar image
Erik Sporns answered ·

Max solar voltage allowed on the mppt is 100V. Since your cells have an mpp at 30.3V, you could 3 panels in parallel or two in series (= 60.6V).


Note: Output at 12V is ~360W. You can run more solar input, but the mppt wont give you the whole power of the array. It does still increase solar input out of max sunlight. e.g. more than 2 cells dont make sense.

As wattage is doubled at 24V, therefore three panels in parallel are perfectly fine.

Id personally, without taking money into consideration) would run two panels in series for now and switch to three panels in parallel after the 24V switch.

edit:

three panels in parallel at 24v is not a good idea, as the voltage difference is not sufficient. They should be put into series + mppt with higher allowed solar voltage.


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Mark avatar image
Mark answered ·

Ensure that you do NOT use 3 of those panels wired in series, 2 in series is the maximum allowable for that solar charge controller.

When considering the solar charge controller max PV voltage limit, you need to look at Voc and not Vmp.

The Voc for those panels is 37.6V, which is 112.8V for 3 panels in series, however the absolute max limit for your charge controller is 100V.

So it would blow up the charge controller and this is not covered under warranty.

Also, you need to remain under the solar charge controller max PV voltage limit in the coldest conditions, when PV voltage can be even higher than rated Voc.

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Erik Sporns avatar image Erik Sporns commented ·
I never said 3 in series :(
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Mark avatar image Mark ♦♦ Erik Sporns commented ·

Hi Erik, yes sorry I just re read and updated. You threw me off because you were referencing Vmp rather than Voc. When making assessments against the solar charger max PV voltage limit you need to consider Voc plus an extra margin to account for even higher voltage in cold weather.

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klim8skeptic avatar image
klim8skeptic answered ·

3 of those panels in parallel is broken for a 24v battery. Not enough Vmp.

Choose an 150v mppt if you intend to use those panels with a 24v batt.


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Erik Sporns avatar image Erik Sporns commented ·
yes, you are right. i forgot the 5V+ necessity.
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