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cbitterfield avatar image
cbitterfield asked

How to select a solar charge controller? and associated questions

I am trying to select a charge controller for generic solar panels. I am trying to put 12 panels of 300w in to two arrays (6 each). The panels will be installed horizontally on camper

The panels are:

EFTE: Flexible
Open circuit voltage: 22-24
Short circuit current: 5A-15
Maximum power point operating voltage: 18V
Maximum power point operating current: 15A


I am planning on 4 x (400AH): I currently have 1 for testing. The manufacture says 225A is maximum before the BMS shuts down the battery. They said it can take current at the same rate; but I am unsure about that. These are the published specifications.

Model: 12v 400Ah battery pack
Battery type: 3.2v LiFePO4 Battery
Nominal voltage: 12.8V
Nominal capacity: 400Ah
Maximum charging current: 5A-20A
Instantaneous discharge current: 200A
Continuous discharge current: 100A


I plan to arrange the array in as follows:

Panel 1 + Panel 2 + Panel 3 (Series) ----(Set 1) 54V / 45A (1800W)

Panel 4 + Panel 5 + Panel 6 (Series) ----(Set 2) 54V / 45A (1800W)

Set1 + Set2 (Parallel) 54V / 90A


Additional Equipment Planned:

MultiPlus-II 12/3000/120-50 2x120VA
Lynx Smart BMS
Lynx Distributor
   P1: Multiplus II
   P2: Charge Controllers (180A)
   P3: DC/DC Chargers (120A)
   P4: DC Distribution
Cerbo GX
GX Touch 50

If I do this twice that should add to 180A.


ps: I have ask a couple of dealers but the answers don't always make sense.

Question 1:

How do I select the correct solar charger? Does 54V / 90A all I need to go by or does the 1800W of solar factor in somehow.

Would SmartSolar Charge ControllerMPPT 150/100-Tr be a good choice?

Question 2:

I am seeing a lot of conflicting locations for fuses and shut offs on these arrays. If I put a PV 100A disconnect between the panel array and the charge controller, do I need fuses, surge protectors or other devices between the MPPT Controller and the Lynx distributor? (Is the fuse there sufficient) and how do I size that?

Question 3:

If the 4 batteries can only take 80As maximum and that leaves 100A (out there) will the Multiplus use that 100As for DC->AC conversion or is it just a waste?


Question 4:

Solar Panels rarely produce what they are rated for, based on shade and position. Should I engineer for the maximum or some delta in power? I am looking into a test device that will show actual production (I know that the charge controllers can show that as well). I am looking at should I check the panels individually to check production?


Question 5:

Do I need fuses (if so what size or how to size) between the panels or sets?







Multiplus-IIMPPT Controllersfuses
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3 Answers
nickdb avatar image
nickdb answered ·

The best thing to do is to use the MPPT calculator available via the solar charger product page.

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Michelle Konzack avatar image
Michelle Konzack answered ·

Since you want to run a 12V system, you need anyway at least 2 MPPTs.


I would suggest you to use two SmartSolar MPPT 150/100 abd put on each a string of 6 panels. The high voltage of the panels ensure, you get also in the winter a nice solar output.

2 comments
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kevgermany avatar image kevgermany ♦♦ commented ·
Six panels in series on this MPPT is dangerously close to too much, we've no idea of winter temps. @nickdb suggestion of using the calculator is much safer.
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Michelle Konzack avatar image Michelle Konzack kevgermany ♦♦ commented ·
His panels have an


Open circuit voltage: 22-24


and if you assume a temperature coefficient of -0,3%/K then you can have around -25°C before you hit the MPPT hardlimit.


Anyway I ignored that his panels have 300Wp each, hence he would need 3 SmartSolar MPPT 150/100 and then he hit the hardlimit at maybe -120°C. Oops!


However, running a 3kVA inverter is tough!

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matthias-nagel avatar image
matthias-nagel answered ·

Regarding question 2 and 5 ("fuses"): There is no general answer to this. It depends on the arrangement of your electrical installation, jurisdiction and local regulation and trade-offs. The Lynx distributor is a fuse holder for midi fuses. Hence there is no actual need to place separate fuses there. If the wire between the PV array and the MPPT is rated for the maximum current which the PV panel can provide, then there is no technical reason to place extra fuses. However, local regulations may require some anyway. Same holds for surge protection. For example, in Germany, surge protection is required for permanent PV panels on buildings (due to building regulations), not for campers. I don't know the regulations for your jurisdiction. Also note, that proper surge protection is not easy as it is all about a good grounding. (I do not even know how one would achieve that in a camper.)

PS: Your questions are actually not well suited for this forum (see forum rules). The problem with that kind of question is that they are not specific to VE products, but more about general electrical installations. There are too many variables to give a succinct and proper answer.

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