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jonf3n avatar image
jonf3n asked

100 A Charge controller too much? (wont work in low-light!?)

I am considering installing 8 x 610w pannels (Aiko MAH72Mw)
Therefore the absolute peak will be 4880w right?

One installer suggested the Victron SmartSolar MPPT 250|100 Charge controller which can handle 100 Amps * 48v = 4800w right?

Another (less experienced) guy said that 100 Amp controller would be "too big" and that on cloudy days it may not charge the batteries at all if the panels are not producing a minimum amount of current. He said I should go for the 85 Amp charge controller.

Please help advise.

charge controller compatibility
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2 Answers
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pwfarnell answered ·

As you will typically be charging batteries at 54V or higher the 85A controller is just under your panel limit so it may suffice.

However, the reason put forward by the second installer is rubbish, as long as the panels produce 5V above the battery voltage to begin charging then there is no other limitation. Here in the UK winter my small boat system has 680W of panels with a 60A controller is charging the 12V batteries even though it is producing only 50 to 60W.

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anthony answered ·

It would be benefical to know in what country this system will be installed and if the solar panels are roof or ground mounted and at what angle? Also battery chemistry, brand and model would help?

Both the 250/100A and 250/85A controller will work. If you get a lot of ideal days (good sunlight at optimum temperatures and angle) and your system alway needs or can use the available energy then the 100A controller would be the better choice and depending on where you are may not be a lot more expensive than the 250/85.

8 X 610W = 4880W

4880/48V = 101Amps

The statement below is not correct and is irrelevant to Mppt controller choice in this context.

''Another (less experienced) guy said that 100 Amp controller would be "too big" and that on cloudy days it may not charge the batteries at all if the panels are not producing a minimum amount of current. He said I should go for the 85 Amp charge controller.''

But it is important to have the correct number of solar panels in a string which is what he might be getting confused about, in terms of having an high enough Vmppt from the string on a cloudy day to charge the battery. This would relate to either controller choice.

Have you seen the sizing calculator: https://www.victronenergy.com/mppt-calculator



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jonf3n avatar image jonf3n commented ·

This is installation in Portugal on the ground.

It is partially in a valley but near the top of the valley. Summers are brilliant, but of course the issue is winter... we sometimes get 10 days of grey & rain, but it's rare.
Panels are basically pointed south, but slightly west.


Batteries will be Pylontech US5000 4.8kkWh LiFePO4.
Inverter: MultiPlus-II GX 48/5000/70-50 GX


I think I'm pretty much set on the SmartSolar MPPT 250/100 48v Tr model

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