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gordondragon avatar image
gordondragon asked

Shared PV Input and Load Output MPPT 75/15

Hello,


Forgive my amateur knowledge in the area.

I have 2 questions, which I am hoping to find a bit of clarification on:

  1. If I have a series of 3x 250W PV modules connected in series to output a Voc voltage of 73V (Less than the max 75V) and an Impp of 13.8A, can I connect these to 3 individual MPPT 75/15 solar controllers (73V connected to the PV terminals of each MPPT controller, sharing the 13.8A)?
  2. Can the 3 MPPT controllers have their load outputs connected in parallel to a single 40A load?


The obvious alternative is to use a single and bigger MPPT (e.g. MPPT 150/60) however this does not provide a controllable load output and it also is 60% more expensive.


Any advice, knowledge or recommendations greatly appreciated.


MPPT Controllers
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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

1. 73Voc is way to close to the maximum. At cold weather the Voc will rise above the 75V and can damage the MPPT.

2. No it's not possible to connect one array to multiple MPPT.

3. I would not recommend to parallel the load output. If one MPPT opens the output earlier than the other you will overload the other load outputs.

So you will have to split your array into 3 strings or use a bigger MPPT. You can also use the load output (or the relay of the bigger one) to drive another relay to control your load.

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gordondragon avatar image gordondragon commented ·

Hi Matthias,

Thanks for the quick response. I have already performed temperature and cable length/size compensation to reach the 73Voc using conservative figures so that should not be an issue.

My hesitation of splitting the array into 3 strings was to take advantage of the efficiency of a high voltage system

Thanks for the suggestion of using a relay, I will explore the possibilities with this method.

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Charlie Johnson avatar image
Charlie Johnson answered ·

Operating any piece of electrical or electronic equipment at full load capacity continuously is not good practice and will overstress the equipment. To be conservative, I design components and equipment that will be operating continuously to operate at a maximum of 80% of their capacity.

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