question

kogut avatar image
kogut asked

Connection of two MPPTs to the batteries

schemat-5.png


The number of solar panels is more , this is just a pictorial representation of the question. For Smart MPPT 100/20 ( 8*60W or 6* 60 W / 3,0 A ,connected in parallel ) not more than 20 A .For Smart MPPT 75/15 ( 8*15W / 1.0A connected in parallel ) not more than 15 A. I will calculate the power of solar panels here, I do not need help in this matter.
The main question is can I connect Smatr MPPT 100/20 and Smatr Mppt 75/15 to such batteries ( connected in parallel )? (see diagram) . Theoretically : The first battery (connected in parallel) is charged with the Smart MPPT 100/20 and the third or fourth with the Smart MPPT 75/15. The 12v/230v converter draws power from the middle battery (connected to the second or third battery). So, the path of current draw to the converter from the batteries is shorter and the path of charging the batteries is optimal.
Is this solution correct? Will there be interference between Smart MPTT? Or what protections should be added to the wires (diodes)?

I don't want answers like "get yourself an inverter or a bigger Smart MPPT, like 5000/500"

Please don't tell me watts and amps,I know how to add Amps or Volts.

The main question is, is it possible to connect two Smart MPPTs to the batteries?
And possibly what diodes to use (reverse current, battery discharge, etc.)
smart mppt
schemat-5.png (40.5 KiB)
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kevgermany avatar image kevgermany ♦♦ commented ·

Guessing that what @Steffen Graap was meaning with his suggestion is that your schematic wiring is not ideal for the batteries.

Ideally connect all batteries with equal length and size wires using negative and positive busbars. Connect the chargers and loads to the busbars.

If you can't do that, connect all negatives together, all positives together take the positive from one end of the chain and the negative from the other end.

Both solutions will equalise the charging and use of the batteries.

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3 Answers
steffen-graap avatar image
steffen-graap answered ·

You can connect MPPT in Parallel, no Problem.
For right Battery-Connection, please read The Wiring Unlimited book from Page 16

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ahtrimble avatar image
ahtrimble answered ·

The short answer is "yes".

But, the method of connection is important, at least to me.

I am doing the same thing here at my off-grid home. I am not seeing any fusing or CBs or switching in your diagram. I am using a PowerIn to parallel my batteries, then the Lynx shunt (connects to my Color Control) with fuse, then another PowerIn to bring in the 2 MPPTs and output to the inverter. Makes it a pretty clean and safe install.

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ahtrimble avatar image
ahtrimble answered ·

Great point! Thank fully I can set parameters on the MPPT to help with that. Also, the 2 LifePo4 batteries can handle 100a of charge each. I will make sure I will have the MPPT shut down at about 95% or so. And I will be adding 2 more batteries as well, both capable of 100a charging.

As I understand the built-in battery BMS's, they will shut off the charging above 100a.

And, if I calculated correctly, the max my arrays can produce is 107a at 100% efficiency, peak time of day. Spread that out over 4 batteries...I think I should be fine.

Do you agree or see a flaw there?

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