question

gozzo avatar image
gozzo asked

MPPT 150/70 solar controller connection to 5 panels

Have to install a MPPT 150/70 solar controller on a boat having 24 Volts system voltage.

Originally there were 6 panels with MPP voltage of 31 and 38 V open circuit voltage on the drawing.

MPP current 7,67 A.

Back then I had in mind connecting 3 of them in series resulting in having 2 sets of 3 panels connected in parallel to the controller.

Efficiency would be good and 93 MPP Volts / 114 open circuit Volts within specs.

Unfortunately the boat doesn't allow for more than 5 panels to be installed.

Means I would end up with 1 set of 3 panels in series having 93 MPP Volts and a 2nd set with just 62 MPP Volts connected together in parallel to the controller.

Something tells me this doesn't work.

Connecting all 5 panels in parallel would be another option but with just 31 MPP Volts on a 24 Volt boat's system efficiency would be way down.

Any idea how to proceed here ?

Thanks.

solar
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1 Answer
JohnC avatar image
JohnC answered ·

Ho Gozzo. In parallel, it's likely you'd lose low-light performance, ie dawn, dusk & clouds.

I'd be inclined to wire them in pairs, and the orphaned panel to a separate cc, even a cheap pwm.

If you haven't yet bought the 150/70, it's likely you could get away with smaller, and of course a 250/60? would handle a full series string of 5x of those panels. Or even 2x smaller mppt's to fit the separate strings you calculated.

"Something tells me this doesn't work." Yeh, he's often right..

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