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oscarmax avatar image
oscarmax asked

Which wire for PV to Smart Solar 75/15 to Battery?

Please excuse my grammar I have suffered a brain injury

My setup will be 2 x80w mono solar panels with Victron Smart Solar MPPT 75/15 to 12 v battery, this should produce in theory 9 amp maximum.

I have fitted a new Smart Solar 75/15, I going to fit my new Smart Battery Sense, the original factory wiring from my old PWM control to battery is 4 metres long in 2.5mm twin core wiring, based on 9 amp this setup will have a voltage loss of 4.08%.

I have read somewhere that the Smart Solar will automatically compensate for this loss or do I need to change the wiring to 4.5mm.

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3 Answers
JohnC avatar image
JohnC answered ·

Hi Oscar. Your grammar is fine.

At the nominal 12V, 160W of panel is closer to 13A. Over 4m distance, and both ways, no point mucking about.

Your 75/15 has terminals specced for 6mm2 wire for good reason. That's what I'd use, perhaps with a 20A fuse on the +ve one to protect them.

And oh, 'auto wire' often is specced including the plastic insulation, so be wary of that. And if you have a solar shop or electrician with some twin-core outdoor 'solar wire', 6mm2 is a stock size, highly insulated, and rugged as hell..

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oscarmax avatar image
oscarmax answered ·

John I am a bit confused my 80w mono solar panels are only rated @ 4.49amp each, 2 x 4.49= 8.98amp?

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nigelfxs avatar image nigelfxs commented ·

Hi Oscar

The Smart Solar MPPT 75/15 transforms the 18V @ 9A (approximately) from the solar panels to the lower battery voltage (e.g. 12.3V @ 13A). This boost in output current is the main advantage of using an "MPPT" type of solar charger compared to the cheaper "PWM" type of charger.

I agree with John that you should use thicker wire between the MPPT and the battery to reduce your losses.

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JohnC avatar image JohnC ♦ commented ·

Your panel ratings are for the panels, not the batts. So a single 80W panel @ 4.49A = 17.8V. That should match the panel 'Vmp' rating. Does it?

To stretch your confusion, I'd recommend you wire those panels in series rather than parallel, giving you 4.49A @ twice the Vmp, 35.6V. Still 160W, hey. They'll work better in low light that way, so overall better performance.

Your 75/15 is a good match, and 6mm2 wire to the batts would make for a perfect installation.

It's the A on either side of the mppt that varies, depending on the V there. Keep asking if you need more help understanding this. The beauty of mppt at work..

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oscarmax avatar image oscarmax JohnC ♦ commented ·

Thankyou for the explanation yes I going to wire up in series, looks like I need some 6mm2 wire.

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oscarmax answered ·

I have some 4,5mm2 and 6mm2 wire, the new proposed position should be within 8-9 inches of the battery and battery sense.

However relocating the MPPT under the caravan upholstered seat may affect the Bluetooth function..

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spirou avatar image spirou commented ·

It won't. I can connect to all bt gear in my van (under the bench) from inside the house 10m away.

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oscarmax avatar image oscarmax spirou commented ·

Thankyou for you quick resopnce

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