Solar wire sizing - advice please!

[jmschmidt]

I get 8.83 amps, say 9 but as mentioned that's max, max. #12 wire over 6 feet (is that round trip?) should be good by why not just use #10.

[Bleemus]

[Copacabana]

Originally Posted by jmschmidt

I get 8.83 amps, say 9 but as mentioned that's max, max. #12 wire over 6 feet (is that round trip?) should be good by why not just use #10.

Here wire is in mm, not awg. The biggest wire the MC4 connector will take is 6mm, which is just a hair bigger than 10awg. It looks like it should be overkill, given the short run and higher voltage/lower amperage.

[Copacabana]

Originally Posted by Bleemus

Attachment 144213

Thanks! Very useful chart indeed.

[kmacdonald]

16 awg is the smallest that should be used on a boat.

[camel2012]

Originally Posted by Copacabana

Here wire is in mm, not awg. The biggest wire the MC4 connector will take is 6mm, which is just a hair bigger than 10awg. It looks like it should be overkill, given the short run and higher voltage/lower amperage.

Overkill is also important for future proof... if you have the space , more solar panels may be in your future and you do not want to have to rewire. If not, future panel replacement and efficiency gains are likely. I am currently replacing 6 yr old 85Wx4 panels with 340Wx2 panels and only adding 10% more surface area...you can always go more series than parallel to compensate on the MPPT input side, but the higher voltage benefits end once your voltage exceeds 40 V on a 12V system, then you start affecting performance with shading and series panel interactions.

[john61ct]

Originally Posted by camel2012

you can always go more series than parallel to compensate on the MPPT input side, but the higher voltage benefits end once your voltage exceeds 40 V on a 12V system, then you start affecting performance with shading and series panel interactions.

Setting shading aside, assuming wanting high voltage wanted to reduce long wiring costs.

Are you saying controllers like the Victron 150/35 or 150/100 don't extract power at those higher voltage levels they're designed for, as efficiently as, say the 75/50?

[camel2012]

Originally Posted by john61ct

Setting shading aside, assuming wanting high voltage wanted to reduce long wiring costs.

Are you saying controllers like the Victron 150/35 or 150/100 don't extract power at those higher voltage levels they're designed for, as efficiently as, say the 75/50?

Yes, I would suggest that one needs to balance the higher inefficiency of converting from the higher input voltage during peak hours with the benefit of getting battery charging earlier and later in the day at thin sun angles.

MPPT controllers are far more efficient at 16 V than at 100 V input for a 12 V system.

[john61ct]

If I were running only 16V I'd just go PWM.

[camel2012]

Originally Posted by john61ct

If I were running only 16V I'd just go PWM.

Agreed , but I would go 40V and MPPT first if I could.