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wandering-parakeet avatar image
wandering-parakeet asked

How does the resistance of MC4 connectors compare with the resistance of 8AWG cable?

I am about to buy cables to connect solar panels to my RV. I'm using an MPPT 100/50. The panels are not mounted to my RV, so that I can move them around to where the sun is. Sometimes the sun is close (20 feet)... and sometimes it isn't (I plan on a max of 40 feet). At first, I was thinking of buying one pair of 40 foot cables with MC4 connectors on the end. Now I am wondering if it makes more sense to buy multiple pairs so that I can make the total length 20 foot or 40 foot, or even dedicate one pair of cables per solar panel (so that the cables are entirely in parallel). I am planning on using 8AWG copper (not CCA) cables. How does the resistance of the MC4 connectors compare with the resistance of the cable?

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klim8skeptic answered ·

The contact resistance of a high quality MC4 connector is 0.35mohm.

The contact resistance of a Anderson SB50 plug is 0.20mohm.

I would recommend using Anderson plugs simply as they are not as fragile as an MC4 connectors.

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wandering-parakeet answered ·

Thanks! This is good info. I've gotten conflicting numbers from different websites. So, given that the 8AWG copper cable has 0.62 ohms per 1000 foot of cable, or 0.62mohms per foot, then it would seem that an MC4 connector has the same resistance as 7 inches of cable ((0.35mohm/0.62mohm)*12inches) or 172 cm. Likewise, an SB50 connector has the same resistance as 4 inches of cable, or 100 cm.

This makes me think that the connector losses aren't that bad, and that it makes sense to buy shorter cables so that you can add them as needed. You also have the option of running parallel cables (if you choose to have your solar panels in parallel.

Thanks!

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wandering-parakeet answered ·

You recommend Anderson connectors. I've just installed one for the solar controller in my trailer. Any recommendations for the type of cable to use for the run to the solar panels? I'm hoping to find "jumper" type cables, where the positive and negative cables are attached (sometimes called a zip cable). This would work well with Anderson connectors. However, I've not been able to find that kind of cable in a 20 foot (or more) length, in a gauge that is 8AWG or comparable. Any recommendations? I think that it would be difficult to use Anderson connectors with separate black and red cables. When you tried to coil it up, it would become a mess.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

8awg twin core sheathed cable is very common and reasonably priced.

Do use genuine Anderson connectors, just way better quality.

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