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Extension cord (gauge) for charging M-Y

brkaus

Well-Known Member
Jul 8, 2014
7,742
6,275
Austin, TX
To me, depends on use, quality, and cost. Agree the heavier duty isn’t going to charge faster.

But, heavy duty can have better insulation, better plugs/receptacles, and more strands of copper in case some break while flexing. So, potentially a bit more resilient.

if it was something I wanted for travel to keep in the car all the time, I’d go lighter. If it’s regular use in a fixed location, I’d round up. There is also a law of diminishing returns, so I wouldn’t go heavier (but I do have a 50a 25ft cord I left at relatives house to access a 6-50 at the back of their junk filled garage the 2-3 times a year I visit).

So yes, 12ga is enough. 10ga is a bit heavier but won’t change the charging in a measurable way. Personally I’d get 10ga if it’s out a lot and 12ga if it’s a travel cord.
 

rick245

Member
Aug 26, 2020
74
8
NJ
It's easy to figure out what the difference is. At 50 feet, let's calculate the difference between 10 and 12 gauge.

10 AWG is 1 mΩ/ft
12 AWG is 1.5 mΩ/ft

Okay, so 12 gauge has 50% more resistance! Sounds like a lot, doesn't it? (Spoiler: no, it's not)

We've got a 50 foot cord; multiply by two because the current flows in both directions. So, 100 feet of wire added to the circuit. The resistance is thus

10 AWG: 100 mΩ
12 AWG: 150 mΩ

The maximum charge rate you can set is 12 A.

E = I * R, so the voltage drop due to the cable is...

10 AWG: 1.2 V
12 AWG: 1.8 V

So the 10 AWG wire gets you an extra 0.6 V to the car. Or in power, it's 0.6 * 12 = 7.2 W

You're getting ~1400 W in either case, so you just have to ask whether spending 30% more and having a 30% heavier cable to haul around is worth it for that extra 7 watts.

I submit that it's not worth it.
Also the cost is almost double. Now I am thinking of 12/3 since the drive will be very much to get groceries and for pleasure. I ordered a 10/3, will get at 12/3 and test it out to see if there is any noticeable difference. If none, I will keep the 12/3.
 

jcanoe

Active Member
Oct 2, 2020
2,173
2,150
Maryland
Keep in mind that any extension cord that you use regularly will need to be inspected, replaced every couple of years. A heavy duty contractor grade cord will hold up better, last longer.
 

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