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I wondered about the coiled up advice as I suspected it related to the original specification of 16 amps for the charging units as used in the USA.

However I did some calculations ....
The I squared R losses for a a conductor of the length of the charge lead I calculate at 15 watts at 10A and 36 watts at 16A assuming an ambient temperature of 25 deg C (although I cannot identify the specific cable type on my calculator, this is fairly close). The coiled up effect means the heat is concentrated in a single spot and raises the temperature of the cable increasing its inefficiency resulting in yet more less and heat generation it is therefore standard advice for any lead carrying a heavy load.

You can see that , assuming a max operating temperature of 70deg C at an ambient temp of 30deg C (ie: a hot summers day) and in direct sunlight with 36 watts concentrated in a small area the cable temperature could move towards its maximum operating temperature. 15 watts would probably not be a problem but there is clearly good reason for the advice.


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