Comment: Electricity for Camping

Submitted: Friday, Apr 19, 2013 at 09:13

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Electricity for Camping

Revised March 2013 On an extended trip it's good to have some of the comforts of home. Electricity is obviously one of them and a good system can make all the difference to how comfortably

Pelikan

Thanks J & V for an excellent article.
Re the formula you refer to for calculating voltage drop.
As I wanted to buy a Thumper battery pack I emailed Home12volt to ask them what the wiring size was on the connection kit for charging (from the vehicle system) that comes with the battery pack. They wrote back to say that it was automotive 6mm (i.e. about 4.5 square mm). They also said that charging is achieved at 35 amps and the twin core cable supplied is 5.5 m long. I suggested to them that 35 amps through an 11m circuit would cause too big a voltage drop and that they should supply more adequate cables. They then got abusive and said that the voltage drop would only be 0.02 volts. They also said that US and UK measurements of cable size in AWG (B&S) or square mm were irrelevant in Australia and that they went by Australian standards. It so happens that Australian Standards these days use square mms, but Home12volt seemingly are unaware of this.
I calculated the voltage drop at about 1.4 volts using the above mentioned formula and cross checking with the tables in Nigel Calder's book (Boatowners Mechanical and Electrical Maintenance). Can you tell me if I have got this wrong. Is it me that's off the planet or this supplier?
Cheers, Peter H

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Reply By: Member - John and Val - Wednesday, Mar 04, 2015 at 00:52

Wednesday, Mar 04, 2015 at 00:52

Peter,

An Australian standard may exist, but it's widely ignored! Specifying the cross sectional area of the conductor is a good way to go, but I think that specifying wire gauge is pretty entrenched and subject to misinterpretations of convenience!

I have no experience with the Thumper, so can't comment from experience, but I understand it's nothing but a battery in a box with some connections and metering, and a VSR to connect it to the alternator when the motor is running. Different advertisers make different claims, but unless there's a dc-dc charger included, (which I doubt) the thing will not charge for long at 35 amps, regardless of the wire size.

I wonder if the expert advising you understands the difference between the diameter of the conductor and its cross sectional area? A 6mm cable (ie 6mm outside the insulation) may have a conductor 4.5 mm in diameter, but the conductor will have a cross section of about 15 square mm, which might be marginally satisfactory.

Are you off the planet? ...... No!

Cheers

John