12V DC distribution in car for radio applications - 2005


The following show key elements of the 12V DC distribution in a Holden Commodore wagon. The car does not have ham gear fitted for mobile operation, but is often used for field measurement and operations.

Power takeoff is from the battery positive terminal with a short unfused line to a 5AG fuseholder (WES FH512). The fuseholder is sealed against ingress of water or other liquids. It is important that this unfused conductor is short and unlikely to chafe against grounded metal.

Cable is 8Ga, single red and black (Jaycar WH 3060 ,WH3062 sold by the metre).

Distribution block at rear of wagon space is WES PDB522.

The inverter is a low cost 300W modified sine wave inverter to provide power for battery chargers, test equipment, and other small appliances.

Most 12V apparatus uses Anderson Power Poles.

The installation provides very low voltage drop from battery terminal to 12V outlet. Measured voltage drop at 20A from the battery post to the distribution block is 250mV in the positive lead, 150mV in the negative return (via the vehicle body)

Bootlace terminals are useful in helping to prevent the conductor strands spreading under terminal screws. The example (Cabac BLPU1000) here on 8 Ga cable (~9mm2) has been crimped, but the bootlace sleeves can just be slid over the strands and crimped by the terminal screw. Uninsulated bootlace terminals are better for this application as the insulation on insulated ones can prevent full entry of the conductor in the terminal block.

Stalk terminations for #0/#4 flexible cable for termination on the input terminals of a 500W inverter. The stalks have silicone boots to prevent short circuits. These stalks are sold into the boom box market, but are good quality, readily available and inexpensive.
The 500W inverter cabled with #4 (~21mm2) flexible copper cable.
Added on top is a Anderson PowerPole 120A connector with fuse directly attached to the battery. This provides for attachment of a high power inverter. The cables are #4 (~21mm^2) flexible cables available from Jaycar.


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