wire / cable size calculations

Have no idea but these people will


http://www.springers.com.au/default.aspx

The answer to your question is yes.

A bolted (not self tapper) chassis earth offers far less resistance than a wire earth so your return path calculations need to change. Calculate for a single wire resistance and add a nominal amount (as you already suspected).

What I like to do is connect a chassis earth AND still run a return earth back to the battery, that way you have created an almost failsafe circuit.

BTW, the PL20 is an excellent unit.

Out of interest, what size do your calculations tell you to run? IMHO for a cab-chassis or normal wagon the lengths of the run are not long hence the length really isn't a worry, its more the current carrying capacity of the cables. I ran 6mm to the back of the Patrol for accessories (active and neutral) and everything runs well but I wouldnet be taking more than 20 amps at any one time.

In my old memory 2.5mm is good for 28amps so 6 mm is easily big enough. If I was charging batteries back there I would run 16mm or 25mm (16mm is around 70amps by memory). Battery to battery under the bonnet I ran 35mm so I could start from the aux battery.

Anyways what'd you end up running?

On a Pajero with monocoque (integrated chassis) construction, I measured the resistance from battery (front left) to the rear right to be the same as 4 Gauge B&S wire run over that distance.

If you have a separate chassis, you would need to bond body and chassis at front and rear, to get the same sort resistance.

Question well asked - and answered.
You probably already know of this site - but if not - worth a look ;
Site Link

regards........................Keith

bungarra

Have you received full instructions from Plasmatronics regarding the connection of additional charging sources to (vehicle alternator) to your solar system? If Plasmatronic (and Steca as well) regulators are not wired correctly then the State Of Charge (SOC) function of the regulator will not function properly (be totally useless.)

There is a good article on how so called experts have wrongly wired up motorhomes - Plasmatronics Regulators

You are talking about using a chassis earth for all the accessories that are forming the loading on the battery. You are also about using the alternator also for charging your batteries. (As you are talking a shunt you may be aware of the problems posed here, but I will continue for the benefit of others reading this.)

The regulator has 3 negative terminals. One for the solar panel, one for the battery and one for the load. If you connect more than one of those to earth you upset the operation of the regulator. This applies under normal simple operation. However if you wish to use an inverter or other load that is bigger than the rated load current for your regulator you must use an external current shunt to increase the load current rating of the regulator.

There is a good article on how so called experts have wrongly wired up motorhomes -

I have seen additional external circuitry to allow an external battery charger used to charge the batteries in addition to the solar cells. Is this what you are intending to use for your generator? May bee you can tell us what Plasmatronics are proposing that you do to allow your alternator to be used for supplementary charging without upsetting the SOC monitoring.

I would advise against using your alternator to assist in charging your battery when there is good solar charging taking place. Your regulator will charge your batteries at over 14V. When your vehicles motor is up to working temperature, The alternators output voltage will be less than 14V. Your battery will charge faster with an applied voltage over 14V than it will with less than 14V.

Consider the case where your vehicles electrical system is connected to the auxiliary battery system and the motor has run for half an hour. If some external power source that is greater than the alternators regulator thinks the system should be running at, the regulator will reduce the output current to reduce the system voltage to its normal level. This means that your solar system will have to make up the shortfall in current to the car that the alternator is now not giving out. This will hold the solar system voltage down and the battery will not receive as much charge as it would if the vehicle system is disconnected.

PeterD