I believe the altenator on the Disco II TD5 is 120 amp Nippon Denso. 15 amps being sucked by a 3 way fridge still leaves 105 amps to play with.
I have a 1000 cca catapiller battery as main, 60 amp deep cycle as auxillary joined together by starter motor cabling (including earth) from the wreckers through a 150 amp solenoid with zener diode built into it so it will not fire uless the voltage on the main side is higher than the auxillary. (Had a pirana isolator but it died)
I have a 50 amp hot wire which goes to the rear 12 socket from the aux which I run a 40l engle plus 70l engle impersonator fridge when travelling. Another 75 amp hot wire runs from the aux to a 50 amp anderson plug which charges 2 x100 amp deep cycle batteries in the caravan and powers the 12 volt heater in the Dometic 150 litre 3 way fridge when travelling. This fridge has a separate freezer in it which will freeze items or keep them frozen while travelling. The fridge is towards the back of my 21.5 foot van.
At night I have run all of the above with high beam, 4 spotlights on, rear lights plus van lights. The batteries have never gone flat and no problems down the back with the 3 way fridge.
The secret is the cable diameter and the terminating lugs as drivesafe has stated. Electrons travel mostly on the outside of the cable. Thicker the cable, the more electrons you get to the end allowing you to utilise the 120 amps available.
Regards,
BradM
