A few misnomers here. ATC always requires its own permanent power supply whether or not the engine is running.It does not run off the same power feed as the 12 v fridge supply which is operational only when the engine is running and the smart alternator etc allows power through. ATC is a bit like a match . You don’t know it works until it is struck and lights. It may operate from time to time but can be very subtle so you you are not aware. It is supposed to kick in long before you get brown trousersđŸ˜œ
Nobody has yet suggested the ATC runs off the same power supply as the fridge, so no "misnomer" creeping in there.
I said the ATC runs off the permanent 12 volt feeds from car to caravan pins 9 +ve and 13 -ve, "the one that also charges the van's battery when the fridge supply switches the habitation relay. "
Once the fridge feed 10 +ve, 11 -ve is powered, then, the car's permanent feed and the caravan's battery, are linked, as the permanent feed from the car is also used for charging the caravan's battery.
What, if any, contribution, then the caravan's battery can make to powering the ATC or not, is down to the use of any system diodes in the charging circuit to prevent it back feeding the ATC.
From my understanding the ATC is powered by the sustained 12 V supply from the car, the one that also charges the van's battery when the fridge supply switches the habitation relay.
Forgive me but that’s not how I understand it. The feed to the ATC is permanently live. Nothing to do with habitation relays. If I have it wrong I apologise now.
Forgive me but that’s not how I understand it. The feed to the ATC is permanently live. Nothing to do with habitation relays. If I have it wrong I apologise now.
The ATC is powered by the permanent feed, but that was not in question. The implications of the fridge feed was.
The permanent feed is switched by the habitation relay, to enable it to charge the caravan's battery.
Borrowing THIS DIAGRAM, from "Caravan Chronicles"; follow the permanent + ve feed from pin 9, into the caravans habitation relay where you will see that relay switches that feed onto or from the caravan's battery.
The relay is excited by the feed used for the fridges +ve, from pin 10.
As simply portrayed there , with no diodes, any ATC in the permanent feed is coupled also to the caravan's battery, whilst the habitation relay is excited by the switched feed to the fridge.
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I take comfort than even without the engine running my ATC demonstrates to me on coupling up, it can operate on the energy available from the car's battery.
The battery voltage will not be lower with a smart alternator with the engine running, than without the engine running. The smart bit it is, it charges when the battery needs it.
They don't affect the ATC as that relies on the car battery for a permanent 12v supply - Smart alternators may affect the fridge operation as some "smart" towing relays aren't smart enough to cope with the variable voltage - despite smart alternators first being used in the '90s.
My 2011 Hyundai Santa Fe was wired with a Ring smart towing relay by a so-called expert towbar fitter but was constantly cutting out the supply to the fridge - I got it rewired by a conventional auto electrician using a Durite 140A relay and it was fine after that.
My present VW Touareg has a factory-fitted towbar and electrics so no issue there.
Roger are the Touaregs wired differently to the diagram JTQ sent? I have towed with the caravan battery removed and the fridge and ATC all worked perfectly.
Which is exactly what would be expected.
The diagram I referenced, is the caravan's wiring, not the car's.
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JTQ's diagram relates to the caravan wiring, not the car - I'd expect any car to cope with caravan battery removed and operate car lights, ATC and fridge as normal.
Can I just repeat my statement, in my experience of my outfit a dead flat caravan battery had influence on the ATC as in it caused the ATC to not come to life, so I did post the flat battery had an INFLUENCE.
Again as soon as I replaced the caravan battery for a new one bingo ATC alive again.
2018 Audi a4 Black edition Petrol
2016 Coachman Pastiche factory fit ATC
Again as soon as I replaced the caravan battery for a new one bingo ATC alive again.
2018 Audi a4 Black edition Petrol
2016 Coachman Pastiche factory fit ATC
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