The function of Smart Alternators and Regenerative Breaking may have been known for years. But so has the problem of incompatibility between car and caravan. The internet is riddled with similar sagas as mine. Different cars, different caravans, different wiring harnesses and different installers.
Not all car/caravans have this problem.
Some folks have developed work arounds to keep the Smart Alternator function from dropping the voltage when it's not required to. Keeping the Air Con on or lights on to name two ways. These don't work for my car. Nothing does.
There are at least four elements in the process.
1. The car and it's associated control functions.
2. The wiring harness.
3. The installer.
4. The caravan.
None of whom want to own the problem.
1. My car, Nissan, will drop the volts at the switched 12v on the connector to below 12v when the ECU decides the alternator can be put into low output mode. Even though it knows there is a trailer attached. It doesn't know what type of trailer though.
2. The wiring harness is dedicated to my Nissan. It has a Canbus connection which indicates to the ECU that something is attached to the towing socket but not what
3. The tow bar installer is a dedicated specialist of many years in fitting tow bars and electrics. They tested the harness with me present and saw the switched 12v drop in or out. But it's not their problem. They just connect up the bits.
4. The caravan supposedly will function - fridge on and leisure battery charging- when towing. But it needs more than 12v at the switched pin to do so.
So despite all this, Nissan are not interested in what I'm towing and don't care that the voltage at the towing connector is below 12v. There is no firmware update to do this.
The wiring harness tells the ECU that I'm towing but the car won't disable the Smart Alternator because that's Nissan's problem. It just delivers what the car generates.
The installer says, ' we just connect the two together'.
The caravan will not function when towing when the volts drop below 12v at the towing connector. Fridge drops in and out but worst problem is that the leisure battery now has a higher voltage than the car and current flows in the reverse direction. Hence discharges.
The habitation relay isn't affected because it will function at a voltage lower than 12v and there's hardly any current flow in that circuit.
So nobody wants to own the problem but I could fix it by installing a DC to DC converter which will keep the caravan internal volts higher than 12.
Much easier and cheaper for me to disconnect the battery when towing.
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