I have to take exception to the part which says it is contrary to manufacturers advice that the fridge will not cool on 12v when being towed.
I have no idea where this nugget of misinformation has come from but I can assure you that it is certainly NOT Dometic, and never has been, neither has it ever been said by Thetford.
The main reasons why it appears that the 12v does not cool the fridge are either not suitable wiring allowing enough power to be drawn, and not a long enough period of time with the engine running to allow the fridge to cool.
All three power sources are quite capable of operating the fridge at its optimum .
There is a third reason - the system voltage is too low because smart charging allows and maintains the battery voltage low. This is my personal experience with Ford and Peugeot. From my recent post in Peugeot forum:
"I followed the suggestion from someone in this forum and got a USB voltage reader. I start by saying that the voltage in cab is 0.1V lower than battery because of the drop as I am powering Garmin from the same outlet.
When using anything but light throttle, the voltage is 12.1 to 12.2, depending on state of battery.
After a
few seconds of trailing throttle the voltage is 14.4-14.8.
So the alternator is controlled for low output when fuel is demanded, and only delivers a reasonable charge when fuel is nearly cut off. (However, if you load up electrically, all lights, wipers, fan on high, seat heaters, the voltage holds at low 12 so it does take up load)
What do I conclude from this?
1. You can easily arrive at the end of a long trip with
lower battery charge than when you started (if you rarely trail throttle on the trip). An auto electrician tried to explain this to me a few years ago in relation to my Australian Ford, which has similar Smart Charging, but I didn't understand him. I was brought up believing a long trip charges your battery.
2.
Peugeot fuel saving is costing us battery life. You need more than ever to regularly use a CTEK or similar clever charger to get reasonable battery life. Peugeot are happy to replace batteries early. They jumped in to replace mine 5 weeks after the car had left the assembly line, when I complained the SS wasn't working. It didn't fix it, but now I understand more about SS pre-conditions.
3. Could some reprogramming be done so the alternator delivers more charge with throttle open. I probably don't want to even look into this in case it introduces other problems, easier to use the CTEK.
3. I got onto this investigation because I was considering running high amperage cable to my Peugeot tow hitch to run caravan fridge and charge caravan leisure batteries while driving.
WILL NOT WORK. Because I mainly travel flat freeways when caravanning, I am always on the throttle when towing (caravan air resistance). Voltage <12.2 minus cable losses will not run the fridge and will not charge the leisure batteries at all.
4. I was considering upgrading the 7 pin plug and wiring supplied by Peugeot dealer with towbar to 13 pin.
WASTE OF MONEY as I will not get any more function from the 13 pin (except maybe reverse light on van).
5. Luckily in Slovakia I can pull the van with the fridge on gas because I have gas Mono Control. These are not legal in Australia so I can't effectively power my fridge while towing there with my 'Smart Charge' Ford.
6. I have picked up another tow vehicle, 2009 diesel Kia Sorento. It's voltage gets up to mid 14s a few km after starting, and stays there. It actually increases at higher revs like the good old days. It will run fridge and charge leisure batteries, and I'll bet my vehicle battery lasts longer.