Caravan battery charging from wheels

[SwissXC90]

Originally Posted by canis

Haha! You're quite right, energy is not free. But the energy has to be paid for in fuel no matter how it gets there, and you'd be suprised how much drag an alternator working hard puts on an engine. I've no figures on the subject

Super easy to calculate.

14V x 160A = 2240 Watts or 2.24 kW

A Volvo 185hp D5 engine is 136kW

So the alternator running at full output is using 2.24/136 = 1.6% of the maximum engine power

But the engine is not at maximum power all the time, at idle it uses around 4kW to 8kW, so at just above idle the alternator is easily around 20% of the engine load.

Not insignficant at all

And remember the downside of charging a caravan using a trailer-wheel driver generator: the energy to pull the caravan comes from the vehicle engine.
You incurr losses through the vehicle transmission and drive system.
So charging the caravan directly from the car alternator is the most efficient as you don't have the drive train losses being added into the equation.

If the caravan battery is not charging to 100%, consider increasing the diameter of the charge wire coming from the trailer plug to the caravan battery.
The larger the wire, the less voltage drop and thus more charge voltage available.