Vehicle Charging systems

In today’s world, car charging systems use “alternators” to charge a cars battery. A car battery has different internals to the common AGM battery found in caravan’s. We can still utilise the vehicles alternator though to help charge our caravan batteries by using what is called a DCDC charger.

Alternators charge lead acid batteries by putting amps back into them. For fuel economy purposes, vehicle manufacturers design alternators so they reduce the amps the more fully charged they become. As a result car batteries are often never %100 charged and at most they only ever get %80 charged.

Trying to charge a caravan AGM battery back to %100 using only a alternator is not a efficient method. This is why when towing a caravan and wanting to charge a battery we can use DC DC chargers to assist. They work by taking a reduced supply of amps from the alternator (EG: 10 amps) and ramping that up to a constant 30 amps.

That constant 30 amps allows 30 amps of electricity to go back into the battery per hour until it reaches %100 charged. Much better than the %80 charged like a alternator on its own would do.

A set of 240ah batteries charged to only %80 = roughly 50 amps short. This is a lot when relying on power from batteries to be off grid to keep the beer cold.

Charging time

Charging batteries takes time. The more amps you can put back into it the quicker it charges (but not too much that you overheat the batteries).

Example: When we were using AGM batteries if our batteries got down to %50 flat, that means its 180amps short of being %100 charged.

So if our batteries are 180amps short of being full and we can charge it at a rate of 15amps, the maths would be as below ..

180a / 15a = 12 hours to charge at 15 amps or 6 hours at 30 amps.

This could mean the difference between running a generator for 12 hours to charge batteries, or 6 hours to achieve the same thing dependent on the charger.

DCDC chargers are only one way of charging the batteries and it should really not be relied on if you only do small trips (like 200km or less). The preferred way and easiest way in my mind is to add solar panels. We have solar on both the caravan and the ute. That way both ute and caravan batteries get charged during the day even when we don’t travel.

PS: the thunder brand dcdc charger pictured below i would not recommend. It charges the battery at 16volts and tends to cook the battery instead of simply charge it.

charging devices — Our DCDC charger set up in the back of the ute

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