There are basically three ways to charge your battery:
- DC to DC
Whatever combination of charging sources you use, you need enough to replace the power you've taken out of your battery each day. To replace this power daily is most important if you have a lead acid battery, as these don't like to be left in a semi-charged state. If you have a T1 Lithium battery, it's not necessary to bring your battery up to 100% state of charge every day.
We've looked at charging from solar elsewhere on this web site, so let's take a look at the other two options available to the RV traveller.
Mains charger: Charging from the grid or a generator
The purpose of a mains charger is convert 240VAC power to low voltage DC power, usual 12V or 24V.
Many larger inverters also have a built-in mains charger that can automatically detect if the power coming into the inverter is DC or AC. When the inverter detects DC power (ie; coming from your battery), it will convert that power to AC (240V) for your AC powered appliances. When the inverter detects AC power (ie; coming in from the mains), it will use that power to top up your battery and also to run your 240V appliances directly.
Because a generator puts out 24VAC power, you will also need a mains charger if you want to use a generator to top up your battery.
DC to DC charger: Charging from your alternator
The purpose of a DCDC charger is to ‘concentrate’ the charge coming from the start battery so that the RV house battery can be charged.
Vehicle alternators are designed to stop charging the start battery when it reaches 14.4V. This is to stop the battery from being damaged by the heat of charging in addition to the heated environment of the running engine.
But 14.4V at the start battery is not enough to charge the house battery of an RV, particularly given the often long cable distance between the two.
DC to DC charging from your alternator is an excellent way to charge your battery whilst driving and an excellent alternative to carrying a generator.
There are some old-school folks who will tell you that DC to DC charging puts too much load on your alternator and uses more fuel, but I'd suggest you challenge them to provide some facts and figures on this assumption. Others will claim there is no need for a DC to DC charger. Take your clamp meter over to their rig and measure how much the alternator is actually putting into the house batter. I bet it isn't as much as thought.
An inverter converts low-voltage DC power to 240V AC power so that you can run 240V appliances. Not everyone wants or needs an inverter, so we look at why you might want one, how to choose a size, the importance of standby current, and the difference between pure sine wave and modified sine wave.