Converter/Battery Charger

[Pat M]

Just ordered a 17' Casita Freedom and it comes with a "converter/battery charger". I am new to trailer/rv life and don't understand a lot. I get it that the converter/charger will alow me to use lights and appliances while on shore power. What I don't know is how does the battery get charged back up after dry camping. Is there some way that my tow vehicle does the recharge or do I need to hook back up to shore power?
I am not planning on getting a generator as I hope to be mostly in sites with at least electric.

[Steve L.]

Converter/chargers are usually rated at some number of 12 volt amps. 45 is typical for Casita I believe.

When you are plugged in, the converter will provide the amps needed to run your 12 volts gadgets. Say you are running a couple lights and the fan, you might be using 5 amps. That leaves up to 40 amps (45 less 5) to recharge the battery. However, the battery will seldom use that much. A 50% depleted battery might use 13-15 amps at the start of recharging (it slowly drops down as the battery fills up). This leaves plenty for your 12v appliances.

Usually, there is a 120 volt side to the converter as well. It provides the power that is converted to 12v for those uses described above and it provides power to the normal 120v outlets as well.

[Orlen Wolf]

Just ordered a 17' Casita Freedom and it comes with a "converter/battery charger". I am new to trailer/rv life and don't understand a lot. I get it that the converter/charger will alow me to use lights and appliances while on shore power. What I don't know is how does the battery get charged back up after dry camping. Is there some way that my tow vehicle does the recharge or do I need to hook back up to shore power?
I am not planning on getting a generator as I hope to be mostly in sites with at least electric.

The converter/charger converts the 120VAC from the shore power line to 12VDC to power your 12V lights and appliances. It will also charge your coach battery if there is enough capacity available to do so.

There is a 12V line from your tow vehicle to the trailer that will recharge your battery as you go down the road (if it is properly installed in your tow vehicle). For a standard 7pin connector it is the black wire (usually a #10 wire) connected to pin 4.

Recharging the coach battery from the tow vehicle 12V line does have some limitations though, primarily due to the resistance of the wire connecting the tow vehicle charge system to the trailer connector. In many tow vehicle installations the wire is undersized so you have a significant voltage drop when you draw current to charge your coach battery. A 12V battery requires about 13.8v to completely recharge it and, if it is significantly discharged, it will try to draw over 10 amps which will cause a higher voltage drop. The end result is that it will take longer for a complete recharge since the voltage available at the trailer will be significantly under 13.8V.

In addition, if you are operating your refrigerator from the 12V line while heading down the road, that current draw that will detract from the total current available so it will take even longer to recharge your battery. Most 12V ammonia cycle refrigerators draw about 120W (about 10A) and usually do not have a thermostat so it is a continuous draw.

Hopefully this response won't leave you scratching your head wondering why things have to be so complicated. Maybe if we repeal a few of the laws of physics the world could be greatly simplified.

[Pat M]

Thanks for the repiies - Orlen you gave me the answer to the big part of my q. And thanks for the detail on the tow vehicle part. I had been scratching my head and I can take a break for now.

[Pete Dumbleton]

Unless your converter comes with a Smart Card of some kind for battery charging, it will not be a good idea to leave the converter plugged in during storage or you risk overcharging the battery.