Battery Charging Question
My tow vehicle has what Ford calls an "Extra Heavy duty Alternator" rated at 220 Amps. I am (as the name goes) planning on switching to a residential reefer. We never dry camp or boondock. I am ...
Forum Discussion
Old-Biscuit wrote:
BUT the issue is resistance...due to length of charge line and small size of wire.
Or to say it another way, "voltage drop" over the length of the wire.
I am a retired automotive engineer.
First, let's start with modern light vehicle charging systems are design to replace the energy consumed from starting the engine and running other electrical devices ON THAT VEHICLE. Once they "sense" (and many vehicles do now have some kind of battery "state of charge" sensor) they cut back the voltage on the alternator to just enough to keep the vehicle battery charged, which is typically between 13.2 and 14.0 volts.
Even at 14.0V, the "voltage drop" (loss of voltage over a specific size and length of wire) is likely to be INSUFFICIENT to keep your fifth wheel batteries charged. If you want to prove this to yourself, hook up a voltmeter to your trailer batteries, hook the trailer up to your vehicle and take a drive.
You have 2 choices:
- use a DC-DC boost converter
- buy a special DC powered battery charger.
There are literally thousands of DC-DC boost converters for sale on eBay. Make sure to buy one that is powerful enough. You simply install it in between the wires coming into your trailer and your existing battery charger and set the output voltage to about 14.8V.
DC battery chargers are harder to find, but they do exist.
