Originally Posted by Brian G.
What gauge should that wire be? What size should the circuit breaker be? What does the isolator look like and where does it fit in the circuit? Thanks.
A good idea would be to add a breaker and a relay at the battery.
The relay should be pulled in by a 12 volt source that comes on with the engine running. The wire should be sized for the breaker used and vice versa.
I installed a 30 amp circuit breaker and relay. Run a wire suitability sized to the trailer plug, the larger the better.
The wire can be oversized, but the breaker not. The breaker protects the wire!
If you consider the distance to be about 20' at 3% voltage drop with that 30 amps a #6 wire would be required.
For a 10% voltage drop over 20' a #12 would do.
A good compromise would be a #10 wire since it will be safe for the 30 amps, but at that current level there would be a fair amount of voltage drop.
The #10 wire is OK for the 30 amp breaker as well.
Usually there is not that much current drawn from the TV, but with too much drop the battery will be very slow to charge while towing, particularly if there is a 12 volt load in the trailer at that time.
If you use a diode isolator you should be aware that the drop across the diode would add to the voltage drop and give less charging voltage.
The diode drop is usually about .6 volts so at that 10% voltage drop current that would be 1.38 volts plus .6 volts for a total of nearly 2 volts less .
If the 13.8 at the battery is dropped that 2 volts you have 11.8 at the trailer and no charging. (Assuming 30 amp load)
Lower load less drop from the wire, but the same.6 volts from the diode