Corwin C wrote:If I understand your application correctly, you could use a converter between the 120v AC and your 12v DC lights when you have access to a wall plug, but you would have to do additional wiring to run the same lights from your tow vehicle when wall power isn't available. There is also the potential to cause problems if you ever had both the converter and tow vehicle supplying power at the same time. You may need to install an "interlock" to prevent this situation from happening.
With DC power there isn't a need for an interlock. The source with the higher voltage will supply the load, and the other one will just sit there inactive until the voltage is drawn down to under it's output voltage. At that point it will supply power. Note, this means paralleling power supplies, the one with the higher voltage will take the load first, then the one with the lower voltage will finally supply loads after the first one can't keep the voltage high enough any more. Sounds like you could parallel 2 60A converters and have 120A. In practice it rarely works that nicely. Usually the first converter kicks out after running in overload for to long. An RV power converter better be able to handle all possible voltage ranges for the batteries it will most likely be connected in parallel with. Having said that, don't hook up a 24VDC power converter directly to a 12VDC battery bank. Yeah, it will supply the load, and likely burn out a few 12V bulbs in the process. It will also try recharging the battery and boil it dry in the process. Might even get it hot enough to catch fire. A note of warning, a number of RV converters don't have proper charge regulation circuitry so they could be bad to keep hooked up in parallel with a battery for a long period of time. Thankfully a number of the RV converter companies supply converters that are led-acid battery aware and will properly charge and maintain batteries. Usually the additional cost isn't that great so it pays to spend the $$ on one that has the charge control circuitry.
On the other hand, AC power does require interlocks. You don't want to hook up an AC source to another AC source without them being in phase with each other. If you do, bad things can happen. Fuses and circuit breakers will pop, and possibly some other more major damage will happen. Years and years ago, one of the workers at the Greenport, LI, NY power company accidentally hooked up one of the generators out of phase. The generator turned into lots of shrapnel as a surge of current went through it. The rotor landed a few blocks away. Modern interlocks prevent that from happening now. Note, your average RV or home generator don't have those interlocks, hence the need for a transfer switch.