We bought a used 1988 Mallard travel trailer and no book for repairs. We have the battery hooked up also electric

Hi and thanks for choosing Just Answer. I believe the noise you hear is the fan for the inverter. The inverter charges the batteries in the coach and is used for other devices as well. It has a fan to help dissipate the heat created when operating. It is not usually to noisy unless it is getting worn out or it could be real dusty or have other obstruction. Does this help any?

Hi....
i will try and answer your questions for you...
first of, onanman is correct, the fan noise is the converter fan running. they are just like the fans on your computer, sometimes they noisier than others.... depending on the load put on the converter, the fan usually shuts down after long period of inactivity.. if it doesnt ever shut down, then it probably has a bad control circuit somewhere.... it wont effect the converter, but can be annoying... the fix is a new converter though, so really, an expensive fix if not causing any problems....

if you are hooked up permenantly, this converter will still provide 12v, even if you remove the battery.... since it is hooked into the 110v circuit.. your monitor panel is 12v only, it wont run on anything else. as are most of your interior lights, and your fridge, air conditioner etc all need 12v for their control boards. so i would still keep a converter in the trailer and you will still require 12v for things to function. having a battery is not required, unless you running the slide rooms, you need a battery for that.
hope that answeres your questions....

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:Nick: