Only 110 volt outlets work. No 12 volt things work

I?m new here but hopefully someone can help me. In my travel trailer (28? Four Winds) I am plugged into shore power and only my 110 outlets work.  Anything that is attached to the trailer does not work, such as lights, slide out, water heater (on electric), air conditioner, etc. Everything I have plugged in works fine, such as microwave, tv, clock, etc.  I cannot hear the converter fan running any longer so I?m thinking the converter may have gone bad.  I checked all fuses in my power center and they are good.  Any thought???

Welcome to the forum. You checked the fuses but did you check ALL the circuit breakers?  You have to shut them off then back on to reset them if they've tripped.
Do you have a battery installed and if you do, check the voltage of it while not being plugged into shore power.

i checked the breakers and they are good. They were not tripped. The batteries were dead, but they are good batteries. At least two weeks ago they were.

Take your battery out and take it/them to Walmart or an auto parts store and have them checked.

Apparently your converter/charger is not working.  Check the output to the battery, it should be 13+ volts while plugged into shore power.  Did you flip the breakers off and on?

12 volt power system

120 vac --- Breaker----Converter--fuses (usually one or more 30 amp in parallel)--- Fuse box---switch or solenoid---battery

Diagnostic. Disconnect battery negative lead, Measure battery voltage.  LOW.
12 volt types pull 'em and have 'em tested Count on buyng new
6 volt pairs (2 6 volt in series make one 12) Hook up a "Smart' automotive charger (Mine iso a 100 dollar Deltran Battery tender 2-20-70 amps for jump starting smart charger)

Let it sit on "Boost" (20- amps) till tomorrow and see if lights now work when hooked up

GC-2 (Golf car 6 volt or GC-12 as well) may recover from this deep a discharge. Most MARINE/deep cycle will not.

NOTE: Very important.  When you disconnect wires from the battery (Batteries) LABEL them, One way is to pain the positive wires red. negative black. And if more than one wire hooked to a post (other than battery to battery jumpers)  TIE them together with string or a bread tie. or zip tie.

If the converter is part of your power distribution panel the 30 amp reverse polarioty fuse(s) are often on the right end of the fuses... But may be elsewhere

If the converter stands alone they are often near the heavy 12 volt wire connections

IF one is blown, the rest will be as well. UNPLUG before replacging all of them and then plug in How many you have depends on the converter 1-2 or in my case 3

Now. batteries disconnected (Either by lifting negative cable or the disconnect switch)

Measure voltage at the converter output you are looking for 13.6 to 14.6 give or take a small amount.

Shorted battery cells can keep the output low.

If converter is bad I recommend Progressive Dynamics Intella power

If the converter is part of the power panel 4600 series (Last two digits will likely match as close as possible existing converter. IE  7345 you want 4645 or 4640 whichever exists)

if it's a stand alone. 9200 series same deal on the last two digits.

Mine is a stand alone 9180 with charge wizard (same as 9200 with optional dongle)

John gave good information.  Here are some basics:

RV's have two nearly separate power systems.  The 120V AC is clear.  The 12V DC powers many things, including most lights, slide outs, motorized levelers / stabilizers, the furnace and ceiling fans.  Other systems, including fridge and water heater require 12V DC for control circuits, regardless of primary power supply (Propane or 120V electric)

This 12V comes from the battery  and / or the converter.  The converter takes 120V AC and converts it to 12V DC to keep battery charged and supply 12V to the camper.

Since you have no 12V power, either the converter is not getting power (breaker tripped), the reverse polarity fuses are blown, or it is not working.  Sounds like the converter from what you already checked.

Note also a fully charged battery puts out 12.6 V.  A functioning converter puts out 13.5 V or higher.  If your voltage at the battery is less than 13V, it is not receiving anything from the converter.