I tried this and it didn't work - what am I doing wrong?  I bought a 1600 watt Whistler inverter, connected it to my battery, turned off the breaker to my converter, plugged shoreline power cord (30A) into an adapter, then plugged it into the outlet in the inverter, turned the inverter on, and within 2 seconds the inverter was alarming and shut itself off.  Nothing in the camper is turned on, and I even tried it with all the breakers off.  Same thing - alarm, then off.  I plugged a crockpot into the inverter, and it worked fine, so I know the inverter is functioning. Any ideas?