Like many have said it may be the converter which can be tested. I know the smell because i had it in my trailer and when i figured it out was kinda embarassed and felt pretty stupid. When i hooked up my batteries i became distracted and hooked up the cables wrong. I hooked positive to negative and negative to positive. Eventually it did boil the batteries, smelled terrible when it was plugged into 110 and caused the battereies to cook dry and bulge the side. I'm not proud of what i did but very thankful something worse didn't happen.