I'm having difficulty soldering components with 1 mm thick or larger wires. The solder melts fine, but it does not 'stick' and just falls off. Components with smaller prongs like regular LED's are no problem. Right now I'm trying to solder some diodes to make a bridge rectifier and the solder is just not sticking.
What could be the problem? I'm using a battery-powered RadioShack soldering iron that works fine for the small stuff, and lead-free flux solder. Any tips on how to solder the heavier stuff that seems to reject solder? I've looked all over for this issue and don't seem to be able to find an answer.