Combining two DC-to-AC converters

i have two 750 watt dc-to-ac converters that have the clamps that connect to car battery. I have three 500 watt lamps i want to hook up. If i combine the two converters by hooking posistive cable of one converter to the posisitve cable of the and the same with the neg. will it make it a 1500 watt inverter?

No. I am assuming you are asking about paralleling the outputs? (the 120 volt end) The internals will want to continue to run at their frequency, which is CLOSE to 60Hz, but not exactly, and they will cause problems with each other, up to and including the complete and total annihilation of one or the other of them. Not really, but they will eventually burn one or both of them out. Yes, you can parallel the inputs, (the 12 volt end) but that will just give you two 750 watt power sources, NOT (and not ever) one 1500 watt source.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."