24V to 12V Heater

Hi I tried with 24V DC Power Supply, The problem is, I have 12V ceramic heater which need to work with 24V, so I thought to use a buck dc converter
I measured the current in the heating element (ceramic heater) It is 6.5 Amps I could not find any buck converters that can be used for this high current

Tried LM2956 a ready made one http://www.ebay.com/itm/1pcs-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-/251066005460 but gets too much heat and doesn't work well !

can you help me in building circuit or an alternate option

Thanks in Advance :)