whats a triac and how is it different from a FET or SSR

[monster]

whats a triac and how is it different from a FET or solid state relay? and could we use it to control charging or in diy motor controllers?

i read in wiki that it can be used in light dimmers to limit power? is this more efficient than my light bulb technique or will the triac just overheat & melt ?

 

[dirty_d]

its used to control AC, when the gate is given current it allows current to flow through the triac even after current through the gate is stopped, but current stops flowing at the zero crossing of the AC current.

 

[monster]

could i use some thing like this to charge my battery?

http://www.diy.com/diy/jsp/bq/nav/nav.jsp?isSearch=true&fh_search=dimmer&selected=products