My own opinion on this is that if you intend the charity to be an act that you perform for the sake of God, then it should be paid through pure and legitimate sources of wealth, and lottery winnings don’t characterize this.
I have also read fatwas that proclaim that it is permissible to give monetary winnings from gambling as a charity, but you shouldn’t expect to be rewarded for this act… which I suppose sort of goes along with what I stated above.