I got a used motor and wired it up to a wall wart adapter to open and close a light coffin door (made of foam). The wall wart was 12v and 1 amp output. Well it turned the motor slowing down a bit at the heaviest pushing point. It would keep going for a while but slowly decreasing speed. When I turned it off it would not come back on. The wall wart adapter was warm. Now I have tried this with 3 different voltage and amperage rated adapters. From 12v-16v and about 800Ma to 1 amp. And it did the same thing. Stopped working after a few minutes. What is the problem? I need help. Thanks for any help.