Do patents have to work?

I have been doing some reading and I came accross a invention called the Electric Dynamo patented by Barbara Hickcox that Howard Hughes helped develop. and to summarize what I have learned about it if it was made correctly it could produce more electric than what it took to run it. If I my understanding is correct that would fall under the guidelines of perpetual motion and I know thats not possible so how could they have a patent on something that dont work. Maybe my understanding on patents isnt correct maybe it was a umption of mine that all patents have to work. Thanks for you answers