In English, you call a person a dynamo to say that he or she is extremely energetic (e.g., she was a dynamo in London politics), but Russians mean something entirely different when they call someone a dynamo (spelt in Russian as динамо or, more commonly, динамщица): a woman who refuses to have sex after a date.
As I understand, a more accurate definition of the Russian meaning of dynamo is this: A woman who accepts a man's invitation to a restaurant to have an expensive dinner, which has, in accordance with the Russian tradition, to be fully paid by the man, but afterwards, after the dinner, unexpectedly refuses to have sex with him, contrary to the man's expectations, which are based on the Russian tradition and have been fueled by non-verbal signs and indirect hints given by the woman herself, at least in the man's interpretation of them.
At any rate, the Russian culture of dating is very special, as very well highlighted by @Anixx in his comments under a different question of mine, so I am not asking to explain me all subtleties of dating in Russia, but I am really curious about the etymology of that Russian word. I guess it is related to the English word dynamo, but how? What is the logical connection? I tried to find an answer on the Internet, but found no plausible explanation.
So what is the etymology of that word?