OT electrical question

Hi All, This is off-topic, but seasonal question, About 20 yrs ago I bought some "animated" Christmas tree baubles of eastern European origin, these contain a synchronous motor and were made to fit in replacement for a bulb in the now old style 20 lamp string of fairy lights. When bought originally I was wary of the safety of these things, but they did look very nice, ( also v cheap ) Being a safety conscious sort I thought that they would make a nice display running off a 12 Volt transformer - and as each bulb in a 20 light string being a 12 V bulb, also being a synchronous motor, obviously AC. I was therefore surprised when these things burnt out spectacularly in seconds on my bench when 12 Volt AC applied to them, (and I did check the applied voltage carefully).I destroyed three like that. Eventually I set the remaining baubles up in series with a 20 string lamp set, arranged with the lamps remote from kids reach and used this set up till the kids in due course grew up & departed. After a brief period of freedom we now entertain grandchildren at Christmas and I want to resurrect these motor driven baubles, again in a safe way. After all that preamble, I still do not understand why these things will not work when run off a 12 v transformer, There is only a synchronous motor inside them, exactly like in the old electric clocks, I dont want to blow any more up, but do want to have them out on display in a safe, and energy efficient way. So if anyone knows the answer to why I seem to need a dropper resistor instead of a 12 V. AC supply, or has a better idea of running these safely-feel free to post, Otherwise - Merry Christmas to all Mark G.