Originally Posted by BonneMeMN
If a power one doesn't go down all the way, it will try and try till it does.
It will suck battery by doing this.
Um, yes and no. If the internal core breaks, it will run endlessly until the battery goes dead.
In normal operation, it runs in either direction until it hits its stop at the end. The kickback from hitting the stop is what shuts the motor off: it deflects the worm drive one way or the other, opening the pair of contacts that'* in use (to switch off) but leaving the other pair closed, ready for when it needs to go in the other direction. You can hear this kickback functioning in normal operation if you listen carefully: When it gets to the end of its travel, it doesn't click off crisply; it kind of goes "Grrraunch..." instead.
So when the core breaks, there'* no kickback, and the motorized reel turns endlessly until there'* no power left.