Sorry, just noticed this question. Actually, most openers are 12 volt, so no chance of burning it up from over voltage. Also, two answers to the second question. First, the power goes to the opener only when the high beams are fired. Second, the power is momentary; for example, if you hold your opener button down, you don't cause the garage to go up and down. It only moves once per push, which indicates that it only pulls power once per depression. Hope that explains it, and again, sorry this is so late.
Bill