I had a graduation party today and planned to take relatives flying. With the 150 long gone and no other airplanes to rent in Clintonville, I had to look elsewhere. I pried myself out of bed at 6 a.m. to get checked out in a 172 in Green Bay. I did three landings in an old 172 with an instructor. Everything went fine minus my morning toungue-tiedness on the radio. My friend Kevin and I were taxiing out to leave when the ammeter indicated a discharge during the runup. We taxied back in and waited a while. A mechanic looked at the plane and decided it was the voltage regulator causing the problem. He fixed it and I taxied out again. The system failed after I put full throttle in on the runway. I aborted that takeoff, taxied back and called it quits. There weren’t any other planes available, so my friend and I had to drive back to Clintonville and no one got an airplane ride.