FOLLOWING A COMPLETE ELECTRICAL FAILURE; PRIVATE PLT AND FLT INSTRUCTOR OF C172 MAKE A NORDO APCH AND GAR AWAITING LIGHT SIGNAL FROM TOWER. LAND SAFELY FOLLOWING SECOND TOUR OF THE TRAFFIC PATTERN.

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WAS CONDUCTING A FLT REVIEW FOR A PVT PLT WITH APPROX 400 HRS TOTAL TIME. THE STUDENT WAS GIVEN A SIMULATED EMER; WHICH CALLED FOR RESETTING THE CHARGING SYS BY CYCLING THE ALTERNATOR OFF; THEN BACK ON. UPON RETURNING THE ALTERNATOR SWITCH TO THE ON POS; WE NOTICED AN EXTREMELY LARGE RATE OF CHARGE INDICATED (60 AMPS) FOLLOWED SEVERAL SECONDS LATER BY A COMPLETE ELECTRICAL FAILURE. AFTER A FEW MINS OF TROUBLESHOOTING; WE DETERMINED THAT WE WERE UNABLE TO RESTORE PWR. WE DECIDED THAT DUE TO THE SUDDENNESS OF THE FAILURE THERE WAS A CHANCE THAT THERE WAS A SHORT IN THE SYS THAT MAY POSE A FIRE HAZARD; SO IT WOULD BE WISE TO DIVERT TO THE NEAREST ARPT. WE ELECTED TO LAND AT ZZZ1 AS IT WAS THE NEAREST ARPT. ZZZ2 WAS ALSO NEARBY; BUT ITS RWY HAD BEEN CLOSED FOR REPAVING. THE NEXT NEAREST NON-TWRED ARPT WAS ROUGHLY 20 MI AWAY. WE ENTERED THE AREA; AND CIRCLED THE TWR AT 2500 FT MSL OR 600 FT ABOVE THE PATTERN. AFTER SEVERAL ORBITS AROUND THE TWR WE HADN'T YET RECEIVED A LIGHT SIGNAL; WE DETERMINED THAT IT WOULD BE BEST TO SURVEY THE TFC FLOW; ENTER THE PATTERN AND LAND. WE DECIDED THAT IF WE DIDN'T SEE A SIGNAL ON FINAL; WE WOULD MAKE IT A LOW APCH TO AVOID A POSSIBLE CONFLICT WITH POTENTIAL TFC ON THE XING RWY. AS WE HAD NO VISIBLE SIGNAL; WE MADE A LOW APCH HOPING TO REVIVE A SIGNAL AT WHICH POINT; WE COULD CUT THE PWR AND LAND ON THE REMAINING RWY. WE DIDN'T GET A SIGNAL; SO WE WENT AROUND AND DECIDED THAT WE WOULD MAKE THE NEXT LNDG WHETHER WE RECEIVED A SIGNAL OR NOT. WE KNEW THAT AFTER THE LOW APCH THE TWR WAS OBVIOUSLY AWARE OF OUR PRESENCE WHETHER OR NOT WE GOT A SIGNAL. WE MADE OUR LNDG WITHOUT INCIDENT. AFTER DEBRIEFING WITH THE CTLR; I ASKED IF THERE WAS ANYTHING I COULD HAVE DONE DIFFERENTLY. HE STATED THAT HE WOULD HAVE MADE THE LNDG ON THE FIRST APCH AS HE HAD GIVEN US A SIGNAL; BUT I WAS UNABLE TO SEE IT; AS WAS MY STUDENT WHO I HAD INSTRUCTED TO WATCH FOR A SIGNAL WHILE I FLEW THE ACFT. WE DETERMINED THAT THE BRIGHT LIGHTING CONDITIONS HAD MADE THE LIGHT DIFFICULT TO SEE. IF I HAD TO DO IT AGAIN; I PROBABLY WOULD HAVE MADE THE FIRST LNDG ATTEMPT AS I COULD HAVE STOPPED SHORT OF THE XING RWY NEGATING THE RISK OF A COLLISION AT THE INTXN.