Honda Computerized Alternators By Alan Melton I don’t know how many times I’ve been called and asked why Honda cars will initially charge at 14 1/2 volts— which is what we all expect—but a moment later the charge drops to 12 1/2 volts. This is supposed to happen. The “C” terminal function of the regulator has been activated. Honda internal fan alternators come in three-wire and four-wire versions. These alternators are produced by Nippondenso and Mitsubishi. First let’s talk about the three-wire version with the “C” terminal. The three-wire “C” type alternator is found on 1984 to 1987 Honda Civics. The “C” terminal regula- tor is marked “C”, “L” and “IG” (“C” being computer, “L” being light and “IG” being ignition). The “IG” terminal is an ignition source and is fused. The light terminal is also fused, puts out battery voltage and can operate electrical devices on the car other than the light in the dash. In carbureted vehicles it could power the electric choke and air mix control servo motor. It must be able to put out the proper amount of power to make sure these devices function correctly. The “C” terminal interacts with the driving computer through the alternator control unit. When the computer wants to reduce the load of the alternator on the engine, it will tell the alternator control unit to ground the “C” terminal and reduce the output of the alternator to 12 1/2 volts and approximately five amps. On the four-wire version the alterna- tor is marked “C”’, “FR”, “IG” and “L.” The “IG” and “L” are the same as the three-wire version. The “FR” terminal is a field monitor connected directly to the programmed fuel injected electronic control unit (PGM-FI-ECU). The “FR” terminal and the electric load detector (ELD), which is also connected to the PGM-FI-ECU, tell the computer how many amps the alternator is putting out. By knowing the load of the alternator on the engine, the computer can adjust the fuel injection system according to the load of the alternator. Remembering that alternators draw up to five horsepower off a running engine at full output, the ELD and the “FR” terminal let the computer know how much horsepower the alternator is taking and will compensate for the load of the alternator on the engine. The “C” terminal on the four-wire alternator is also connected to the PGM- FI-ECU and when certain conditions exist the alternator output again drops to 12 1/2 volts and approximately five amps. These conditions are: * electrical load below 10 amps ¢ vehicle speed below 40 mph * engine speed below 3600 rpm * coolant temperature above 140 degrees * air conditioning off * intake air temperature above 65 degrees * brake switch off ¢ fuel cut out control function off When all of these conditions are met the “C” terminal is grounded by the computer and the voltage drops to 12 1/2 volts. In both three-wire and four-wire versions, the easiest way to bring the voltage back to 14 1/2 volts is to step on the brakes. Alan Melton is owner of Northwest Regulator Supply, Portland, OR.