Charging system question, not Corvette but still Chevrolet (68 Camaro)

[Joseph E.]

I've noticed my '68 prostreet Camaro doing something odd when I watch the voltage gauge. The car is a blown big block with an aluminum radiator and two thirteen inch cooling fans attached to an aluminum shroud. The ignition system is a Mallory distributor with an MSD Blaster 2 ignition coil. At idle, the voltage gauge shows the system to be putting out fourteen volts, however, when I turn the fans on one at a time, the reading drops. With one fan running the reading is at about thirteen and with both fans running the reading is at twelve. The manufacturer of the fans says that each fan will draw 18 amps when running. The alternator is an aftermarket single wire unit which the manufacturer rates at 78 amps output at 2500 alternator rpm and 108 amps at 7500 alternator rpm. As close as I can figure, for ever crankshaft rotation, the alternator is turning about 2.75 times. The engine idles at 1000 rpm so it should be putting out just over 78 amps and idle with the max output of 108 at about 2700 engine rpm. Are my calculations correct?

My other C2's as well as my daily driver do not show such a drop even when using other electrical accessories. Is the output of the alternator too low for the electrical draw on the Camaro or is it possible that the battery is bad? The battery came with the car and is an Exide model that is two and one half years old. The battery is out of the car when it is not being used and is on a CTEK charger to keep it fully charged. Would adding another twelve volt battery hooked in parallel maintain the volt rating at a level closer to fourteen? I understand that hooking the batteries in parallel keeps the voltage level at twelve while doubling the amp rating. Would a bad alternator cause such a drop? The unit is brand new but nothing would surprise me today. Any input from the members would be most appreciated. Thanks.

Joe 45420

[Edward J.]

Re: Charging system question, not Corvette but still Chevrolet (68 Camaro)

Joe, normal alt. voltage output is 13.4-14.2 it is all depending upon the load on the alt. sometimes with high load componets such as your fans you will see a voltage drop. the main concern is amp. output with a load. generally the alternators have a way to full field them to test output, But you can apply a just about full load with fans, lights, wipers, heater fan you should be able to see about 3/4 of the output at spec RPM. you will need a meter with a amp clamp to test. The Battery state of charge as dictates the alt. output. a fully charged battery is 12.66 at rest.

Also if you are using your car voltage gage, they may not be as accuracte as the automotive test meters.

[Joseph E.]

Re: Charging system question, not Corvette but still Chevrolet (68 Camaro)

Edward,

Thanks for the reply. I'm going by the Auto Meter voltage gauge that is installed in the car for the readings I noted. I have a multimeter but have not yet used it since it's brand new. Would this type of meter be a suitable measurement device to determine the voltage reading more accurately? Thanks.

Joe 45420

[Edward J.]

Re: Charging system question, not Corvette but still Chevrolet (68 Camaro)

Edward,

Thanks for the reply. I'm going by the Auto Meter voltage gauge that is installed in the car for the readings I noted. I have a multimeter but have not yet used it since it's brand new. Would this type of meter be a suitable measurement device to determine the voltage reading more accurately? Thanks.

Joe 45420

Joe , Yes a automotive meter is more accurate, but like I say the voltage is not the most important part of charging, its the amperege output. if your voltage gage is reading 13.4-14.2 (no load) chances are the alternator is functioning correctly.