How would I be able to physically test the output of my alternator? I know what it is supposed to be at, but I'm suspecting that it may be failing.. Any info will help.

Thanks,

Alfred

 

Its tough to do directly without some special equipment but you can indirectly check some things with a voltmeter. The output of the alternator is controlled by the voltage regulator and the voltage regulator just tries to keep the alternator outputting enough to keep the system voltage around 13 to 14 volts. The precise voltage varies a bit from car to car and may increase by 0.5 to 1 volt as the engine speed goes from idle to 2000+ rpm. As you add more loads like the headlights, stereo, and heater/AC fan, a healthy regulator/alternator will increase the required amperage to keep the voltage at the same level. A charged car battery will show about 12.5 volts.

A quick check: Car off - check the battery voltage with and without the headlights on. You may see a slight drop in voltage from maybe 12.5 to 12.3 volts. A bigger drop may indicate a weak or poorly charged battery. Turn the lights off and start the engine. Turn off the AC, stereo, and all that stuff. Check the battery voltage now. It should be up around 13 to 14 as I said earler. The fact that the voltage is now higher means that the alternator is charging your battery. Have a friend slowly rev the engine while you watch the voltage. Look for that small increase of 0.5 to 1 volt. You may not see much of it if you have a high idle but I am mentioning it so you will know it may be there. If the voltage never gets higher than your original battery voltage (with the car off) your regulator or alternator is not functioning properly. Now that you have some baseline info, lets check the output of the alternator. The high beam headlights take 14-18 amps. Parking lights 2-4 amps. Heater fan on high setting 8-15 amps. A stock radio turned up 2-5 amps (AVERAGE DC). Rear window defog 10-15 amps. With the car running, turn on these items one at a time and watch the voltage. At idle you may see the voltage begin to drop as the loads are added, but it should come back up as the engine rpm increase over 2000 rpm. In short, if you can add 30 amps of load (Headlights and heater fan) without seeing a voltage drop - the regulator and alternator are just fine. Don't expect a regulator or alternator to begin to fail slowly. Good Luck

 

I agree with most all said. But would add a couple of items. Car batteries are 6 cell Lead Calcium. The individual cell voltage is approximately 2.2V/cell. So 6 cells x 2.2 = 13.2VDC. This is what a normal battery should read when charged. The alternator needs to put out more than this to be able to push electrons into the battery. So the normal alternator puts out about 14.5VDC. I would say 13.6V would be an absolute minimum.

A quick test to see if it works is to add some load by turning on the lights, air conditioner, etc, and then remove the positive on the battery terminal. Do this while the car is running, if it continues to run you know its carrying that load. If you have your voltmeter hooked up, then you should also not see a change in voltage when you disconnect. But re-attached the pos terminal before turning the car off, or else you will have to reset all you clocks and radio stations, as for that moment you had no power at all.

Most alternators today have built in regulators. I am not sure about the Ford ones. It would not be easy to actually load your alternator to full capacity. First you would have to have a load that could absorb it, second you would have to manually control the field current. If the alternators continues to run the car with absolutely every electrical load possible running, and still maintains 14VDC, then what more do you need.

 

Be carefull if you disconnect the battery while running. You may blow up the computer with the voltage spike that it makes. It could also blow up the battery.(the battery puts off fumes+spark from connecting/disconnecting=BOOM) Neither may happen but both could happen. Just be carefull and always wear saftey glasses!!

Good info on testing!!!

Good Luck,
Mike