Hi All,
In my 66 with 352, I have two electric fans, Universal A/C, Radio, Carb Cheater and charger for my phone. I purchased a rebuilt 100amp alternator that has been dead on for about 1 year. I had the voltage gauge go down to 13 volts and even to 12 volts. The tester for the parts store reported that the regulator needed to be replaced. I did that. I do understand that the amount of amps will go up and down due to the speed of the motor, but I didn’t think that this might affect the voltage reading. The question that I have is can the load on the system cause this? Could I have replaced the voltage regulator with a new bad one? Should I be looking at replacing the alternator with another 100amp or maybe my removed 65amp alternator. I don’t know if the 65amp is strong enough for everything I now have. Thanks for the help.
Lawrence

 

Lawrence, I'm sorry I can't answer your question very specifically, but I have a couple suggestions that might help you. I'm not sure why you would have a voltage regulator if you have an alternator. As far as I know, the VR is a part of the alternator. Unless someone can educate us further on this. The items you describe shouldn't draw an extreme amount current. The A/C would be the lion's share of that. Radio and phone charger should be rather insignificant. The Alternator's charging ability should also not change very much with engine RPM. Not as much as would a generator. Alternators generally have smaller pulleys and rotate faster than generators, so their current output is more consistent. Make sure your alternator belt is tight. Also, having an alternator with a higher amperage rating has no disadvantage. So, if in doubt, go with the higher output. Your battery should be charging at about 13.5 to 14.5 volts under most circumstances, even at idle. Check it with a voltmeter and don't necessarily trust the gauge. So, if the voltage feeding you battery drops to 13, then to 12, you are not charging the battery. At rest, the battery voltage should be about 12.5 volts. Amps and voltage are directly proportional. So if your alternator puts out a certain number of amps, that will be equivalent to a certain number of volts, as the circuit's resistance has remained the same. All that said, after reading your post again, I'm not sure exactly what problem you're having at the present time. You have replace the "Voltage Regulator", but you don't mention what is the result of that. Keep in mind that a bad battery, won't take a charge, just in case its starting up that you're having trouble with. What are the current (ha ha) symptoms??

 

Resonateur,
Thanks for the reply. I believe that I may need to be more clear. I purchased a reman'd high output 100amp alternator and replaced the 1 year old 55 amp alternator. I replaced the Ignition Voltage Regulator and the battery just this month. From my understanding that if you have a Alternator with the regulator built in, it would have a black bulge on the back. This one doesn't. I need to check the amount of pull of the AC system on the electrical system. Im always open to more learning and suggestions.

 

I'm certainly no expert on this, just have worked on a few. I'm still not clear on what problem you're currently (haha) having.....You have a 100 amp alt, new VR and newer battery. So, what's wrong? Or did I miss it? On the other point...to measure the "pull", or you mean current draw on the system you would need an ammeter of sufficient range, which I'm guessing you don't have. It would have to be (guessing) a DC ammeter capable of measuring a draw of 10-20 amps. Again...I don't know exactly, someone may be able to correct me. Another way is to measure the battery voltage at idle (should be over 13 if its charging) and measure it again with the AC on. If it drops close to 12, then you're not charging adequately with the AC draw.

 

I had to re read your post, The one you speak of that has the black box in back of the alternator is a series 2? It is not a very high voltage alt. The series 3 is a higher voltage. Better to have higher voltage than not enough. If you upgrade more, it can handle it later. First off your battery has to be tested.
It needs to be load tested. and the cells also have to be tested. If that is ok, your alternator has to be tested. Auto Zone and others will test them for you hoping you will buy from them.
I used to check them on the truck. You can disconnect the voltage regulator plug and by pass with jumper wires at the voltage regulator connection. I can't remember the exact terminals. I did post this info on one post years ago. The alternator should start charging and keep climbing because the voltage regulator isn't limiting it's output. This is not recomended because you can mess up your alternator with to much voltage applied. I used to shut them down around 16 or 17 volts. Meanwhile I will try to find out the by pass terminals.

 

Pull off the voltage regulator plug and Connect the A" terminal to the F" terminal. This will make the voltage climb if the alt. is good. You could have bad regulator or faulty wiring. Do this with the engine running. The alternator is capable of charging up to 250 volts be very careful. Shut it down when it starts to climb. Good luck

 

Thanks for the input. The battery is new (walmart replaced), regulator is new (OReillys), wiring less than 2 years old (Dennis Carpenter). The 100amp alternator was pulled and tested. It tested bad and Chargers Auto Electric (I'd purchased it from) was cool about me sending it back for warranty work. I put in the old alternator today. Its a motorcraft from OReillys that is 55 amp. While I was there, I changed the wiring for the electric fan so that it can be overridden by a switch in the cab. While test driving this evening it was running at 14.2 for about 15 minutes, then started to drop to 13.8. This was at dusk with no efan but lights (old style) on. At the stop light it dropped down to 12.8, but picked back up to 13.6 to 13.8. While driving the engine temp didn't raise enough for the efan to come on, but I hit the efan swith and it dropped to 12.7 at 45 mph about 2700 rpm.

Thrify, I will need to try that test tomorrow.

Im honestly thinking of reverting back to the traditional pulley fan instead of the efans. It may not fix the current issue but there is some thing to to the KISS method.