Alternator/Charging Issues

splenderleith · #1 (**permalink**) 08-07-2021, 08:43 PM

I have recently inherited car #SP150. I am having trouble getting the system to charge. I took the alternator to Oreillys and they tested it and said it is perfect. When I use a multimeter I get very little voltage, almost as if the alternator isn’t doing anything at all.

Any ideas?

Got the Bug · #2 (**permalink**) 08-07-2021, 09:29 PM

What’s the reading from your alternator? It should be in the 14.5V range. If you turn on all of the accessories and try a reading at the battery terminal, I think it should be about 13.85V. Last thing is to check your battery with everything off to see if it’s fully charged. Full charge I think should be ~12.6V.

splenderleith · #3 (**permalink**) 08-08-2021, 06:21 AM

When oreillys checked it they told me 14.4 volts. When I put my multi meter on the red post and ground it on the chassis, I get less than 1 volt. The battery reads in the upper 12.6 volt range after I disconnect the trickle charger. When I start the car (fuel pump and radiator fan running) the voltage drops to 12.2 and continues to decrease slowly until the battery is drained so much the car won’t start. I would have bet the alternator was bad, but the test said otherwise. I don’t know what to look for, at this point.

Thanks.

ERA174 · #4 (**permalink**) 08-08-2021, 06:30 AM

If the voltage regulator is not integral to the alternator, the regulator could be the problem. Also, check to make sure all your grounds are properly attached.

Blas · #5 (**permalink**) 08-08-2021, 07:04 AM

Is this a Superformance car? If it is in standard configuration there is an external voltage regulator, probably located in front right corner on engine compartment. Inexpensive and easy to replace.i would remove the battery and have it load tested too.
Blas

splenderleith · #6 (**permalink**) 08-08-2021, 07:33 AM

It is a superfomance cobra, purchased in 1996 with the 460 crate motor. I replaced the external voltage regulator yesterday, with no apparent change. The battery is brand new, but there was no battery in it when I received it. I purchased one that fit in the space and hooked up the + and - thick wires to the battery. The battery starts the car well and runs all of the accessories, but it completely drains within about an hour of driving.

I am not sure if there are any smaller wires that need to be hooked up to the battery terminals. I may pull it back out to see if I can see anything. The guy at the auto parts store said that if I probe the positive post on the alternator and ground the other probe, I should get 14.4 volts, but I get almost nothing. I am wondering if the wire positive wire may be grounding out somewhere, due to a worn insulation issue. I am not very strong electrically, so it is quite possible it is something very simple.

ERA174 · #7 (**permalink**) 08-08-2021, 09:23 AM

Give this thread a read, my provide some insight.
Electrical Issues

HighPlainsDrifter · #8 (**permalink**) 08-08-2021, 09:34 AM

Hi,
take the alt off and clean and sand down the rear bolt hole that goes to the block to get a good ground connection. If the alt has chrome then sand the chrome off.
Perry

splenderleith · #9 (**permalink**) 08-08-2021, 12:48 PM

I replaced the alternator, just to be sure. I ran a wire from the positive battery terminal to the positive terminal on the alternator and a cable from the negative terminal to the alternator ground. Still no voltage increase when I start the car.

It seems to me like there is some kind of signal telling the alternator not to create charge, but I am really not sure how that part works. The voltage between the battery and voltage regulator seems to be full battery volts, but between the alternator and the voltage regulator, it seems to be less than 1 volt. I don’t know if that is normal or not, but with the positive and negative battery terminals wired directly to the alternator, I am not sure where else the issue could be.

cycleguy55 · #10 (**permalink**) 08-08-2021, 12:52 PM

Quote:

Originally Posted by splenderleith

It is a superfomance cobra, purchased in 1996 with the 460 crate motor. I replaced the external voltage regulator yesterday, with no apparent change. The battery is brand new, but there was no battery in it when I received it. I purchased one that fit in the space and hooked up the + and - thick wires to the battery. The battery starts the car well and runs all of the accessories, but it completely drains within about an hour of driving.

I am not sure if there are any smaller wires that need to be hooked up to the battery terminals. I may pull it back out to see if I can see anything. The guy at the auto parts store said that if I probe the positive post on the alternator and ground the other probe, I should get 14.4 volts, but I get almost nothing. I am wondering if the wire positive wire may be grounding out somewhere, due to a worn insulation issue. I am not very strong electrically, so it is quite possible it is something very simple.

Ford-type alternator or some other type (e.g. GM 1-wire)? What wiring connections do you currently have?

I'd be inclined to not only double-check the grounds, but install a ground wire from the alternator to the chassis / frame. You can never have too many grounds (within reason).

splenderleith · #11 (**permalink**) 08-08-2021, 03:49 PM

Just to try to rule out more items, I jumped the voltage regulator and I was able to get voltage out of the alternator. With that, I put the old voltage regulator back in. I was hopeful that whatever was wrong was fixed, but no such luck. I unattached the red wire and ran one from the alternator to the solenoid. It seems like the alternator is now generating more current than the battery. My thoughts, at this point, are that I may be able to run some new wires and get some positive results. The light above the ignition goes off when it is running, but the amp meter still stays negative. The ignition light going off is the most progress I have made in days. Hopefully this works enough for me to rule out some things.

splenderleith · #12 (**permalink**) 08-08-2021, 03:51 PM

The alternator has 4 wires. One red, one white, one black and a brown for ground. It appears that there is a 5th post that is not used.

Blas · #13 (**permalink**) 08-09-2021, 05:58 AM

You have a message
Blas

1795 · #14 (**permalink**) 08-09-2021, 06:39 AM

Not sure if your alternator is similar to the one that I had in my MGB race car. I was having a similar problem as I completed that build, in that the alternator (which tested as being good) was not charging the battery. Turned out that I had to wire in an idiot light that would turn on and tell the alternator to charge the battery. Your alternator may require a signal as well.

cycleguy55 · #15 (**permalink**) 08-09-2021, 11:21 AM

If you don't care about a 'period correct' alternator, do yourself a favour and switch to a Ford 3G alternator. Internal regulator and fans, higher output (especially at idle and low RPM). Mine was built for a 1995 Mustang V6 and is rated for 130 amps. Your pulley will swap over if you're running V-belts, though it may require a thin shim (mine didn't) so the pulley will clear the alternator case. Mounts are the same.

Here's some interesting output curves:

Some re-wiring is required, but the 3G is a big improvement over the 100 amp 1G large frame alternator that was there before. Lots of information available on the Internet about how to do this. Here's one source: https://www.motortrend.com/how-to/in...r-older-fords/

Blas · #16 (**permalink**) 08-09-2021, 01:23 PM

That’s a lot of Amps for a Superformance….. I’m just saying….��
Blas

cycleguy55 · #17 (**permalink**) 08-10-2021, 11:40 AM

Quote:

Originally Posted by Blas

That’s a lot of Amps for a Superformance….. I’m just saying….��
Blas

Yes, but of course that's maximum capability and the alternator will only produce what's necessary to supply the current load.

patrickt · #18 (**permalink**) 08-10-2021, 03:16 PM

Well you never know when you might have to dump 200 amps in to a winch to pull your ass out of a ditch.

cycleguy55 · #19 (**permalink**) 08-10-2021, 07:42 PM

Quote:

Originally Posted by patrickt

Well you never know when you might have to dump 200 amps in to a winch to pull your ass out of a ditch.

I haven't seen too many Cobras with winches. I need to get out more often.

jhv48 · #20 (**permalink**) 08-11-2021, 07:42 AM

Quote:

Originally Posted by 1795

Not sure if your alternator is similar to the one that I had in my MGB race car. I was having a similar problem as I completed that build, in that the alternator (which tested as being good) was not charging the battery. Turned out that I had to wire in an idiot light that would turn on and tell the alternator to charge the battery. Your alternator may require a signal as well.

I think he may have hit on the answer. Does the red light on your dash glow? With a one wire alternator, the light is left out. If you have an external regulator, the light must be connected for the circuit to complete.