Charging system can't handle load? - new 3g alt and battery - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 11 Old 10-31-2011, 08:05 PM Thread Starter
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Charging system can't handle load? - new 3g alt and battery

Hi Everyone,

I am sorting out my 1990 Mustang convertible and am having an electrical issue. With the car running with lights and a/c on the volts at the battery drop to 12.3 Volts or so. With lights and a/c off, it reads almost 14.4 volts. This is at a stock idle - car is warmed up. I listed the volt reading below for reference.

This is on a brand new batt and 3G alternator - old battery was toast from sitting and old alt had a bad diode but did the same readings aproximately but with a smaller alt pulley. The 3G conversion was done by the previous owner. This is a vortech car so the alt is under the smog pump. I took the new alt back to the parts store and they load tested it to confirm it was good. The old one failed this test.

The power and ground cables on the batt are HUGE - definately upgraded...looks like a 0 or 2 gauge? Fog lights are not hooked up, there is a stereo system in the car - two amps, a crossover and head unit hooked up to power. Turning them on or off doesn't affect voltage readings.

engine running at stock idle:
no accy: 14.4V
just a/c or lights: 12.8V
a/c and lights: 12.3V

Engine off:
no accy, key off: 12.93V
no accy, key on: 12.38V
Fan or lights on, key on: 12.19V
Fan and lights on, key on: 12.05V


With a new batt and a new 3G alt I know I have an issue somewhere - i have another 90 stang with OEM alt and it's at 14.4V until I have lights, a/c and something else on. Where should I look/test? I'm confused as the issue seemed to point to a bad alt bu obviously it's somewhere else?

Thanks the the help!

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post #2 of 11 Old 11-02-2011, 10:40 AM
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hope someone chimes in on this one. I have a 3g alt also and when my dual electric fans kick on i wander sometimes if it is going to kill the car.

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post #3 of 11 Old 11-02-2011, 12:56 PM Thread Starter
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me too...I don't even have an e-fan setup yet...I definately won't try it until I get this figured out...
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post #4 of 11 Old 11-02-2011, 02:34 PM
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do you have pulleys on your car?? it made i little bit of difference on mine but not that much. i have went back and forth between pulleys and no pulleys. for th past 3 months i have kept the stock ones on there. just to keep the alt charging as high as it could.

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post #5 of 11 Old 11-02-2011, 09:54 PM
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When I installed the 3G alt on my 93 coupe, I tore into the harness that houses the original alternator feed wire to battery and replaced it with a single 4 gauge wire. The original setup appears to b 2 10 gauge wires that feed power from alt to battery but is actually only 1 10 gauge that splits into 2 at the beginning and end of harness. This wire is just under 9 ft long. With that length and only being 10 gauge.....not GOOD!!! My setup works great with no problems. Msd 7530 with hvc2 coil, taurus fan, aeromotive pump, and a/c. Hope this helps.
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post #6 of 11 Old 11-02-2011, 11:50 PM Thread Starter
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Good point, I do still have those 2 10 gauge wires on the alt...Does that wire just go the batt or does it go somewhere else as well?
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post #7 of 11 Old 11-03-2011, 06:19 PM
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Quote:
Originally Posted by drhill View Post
Good point, I do still have those 2 10 gauge wires on the alt...Does that wire just go the batt or does it go somewhere else as well?
That single 10ga wire runs directly from the altenator, under air box location, across the front between radiator/condensor(along with all of the headlight and marker wires), back under the stock battery location and then back up to the starter solenoid. If im not mistaken, it turns into the two black w/ yellow stripe wires with single eyelet terminal end on it about 8" from the end. Attaches to solenoid on the same terminal as the positive battery cable, so basiclly, the positive batt terminal.... thats it.
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post #8 of 11 Old 11-03-2011, 09:30 PM
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Quote:
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Good point, I do still have those 2 10 gauge wires on the alt...Does that wire just go the batt or does it go somewhere else as well?
A 3g alt with the stock wiring is asking for an engine fire. Get that replaced with a quickness.

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post #9 of 11 Old 11-03-2011, 10:17 PM
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A 3g alt with the stock wiring is asking for an engine fire. Get that replaced with a quickness.
what he said...you are going to have a fire if you continue to feed the battery with the stock wires......use a 2 gauge (like a battery cable) and a fuse.....

Easiest way to think about amps and wiring is like water and pipe size.....the bigger the pipe, the more water you can push through, so the bigger the wire, the more amps you can push

I have a 200 amp taurus fuse coming out of the charge post on the alternator, then the cable, directly to the battery. When I have both fans running, stereo on, lights on, and a/c going my voltage still drops at idle, but not enough to leave me stranded.....I ran that way down ocean blvd all week during Mustang Week and car never failed to start......forgot to mention, running a steeda overdrive pulley, helped a little.....

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post #10 of 11 Old 10-29-2012, 12:01 PM
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post #11 of 11 Old 10-29-2012, 12:08 PM
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You need to check the crank pulley to alternator pullie ratio. The 3g needs to be spinning a min of 1600rpms and a max of 16000. You may need a smaller alternator pulley if your not spinning it fast enough. There is a youtibe video how to check it.
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