I have a 73 Duster with a mildly built 360. I currently am running a 75amp alternator, but I'm having problems with low voltage output. I have an aftermarket stereo system and one group of aftermarket underdash gauges. The stereo cuts off when idle is below about 750 rpms. During night driving, the lights dim considerably when I come to a stop light or sign and forget about the radio. I've replaced the voltage regulator. I've checked with a meter and the output is very low with everything off and the car just at idle. I know I can increase the idle speed some (typically idles around 450-500rpm), but was wondering if a larger amp output alternator would also help. I've seen two wire alternators (chrome case) at 100amp for sale. I could also change to a single wire GM style and go up to 140. I've also been told to use a smaller pulley on the present alternator as to speed up the rpms at the source. The car is restomoded. I really want to fix this once and for all. Ideas?

From the archives (if you don't mind running a Denso alternator) -

http://www.moparts.org/Tech/Archive/elec/34.html


Tim

I'm guessing the alternator you have is a standard Chrysler case alternator, likley a Powermaster.

The small case Chrysler makes 40-50 amps at idle maximum... even the 100 amp souped up versions have the same low output at idle. Low idle output is likley causing your problems. Speeding the alternator up with a bigger crank pulley or smaller alternator pulley will help the idle output... but may make the alternator fail as a result of excessive RPM at high engine speeds.

The solid fix is an alternator with better idle capability. The GM style Powermaster alternators are good as are the Denso alternators. There is a decent chance the Powermaster MOPAR specific alternator will bolt in your current brackets with little or no modification. Denso alternators can be adapted with modifications. As Robert said, there are lots of posts on this.

With any of the high output alternator options, you need to increase the size of the charge wire. The factory wiring cannot handle it. Easiest is to run a 6 guage wire directly from the alternator output stud to the battery terminal on the fender relay. A length of 10 guage fusible link or a 150 amp fuse on the 6 guage wire is a good addition in case of "oops". Also add a voltmeter to monitor system condition. The OE ammeter will not register with the added wire to the fender relay.

I run a Denso off a Suzuki Samuari. It's rated at 50 amps. I run all stock wiring, it's not a fancy one wire, even run the alternator gauge.... Works awesome!! Doesn't dim at all at idle.

ARengineering make a bracket for those.

I rigged one up myself that doesn't look nearly as nice.

Your original style alternator should be able to handle your load unless you've gone all out with the stereo. I'd be wondering if there is something wrong with the alternator itself or the old wiring somewhere. Usually dimming at idle is a sign of bad voltage regulator but replacing it should have fixed that.

have you done the mad electric bypass yet?
have you checked the bulkhead connectors to see if they are clean?

it is possible that alt is powerfull enough, but you are getting enough losses through the bulkhead connectors and the amp meter to drop things out at idle.