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Low Alternator output at idle

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69 ambassador 390 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2011 at 8:07pm
The lights may dim but they should not go out at all weather the alternator is putting out or not.  Think lights on and engine off.  With 12+ volts in the system the lights should be on.  There are two things that will cause this.  A bad switch breaker so replace the switch.  Or a weak relay if somone added one.  Actually there could be 3 things.  Check the foot dimmer  connectors for corrosion or high resistance and maybe put in a new dimmer switch also. Has anyone mentioned that the early and late regulators are not interchangeable nor are the alternators.

Edited by 69 ambassador 390 - May/07/2011 at 8:11pm
Steve Brown

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ddfarm View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/08/2011 at 6:25am
Yes I know that the Reg and Altn are not interchangeable. The lights do not cut off all the time. They only cut off when I allow the car to idle at 800 rpms with the lights on for a long period of time. Maybe 5 mins. Then the lights will cut off completely. If I turn off the switch and then turn it back on, the lights will come on. If I continue in the 800 rpm idle(with the lights on) the lights will go off again. But if I increase the rpms the lights brighten and they do not cut off. As long as I am above the 1200 rpm level the lights are very bright and they never cut off. There is no relay added to the light circuit and the dimmer switch is new also. 
Please let me know if you have other advise!!!!!!!!!!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken Doyle Quote  Post ReplyReply Direct Link To This Post Posted: May/08/2011 at 9:48am
One of the main benefits of switching from generators to alternators, which AMC did in 1965, is that an alternator charges at idle.  Ddfarm's car idles at a whopping 700 rpm in gear, the lights should not dim.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/08/2011 at 11:24am
No, they should not.
My 1970 doesn't dim the lights.
However, not being there to actually check voltage drop across key connections, etc. - it's hard to say what else is going on.
The fact the lights "went out" means there are other issue and it's not charging system related.
Of course one needs to define "dim" as well.
My car will idle at a stop light, in gear, and you can't really see the lights dim down.
I also can't account for the battery either - I've not tested that battery personally.
(and some parts store burger flippers would have trouble testing a flashlight battery, so not sure what to say there)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: May/08/2011 at 4:35pm
My point exactly.  It does not appear charging system related but current related.  As long as the voltage is nearer to 14 the lights stay lit.  Closer to 12 they will go out.  Try to leave your lights on with the ignition off and see if they go out after a few minutes.  If they don't then try with the ignition on but not running.  Make sure your points are open if you are running them so as not to heat the coil.  The results for not running should be the same as idling but quicker.  Did this problem start with the new switch or did you change the switch to fix this issue.  It is rare but this could be a bad fusable link connection that gets hot at low voltage and disconnects.  My Ford truck does the same thing and I Know it is the light switch.  I put a new one in when I was in there just because and the new one trips if I idle a long time.  I am going to put back the old one which was fine.  New is often junk nowdays.  
Steve Brown

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/09/2011 at 6:16am
Thanks for the suggestion. As far as the new switch is concerned, I restored the car 12 months ago and had no problems after restoration. The problem seem to start a few months later. This was a off frame restoration and I know all connections were cleaned. However, I did use a stock harness and did not take it apart. After hearing all the suggestions I think it is best to focus on the wiring rather than the alternator and regulator. I will try the "lights on" test. BTW the battery is brand new and has a 750 CC Amps and is fully charged. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ddfarm Quote  Post ReplyReply Direct Link To This Post Posted: May/09/2011 at 10:42am
I have done a few more test that I would like to get some feed back on before I start tearing apart the wiring. Below are the voltage outputs at the back of the alternator(battery terminal) to a good ground.

These test done with standard 2 1/2 inch alternator pulley, full charged bat, engine hot, new regulator and new alternator(both rebuilt Autozone).
Rpms                  Output with lights off                Output lights on-bright
1000                        13.9                                               13.1
600                           13.1                                               11.6

This test done with same conditions except using a 2 inch pulley on the alternator.
Rpm                     Output with lights off                Output with lights on-bright
1000                         13.2                                                11.7
600                            12.6                                                11.0

If anyone can make any sense out of this PLEASE let me know
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: May/09/2011 at 9:09pm
Something is very wrong.  You actually are saying that you have no charging at idle and the voltage is actually less with the small pulley and faster spinning Alt. with the lights on.  Does your dash warning light work?
Steve Brown

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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/09/2011 at 10:45pm
I'll say something is amiss - since Motorola only used 2 5/8" or 2 7/8" pulleys on the alternators they furnished AMC for non-fleet cars.
 
You might also see why I don't like "reman" stuff from parts stores.
i don't care if the unit was carefully assembled in Mexico or Indonesia, I do not trust them, period.
Fully charged battery - but is it TESTED - load tested by a tech using a Sun machine, and not a pocket tester?
Anything that properly checks a battery and alternator puts out some incredible heat, and uses BIG cables. If they pull it out of their shirt pocket and test with it, go elsewhere.
It takes a good chunk of carbon pile and some heat dissipation to test and no tester they can carry around in their hand will do that very well.
From here -
I don't trust:
Battery - you say it's new - but tested? When did this start?
Alternator
Regulator
 
Used a used wiring harness? Connections to the chassis might be good - but what about where the wires go into the terminals on the ends of the wires? No, you can't look and tell........
Two voltage drop tests are needed at the end of each wire - terminal to chassis or engine or device, and wire to terminal. Remember, when you bolt that ground strap to something, there's two connections at each end of the ground strap - strap to terminal, terminal to chassis (or block)
What about dash wiring? What about the regulator tie-in to the ignition wiring? Is it proper for your engine? (AMC did some REALLY funky things with the alternator wiring/ignition.)
 
What sort of volt meter are you using? Have you verified it against something like, say, a Fluke meter?
Agreed - does the dash light come on?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: May/09/2011 at 11:03pm
Some of this "new" stuff doesnt mean much...............Id say Im with billd on what he's saying.    theres issues there, and you need to start at the battery and go from there.   just because the battery is new doesnt mean a thing to me......has it been  load tested??   and not with a dinky voltmeter either..............
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