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Low Alternator output at idle

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Forum Name: Electrical - non engine
Forum Description: Charging systems, lights, non-ignition system, it goes here.
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Topic: Low Alternator output at idle
Posted By: ddfarm
Subject: Low Alternator output at idle
Date Posted: Apr/30/2011 at 8:10am
I have searched this topic and found several good threads. But none seem to answer my question. I have a 73 AMX 304 (AT)with a Edlebrock performance package( including cam). My car idles at 1200 rpm out of gear and 700 in gear. This car is a off frame restoration and all connections are clean. The alternator is a 55 amp stock(new). The lights dim at idle(700) and if the rpms remains there for a extended period the lights just cut off. If you put it back in neutral(1200 rpm) the lights come back on. I do have a electronic ign. So I have 2 questions.

1.Is there another alternator that I can get that will put out more at 700 rpms?

2.Why would the light just cut off completely? Then cut back on with more rpms.


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cindys1971



Replies:
Posted By: FuzzFace2
Date Posted: Apr/30/2011 at 8:42am
1. I dont know but if the ALT puts out the right volts & amps at higher rpm then I would say the ALT side is good but the REG side on the weak side. Recheck ALL grounds and if everything has fresh paint it may not be getting a good ground. You have the ground cable from motor mount bracket to cross member?
2. If I under stand right as volts go down the amps go up. Running at low volts as you say may be over loading the breaker in the head light switch and why the lights go out.
Dave ----


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TSM = Technical Service Manual

75 Gremlin X v8 for sale
70 Javelin 360/auto drag car
70 Javelin 360/T5 Street car


Posted By: ddfarm
Date Posted: Apr/30/2011 at 10:23am
Thanks Dave. Yes I do have the ground cable  from mount bracket to cross member. And it is a good clean connection. The voltage reg is new but I will recheck to see if I have hooked it up correctly. I did not know that the the head light switch had a breaker in it. Now I understand the lights cutting off.  

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cindys1971


Posted By: billd
Date Posted: Apr/30/2011 at 11:05am
First, we can't diagnose anything until you measure the actual voltage at the battery. Until then we are just guessing about grounds, connections, etc.
55 amp is MORE than enough, even with electronic ignition, which really doesn't take much more than stock, some less (more effecient)
Measure voltage - if it's in the 14v range, then the alternator is fine. If not, then you may have:
bad/worn brushes
worn/burned slip rings
bad diode
bad regulator
bad stator
 
Your problem is not a 55 amp alternator, you problem is a connection, ground, switch, or problem with the alternator or regulator.
A light switch will cut out much easier once the breaker has tripped a time or two. They are weakened by tripping - IF that's what is happening.
Take voltage measurements at the battery, at the back of the alternator, at the headlights themselves.
Check grounds - good looks doesn't mean good connectivity, and cables can be bad where the wire connects to the cable end - down inside where you can't see.
Measure for voltage drop across connections, too.


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Posted By: ddfarm
Date Posted: May/01/2011 at 6:00am
Okay, I have checked my grounds at the wiring harness and cross member. There is hardly any resistance at both(voltage is same). I also jumped a ground wire from the battery to the harness. Also jumped a ground wire from the battery to the lights. Also jumped a ground wire from battery to regulator ground. All results were no difference. The lights still dim at idle in gear. Voltage across the battery 13.9 at idle out of gear(1200). 12.8 at idle in gear(800prm). Voltage at back of alternator is same(12.8/800, 13.9/1200). Voltage at headlights is same as other test. Headlights are diffiently dimming due to voltage drop.

Is there another test I can run? 


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cindys1971


Posted By: ddfarm
Date Posted: May/01/2011 at 8:08pm
One additional thing. My AMX has a amp meter in the dash gauges and the meter falls below the middle point when the rpms are dropped below 1200.

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cindys1971


Posted By: offroaddodge
Date Posted: May/01/2011 at 8:27pm
the diode is bad that will stop output at low rpms

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Retired 70 Machine Owner

Had to get feet wet again

Started Another Chapter

Why????????

Bringing life back to 1973 Matador


Posted By: offroaddodge
Date Posted: May/01/2011 at 8:29pm
is that a motorola alt does it have a red bridge on the back that needs to replaced


-------------
Retired 70 Machine Owner

Had to get feet wet again

Started Another Chapter

Why????????

Bringing life back to 1973 Matador


Posted By: offroaddodge
Date Posted: May/01/2011 at 8:30pm
bad regulator maybe or wrong one

-------------
Retired 70 Machine Owner

Had to get feet wet again

Started Another Chapter

Why????????

Bringing life back to 1973 Matador


Posted By: poormansMACHINE
Date Posted: May/01/2011 at 8:34pm
With a 9% change in voltage, lamps will dim and brighten accordingly.
Pretty normal for the era.


Posted By: ddfarm
Date Posted: May/02/2011 at 6:18am
it is  a motorola alt

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cindys1971


Posted By: billd
Date Posted: May/02/2011 at 6:43am
You may have a;
Bad diode,
Bad stator winding,
Bad brushes
All or any combination of the above.
You can check the isolation diode pretty easily with a voltmeter.


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Posted By: ddfarm
Date Posted: May/02/2011 at 2:55pm
Okay I took the reman alternator back and replaced it with a new one. Still the same problem, at 800 rpms lights dim considerably and the meter in gauge cluster goes below the middle line(discharge). I have also checked the volts with another meter and get the same result. So could this be in the regulator? Or eventhough I have checked all the connections, could this still be a problem?

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cindys1971


Posted By: poormansMACHINE
Date Posted: May/02/2011 at 3:13pm
The voltage drop numbers aren't abnormal and neither is the dimming of the lights.
It's not a late model with a 150 amp alternator.


Posted By: billd
Date Posted: May/02/2011 at 3:23pm
Not the regulator if the thing charges at the correct voltage at speed.
Too large a pulley? What size pulley is on that thing?
You should sit and idle at higher voltage, however, if you turn the headlights on and esp bright, you will drop to 12.6v or so normally.
Maybe you are used to modern cars with halogens and all the modern junk?


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Posted By: ddfarm
Date Posted: May/03/2011 at 6:54am
Outside dia of pulley is 2 5/8 inch. If I were to change to a 2 3/8 (1/4 inch smaller)would that make a considerable difference? 

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cindys1971


Posted By: billd
Date Posted: May/03/2011 at 7:03am
Originally posted by ddfarm ddfarm wrote:

Outside dia of pulley is 2 5/8 inch. If I were to change to a 2 3/8 (1/4 inch smaller)would that make a considerable difference? 


Smaller pulley would spin the alternator faster. Might help.
BTW - what was the idle speed again? Is the idle too low?
Is the belt slipping? A worn/glazed or loose belt will dim things at idle.



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Posted By: ddfarm
Date Posted: May/07/2011 at 7:32am
Okay, I am still having the same problem at idle. The voltage across the back of the alternator at 800 rpms is still 12 volts with lights on and the lights are dim. If i speed up the lights brighten. I have changed the alternator and voltage regulator with no change. I must assume that it is in the wiring. So where do I start in the wiring. I know the grounds are good at the cross member and the firewall ground. If you need additional info on my diagnosis, check previous post,

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cindys1971


Posted By: poormansMACHINE
Date Posted: May/07/2011 at 7:40am
You want it to operate like a late model then rip it out and convert to a late model high output alternator.
The car isn't broke. This is how it was in 69.




Posted By: ddfarm
Date Posted: May/07/2011 at 7:17pm
Thanks for the observation but this is not how a 73 Javelin should act. I have had javelins since I was in high school ( since 71  ) and none have acted this way. Not sure how many you have had. I have bought them new off the lot and also used, but never had one act this way. In fact I currently have a 1971 Javelin that I restored 10 years ago and I do not have this problem. It has a stock alternator too. Maybe that was the way is was in 69 but it was not that way in 1971!

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cindys1971


Posted By: 69 ambassador 390
Date 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.

-------------
Steve Brown

Algonac, Mi.

69 Ambassador sst 390

84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special





Posted By: ddfarm
Date 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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cindys1971


Posted By: Ken Doyle
Date 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.
 
Ken D.


Posted By: billd
Date 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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Posted By: 69 ambassador 390
Date 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

Algonac, Mi.

69 Ambassador sst 390

84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special





Posted By: ddfarm
Date 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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cindys1971


Posted By: ddfarm
Date 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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cindys1971


Posted By: 69 ambassador 390
Date 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

Algonac, Mi.

69 Ambassador sst 390

84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special





Posted By: billd
Date 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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Posted By: purple72Gremlin
Date 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..............


Posted By: BDCVG
Date Posted: May/10/2011 at 9:52am
Originally posted by 69 ambassador 390 69 ambassador 390 wrote:

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?
Wouldn't a larger pulley actually spin faster because the belt has to cover more circumference in the same amount of time, A.K.A.  buy underdriven pulleys to gain HP but sacrifice at the alternator. This would explain the #'s with the pulley swap above.

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1970 AMX 390 5 spd full Control Freaks front and rear suspension
2014 E63 AMG-S wagon
1965 Austin-Healey 3000 MK III              


Posted By: billd
Date Posted: May/10/2011 at 10:55am
Originally posted by BDCVG BDCVG wrote:

Wouldn't a larger pulley actually spin faster because the belt has to cover more circumference in the same amount of time, A.K.A.  buy underdriven pulleys to gain HP but sacrifice at the alternator. This would explain the #'s with the pulley swap above.


No, the alternator is the "driven" pulley...... look at the cam to crank ratio, or a multi-speed bicycle... you derail the chain to a larger diameter sprocket to slow it down, and gain power.
To make the alternator spin faster, you decrease pulley size, like you'd decrease rear sprocket size to make the bike move further for every push of the pedal crank.


-------------


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Posted By: ddfarm
Date Posted: May/22/2011 at 7:15am
I still have the problem!!!!! Here are some other facts that I have done/found during my ordeal.

 Cleaned and tested every ground under the hood.
Had alternator and regulator checked at the alternator shop, which checked out OK.
Tried a smaller pulley from 2 5/8 inch(orginial) to 2 inch with no noticeable difference. 2" is smallest available.

Here are the results with the orginal pulley with car in gear. 

Test 1=@600 rpms alterantor works great with Lights-off, fan-off......13.9 voltage at back of allt
Test 2=@600 rpms alternators works great with lights-off, fan-on......13.8
Test 3+@600 rpms alternator stops putting out with lights-on, fan-on......12.1 at back of alternator and working strickly off the battery. No help from alter

With car in neutral and rpms @900 I get 13.7 volts at back of alternator even with everything on.

What other test should I do? Are the lights pulling too much Voltage? What should the voltage be at the yellow wire going into the regulator even when the lights are on? If this voltage is below 12 volts would the alternator stop output. If so at what point would it drop out?



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cindys1971


Posted By: poormansMACHINE
Date Posted: May/22/2011 at 7:44am
Smaller pulleys work nice on paper but now you have less less area for the belt to actually drive a greater load that you're introducing so it will slip.
What rpm and load is the shop testing the alternator at that your home made test isn't?
 



Posted By: ddfarm
Date Posted: May/22/2011 at 1:31pm


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cindys1971


Posted By: ddfarm
Date Posted: May/22/2011 at 1:35pm
Not real sure but I think they had a chart for this alternator. I will check tomorrow. Can you answer the questions in my last post without this info from the shop/

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cindys1971


Posted By: 69 ambassador 390
Date Posted: May/22/2011 at 2:04pm
Try a different regulator.  They are temperature regulated and there may be a malfunction.

-------------
Steve Brown

Algonac, Mi.

69 Ambassador sst 390

84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special





Posted By: billd
Date Posted: May/22/2011 at 2:18pm

There is a thermistor in the regulator. When it's cold, it charges about a half volt or so higher (I'd have to refer to my Motorola references to get the temp and voltage charts.)

As it warms up (ambient temp warms, as in under-hood temp) it drops the charging rate (voltage)

The reason is that cold batteries take more to charge. That's one reason the regulator is near the battery.

In any case, 13.6 or whatever you stated is low. It should be up higher than that.

I'll get the exact specs for your alternator later tonight if I remember.



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Posted By: ddfarm
Date Posted: May/22/2011 at 3:46pm
Thanks, the specs would be great. I have already tried 3 regulators and all produce the same thing. And not all these regulators were bought from the same place.

I might add to my observations. 

@900 rpms with everything OFF the volage from the back of the alternator is 14.1


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cindys1971


Posted By: ddfarm
Date Posted: May/23/2011 at 6:16am
I checked out the Alternator shop and they are telling me that it is NORMAL for these alternators to "cut out" around 700-600rpms considering the size of crank shaft pully used on AMCs. Can anyone tell me if this is true? If it is true, then my problem is not the alternator nor the regulator.

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cindys1971



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