HOW TO TROUBLESHOOT ALT/VR

Posted By: frank

HOW TO TROUBLESHOOT ALT/VR - 05/05/13 12:36 AM

Battery is not charging. I believe the alt is not putting out voltage. Alt was rebuilt at a local shop and tests good on the bench. Alt has 2 spade terminals. Green field wire to one and keyed 12 volt power to the other. Each wire ohmed at .1. I have battery voltage to the VR at the IGN terminal. I have the same voltage at the alternator spade connector. Do I need to use a ground wire on the alt? How do you rule out VR or alt? Additionally, when the car was running I put my meter on the spade terminal with the 12 volt power; there were a few sparks when my hand slipped, nothing major. Could this have shorted the alt or vr somehow??

Posted By: RapidRobert

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 12:47 AM

Set the throttle on fast idle. Take off the green wire field terminal connector off of the alt field male spade terminal & ground the alt spade terminal (not the wire you removed from it) for 3 seconds max & if this full fielding makes the alt max charge then all is good in the 'hood except for (1) the green wire from the alt to the reg "you checked it" (2) reg ain't grounded "I'm thinking it is" (3) reg is fried. I believe you said the alt/reg are both getting switched 12V on the blue wire. Have all bulbs/accessories OFF when full fielding & I like to run an 8 ga or larger jumper from the alt to the batt when doing this. A bit picky but that's me. Holler how it goes.

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 01:03 AM

I put the car at fast idle. Disconnected the green field wire from the alt. Attached a jumper to the alt field terminal and touched the alt case with the other end of the jumper wire. The voltage went from 12.3 to 13.1 for a second (one second). I did the test again and the voltage only increased by .5 volts. All voltage measurements were taken at the battery.

Posted By: RapidRobert

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 01:12 AM

Check the voltage at the alt "batt" stud. Just to be sure jump from the green wire spade to the batt neg post rather than to the alt case but so far it's looking like the alt is bad. Might jump fire from the batt positive post to the blue wire spade field terminal on the alt just to be sure the field is getting fed full voltage

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 01:29 AM

OK attached ground to negative battery terminal (8 gauge wire) Set car at fast idle. Touched alt stud with ground wire; voltage increased to 15.8. Voltage was measured at alt batt stud.
Bad VR??

Posted By: RapidRobert

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 01:40 AM

"For future reference" The 8 ga wire was to go from the alt "batt" stud to the battery positive post just so the full voltage when full fielding would go directly from the alt to the batt rather than the circular route thru the problematic bulkhead but no big deal. yes the alt is putting out. If the green wire from the alt field to the reg side terminal has continuity and the reg is grounded then yes the reg is fried. The blue wire at the alt was hot since full fielding it by grounding the green terminal made it charge & we're assuming that the blue wire at the reg top terminal has fire at the same time

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 01:55 AM

Copy all

Thanks Robert for the help and info. I hate just replacing parts to try to solve problems. Again thanks!

Posted By: RapidRobert

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 01:56 AM

was it the reg?

Posted By: Twostick

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 02:43 AM

Before you dash off to the parts store, clean up the area where the regulator bolts to the firewall or better yet, run a ground wire to the regulator just to rule out a bad regulator ground as the problem.

Another obscure cause might be a bad ammeter connection. My father had a 75 Gran Fury when I was growing up that would fail to charge after replacing alternators and regulators. He blamed the "new fangled" electronic regulators as the culprit and switched it back to the mechanical style regulator and it never gave another minutes trouble.

Fast forward a few years and one day when he was into the dash to change something, found that the ammeter connection was IIRC just a push on friction connection and it was as green as grass. Cleaned it up and the electronic regulator worked fine. The only thing we could figure was that the regulator saw the resistance from the green corroded connection as a full charged battery and never turned on the alternator.

Kevin

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 04:23 AM

Quote:

was it the reg?

No. Put a new one on and same gig.

Posted By: Moparteacher

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 08:20 AM

Have you tested the battery? A faulty battery may not take a charge and will confuse the VR which monitors battery voltage. Have the battery properly tested after it is at least 50%charged with a disconnected standing charge of 12.2V or higher. Confirm your battery connections are clean and secure. Confirm the VR and alternator is grounded with clean, secure fasteners. Bypass the dash-mounted ammeter by running a heavy jumper wire from the alternator positive post to the battery positive post and then check high idle voltage, 13.2V-14.8V give or take a 1/10th. Confirm continuity on the green field wire between the VR and the alternator with an ohm-meter while both ends are unplugged. Should be less than .5 ohms. Wiggle the wire harness while testing to check for concealed breaks in the wire.

FYI: Your VR supplies a ground for the alternator field. It's a cycling switch. When the green field wire is grounded through the VR the alternator's magnetic field grows and produces an increase in voltage output. It connects and disconnects the ground rapidly to regulate the strength of the field. The VR monitors battery voltage that's coming through the ignition switch to determine the duty cycle of the grounding of the alternator field. When you full-field the alternator your duty-cycle is 100% and the alternator produces maximum output in voltage and heat.

The power for the field also comes through the ignition switch.

The alternator output goes to the ammeter in the cluster to swing the needle and then goes to the battery usually by way of the post on the starter relay. From there the current is distributed to the battery, starter solenoid, and fuse box for further distribution. You can check this wire by either by bypassing it or performing a voltage drop test.

You can perform a voltage drop test on any positive or negative circuit when current is flowing, or supposed to be flowing. With the engine at high idle, turn headlights on to load the alternator. Connect a digital voltmeter (don't use one with a swinging needle, analog) between the battery positive post and the alternator output post. DVOM common lead (black) on the battery positive and red lead on the alternator positive post (positive to positive). The voltage drop should read no greater than .5V. (half a volt). You can do the same with the ground. Alternator case to battery negative post (ground to ground), again expect a low number of .1V to .3V. High numbers, above .5V, mean there is an open or high resistance in the circuit. Older cars may see as high as .8V and be OK.

Let us know what you find.

Posted By: RapidRobert

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 04:24 PM

Quote:

Put a new one on and same gig.

What did you get on the voltage checks?

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/05/13 06:08 PM

I did not do voltage checks with the new VR.
I'm going to start from scratch on this. I'll post after a few more checks. Appreciate all the info and help

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/08/13 02:43 AM

More problems. Before I could make any new readings the car died; like turning the key off. Car would not restart. Today I ohmed the coil (MSD Blaster #8222) Primary 1.1 ohm and secondary 5.433 Kohm. MSD website says for this coil primary .7 ohm and secondary 4.5 Kohm. Should this coil even work at all??
Car started and ran just fine but alternator is still not putting out. FYI battery voltage is 12.77. Voltage at + coil (blue wire) 12.61 and voltage at Alt terminal (blue wire) 12.61

Posted By: RapidRobert

Re: HOW TO TROUBLESHOOT ALT/VR - 05/08/13 03:36 AM

Quote:

voltage at Alt terminal (blue wire) 12.61

You have switched 12V to the alt field. Find out why the green wire (the other alt field wire) ain't being grounded by the reg

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/08/13 03:49 AM

I'll try the original mechanical regulator tomorrow. BTW I bypassed the amp gauge this last test. Same results

Posted By: frank

Re: HOW TO TROUBLESHOOT ALT/VR - 05/11/13 02:59 AM

FIXED.
Removed the switched 12 volt power wire and ran a ground wire to the second alternator field terminal. Everything works now. Thanks for your help.