Ammeter is making me nervous

-
TylerW

TylerW

Well-Known Member
Joined
Feb 29, 2008
Messages
1,041
Reaction score
150
Location
Elkton, TN
Hey guys: Getting my '73 Plymouth ready to go on the road and something weird is going on. I have noticed my ammeter swings nearly all the way over to 40+ at anything over idle speeds. From my other A-bodies I know this is normal right after a start but the ammeter should settle down to just above halfway afterwards. This one isn't.

So, I got out my multimeter and did some testing with that. At the alternator stud I get 13.9V at idle. At the battery I get 13.0V. Speed the engine up to 2000 rpms and I get 15.5V at the alternator and 13.9V at the battery.

Observation #1- The above-idle voltage at the alternator seems high Observation #2- The voltage at the battery seems in line, but there is a big drop from what's coming out of the alternator to what's measured at the battery.

Observation #3- The alternator seemed hot to the touch after running about 10 minutes. The only changes are: I had to replace the battery because it partially failed. It would still start the car but just barely, so the charging system had to work hard to get it recharged. I also swapped voltage regulators which had no effect at all.

Everything is stock with 49,000 miles including the original alternator. I've only driven this about 30 miles in the last year so I don't know it's something I inherited or not So, what's to be believed here..ammeter, voltmeter or both?
 
First you must actually determine IF THIS IS the VR at fault

1....voltage drop in the ignition harness. This can be intermittent due to harness connectors that wiggle, vibrate, etc

2....voltage drop in the ground. IF the VR does not "see" the same exact potential (voltage) as the battery neg post, then you will have higher voltage.

3....bad brush holders or a bad rotor in the alternator. If one brush holder is broken, and intermittently grounding, on the "green" connection, it will "full field" and charge full output

4....if the VR are actually failing, the rotor in the alternator may be drawing excessive current. Read the shop manual. There's a simple procedure in there to check rotor draw.

What all have you checked / replaced/
 
67Dart273 said:
First you must actually determine IF THIS IS the VR at fault 1....voltage drop in the ignition harness. This can be intermittent due to harness connectors that wiggle, vibrate, etc 2....voltage drop in the ground. IF the VR does not "see" the same exact potential (voltage) as the battery neg post, then you will have higher voltage. 3....bad brush holders or a bad rotor in the alternator. If one brush holder is broken, and intermittently grounding, on the "green" connection, it will "full field" and charge full output 4....if the VR are actually failing, the rotor in the alternator may be drawing excessive current. Read the shop manual. There's a simple procedure in there to check rotor draw. What all have you checked / replaced/
Click to expand...

This evolved into another issue, you may wish to edit this like I had to, thanks for your help.
 
Have you searched for how to test for voltage drop ?? 67dart has helped quite a few folks on here including me how to do it. Bypass that ammeter.
 
Not sure why one would need to edit perfectly good english text....?? Better presentation on a hand held device?
 
nm9stheham said:
Not sure why one would need to edit perfectly good english text....?? Better presentation on a hand held device?
Click to expand...

It was in Korean the first time around.

Actually I rewrote the title and post after I realized I had another problem besides what was first talked about.
 
Well the high voltage out of the alternator and the large voltage drops to the battery are problems. The high alternator output may have cooked your old battery and may be causing the large + ammeter readings. Have the high ammeter readings and large voltage drops from alternator to battery settled down at all with the new battery? I ask, in case the old battery had a partially shorted cell that was causing a high current draw. I would put the new battery on a charger overnight, disconnect the charger the next AM and let the battery rest for an hour, and check the battery voltage to see if it shows 12.6-12.7 v after a good charge and resting. This let's you know if the the battery is solid and not internally shorted. It is important to do this in this sequence, even with a new battery, with your high current draw symptoms. (BTW, I have had 2 bad brand new batteries in a row one time so take nothing for granted!)

Start with all the tips written on how to test for voltage drops. But it seems likely that you have one of a few issues. (And this is not new, just saying it again....):
1. You have some bad voltage drops in the main output wire from the alternator, through the firewall, and to the welded splice, then on to the regulator via the red wire to the ignition switch and then on the dark blue wire that goes to the ballast and VR. (Would not explain the heavy current draw though).
2. The ground leads are bad somewhere. (Would not explain the heavy current draw though).
3. There is some heavy current draw in the battery side of the ammeter; there is not much there except the ammeter itself, the harness, the firewall connector, the fusible link, the starter relay, the big lead to the starter, and the battery.

Not sure what to say about your observation #3; how hot is 'hot'? It could be a sign of the heavy current draw or just engine heat.
 
Re the VR itself, all it knows (and controls to) is the voltage difference between its case and the IGN1 input (usually blu wire). It strives to keep that at ~14 V. If that is true, it is doing its job. You need to insure its case = BATT- voltage and blu wire = BATT+ voltage, within say 0.2 V each.
 
You must log in or register to reply here.
-

Back
Top