Ammeter Over Charging Issue help

[Lee Patterson]

Situation: 1971 Pantera - stock 351C motor. Stock Ford distributor with Pertronics ignitor unit. Stock Ford alternator and separate voltage regulator. Up until today, no issues with the car. Starts, charges, all normal. Battery is on a BatteryTender at all times when not driving. Last time car was driven was the day before.

Went out today and car starts and warms up fine. I immediately notice once RPMs get about 2500, the ammeter is on full charge (+ 80 amp side of gauge). Note, I have a VDO +/- 80 amp ammeter that sits across the main feed which is how DeTomaso wired them. When the car is at idle RPMs, the ammeter is reading a slight charging + side like it normally does (BUT, seems higher than normal). When I apply load to the system - headlights, windows, you see a slight discharge on the meter as normal. However, my electric cooling fans are wired directly off the battery and when turned on, the ammeter no longer responds (like it used to). I drove the car for about 15 minutes - the ammeter continues to show full charge when at running RPMs and drops to a very low charge at idle.

What I have checked:

1. Primary lead wires to the ammeter - solidly connected and tight

2. Battery terminals - clean and tight. Battery disconnect switch tight.

3. With car not running, battery shows 12.6 - 12.7 volts. Car turns over fast as always and does it many times over and over. Battery water is topped off

4. With car running on fast idle, alternator shows charging voltage of around 13.6 volts, so system is charging.

5. Chassis ground is tight and clean.

What I have not checked:

1. The battery with a load tester

2. The terminals at the alternator



So, what do you think could be causing this?

1. The ammeter is bad and reading excessively now?

2. The battery is bad, but somehow continues to start the car?



Appreciate the electrical insight and help.

 

[Neal]

Possibly field wire shorted to ground or battery short.

 

[Lee Patterson]

Update: I measured the battery voltage this morning. 11.6V. Car started, rather slowly, but turned over. Voltage at idle was 12.0 v; at about 1500 RPM 13.2 v; and at about 2500 RPMs (which maxed the ammeter at 80+ amps), 13.6 v.

So I would conclude the alternator is doing its job as is the voltage regulator and the battery is bad?

thoughts?

 

[Ian Anderson]

Disconnect the battery…… you mention a disconnect switch.
Test battery voltage
Leave overnight without tender etc and disconnect switch disconnected

Test battery voltage in the morning…should be the same if not then I would agree battery is US and time for replacement.

Ian

 

[Blas]

Charging is within proper range. Sounds like a battery or perhaps the battery ground cable. How old is the battery?

 

[Lee Patterson]

Did further investigation with my multi-meter and test light. Determined something is draining battery. Started at the Voltage Regulator. By disconnecting it, drain stopped.

Looks like a bad VR. Had this once before years ago. Lance Nist taught me this troubleshooting technique.

Alternator is charging. But if VR is shorted, clearly not gonna work. Will replace VR and report back.

 

[Randy V]

Lee - You may want to consider removing the ammeter and replacing with a voltmeter - a far safer alternative for monitoring your charging system…

 

[Lee Patterson]

Replaced the VR which solved the short but the ammeter was still pegged. Battery could not hold 12.3V. Got a new battery, resolved issue. Checked Alternator output which is 14.6 V running fast idle. Battery voltage not running 12.7 V.

Ammeter behavior back to normal - shows load, charge and quickly returns to neutral with little load on it.

If I had to "guess", the battery (which is over 4 years old) had a bad cell which ultimately screwed the VR.

Yes, Randy, I would agree the ammeter is less than desirable and I may do just that.