Charging woes

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Evan Dutch

Evan Dutch

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Merry Christmas everyone,

I’m having some issues with the charging system on my 1971 Plymouth scamp. The car has a 360 magnum and I’m using a Holley terminator computer to control the fuel injection. I’m using a magnum front drive and the alternator from a 360 magnum.

When running, the car appears to be overcharging the battery. I’ve seen anywhere from 16-18 volts. This battery is located in the trunk and is brand new and fully charged and has been verified to be a good battery. It is an AGM battery (unsure if that makes a difference)

I’ve got the blue and green field wires from the factory harness attached to the rear of the alternator and the charging wire running from the alternator to the trunk mounted battery. I’ve replaced the voltage regulator, checked continuity between the regulator and the alternator lead wires and I have tested to check and see if 12volts is present at the blue field wire when the key is in the run position. I’ve also checked voltage drops across the field wires and ensured the regulator is well grounded. Everything has come back good so far. Ammeter bypass has been performed as well.

I’m stuck as to why it’s still overcharging. Any ideas?

Thanks guys

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Evan Dutch said:
I’ve got the blue and green field wires from the factory harness attached to the rear of the battery and the charging wire running from the alternator to the trunk mounted battery
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Did you mean rear of the alternator?
 
Evan Dutch said:
. I’ve replaced the voltage regulator, checked continuity between the regulator and the alternator lead wires and I have tested to check and see if 12volts is present at the blue field wire when the key is in the run position
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Do you know for a fact that the magnum alternator works the same as the earlier isolated field alternators?
 
Typically an overcharging isolated field alternator is getting 12v to one field terminal and a full ground to the other.

The isolated field voltage regulator provides a variable ground to the field wire.

It requires a GOOD 12V voltage source or it will assume that the alternator needs to output more.

Think of it this way...

If the VR only sees 11v it will try to increase the alternator output to get it up to 12v (nominal voltage numbers for illustration only)

So the alternator might output 15v to meet the load / voltage requirements.

Say the VR sees 10v, same process,
But now the alternator outputs 18v

With the battery in the trunk if the wires feeding the VR are not of sufficient size to carry the load there will be a voltage drop. This drop could cause the over charging.

Measuring voltage with no load gives incorrect readings.
 
Dana67Dart said:
Typically an overcharging isolated field alternator is getting 12v to one field terminal and a full ground to the other.

The isolated field voltage regulator provides a variable ground to the field wire.

It requires a GOOD 12V voltage source or it will assume that the alternator needs to output more.

Think of it this way...

If the VR only sees 11v it will try to increase the alternator output to get it up to 12v (nominal voltage numbers for illustration only)

So the alternator might output 15v to meet the load / voltage requirements.

Say the VR sees 10v, same process,
But now the alternator outputs 18v

With the battery in the trunk if the wires feeding the VR are not of sufficient size to carry the load there will be a voltage drop. This drop could cause the over charging.

Measuring voltage with no load gives incorrect readings.
Click to expand...
Wire size should not be the issue. With what you have said, I need to back probe the blue wire going to the voltage regulator to see how many volts the voltage regulator is receiving while the engine is running?
 
Evan Dutch said:
I need to back probe the blue wire going to the voltage regulator to see how many volts the voltage regulator is receiving while the engine is running
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Is the blue wire you refer to the wire coming from the ignition switch going to power the regulator.

Or the blue wire that feeds 12v to the alternator field terminal.
 
Most likely there regulator is sensing low voltage.
Low voltage for the regulator is less than 14 something.

My best guess based on what you've written is there is a voltage drop between alternator output and the regulator's sense terminal.
Continuity will not reveal a voltage drop.
Measuring with the electrical loads off will not reveal the voltage drops.
To determine the problem.
A. Charge the battery on a charger (I know you think you've overcharged it but if it really was charging at 15-16 Volts it may have got hot and will actually be undercharged. Without an ammeter on an isolted charge line the charge rate is unknown. The voltmeter only indicateds the potential. That's the trade off)

B. Run the engine and measure the voltage difference between the alternator output and the closest location you can access to the regulator's sense terminal. The field terminal connection (blue - ignition feed) will work or the ballast resistor connector if its still there. Leave them in place - Just back probe them.
 
Think I’ve got it. Went through 4 different voltage regulators but the charging voltage is now 13-14.5 volts

I didn’t change anything with the wiring nor did I find any concerning voltage drops. I guess what everyone says about todays parts store voltage regulators is true.
 
Evan Dutch said:
Think I’ve got it. Went through 4 different voltage regulators but the charging voltage is now 13-14.5 volts

I didn’t change anything with the wiring nor did I find any concerning voltage drops. I guess what everyone says about todays parts store voltage regulators is true.
Click to expand...
As bad as they are I find this hard to believe. The voltage is set by a zener diode in the VR. Most of the time they either work or they dont. Could be a poor ground, AKA the mounting bolts, or even corrosion/ looseness in the connector. Perhaps you pulled and re-installed the connector so many times (LOL) you finally scrubbed the terminals clean.

I often recommend that folks pull and push connectors to "feel" for tightness and to scrub the terminals.
 
67Dart273 said:
As bad as they are I find this hard to believe. The voltage is set by a zener diode in the VR. Most of the time they either work or they dont. Could be a poor ground, AKA the mounting bolts, or even corrosion/ looseness in the connector. Perhaps you pulled and re-installed the connector so many times (LOL) you finally scrubbed the terminals clean.

I often recommend that folks pull and push connectors to "feel" for tightness and to scrub the terminals.
Click to expand...
Cleaning the connectors is the first thing I did. Even ran a ground from the regulator to the engine ground point. All contacts cleaned and dielectric greased. Even ran through all the voltage regulators again to confirm. They all gave high values except for one
 
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