Overcharging

[67Dart273]

I have the same problem of overcharging. I have changed the amp gauge to a voltmeter. Also have a MSD ignition, so I do not have a ballast resister, I installed a terminal strip with the wires are connected to
What I am seeing is you start the car the voltage is 14, but when you increase the rpm the voltage goes to 16.
The test from the battery voltage to the Bark Blue wire has a 1.18 volt drop I have 11.6 at the strip. So I have a voltage drop in the ignition circuit somewhere.
My general question is if I am taking volts from the same place: to the regulator and to alternator, no matter what the volts are, should the regulator still work properly? Or does or get the difference from the battery side of the alternator? or from a voltage drop in the ignition side?
I am still chasing things down, this wiring has been butcherer way too much over the years.

One way to fix this is to cut the dark blue "ign1" ignition run power and use the end coming from the key to key a relay, and connect the other end feeding to the underhood loads to the relay contact output. Feed the relay with large wire, say no12 from some place like the starter relay "stud" with a fuse or breaker.

The VR and alternator field must be switched power, and there is only one source.........from the key........"ignition run." The only other source, which does not appear underhood, is the key "accessory" position, and you don't want the VR powered in accessory, plus (or rather minus, LOL) acc is likely a problem with voltage drop, as well

 

[Steven190]

This car has been botched a lot, I think the problem of the voltage drop is from the ignition switch. I am going to get a new one and try this one first. I have been thinking about running a separate wire.

 

[Mattax]

This car has been botched a lot, I think the problem of the voltage drop is from the ignition switch. I am going to get a new one and try this one first. I have been thinking about running a separate wire.

Why not measure where the drop is rather guess?
With the engine running, battery fully recharged, measure the drops at different access points (backsides of connectors). Then do the same with turn on some additional loads (like fan, lights).
Do the same with key on, or lights and engine off if you think there is resistance in the line from the battery to the main splice.


The downside of installing a relay for the run circuit is that the rest of the circuits may continue to see the voltage drop in their supply.
Lets say there is a 1/4 ohm resistance in the alternator output's bulkhead connection, .1 ohm in the battery feed's bulkhead connector, another .1 ohm in the column connector, and .05 in the ignition circuit's bulkhead connector.
Installing a relay for the ignition will get the alternator to produce at the correct voltage and remove 3-5 amps load. But current for everything else will still be going through some of those high resistance connections. Stuff like the brake light, headlights, dome light, heater fan, batttery when it needs charging, etc. So that stuff will still see voltage drop whenever they are turned on.

Since your car's wiring has been modified, sketch out what you have. Feel free to borrow any of the diagrams I've posted and modify them if. Best if you refer to the FSM for your year/model/options. That way you'll have the correct colors, connections, etc. If you like doing some of the drawing on the computer, MS Paint is all that's needed and save as a PNG file.

 

[Steven190]

I have a 1.18 volt drop from the battery voltage to the output side of the ignition switch.
What would the ohm be from the red wire to the blue wire out of the switch?

 

[Steven190]

I have 0 ohms between the two, and 11.8 volts at the red and 11.3 bolts at the blue.

 

[Pawned]

one very sinple thing to do is, R/R the brushes on the alternator

 

[Steven190]

Thanks
it is a new alternator and tested, which's had a output to 18 volts. I do not know if this is really is the cause, but I am open to all.

 

[Mattax]

I have a 1.18 volt drop from the battery voltage to the output side of the ignition switch.
What would the ohm be from the red wire to the blue wire out of the switch?

You need to know the current.
We can estimate current draw from most devices, or use a typical draw as a generalization.
Batteries are an exception. How much they will draw at any voltage depends on the battery condition. We can put a 14 Volt power supply across a charged battery and it will draw 0 amps. The same battery 20 % discharged with a 14 Volt power supply on it could draw 35 amps.

I have 0 ohms between the two, and 11.8 volts at the red and 11.3 bolts at the blue.

Few ohmmeters can read the resistances we're discussing here.
Most work by placing a small current through the system being tested.
And you can not measure voltage on a live system.

This is why we trace poor connections by putting current through a circuit and using voltage drops.

 

[moparker]

Im gonna check the bulk head connections today. They have never been removed. Maybe if I go through the series of events something will jump out at you guys.
I accidently left the key on about a month ago. Didnt kill the battery. Drove it after that. Then a few day later and battery was dead. It was very old. I charged it and got it running. Thats when I noticed the overcharging started. So, new battery, vr, alternator tested and new cm. 15.8, 15.9 volts. Spikes at start up. Wiring has never been touched. Bone stock. I have checked connections br, vr, cm, alt. Any help will be greatly appreciated.

 

[Mattax]

Im gonna check the bulk head connections today. They have never been removed. Maybe if I go through the series of events something will jump out at you guys.
I accidently left the key on about a month ago. Didnt kill the battery. Drove it after that. Then a few day later and battery was dead. It was very old. I charged it and got it running. Thats when I noticed the overcharging started. So, new battery, vr, alternator tested and new cm. 15.8, 15.9 volts. Spikes at start up. Wiring has never been touched. Bone stock. I have checked connections br, vr, cm, alt. Any help will be greatly appreciated.

Take photos.
Follow the battery feed as best you can back to the bulkhead.
It may also lead to a grommet in the firewall.
Without a FSM we'll have to figure out the circuit based on what we see. It may be like a '74, but could be different. '76 is very different.

 

[moparker]

I have a 75 shop manual for it. Was gonna get it out today. The guy who tested the alternator was leaning toward the ampmeter or the ignition. Hate to go screwing with either without some sort of smoking gun.

 

[Mattax]

I have a 75 shop manual for it. Was gonna get it out today.

Great!
Take some photos anyway.
And then to make it easier on us, a photo of the electrical diagram will help us on this side of the screen. Engine compartment side will be enough to see if more is needed.

The guy who tested the alternator was leaning toward the ampmeter or the ignition. Hate to go screwing with either without some sort of smoking gun.

Your thinking a lot more clearly than the guy who tested the alternator.
Follow the schematic in post #26 and you can see the ammeter has nothing to do with alternator producing high voltage.
And while it may relate to the 'ignition' circuit, its not the ignition either. It just happens that the ignition circuit is also the feed circuit for other things that get power when key is in run position.
Besides, we're not 100% sure about how the circuits are wired. If it has something like the optional wiring arrangement that was available starting in '73, or has some spliced feed junctions in the engine compartment like '76, that could change the analysis.

 

[67Dart273]

Don't overthink this:

1...You can NOT MEASURE low resistances with a meter. You must measure them with current flowing to create a voltage drop, in other words, "operational."

2....The simple deal is, the VR power (and ground!!) MUST be same as battery. MUST

3....There are only so many places for voltage drop in that circuit, just follow the path. (Might by a bit different for the 74/75, but essentially same)

The "functional path" is from battery, ..........to starter relay stud.......through fuse link.........through bulkhead connector.........to ammeter (big RED).........through ammeter........out on big BLACK.........to underdash WELDED SPLICE..........and branch off from the splice............to IGNITION SWITCH CONNECTOR..........through the SWITCH..........back out the SWITCH CONNECTOR (on ignition run line)...........back out BULKHEAD CONNECTOR.......and out into engine bay, l branch off to ignition, and to VR

EVERY POINT itemized above is a place for some drop. The major offenders are the bulkhead connector terminals, and the ignition switch

One again, adding a relay is likely the easy way to eliminate this

4...Don't forget the ground.........I like (on a v8) to use the unused holes in the rear of the driver side head. You can install a short starter cable (eyelet to eyelet) a foot or foot and half long, and bolt the other end to the master cylinder stud, or a good bolt through the firewall

Remove and scrape around the boltholes on the vr, and the firewall. Remount with star lock washers. Some guys use no10 ground jumpers between the ECU and VR and a good ground point such as the block. The block is actually the central main ground as that is where the battery is grounded. The body is often "poorly grounded" to the battery

 

[moparker]

Replaced the ballist resistor and now Im getting 14.2 volts at the battery but, gauge in dash still shows overcharging. Thoughts?

 

[Mattax]

Replaced the ballist resistor and now Im getting 14.2 volts at the battery but, gauge in dash still shows overcharging. Thoughts?

Please be more specific.
The ballast resistors shouldn't have anything directly to do with the voltage at the battery.
But without seeing how your '75 is wired, its only a guessing game.
Which ballast was replaced? - there originally were two .
What does the gage in the dash actually show (5 amps? 40 amps?) and how long and under what conditions (idling? driving?)?
Before starting was the battery fully charged using a charger ?
Also measure the alternator output voltage is at the same time you're taking the reading at the battery.

 

[moparker]

Gauge doesnt have numbers on it. I only see one br. I agree it shouldnt have anything to do with it. However it changed the reading at the battery. The car was at idle. Battery a little weak from me cranking on it til I figured out no spark. Battrry is new.

 

[Mattax]

Gauge doesnt have numbers on it. I only see one br. I agree it shouldnt have anything to do with it. However it changed the reading at the battery. The car was at idle. Battery a little weak from me cranking on it til I figured out no spark. Battrry is new.

It may be just normal charging.
The ammeter shows 40 to 0 to 40 amps. When someone jumps in an existing thread, I assume they've read through it.

If its charging at 20 amps for a minute and then starts to drop toward zero, that would OK considering the battery is probably pretty run down.
If it's pegging the 40 amps - that's not good, but can happen with a depleted battery and some alternators - especially at fast idle.
But also could indicate something is wrong. In either case, the wiring can get overheated and damaged, and the battery acid can get boiled out.

If its an traditional battery the charge can be checked with a cheap hydrometer (battery checker with 4 or 5 balls in it).
A very rough idea of the condition can be estimated using a voltmeter.
Engine off for a few minutes or more, a fully charged battery should be around 12.8 Volts.
During start, a weak but good battery will drop under 10 Volts, and if below 9.6 almost certainly needs a charging.

 

[Mattax]

When supplied with a power source, the amount of current drawn by the battery varies with charge level.
I posted a photo sequence in another thread where a discharged battery was provided power at 14.2 volts, and it drew over 30 amps.
Later, when it was mostly charged up, it drew hardly any current at 14.7 Volts.
That's normal.

 

[Mattax]

Charging a battery at 20 or 30 amps is not good for a battery, even when using a charger.
Its alsways best to have a charger that either limits the current, or the supply power can be manually turned down.
That's what I did with the old charger above.
Charging Battery with Alternator - Warning

 

[Steven190]

What we founded out was the voltage regular had too much resistance. We measured it and it was 380, we found one that measured 187, now we have 14.6 volts in the system.

 

[moparker]

Forgot to mention I cleaned the terminal on the starter relay and the wire ends. They didnt look bad. Also my red wire has a plastic connector. I took it apart and did whaT i could with that. Not sure if any of that had any bearing on my voltage being lower at the battery. I checked the battery not running it read 12.6.