Overcharging Problem
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Senior User
Joined: Sep 2006
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Overcharging Problem
UPDATE September 20
I THINK it's fixed. I finally admitted defeat and hauled it in to a good local auto electric shop. They pulled out the entire 3 wire alternator system and set me up with a GM one wire alternator. It arrived on a trailer and left under its own power, so that was a good start. I have since put about 60 miles on it with no problems.
So what was the problem? I don't know, but I have a theory. First, it was without question overcharging. I burned out 3 Petronix ignitions and one battery throughout this odyssey. The system was wired wrong and in such a way that could cause overcharging. With the help of this forum I got it rewired, but my meter still indicated 15.5 volts across the battery. That's when I sought professional help. Before I left repair shop I checked the voltage, and after the complete system replacement it read 16 volts, even worse than before. The tech came out with a Fluke meter and checked it: 14.6. He put it very succinctly, " $20 meter, $400 meter." I have since confirmed that the electrical noise from the ignition system could indeed cause a false reading on a poorly shielded meter.
So for my theory. The system was wired wrong to begin with, that is for certain. However, after following the advice posted in this thread, I probably had it right. But my cheap meter still said it was wrong, electrical noise was causing an inaccurate reading. It is behaving very well so far.
UPDATE
Rewire as follows:
Alternator #1 to keyed power
Solenoid S to starter button
Solenoid I unused
No other changes to diagram below
Result:
No change. Starts and runs perfectly, voltage across battery terminals ~15.5.
Questions:
The diode / resistor / light in Alt #1 wire: Is the only purpose to prevent the Engine-Not-Shutting-Off problem? If so I'm eliminating it. I used a new diode, a 10 ohm resistor and bypassed it altogether. The voltage was always 15.5 and the engine always shuts off. I understand that's because the wire is connected to a stud on the key switch separate from the wire energizing the coil.
Would the 15.5 volts cause my electronic points to burn out? Almost seems like a separate issue, too low resistance in the coil, for example. Pertronix calls for a coil of 1.5 ohms or greater, mine measures 1.7. Considering adding a 1 ohm ballast resistor. I'll call Pertronix this week.
sLKJ
It's a 1949 Ford F-1, original flathead V-8. Electrical system is 12 volt negative ground with alternator. Main wire harness was robbed out of a 1975 Ford half ton. Electric fuel pump, electronic ignition.
Truck starts and runs beautifully until it burns out the electronic ignition, then it doesn't start or run at all until a new electronic ignition is installed.
On a fully charged battery the multimeter reads about 13.4 volts across the terminals while the truck is not running.
While the truck is running, voltage is about 15.5 and does not drop even after idling or driving for 20+ minutes.
Starter solenoid is a Ford four wire, which I will admit to not understanding very well.
Alternator is your standard GM 3 wire internal regulator.
Ignition is Pertronix electronic inside the original distributor.
Replaced Items:
Alternator. This is alternator #3. The first alternator bench tested good but I tried alternator #2 anyway. #2 was a spare with bad bearings I had laying around, it bench tested good but still overcharged. #3 is a Napa reman just a few months old and only couple hours use. All three alternators tested good and put out the same ~15.5 volts.
Alternator wiring, new 10 gauge main lead to solenoid, new dedicated ground strap to battery negative.
Starter solenoid. Ford 4 wire on the firewall The type that has to two large terminals on either side for the battery and starter, and the two smaller terminals on the front. I cannot say these two front terminals are correctly wired but the solenoid appears to function correctly. Alternator 3rd wire (small gauge with diode) is connected to "S" terminal on the solenoid.
Coil
Spark plugs and wires
Electronic ignition (a couple times)
I THINK it's fixed. I finally admitted defeat and hauled it in to a good local auto electric shop. They pulled out the entire 3 wire alternator system and set me up with a GM one wire alternator. It arrived on a trailer and left under its own power, so that was a good start. I have since put about 60 miles on it with no problems.
So what was the problem? I don't know, but I have a theory. First, it was without question overcharging. I burned out 3 Petronix ignitions and one battery throughout this odyssey. The system was wired wrong and in such a way that could cause overcharging. With the help of this forum I got it rewired, but my meter still indicated 15.5 volts across the battery. That's when I sought professional help. Before I left repair shop I checked the voltage, and after the complete system replacement it read 16 volts, even worse than before. The tech came out with a Fluke meter and checked it: 14.6. He put it very succinctly, " $20 meter, $400 meter." I have since confirmed that the electrical noise from the ignition system could indeed cause a false reading on a poorly shielded meter.
So for my theory. The system was wired wrong to begin with, that is for certain. However, after following the advice posted in this thread, I probably had it right. But my cheap meter still said it was wrong, electrical noise was causing an inaccurate reading. It is behaving very well so far.
UPDATE
Rewire as follows:
Alternator #1 to keyed power
Solenoid S to starter button
Solenoid I unused
No other changes to diagram below
Result:
No change. Starts and runs perfectly, voltage across battery terminals ~15.5.
Questions:
The diode / resistor / light in Alt #1 wire: Is the only purpose to prevent the Engine-Not-Shutting-Off problem? If so I'm eliminating it. I used a new diode, a 10 ohm resistor and bypassed it altogether. The voltage was always 15.5 and the engine always shuts off. I understand that's because the wire is connected to a stud on the key switch separate from the wire energizing the coil.
Would the 15.5 volts cause my electronic points to burn out? Almost seems like a separate issue, too low resistance in the coil, for example. Pertronix calls for a coil of 1.5 ohms or greater, mine measures 1.7. Considering adding a 1 ohm ballast resistor. I'll call Pertronix this week.
sLKJ
It's a 1949 Ford F-1, original flathead V-8. Electrical system is 12 volt negative ground with alternator. Main wire harness was robbed out of a 1975 Ford half ton. Electric fuel pump, electronic ignition.
Truck starts and runs beautifully until it burns out the electronic ignition, then it doesn't start or run at all until a new electronic ignition is installed.
On a fully charged battery the multimeter reads about 13.4 volts across the terminals while the truck is not running.
While the truck is running, voltage is about 15.5 and does not drop even after idling or driving for 20+ minutes.
Starter solenoid is a Ford four wire, which I will admit to not understanding very well.
Alternator is your standard GM 3 wire internal regulator.
Ignition is Pertronix electronic inside the original distributor.
Replaced Items:
Alternator. This is alternator #3. The first alternator bench tested good but I tried alternator #2 anyway. #2 was a spare with bad bearings I had laying around, it bench tested good but still overcharged. #3 is a Napa reman just a few months old and only couple hours use. All three alternators tested good and put out the same ~15.5 volts.
Alternator wiring, new 10 gauge main lead to solenoid, new dedicated ground strap to battery negative.
Starter solenoid. Ford 4 wire on the firewall The type that has to two large terminals on either side for the battery and starter, and the two smaller terminals on the front. I cannot say these two front terminals are correctly wired but the solenoid appears to function correctly. Alternator 3rd wire (small gauge with diode) is connected to "S" terminal on the solenoid.
Coil
Spark plugs and wires
Electronic ignition (a couple times)
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
You’ve definitely got wiring issues. Frankly, I’m not quite sure how it even starts! The “S” terminal on the solenoid should go to your starter push button on the dash or “start” terminal on the ignition switch if you no longer have the button. This terminal closes the solenoid when 12V is applied to it and cranks the engine. The “I” terminal on the solenoid is closed to battery voltage internally through the solenoid and is hot only when the solenoid closes and the engine is cranking. It’s purpose is to bypass the ignition resistor for the ignition coil when cranking and feed the coil a full 12V for hot sparkies and quick starting. You shouldn’t have anything connected to it if you don’t have a resistor in series with your ignition coil. If you do have a resistor or resistor wire in the coil circuit, then this terminal should be connected directly to the “+” terminal on the ignition coil.
As for the alternator, the little white plug has two wires which you already know. One of them loops back to the large battery terminal as you have indicated on your drawing. This is the terminal marked “2” on the back of the alternator. It should be the terminal on the right side when viewed from the back side of the alternator. This wire is the “sense” wire for the voltage regulator and allows the regulator to monitor system voltage and vary alternator output accordingly. The other wire is attached to terminal ”1” which is on the left side of the plug when viewed from the back of the alternator. This wire should connect to the IGNITION SWITCH through the diode so that it is hot whenever the switch is turned on. It should not be connected anywhere on the starter solenoid. This wire is the “excite” wire and prompts the regulator to start charging whenever the key is on.
In addition to making the wiring corrections that I mentioned above, double and triple check that you have the right wires in that plug on the back of the alternator connected to the right places and that you have the diode installed the right way. The lead of the diode marked with a white band is the one that goes to the “1” terminal on the alternator. I can all but gaurantee that this is where your problem lies. Good luck!
As for the alternator, the little white plug has two wires which you already know. One of them loops back to the large battery terminal as you have indicated on your drawing. This is the terminal marked “2” on the back of the alternator. It should be the terminal on the right side when viewed from the back side of the alternator. This wire is the “sense” wire for the voltage regulator and allows the regulator to monitor system voltage and vary alternator output accordingly. The other wire is attached to terminal ”1” which is on the left side of the plug when viewed from the back of the alternator. This wire should connect to the IGNITION SWITCH through the diode so that it is hot whenever the switch is turned on. It should not be connected anywhere on the starter solenoid. This wire is the “excite” wire and prompts the regulator to start charging whenever the key is on.
In addition to making the wiring corrections that I mentioned above, double and triple check that you have the right wires in that plug on the back of the alternator connected to the right places and that you have the diode installed the right way. The lead of the diode marked with a white band is the one that goes to the “1” terminal on the alternator. I can all but gaurantee that this is where your problem lies. Good luck!
Thread Starter
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Senior User
Joined: Sep 2006
Posts: 198
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I want to thank you for the best explanation I have found on this. I made the changes you suggested and learned that the diode is bad - no continuity regardless of input polarity, but it was properly installed. I will chase down a replacement and update.
Another source says that I do need a 10 ohm resistor, but you clearly state that with no ballast resistor on the coil that this is not the case, so I'll skip that.
To sum up:
S terminal --> starter button
I terminal --> nothing
1 on alternator --> switched power on key switch through diode.
Thank you again.
Another source says that I do need a 10 ohm resistor, but you clearly state that with no ballast resistor on the coil that this is not the case, so I'll skip that.
To sum up:
S terminal --> starter button
I terminal --> nothing
1 on alternator --> switched power on key switch through diode.
Thank you again.
Lead Driver
Joined: Oct 1999
Posts: 6,767
Likes: 547
From: Kalispell, MT
Depends on your coil. Some are internally resisted and do not need another one inline. Coils without an internal resistor should have one. It keeps your points from burning.
I run 12V neg grnd and use a ceramic resistor on the firewall. I just tell NAPA I need one for a 70 Plymouth.
I run 12V neg grnd and use a ceramic resistor on the firewall. I just tell NAPA I need one for a 70 Plymouth.
Thread Starter
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Senior User
Joined: Sep 2006
Posts: 198
Likes: 1
How do I know if it has the internal resistor? Isn't that one of the great mysteries of the universe? It measures 1.7 ohms across the small +/- terminals. The resistor goes in the line from the I terminal on the solenoid to the + on the coil? (a line that does not exist at this time) Pertronix calls for 1.5 or greater with the V8.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Stock ignitions ran a 1.5 ohm coil primary winding and another 1.5 ohms (approx.) ballast for about 3 ohms total. Bosch makes a 3 ohm blue coil that might work for you. Splitting up the resistance in half keeps the coil from getting too hot though. If your electronic ignition can handle it, it's best not to use a ballast. If the factory used a ballast don't remove it.
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UPDATE
Rewire as follows:
Alternator #1 to keyed power
Solenoid S to starter button
Solenoid I unused
No other changes to diagram below
Result:
No change. Starts and runs perfectly, voltage across battery terminals ~15.5.
Questions:
The diode / resistor / light in Alt #1 wire: Is the only purpose to prevent the Engine-Not-Shutting-Off problem? If so I'm eliminating it. I used a new diode, a 10 ohm resistor and bypassed it altogether. The voltage was always 15.5 and the engine always shuts off. I understand that's because the wire is connected to a stud on the key switch separate from the wire energizing the coil.
Would the 15.5 volts cause my electronic points to burn out? Almost seems like a separate issue, too low resistance in the coil, for example. Pertronix calls for a coil of 1.5 ohms or greater, mine measures 1.7. Considering adding a 1 ohm ballast resistor. I'll call Pertronix this week.
Rewire as follows:
Alternator #1 to keyed power
Solenoid S to starter button
Solenoid I unused
No other changes to diagram below
Result:
No change. Starts and runs perfectly, voltage across battery terminals ~15.5.
Questions:
The diode / resistor / light in Alt #1 wire: Is the only purpose to prevent the Engine-Not-Shutting-Off problem? If so I'm eliminating it. I used a new diode, a 10 ohm resistor and bypassed it altogether. The voltage was always 15.5 and the engine always shuts off. I understand that's because the wire is connected to a stud on the key switch separate from the wire energizing the coil.
Would the 15.5 volts cause my electronic points to burn out? Almost seems like a separate issue, too low resistance in the coil, for example. Pertronix calls for a coil of 1.5 ohms or greater, mine measures 1.7. Considering adding a 1 ohm ballast resistor. I'll call Pertronix this week.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It's not the voltage per se that causes trouble, it's the current through the primary circuit.
Ignitor 1 wants no more than 8 amps. 15.5 volts is way too high charging voltage for summertime, it will boil the battery dry, maybe not in a day or two but it won't take very long.
If you use at least a 1.5 ohm coil (like the Pertronix Flame Thrower coil) that is rated for full time "12 volts" AND you're using the Ignitor module - you don't need or even want, a ballast resistor.
BUT, you have to fix whatever is causing the alternator to peg to the high side. Want to see 13.8 - 14.3 at idle, something like that.
Ignitor 1 wants no more than 8 amps. 15.5 volts is way too high charging voltage for summertime, it will boil the battery dry, maybe not in a day or two but it won't take very long.
If you use at least a 1.5 ohm coil (like the Pertronix Flame Thrower coil) that is rated for full time "12 volts" AND you're using the Ignitor module - you don't need or even want, a ballast resistor.
BUT, you have to fix whatever is causing the alternator to peg to the high side. Want to see 13.8 - 14.3 at idle, something like that.
Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
This is probably a dumb question and I'll shut up, but why is there a diode in the alternator field circuit?
About the coil: I bought the blue epoxy potted internal ballasted Bosch 12 volt coil. It made a noticeable difference in how much better my engine started and idled over the stock oil filled external ballast coil. This is otherwise all stock ignition components.
Just my 2 cents.
About the coil: I bought the blue epoxy potted internal ballasted Bosch 12 volt coil. It made a noticeable difference in how much better my engine started and idled over the stock oil filled external ballast coil. This is otherwise all stock ignition components.
Just my 2 cents.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
One thing, maybe you know this already - i have a DVOM, made by Triplett, runs on a standard alkaline 9 volt battery.
When the internal battery gets weak in these digital units they still work, but voltage measurement gets inaccurate as hell. I was reading 18 volts one day at the posts. Yikes!!
Popped in a fresh 9 volt battery, voltage output measurement back to normal. Not saying this is your problem, but it's something to look out for. Check with another meter to be sure.
When the internal battery gets weak in these digital units they still work, but voltage measurement gets inaccurate as hell. I was reading 18 volts one day at the posts. Yikes!!
Popped in a fresh 9 volt battery, voltage output measurement back to normal. Not saying this is your problem, but it's something to look out for. Check with another meter to be sure.
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
The circuit on terminal 1 performs two functions: it sends a voltage signal to the regulator to excite it when the key is on and it also operates the idiot light on the dash for the charging system. The resistance of the idiot light bulb prevents the regulator from back feeding the ignition switch when you turn the key off and keeping the engine running. In the absence of an idiot light on the dash, a regular resistor or a diode does the same job. In the interest of nailing down your problem, it might not hurt to remove the diode, resistor, or whatever you have in that wire right now and temporarily rig up a small 12v light bulb in that wire instead. If the regulator and the circuit are working correctly, the bulb should be off with the key off, on with the key on, and then turn back off when you start the engine.
There are two other simple things I think I’d check, both with the engine and key off. The first is the voltage between the positive post on the battery and the alternator housing. This is just to verify you’ve got a good ground on the alternator, although I doubt you’d be charging at all if it wasn’t grounded well. The voltage you see should be the same as across the battery. If that is OK, check between the alternator case and the number 2 terminal on the alternator if you can get the probe into it. Again, this should be the same as across the battery and just verifies that the sensing circuit is seeing the proper voltage.
One last thing you could check is to unplug the connector from the alternator completely and start it up and see what you have for system voltage. It’s possible that that particular alternator has a self-exciting or “one wire” type regulator. Those units are designed to operate without anything connected at that plug at all and having voltage applied there may be upsetting it and causing it to overcharge - but I’m starting to reach a little bit with that. It’s worth a try though.
There are two other simple things I think I’d check, both with the engine and key off. The first is the voltage between the positive post on the battery and the alternator housing. This is just to verify you’ve got a good ground on the alternator, although I doubt you’d be charging at all if it wasn’t grounded well. The voltage you see should be the same as across the battery. If that is OK, check between the alternator case and the number 2 terminal on the alternator if you can get the probe into it. Again, this should be the same as across the battery and just verifies that the sensing circuit is seeing the proper voltage.
One last thing you could check is to unplug the connector from the alternator completely and start it up and see what you have for system voltage. It’s possible that that particular alternator has a self-exciting or “one wire” type regulator. Those units are designed to operate without anything connected at that plug at all and having voltage applied there may be upsetting it and causing it to overcharge - but I’m starting to reach a little bit with that. It’s worth a try though.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Originally Posted by BlueOvalRage
There are two other simple things I think I’d check, both with the engine and key off. The first is the voltage between the positive post on the battery and the alternator housing. This is just to verify you’ve got a good ground on the alternator, although I doubt you’d be charging at all if it wasn’t grounded well.
Turn on all the headlights, heater blower etc., to load up the alternator. Spool up the RPM to a high idle. Set the voltmeter to low range.
Connected in parallel any voltage drop will be displayed through the voltmeter as a positive voltage while the circuit is energized, on account electricity seeks the easiest path. Should not exceed about + 0.1 of a volt. It doesn't take hardly any resistance to cause trouble. This is why an ohms test is of no value in measuring high current low voltage grounds and cables.
Let's say for example the normal resistance in the ground circuit is 0.11 ohms, but it has increased over time to 0.17 ohms, unless I measured it before and noted this, I'd never know right? That extra 0.05 ohms doesn't sound like much, in fact barely enough to measure, but that much extra resistance will reduce the alternator current output by about 30%. High resistance does weird things, on the one hand it makes voltage regulators peg to the high side, but cripples the ampere capacity of the alternator itself. Battery will probably spend a lot of time on the road outgassing, without ever getting charged up.
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
Now I remember why I don’t post much anymore. Oh, I fully realize that there are more accurate ways to check ground path resistance. I’ve been doing this stuff for a minute. It might surprise you to know that it’s my profession. But I’m not here to polish my ego or show everybody how smart I am. I’m just trying to provide the quickest and least complicated basic checks to help a guy narrow down his problem and fix his truck without confusing him. If there is enough resistance in the alternator case ground path to cause the regulator to malfunction, it will most likely show up as a reduced or nonexistent voltage indicated between the battery and the alternator case and that’s all I wanted him to look for. I have serious doubts that your extra stated six hundredths of an ohm will cause his issue. Yeah, I know. You stated .05 ohm, but your math in your own example is incorrect.
Engines are dirty and wiring and connections deteriorate over time. If a few hundredths of an ohm of extra resistance were all it took to cripple a charging system, there would be cars with dead batteries lining the highways. GM 10SI alternators have been successfully adapted to every application imaginable by some much less than “skilled” mechanics. The OP’s problem in not common and after having the same issue with three different alternators, I’ve gotta think it won’t take much to pinpoint.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Huh. Seems to me if you were just trying to help people out, you wouldn't have started pinging, completely derail and crap the thread, and then ramble on accusing me of "polishing my ego" and "showing off" etc. I apologize if I didn't acknowledge anybody's safe space or whatever it's called today.
Jeeze louise, try to learn something new about your chosen profession each and every day, and not get too wound up about personalities.
Jeeze louise, try to learn something new about your chosen profession each and every day, and not get too wound up about personalities.