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Cadillac & LaSalle Club Forums => Technical / Authenticity => Topic started by: Scot Minesinger on April 13, 2015, 08:50:11 PM

Title: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: Scot Minesinger on April 13, 2015, 08:50:11 PM
The generator light on dash of 1972 Eldorado is glowing slightly and voltage from new alternator (with internal regulator) is 14.6, kind of high.  Thinking that it is glowing because internal voltage regulator is not regulating properly and voltage is too high.  Normally I see 13.5 to 14 volts from alternator with car idling, no accessories on.

I tried to find this info in the shop manual to no avail.  It is just not very clear.  The alternator is 6 months old, 200 miles on it, Napa special from China.  Do I replace the alternator because voltage is too high? 

Want 100% correct operation.  I'm thinking that this higher voltage is going to be hard on climate control transducer and other components.  Starter spins real well. 
Title: Re: 1972 Cadillac Eldorado generator dash light
Post by: TJ Hopland on April 13, 2015, 09:17:44 PM
I would say 14.6 is still within the range.  Where are you measuring it?   What the condition of the battery?   Is it possible that its working hard to try and fully charge the battery?    How do the cables look?    What happens if you measure for voltage between the + terminal of the battery to the big terminal on the alternator?   Just wondering if you are getting a drop there.  The short wire from the small connector to the output terminal is the 'sense' wire that the voltage regulator is looking at to regulate the voltage.   Usually with it connected direct to the output the result is low voltage at the rest of the system.   

The light glowing is interesting.   I will have to come back and give the basics of how that is supposed to work.
     
Title: Re: 1972 Cadillac Eldorado generator dash light
Post by: Scot Minesinger on April 13, 2015, 09:39:46 PM
Battery cables and starter are brand new.  Alternator and battery are 6 months old and 200 miles.

I drove the car for about 100 miles and there was no issue, then the light started to glow.  This just happened.  It looks like from the wiring diagram that there is a resistor such that an over voltage situation would make the light glow, and correct voltage would not be enough to get past the resistor to make light glow.  It is not brightly lit, I would say 15-20% bright.  Because this just started happening after 100 miles of success, I think it is not a wiring issue.

Normally plus or minus 10% is OK, so 13.2 volts is fine, but of course no charging happens unless the alternator voltage is higher than system voltage, so 14.6 seems on the very high edge of an acceptable range.  Normally we expect about 13.75 volts or so + or - .25V.

Title: Re: 1972 Cadillac Eldorado generator dash light
Post by: TJ Hopland on April 13, 2015, 09:57:01 PM
Where is the resistor and does it say what the value is?   I don't remember that on the 73 and I don't have a 72 manual.   I'm having trouble wrapping my brain around an over voltage causing the light to come on.  Just because I can't wrap my brain around it at the moment certainly does not mean that is not what is happening, I could wake up in the middle of the night with a 'gen' light lit over my head and go ahhhh!     But also not looking at the diagram for your specific model may be why its not making sense.  They did often change things like that year to year. 

In general the way these work is one side of the light gets a + voltage from a key on dash circuit, usually labeled something like INST.   The other side of the light pretty much goes to the closest to output small terminal on the alternator.   When the alternator is not turning this terminal is basically a ground.  So key on alternator not turning you got + on one side of the lamp and ground on the other side so you get a fully lit light.   The regulator 'sees' the + voltage coming through the light and this tells it that you want it to be on so once its turning it will start making power.  When its making power that terminal becomes a + so you get 2 +'s at the bulb which is not a complete circuit so bulb does not light.    This is a simplified general explanation not specific to any car.   They do often mix other things into the circuit so you can get stuff back feeding and doing all sorts of strange things.   
Title: Re: 1972 Cadillac Eldorado generator dash light
Post by: "Cadillac Kid" Greg Surfas 15364 on April 13, 2015, 10:03:07 PM
Scott,
If all connections are good and everything is installed correclty you either have a bad diode trio or a voltage regulator in the "rebuilt" alternator.
Greg Surfas
Title: Re: 1972 Cadillac Eldorado generator dash light
Post by: 35-709 on April 13, 2015, 11:18:44 PM
A glowing light on my '73 turned out to be a bad internal regulator --- it was overcharging.
Title: Re: 1972 Cadillac Eldorado generator dash light
Post by: Scot Minesinger on April 14, 2015, 12:01:29 AM
Greg, Geoff,

That is what I thought, and will replace the alternator.
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: Scot Minesinger on April 22, 2015, 08:14:42 AM
Overcharging!  Three alternators later from two different suppliers/manufacturers and the problem will not go away.  The dash light for generator glows and 14.7 volts is always delivered.

The electrical system seemed great for about 100 miles after replacing the engine wiring harness due to past severe molestation with a better junk yard wiring harness.

The shop manual does not have anything much to read about this.

Does anyone have any ideas?
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: TJ Hopland on April 22, 2015, 08:53:57 AM
Does this just have the short jumper wire from the farther from the main post terminal to the main post?   And the close to main post small terminal is the one that goes into the harness?   Having those reversed could cause that issue plus would leave the regulator on all the time which would eventually drain the battery.     If the far terminal is going somewhere else disconnect that and rig up a short wire to connect it to the back of the alternator. 

Far terminal is the 'sense' terminal that the regulator uses as a reference to what the system voltage is. 
Close terminal is the 'turn on' terminal that is routed through the dash light. 

You said on the diagram there was a resistor on the light circuit?   Can you post a photo or sketch of that part of the circuit?   I could look at a 73 drawing but don't know for sure that would be the same.    Did the new harness come off a 72 Eldo?  OR a different year?  If different maybe there was some slight difference?
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: Scot Minesinger on April 22, 2015, 09:33:29 AM
I will take a look at the alternator connections, thanks. 

There is a 1.35 ohm resistance to positive on coil in 72 Eldorado and this is accomplished at the factory using a resistance wire.  This wire was trashed and so used a ballast resistor mounted on firewall.  There is not other resistor we added.  Fairly certain that this was from a 72 Eldorado, but cannot be 100%.

Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: walt chomosh #23510 on April 22, 2015, 10:02:42 AM
Scot,
  In reguards to the poor quality of parts available now days,I suggest you find a local alternator/starter repair shop. I found one in my area and he uses USA made kits....cost about $40 for a complete overhaul of a unit.(and a bench check!) NAPA used to have a factory that did alternators but apparently have outsourced it.....walt...tulsa,ok
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: TJ Hopland on April 22, 2015, 10:08:50 AM
The alternator wire is tied to the ignition coil circuit?  That does not sound correct.    It should be a somewhat direct route back to the dash light.   Maybe 72 is odd since its fairly new to the internal regulator?  Or was it internal originally?  The last 72 I worked on was a ambulance so it had the big monster alternator so I don't know how the stock size one was setup.   I just can't imagine a reason there would be anything else on that circuit.

close small terminal - light - 'inst' or similarly labeled fuse that comes on with the key  is the control and light circuit.

If something else wacky was going on under the dash that could explain the light but not the high voltage unless the small terminals were reversed at the alternator.   That is why I wonder if there were slight differences in the circuit over the years and between the past owners hacking and maybe getting a different year harness now things have got crossed somewhere.

Did the alternators have a inspection tag on them or in the box?  What voltage did they say?    What voltage did they test out at at the parts store?   IF you have not had one of em tested I would find a store to test it and see what the voltage does on the test machine.  If it comes out lower on the tester you will know its something in the car causing the high voltage.

And when I keep saying close and far terminal I am referring to the small 2 pin connector on the alternator and those 2 pins physical relationship to the main output terminal on the back.   The one closest to the output terminal is the control one that goes to the light.  The far one 9 time out of 10 just has a jumper to the output terminal. 

Just for fun have you tried taking a set of jumper cables and use them to add temporary grounds between the engine, chassis, and battery?   A marginal ground between those 3 areas can cause all sorts of weird issues.    I would even try clamping to the alternator itself.   I have seen so many pictures recently I don't remember which ones were this project but I remember seeing a freshly painted engine.  If that was this one maybe the paint is not letting the alternator fully ground to the engine so its confused about how much voltage its producing?   That sense terminal is very low current so it does not take much of a connection issue to throw it off.  Its not like the starter that will just arc its way through for a while. 

 
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: "Cadillac Kid" Greg Surfas 15364 on April 22, 2015, 10:42:51 AM
Scott,
Make sure you have the correct bulb in the "generator" indicator light socket.
Greg Surfas
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: curly on April 22, 2015, 02:03:09 PM
Gm used a resistor in parallel to the bulb on many models.  The electricity will follow the path of least resistance, in this case the bulb.  The bulb is used to drop the battery voltage going to the field terminals in the Alt. The Alt does not require a full 12 volts to begin charging. It is my understanding that the resistor is there to allow the Alt to continue to charge even if the Charge bulb burns out.  See Generic diagram below.

BTW, putting a full 12 volts to the charge terminal of the Alt. will cause "Full Fielding" of the Alternator. This will cause the Alt to charge at full power all the time regardless of the battery's state of charge.

The charge light glowing while the Alt is charging makes me think one leg of the diode trio is bad.  New Alt time.

T Lewis
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: Scot Minesinger on April 22, 2015, 02:25:54 PM
I will keep plugging away at the problem and thanks for the help, here are the things I have ruled out:

1.  Alternator is good, have installed three new ones from different suppliers all with same result.
2.  Connections at alternator are correct, just checked that out.

I will check the grounds, that is a good idea.  I will check the resistor between bulb and charging because I think that knocks off the top 13.5 volts so that an overcharging makes the bulb glow (say 14.7 volts - 13.5 volts, means a slight glow of 1.2 volts worth).  However the reading is 14.7 volts at alternator so the bulb is just identifying a problem, not part of it.

Any more new ideas or reinforcement of something I'm missing will be valuable.

Thanks,

Scot
Title: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: bcroe on April 23, 2015, 12:13:25 AM
Talking an internally regulated alternator here, not a 72. 

Some larger alternators need more starting current than the bulb can supply; this can be
aided by a resistor in parallel with the bulb.  The alt in my diesel used 2 bulbs in parallel,
one hidden behind the dash. 

Sometimes a bad alt diode can make a bulb light dimly with alternating current pulses,
not measurable with a voltmeter.   But 3 different alts makes that unlikely.  If the alt is
properly maintaining charge at 14.7V, but the bulb is still glowing, it means the voltage
at the other end of the bulb is different.  Most likely it is too low.  This can be caused by
resistance in the wiring, dropping too much voltage under some load.  Keep your negative
voltmeter reference point fixed (engine block), and see if this is true.  Walking the +
probe along will find the bad spot.  If the difference isn't enough to hurt, a diode in series
with the bulb can keep it from glowing.  Bruce Roe
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: TJ Hopland on April 23, 2015, 01:26:22 AM
Quote from: curly on April 22, 2015, 02:03:09 PM
BTW, putting a full 12 volts to the charge terminal of the Alt. will cause "Full Fielding" of the Alternator. This will cause the Alt to charge at full power all the time regardless of the battery's state of charge.

I don't claim to be any sort of expert on these but this is the first time I have heard of that.   I thought if you wanted to make one go to full power you stuck a screwdriver in the D shaped hole in the back?   I have worked with delco alternators hacked onto all sorts of equipment that seemed to operate fine and none had a resistor in that circuit that I remember.   One tractor I remember running there was a single chunk of wire soldered to both the small terminals that just stuck up and before you started it (with a screwdriver) you had to clip a battery lead to the wire to that wire.  It seemed to work fine except the times I forgot to un clip that wire because it would drain the battery overnight.   I think I ran that tractor for 3 years and I got the impression it had been like that for a long time.   
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: curly on April 23, 2015, 02:19:20 AM
Quote from: TJ Hopland on April 23, 2015, 01:26:22 AM
I don't claim to be any sort of expert on these but this is the first time I have heard of that.   I thought if you wanted to make one go to full power you stuck a screwdriver in the D shaped hole in the back?   I have worked with delco alternators hacked onto all sorts of equipment that seemed to operate fine and none had a resistor in that circuit that I remember.   One tractor I remember running there was a single chunk of wire soldered to both the small terminals that just stuck up and before you started it (with a screwdriver) you had to clip a battery lead to the wire to that wire.  It seemed to work fine except the times I forgot to un clip that wire because it would drain the battery overnight.   I think I ran that tractor for 3 years and I got the impression it had been like that for a long time.

Back in "the day" there were several different adapters that were available to plug into the Alternator harness to check for proper operation, basically to see if the problem was in the alternator or regulator.  Unplug the regulator, install the adaptor and then test for output.  Putting a screwdriver in the "D" shaped hole of a Delco Alternator did the same thing as I mentioned, it full fielded the alternator. (bypassing the regulator) Sun equipment used to sell the adapters.  I think I still have a set out in the barn, I'll have to see if I can find them.

T Lewis
Title: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: bcroe on April 23, 2015, 05:44:46 PM
I don't care how much the alternator is putting out, a glowing bulb means its 2 leads are at
different voltage.  Bruce Roe
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: curly on April 24, 2015, 10:02:02 PM
Found my Adapters, I realize this thread is about internally regulated Alternators, but for those of you with external regulators, the adapters pictured below were used to 'full field' the alternator by applying a full 12 volts to the field windings. The same thing can be done with a simple jumper wire, but these made it easy to do without memorizing different brands of alternators.
T Lewis
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: Scot Minesinger on April 25, 2015, 05:09:13 PM
I'm really stumped on this one.  The "sense" wire that tells the alternator the voltage it is receiving that must be the governing factor with the internal regulator reads 14.4V today and output is 14.4 volts, plus light on dash remains on.  Very frustrating.  Will continue to look for problems.  I have had three different alternators on the car - all do the same 14.4 volts to 14.6 volts and dash "gen" light is on.
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: curly on April 25, 2015, 05:23:47 PM
Scott, what happens if you disconnect the 2 wire connector from the alternator and turn the key on (engine off)? The bulb grounds through the regulator, so it shouldn't light with the connector unplugged. If it does, you have a short to ground in the wiring.

T Lewis
Title: Re: 1972 Cadillac Eldorado generator over charging - not alternator
Post by: Scot Minesinger on April 25, 2015, 08:24:31 PM
T Lewis,

Thanks the bulb does light with alt connector two wire unplugged from alternator, key in run position, and engine off.  Will look for short.  The electrical was major messed on this car, so not surprising.  Amazingly got the climate control operational today, but there was a refrigeration leak to fix (found it, just have to fix it).

Thanks,

Scot