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Voltage at coil 62 390

Started by hotrodln, September 09, 2021, 08:25:58 PM

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hotrodln

The factory manual says it ought to be 9 volts when running. I have around 6.6....it's not running well. I've only found this after changing everything else. Should i replace the  entire wire from the ignition switch to the coil? was it a resistor wire? or is there a resistor somewhere in the wire harness? Thanks Pat
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Pat Prendergast

bcroe

You mean the ignition side of the coil?  When running, the voltage
goes from 12V battery, to a much lower value, how that reads
depends on the kind of DC meter used.  I would not use that
measurement as useful.  Bruce Roe

fishnjim

Before U jump.  Disconnect the wire from the switch and coil and check the ohms/voltage drop.     
I'm not sure if they were resister(later?) but doubt.   Kirchhoff's laws apply.   I suspect there should not be much voltage drop along this ~6' wire.   Check the manual electrical diagram for gauge, etc.  Charts of ohm/foot by wire gauge and material exist.    I never worry about the voltage there so agree with Bruce.   It's what comes out the other side that counts.   If the input is good and the parts are good, that's all I need to know.   
Wire could be burnt up a tad, if lots of ohms - not necessarily means resister, that one runs over the engine.   Doesn't hurt to shield those engine wires.   Resistance should be noted on electrical diagram, if so.
If the wiring's never been redone, then you might have more electrical issues down the road.

This is that funky period when they were using transitioning from 6V coils to 12 V systems and internal and external ballast resisters because they still had points.   Refer to your shop manual for the specs.    You just need to make sure you got the right type coil for that car.   They're not that expensive, I'd just replace.   If you have an auto electric shop they can test all that for you.   But it's a dying art.

TJ Hopland

Does the manual say where you are putting both test leads?    You would get a way different reading measuring across the coil than you would going coil + to a ground.   I would guess they would be wanting you to read coil + to a good ground.

I would suspect the resistor or resistor wire so you will have to locate that for at least a good inspection.  One reason I suspect it is there is usually dissimilar metals involved that are joined in some way.  What ever the resistor is isn't copper so its joined to copper somewhere somehow.   How ever they did it was pretty good but I don't think they intended it to last 50+ years.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

hotrodln

ok just to clear it up. i measured from the + side of the coil to ground. Factory manual says it ought to be 9 volts. i've got 6.6. car stumbles and runs like crap. i've replaced: coil cap rotor point wires carb filter used a small gas tank fed directly to the fuel pump to see if the gas tank screen was plugged. everything was done one step at a time...with the same result....sometimes it will run ok for a minute or two. I'm going to rig up a wire from the battery with a resistor in it and see if it runs better. pat
Pat Prendergast

wheikkila

This is when you would like to have a good wiring diagram for your car. They are not that expensive, but worth every penny. I purchased one for every car I own from a place in Florida. They are 11x17 in color. They cost like $20.00 each.
                              Thanks Wayne     

Scott Halver

Pat,   I would check the voltage at the battery, one lead on the negative and one lead on the positive-   takes only a minute to check.   You can look up the specs in the shop manual (certain voltage at a certain temperature) ........ probably should be about 14.25 volts when the engine is at say 1,500 rpm.    You may have a voltage regulator that is not keeping the system voltage up where it needs to be "before" the resistor wire reduces the voltage to the coil.....  or a generator that is not up to the job.   SHalver #24920
1960 Eldorado Seville, Grandfather Bought New
1970 Corvette Convertible 350/350

J. Gomez

Quote from: hotrodln on September 10, 2021, 10:55:06 AM
ok just to clear it up. i measured from the + side of the coil to ground. Factory manual says it ought to be 9 volts. i've got 6.6. car stumbles and runs like crap. i've replaced: coil cap rotor point wires carb filter used a small gas tank fed directly to the fuel pump to see if the gas tank screen was plugged. everything was done one step at a time...with the same result....sometimes it will run ok for a minute or two. I'm going to rig up a wire from the battery with a resistor in it and see if it runs better. pat

Pat,

It will be difficult to analyze your condition or provide possible remote resolutions with minimal details.

I believe the '62 has the resistance wire from the Ign. switch to the coil and the coil would need to be the type that required "external resistor". Do you have the correct coil?

If you have the resistance wire with a coil that has internal resistance already built-in the voltage would drop below to the minimum required (as per the manual the 9V-10V would be the appropriate voltage at the coil while the engine is running).

If you have the correct coil yes you can rig a ballast resistor from a +12V source and connect it to the "+" side of the coil (making sure the original resistance wire is removed) and see if that solves the issue. If however you have a coil with a built-in resistor just connect a +12V and again remove the original wire.

Good luck..!
J. Gomez
CLC #23082

hotrodln

Quote from: J. Gomez on September 10, 2021, 05:52:13 PM
Pat,

I

I believe the '62 has the resistance wire from the Ign. switch to the coil and the coil would need to be the type that required "external resistor". Do you have the correct coil?

If you have the resistance wire with a coil that has internal resistance already built-in the voltage would drop below to the minimum required (as per the manual the 9V-10V would be the appropriate voltage at the coil while the engine is running).

If you have the correct coil yes you can rig a ballast resistor from a +12V source and connect it to the "+" side of the coil (making sure the original resistance wire is removed) and see if that solves the issue. If however you have a coil with a built-in resistor just connect a +12V and again remove the original wire.

Good luck..!
OK so i bought an external resistor that was rated for 1.5 ohms. ( and yes i do have a full size wire diagram for the car) i ran 12 volts to it...when the car is running the voltage going to it is high 13's.....out the other side is about 11 volts....the car runs good like this...unlike before when i had 6.6 at the coil...but the book says it ought to be 9 volts...so is 11 going to burn up my points?
Pat Prendergast

bcroe

Quote from: hotrodln on September 22, 2021, 08:58:40 PM
OK so i bought an external resistor that was rated for 1.5 ohms. ( and yes i do have a full size wire diagram for the car) i ran 12 volts to it...when the car is running the voltage going to it is high 13's.....out the other side is about 11 volts....the car runs good like this...unlike before when i had 6.6 at the coil...but the book says it ought to be 9 volts...so is 11 going to burn up my points?

The objective is to limit the max points current, to nominally about
4A.  You could get a handle on that, by getting the crankshaft into
a position where the points are closed, then turn on the key and
measure the voltage across your 1.5 ohm resistor (the original
ballast is disconnected).  Using ohms law, I = E/R or current =
resistor voltage divided by resistor ohms.  So if you measure 6
volts across 1.5 ohms, the current is 4A.  Increase the resistance
ohms to decrease the amps. 

This only works with the engine stopped, you would need an Oscope
to measure the peak with the engine running.  However the bat
voltage might increase a bit with alternator input, expect the static
measured current to increase in direct proportion.  Bruce Roe

J. Gomez

Quote from: hotrodln on September 22, 2021, 08:58:40 PM
OK so i bought an external resistor that was rated for 1.5 ohms. ( and yes i do have a full size wire diagram for the car) i ran 12 volts to it...when the car is running the voltage going to it is high 13's.....out the other side is about 11 volts....the car runs good like this...unlike before when i had 6.6 at the coil...but the book says it ought to be 9 volts...so is 11 going to burn up my points?

Pat,

The logic is the ballast resistor would have to match with the type of coil and vice-versa.

Ballast resistor as well as resistance wires very on the total resistance that the coil would require these range from 1.5 to 2 ohms (or possible higher).  I'm not sure what would be the total resistance the "resistance wire" on the '62 would be maybe someone can chime in so you can match it via a ballast resistor.

Check your ignition coil has a primary resistance of between 1.5 – 1.7 ohm with the ballast resistor of 1.5 ohm the drop would be in the range of 8-9V. Also not sure how accurate your voltmeter may be but 11V is a bit too high of a reading "IF" the coil is the correct one and in good working order.

At least you are getting closer, so good luck..!  ;)
J. Gomez
CLC #23082

hotrodln

ok this may sound dumb...but i have been measuring the voltage at the + side of the coil...should i be measuring it on the other side?
Pat Prendergast

V63

#12
You might want to verify that your Existing coil is correct EXTERNAL resister (OEM correct)  or INTERNAL resistance.


Couldn't hurt to verify your engine has a good ground and all your connections are clean. I want to say 1962 still had external ceramic ballast resister on the fire wall? I had a few 1962's but too long ago to remember that detail.

35-709

There should be no ceramic resistor on a '62 --- last year for those was '58 or '59.  The resistor wire, which your car should have, runs from the firewall to the coil, on the other side of the firewall the resistor wire is connected to the pink wire coming off the ignition switch.  11 volts is too high.  In your list of things you have already changed out, you mentioned points but not the condenser, faulty condensers can cause all kinds of running problems.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

jackworstell

#14
This issue comes up often .....and the questions are always the same...
external resistor or internal resistor.....ballast or resistor wire or no resistance other than the coil
primary winding...
.correct voltage and where to measure the voltage  etc etc etc

Bcroe's comment cuts thru all of this.....when you have about 4 amps going thru the primary circuit
with the engine running...that's it and go no further

If I run into this problem and have a 12V car with coil/condenser/points
I would start by checking the resistance of the primary coil of the coil.
If  about   1.5 ohms.....I would add about 1.5 ohms to the circuit  ie  ballast or resistor wire
Or if about three ohms...I would try the coils as is.

Then insert an  ampmeter in the primary circiuit  and check amps
to see if about 4amps.   If much higher amps add resistance to the circuit
to reduce amps....using ohm's law as bcroe said.
If much lower than 4 amps...remove resistance in the primary circuit..that is
.....reduce ballast or reduce resistance wire or get another coil with lower primary resistance
....again use ohm's law to figure out how much to remove.

HOWEVER...if not enough amps...the very first step is to check for poor connections
as   a  possible cause of low amps.

I've tinkered with coils a little...the best I can figure out is that coils for
6V cars usually have about 1.5 ohms in the primary winding of
the coil...and do not use external resistance....neither ballast nor resistance wire

Coils for 12V cars either have primary winding resistance of maybe  3 ohms 
...or   about   1.5 ohms ...in which case  and use external resistance ( ballast or resistance wire )
to bring total resistance in the primary circuit  up to about 3 ohms

It seems to me that "6V"  coils    can be used with 12V  cars so long
as external resistance  ( maybe an extra 1.5 amps) is added to get the amps to the 4 amp target

I run into two practical problems in dealing with coils
First of all....there's no way to really test them  The resistance
of the primary and secondary windings can be checked but this
doesn't tell the whole story   eg   no way to check for insulation break down under load
Second issue...most VOM instruments I have come across can't accurately measure
low ohms down in the single digit range

I've changed out a number of coils over the decades.  I can't rember a single instance where
a coil was causing an ignition problem.  Maybe a few times I
found wrong primary circuit resistance and hence wrong primary amps
I always check connections first   then dwell and timing...then condensers   then   points   and  last,....the coil

No doubt others may not agree with some of this.   Have at it...I'm not
an electrical guy....but a lot of experience  with old cars

Good  Luck     Jack Worstell

CORRECTION...after reading bcroe's post again...I made a mistake.  Check for 4 amps with points closed and  engine  NOT running
Read  bcroe's post above.     My error
I would made one change from his method...put an ampmeter in series in the primary circuit to measure amps

bcroe

An ammeter works fine, it is just more trouble to connect.  Bruce Roe

35-709

In my half-vast experience over the years, I have had 3 coil failures.  One a complete failure where a car that was running well the night before would not start in the morning ('62 Cadillac, less than 10,000 miles).  The other two (a 1951 International Harvester van and a '60s Rambler wagon) would run fine cold but fail when the coil got hot.   :) 
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2