Help - Ignition Coil Questions???

Wondering about the actual differences in
6V and 12V rated ignition coils and also
the difference between coils for point-type
and electronically-triggered ignitions

1) First , for points type ignitions, the
difference between 6V and 12V rated coils.
If I understand things correctly, the only
difference is the internal resistance of the
coil, with 12V coils having a higher internal
resistance to limit the total current draw
across the points to to about the same
current draw as that of a 6V system
running a 6V rated coil . Is this correct?
Also, how much current across the
points is considered acceptable? Would
running a 6V rated coil on a 12V system
without adding a resister to the coil to
reduce the current draw, cause the
point life to unreasonably short?

2) Second what is the difference between
ignition coils used in point-type and
electronic ignitions? I'm ^guessing* that
points-type coils have a higher internal
resistance than coils intended for use
with electronically-triggered ignitions? Is
this correct? Are there any other
differences? Will (or how well will) a
standard ponts-type coil work on a
electronically-triggered system?

3 (And one of the reasons I'm asking all
these coils questions!) Who here is familiar
with the '40-'50's and early '60's vintage
finned Delco-Remy coils? (see attached
pics) These things were used on various
heavy-duty truck, military and industrial
applications over the years, came in 6V
and 12V versions. Does anybody know the
resistance numbers for these coils - either
6V or 12V - and if one could be used with
a modern-day electronically-triggered
system? If so, what would the results
be? 'Back in day - circa early 70's, I used
to hunt for these heavy-duty Delco 'truck"
coils in the boneyards and used them on
several points-triggered cars and on a
ponts-system anyway, besides looking
absolutely killer, the spark output of them
was phenomenal too . Proof of that for
me, was on the built, solid-lifter 283 in my
64 Chevelle, shifting it at at 7000 rpm,
using a standard GM coil, the car ran best
with the plugs gapped at .028, - but with
a finned Delco truck coil, I could open the
plug gap up to .040 before the ET and
MPH would start to fall off, so I know
these coils can put out some serious
spark!


Mart3406
=============================

 

btt

 

I guess timing is everything, as i just happen be working on the handout for Bubbas Ignition cl*** in Indy next month.
Your post is a big one and i will attempt to answer in sections , lets start with the first one...

1) First , for points type ignitions, the
difference between 6V and 12V rated coils.
If I understand things correctly, the only
difference is the internal resistance of the
coil, with 12V coils having a higher internal
resistance to limit the total current draw
across the points to to about the same
current draw as that of a 6V system
running a 6V rated coil . Is this correct?
Also, how much current across the
points is considered acceptable? Would
running a 6V rated coil on a 12V system
without adding a resister to the coil to
reduce the current draw, cause the
point life to unreasonably short?

Actually there are serveral design differences between six and twelve volt coils from windings to primary / secondary turns ratios etc. So lets do the discussion with 12 volts and make the math easier and a little more up to date. ( although the discussion would be the same with six volts as well)
Lets use this example of a system:



Using this system ( a series ignition circuit) one answer is how much voltage should be at the points ??? The answer is almost ( not really) zero!!! The circuit resistance should burn up and use up all of the 12 volts. The ballast ressitor drops six volts and the ignition coil drops 5.9 volts leaving .1 of a volt to cross the points and even that should be dropped by the final primary lead into the distributor.
Now that all the voltage ( electrical pressure is gone, lets talk about current ( electrical horse power) .
If the resistor is 2.0 ohms and the coils internal resistance is 2.0 ohms , system resistance is considered to be 4.0 ohms.
4.0 ohms divided into 12 volts would be 3.0 amps ( approx the comfort level of the point system.)
Now start the engine and lets let the system battery be charged at 14 volts. The aditional voltage would be eat up by the heat generated in the resistor and ignition coil including the small gauge finely stranded calibrated lead wire, to again allow a 3 amp current level across the points. OK with that part ???

Now lets create a problem!!
Lets say that Hot rodder "A" just attended a swap meet and bought a new ignition coil with less resistance !

Pick one .....(these are ones that we often use)



Lets use the 8145 Acell unit at .7 ohms primary ressitance....
Resistor is 2.0 ohms and coil is now at .7 for a total of 2.7 ohms...divided into 12 volts = WOW 32.4 amps Points are doomed for sure now......

This is very typical of what we see every day......systems must be calibrated with correct components.........
More later.... comments , questions etc ????????

 

Ok , part two:

2) Second what is the difference between
ignition coils used in point-type and
electronic ignitions? I'm ^guessing* that
points-type coils have a higher internal
resistance than coils intended for use
with electronically-triggered ignitions? Is
this correct? Are there any other
differences? Will (or how well will) a
standard ponts-type coil work on a
electronically-triggered system?

I kinda answered that in the above example.
Each and every year the oem has been looking for stronger spark out put as well as quicker rise time of the coil saturation and build up..A pretty typical late ignition will use a coil thats approx .5 ohms primary resistance
The oem use a current limiting circuit that only allows a set amount of coil rise time and current levels .
Ex: The GM 4 pin HEI control module allows the .5 ohm coil to build up to 5.5 amps in 2.3 ms of time. Each firing of the coil is always exactly the same.
Now the HEI module WILL run the engine with a higher resistance older coil, however without the lower resistance ( .5) the current limiting circuit wont be reached and the ignition current will be much lower than the 5.5 amps of the .5 ohm coil..and the spark out put will be much lower than it could be...

 

Part three:

3 (And one of the reasons I'm asking all
these coils questions!) Who here is familiar
with the '40-'50's and early '60's vintage
finned Delco-Remy coils? (see attached
pics) These things were used on various
heavy-duty <NOBR>truck</NOBR>, military and industrial
applications over the years, came in 6V
and 12V versions. Does anybody know the
resistance numbers for these coils - either
6V or 12V - and if one could be used with
a modern-day electronically-triggered
system? If so, what would the results
be? 'Back in day - circa early 70's, I used
to hunt for these heavy-duty Delco 'truck"
coils in the boneyards and used them on
several points-triggered cars and on a
ponts-system anyway, besides looking
absolutely killer, the spark output of them
was phenomenal too . Proof of that for
me, was on the built, solid-lifter 283 in my
64 Chevelle, shifting it at at 7000 rpm,
using a standard GM coil, the car ran best
with the plugs gapped at .028, - but with
a finned Delco truck coil, I could open the
plug gap up to .040 before the ET and
MPH would start to fall off, so I know
these coils can put out some serious
spark!

My favorite coil for sure.
These were listed in the 1950 Delco manual as a " City Service or High Ratio Ignition Coil" and were consider 12 volt coils as they were primarly on 12 vgolt buses and city delivery trucks.
I have found a perfect fix for these old coils is to remove the old coil and place the Bosch Blue 3-4 ohm coil with no ballast resistor and have quite a few running across the country with the Grant Flamethrower Dual Coil systems. Using the 4.0 ohm resistance and a good condensor, these units have proven to run a long time with great contact point life....



Hope this helps.................

 

Thanks, very good explanation.

I am not sure if this calculation is correct, though. I get 4.44 amps for 2.7 ohms divided into 12 volts.

 

You are correct i didnt include the resistor.
The main issue is that the points shouldnt ever have over 1/2 volt going thru them..
We just tested some actual units in our Hot Rod Spark cl*** and found fro, .19 to .73 depending on the connections etc,,,

 

Is Bubba saying if you put a volt meter on the points side of the coil, with points wire off, you should only see 1/2 volt?

 

No , to see voltage drop the circuit must be loaded or in the on position. Starting at the battery the resistor would drop approx 6 volts leaving 6 to supply the coil. Then the internal resistance of the coil would drop another approx 6 volts etc....the final lead wire would drop the final 1-2 volts ***uming the battery started with 12.2 volts ..

 

Thanks Bubba. So I'm running an 8V battery, came in my old Intl 6 banger truck and in good nick. About 9V when running and charging. Using your information above it sounds like I need about a 3 ohm coil with no external resistor, sound right?

 

Yep , use a bosch blue # 0012 , great coil......

 

Bubba maybe you can answer a question. I am running a Ford thick film module and matching coil cabbaged off a 90s Ford from a junk yard.

Triggered by a points distributor in a Non Hamb Worthy vehicle *cough* 1975 Porsche 911 *cough*.

It seems to be working fine and is about 5 times better than the stock Bosch setup at 1/50 the price.

Wonder if you have any opinion of this setup in general, that is using the Ford module triggered by points in a non stock situation?

 

The Ford tfi is a good unit .........works on a lot of different stuff....

 

Bumping a very informative thread.

My Ford flathead has had a misfire from mid-throttle on up. I finally cured it today by swapping out the coil. Here is the thing: it's running 12 volt through the stock pancake distributor with dual points. No ballast resistor. I was using a 4 ohm coil as recommended above (if I'm doing it right). Today I swapped in a 1.5 ohm coil which eliminated the misfire. I then swapped in another 4 ohm coil and the misfire again occurred. All coils are used but what are the chances of the two 4 ohm coils both being bad? Starts and idles OK with them.

So where to go from here? The low resistance coil will burn the points right?

 

Bubba!!!

Today I tried a stock GM coil and ballast resistor, about 4 ohms combined. Better than the other coils but still breaking up in the mid-range a bit. Then I byp***ed the resistor, again ran great. I do have over 12 volts at the coil, but did notice the digital volt meter jumps all over when running.

I have a new Pertronix Ignitor 2 on the shelf, may have to try that, which means replacing my solid core wires. Rather not.

 

WOW , very old thread on coils etc , pretty busy with some confusion.
A 4 ohm coil with a ballast is a little low on current flow. I actually prefer a 1.5 ohm coil witha 1.5 ohm ballast for most point applications . That way the watts (heat) is divided.
Are you running positive or negative ground. If a coil has been ran positive and then switched to negative it will cut out mid range etc as the magnets inside the coil retain some polarity...

 

Bubba, you're a genious! These coils could well have been run positive ground before, came out of my giant box o coils, many from British stuff. Time to buy a brand new coil but I'll have to decide if I want to wire up a starting circuit and ballast resistor or just go with the Bosch 4 ohm and no resistor.

Thanks!

 

I am just wondering if Bubba is still in the mood for discussing coils and ignitions systems whether he could tell me/us how to match a coil to a an unknown HEI small dizzy?
There are many unbranded dizzy's around the place, some of which have been discarded simply because the owners were unable to get them running right.
It seems to me the possibility is, that it was not that the dizzy was bad, but nobody has been able to determine how to know what coil to use.
I note that Bubba has suggested that HEI coils need to be in the approx. 0.5 ohms range, but is that good enough just to select a 0.5 ohms coil and run with it or is there more science to it???

 

The issue is the module in the unknown HEI Small. For instance the Pro Comp generally use a .7Ω coil. The MSD small vary depending on the model. some use a .7 others use a .355.
With PerTronix HEI we offer both .5Ω and a .35Ω depending on the module used.

Since you don't know what you have, I would err on the conservative side and use a .6 to .7Ω personally

 

So, things are not that tricky then, if you own a HEI dizzy of unknown info, it would be as easy as changing out the module and matching a coil to the module???
How does one determine the module requirements, to know what coil to be looking for???

 

I would suggest finding some Delco SD service dealer magazines used in the 70s for training.
Just the module finction alone could take a few hours . I usd to teach a 4 hr cl*** on just the GM HEI module from GM.


ebay:

http://www.ebay.com/itm/1988-GM-DEL...ash=item1ebfdd9b4a:g:6U0AAOSw4GVYSpMp&vxp=mtr

 

Thanks Bubba, I will do a little more research now I know where to look.

 

I have a 52 216 that was converted to 12 volt. I just got the truck and while trying to clean up the engine bay I noticed the old coil is leaking. Which I think makes sense bc it idled fine but when I started driving and giving it gas it bogs down. Unfortunately the existing coil doesn't have any markings on it besides China. Anyone have a part number of something that will work off the shelf to get it back on the road? I saw your post Bubba about 1.5 with 1.5 resistance. I have not seen any ballast resisters on the truck, so I have been looking for a coil with an internal one. The issue is these sites under description doesn't always say what the ohms are for the coil just for the primary resistance. Suggestions would be much appreciated.

 

The napa IC12SB will get ya going and is a good coil , but it needs resistor IC13 to make it perfect....
The Bosch Blue #0012 is a 3 ohm unit and needs no resistor , could be the best coil ever made. Amazon has them on sale from time time.....

 

Amazon Bosch Coil
NAPA Coil

 

If a feller is running a points eliminator such as a Pertronix, though, a 1.5 ohm coil without no ballast is OK, correct?

Pertronix cautions not to exceed 8 amps. Shouldn't 14 or 14.5 volts really be used for the math, since "12 volts" is never seen in real life, in operation? Then, to be accurate, figure an ignition coil is only "ON" about 2/3rds of the time. Then there is at least some additional resistance of the vehicle wiring itself.

14.5/1.5 = 9.66 amps x .66 = 6.375 amps, well under 8 amps. Coil still gets pretty toasty after a while.

 

To answer a couple questions:
There is only one HEI ignition system and thats the orginal GM HEI from 74 to 80 etc with the large cap . It was developed due to a gov emissions law requiring the engine to stay in tune for 50,000 miles. It would in fact allow the car to run 50 to 60,000 mile but what a mess it was at this mileage. The slighest leakage of primary or secondary ignition would burn every thing up. Then the aftermarket did a terrible job of making parts for this system using a one fits all approach etc. Example" The Monte SS and the Corvete used a different module and dwell circuit controls that the aftermarket never figured out. Replace the wrong module and you had a vehicle with a misffire etc at rpm!!!!Many shops replaced the wires , cap rotor, coil ( also different) costing tons of money and not fixing the car!!!!!
Today people call about anything electronic a " HEI" and it isnt even close.... Add the fact that many parts are made off shore makes it even worse.....

I just had a discussion regarding current build up with a module manufacture engineering group and was told the module had a current limiting design and wouldnt ever see the numbers i was seeing based on igniton coil "time constants" When i asked about time constants with engine NOT running with the key on the discussion was over, i feel thats where we as mechanics do the most harm to these modules!!!! I mentioned the SD Delco manuals above , find ya one and study it. Be glad to lead the discussions.....

 

Just another note you might google Jim Linder Coil Current Ramping as i have done videos and books concerning this issue for many years....

http://www.aeswave.com/jim-linder-s-current-ramping-1-2-3-p8565.html

 

I have a silly question might be a tad off subject thou, I have a 83 gmc with 350 using internal hei coil, I want to run my coil power wire to a separate toggle switch and not off the ignition key switch and don't know what amp toggle switch to get, or if I should run a relay, if I need a fuse and if what size? Reason being, I need to be able to shut down engine with out turning key off (checking spark plug colors) also to be able to crank the motor over a few times before firing and I do alot of street driving where the engine isn't just ran for a couple mins at a time but for hours, so I don't want to heat up or burn up switches and wires. And after reading your comment about time not running with key on, I do need to be able to keep key on to read gauges etc. Any help would be greatly appreciated.

 

The factory Delco HEI is a 5.5 amp current limited distributor. So a 10 amp switch will work just great!