There is so much incorrect information and strange opinion floating around about the ballast resistor , I thought an explanation might help.
Some EE needed —but easy .
Every coil has a characteristic called time constant , set by L over R . The time it takes to fill the windings up , —is how to think of it . No matter what you do it comes out around .005 sec . R is resistance of the primary coil wire , L is inductance , a measure of energy stored in a magnetic field , related to the number of primary turns . More turns changes L upward ( more time to fill it) as the square of the turns , but R then goes up too , dropping the current you can draw , Also wire gets thinner then for same physical outer size Coil = Even more ohms . Less power , despite higher L . . Less ohms in primary requires fewer turns, drops L which is the power store . So no free lunch here. All this was settled / optimized by 1930 , why coils are the size they are . Messing with any parameter trades in a bad direction , unless selling snake oil claims .
Both R and L go up together with a physically larger coil — and then you do have more energy . Some Mallory coils went this way . So rule 1 = only real way to get “more spark “ is a larger bigger heavier coil . ( it is a transformer!)
But more spark is not the real problem , the problem is that .005 time to fill it —with 8 cylinders at ~ 6 k you need a spark every .002 , coil is NOT full up any more at 6000 rpm ( 1 time constant ), spark starts fading . But if you CAN add more ohms ,outside coil , note R is in denominator of L/R , time is smaller it fills faster ! If end full current fill is still high enough with added R ( around 5 -7 amps) —called coil saturation current , full power happens~ .005 after start .
If you did not have R , it will fill as fast yes but end current it reaches in auto spark circuit would be twice as much , it will go beyond 5-7 , maybe to 15 (!) and so trying to overfill winding will burn up coil or points . All known . When 12 v came in , some very good engineers added a special resistor to essentially a 6 volt coil, ( coil was fine , already optimal) to cut that “fill up “ time by a lot, as note total R with a ballast R added is ~ doubled . And as that full current only actually appears .005 AFTER points close , only then does the ballast drop action starts . But coil is full then !
Why is ballast a special R ? It is iron wire — when cold it has low ohms , about .5 and stays low at high rpm . But at idle each spark still only needs .005 —but points are now closed 5x that long , so current would go way too high trying to over fill for each spark at low rpm . Now the iron wire gets very hot and R of ballast goes up maybe to one ohm . Limits coil draw . AT IDLE Note measuring drop etc and saying anything about that number is totally meaningless in all this , as it depends on rpm, dwell etc .
By controlling dwell by adding electronics ( HEI or Pertronix etc ) you can shorten that dwell at idle / low rpm by delaying the start of coil fill ( but a ballast does same thing ) , and so eliminate ballast cost , but over 5k or so —all else equal — they are close to the same spark ( despite BS ignition co marketing claims ) So Danny is right .
Shorting it at start as mopar did for a while gives a stronger spark when battery volts drop during crank but no one else did that . And their cars start fine . Your call .
Even more important consider that electronic ignitions will lose 1 volt in the transistor switch , points will lose zero . As circuit spark current ( a full coil ) is driven by volts , energy in spark goes as the square of the coil supply volts , so we have 12v = 144 , 13 sq = 169 . One hell of a lot more relative spark from points !
And why you see drag race 16 v batteries . OK for a short time .
As far as reliability , you walk when Pertronix or MSD punts . Maybe a very long walk at night . Matchbook and screwdriver I drive on . But points do have to be set perfectly , tight distributor and especially a good capacitor not chinese junk. And they are fine for 20 k miles at least , after initial wear in , if golden screwdriver stays in pocket
So alternate realities around what ballast does , are just that .
All this was driven home on dyno for me one day ( the MSD punts, while another guy’s 300 B motor is on dyno —MSD punt “ Happens all the time” per dyno guy ) we swap on a stock B distributor , we get exact same 380 HP right to 6000 . He was amazed ( being a single point Chevy guy)—the dual points still give us that .005 (?) at 20 % more rpm due to higher dwell of dual points before spark fade .. much more dwell than single points . Why our cars went 140 mph .
Imho , 85% of the problems claimed around points are the capacitor . Or inept setting without a dwell meter . Just mho .
Remember the 64 Daytona ,1234 hemi , dual points , win. Chrysler knows more than MSD . And a second too late spark is good for what ? Not much ..
John
Sent from my iPhone
On Jun 10, 2022, at 5:30 PM, Ray Melton <rfmelton@xxxxxxx> wrote:
If using Pertronix, also remember that per instructions in every
Pertronix box for the last five years, you MUST use resistor-core
RFI-suppressed ignition cables (including coil wire) or else the
Pertronix unit is prone to premature failure due to the high RFI
produced during every spark. After direct conversation with a
very patient and helpful Pertronix representative a few years ago,
I clearly understood that the coil MUST be fed constant 12v; the
ballast resistor was intended to reduce sparking and erosion of
the points by enabling full 12v for the short duration needed by
the starter; thereafter, the points were operating only as a
switch and could easily function on the reduced voltage out of the
ballast resistor while reducing spark-induced pitting/erosion of
the points.
I custom-made black 7mm stainless steel spiral-wound ignition
wires from scratch to maintain stock appearance when installing a
Pertronix while restoring my late father's 1957 300C. Also used a
high-voltage, low-resistance coil recommended by Pertronix to
match their module, plus modern fine-wire Iridium NGK spark plugs;
now have near-instant starting, sometimes less than one engine
revolution!
No more trying to adjust persnickety dual points in the
impossible location on the 392 Hemi with the distributor up
against the firewall! No more incessant (often very creative and
physically impossible!) cussing, back-and-forth testing with dwell
meter and risk of scratching the fender, etc.!
Ray Melton Las Cruces, NM
**********************************************************************************
On 6/10/2022 1:22 PM, dplotkin wrote:
Among the problems with diagnosis of old car
running problems is that a problem such as a rough idle can be
caused by a multitude of causes. Chief among these is a vacuum
leak and I would begin there.
I understand many have luck with Pertronix and
similar substitutes for breaker points. These are in my opinion
one size fits all solutions to problems that don't exist.
Properly installed and adjusted breaker points
available at NAPA will last our average tenure with the car. Yes
electronic ignition is far superior to that of breaker points.
But that does not include some of the one-size-fits-all under
the cap substitutes that offer poor heat rejection and often
fail without notice on the Road.
If you insist on using pertronix make sure your
mechanic realizes that in most cases the quail must have a
ballast resistor in its primary circuit but the module itself
must be fed directly from the battery or ignition switch and not
through any ballast.
Danny Plotkin
Sent from
my Verizon, Samsung Galaxy smartphone
-------- Original message --------
Date: 6/10/22 2:36 PM (GMT-05:00)
Subject: {Chrysler 300} 1964 300K Idle
I have a mechanic who has not been able get a
smooth idle for me, I replaced the distributor with a pertronix
2 times, put back original distributor runs better, put in new
Edelbrock carburetor, fixed intake manifold vacuum leak, also
ammeter needle jumps when rough idle occurs, was worse with
pertronix. Thanks in advance for any ideas on this issue.
Harry Torgeson
971-221-4699
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