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:
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