John- I fully appreciate your classroom just now. If you don't mind I would like to share that with my friends on the Corvette forum. We argue about this all the time. GM cars I'm familiar with short the ballast or resistance wire in the crank position. Best Danny Plotkin Sent from my Verizon, Samsung Galaxy smartphone -------- Original message -------- From: John Grady <jkg@xxxxxxxxxxxxxxxxx> Date: 6/23/22 8:30 AM (GMT-05:00) To: Ray Melton <rfmelton@xxxxxxx> Cc: dplotkin <dplotkin@xxxxxxxxxxxxxxxxxxx>, 300 Club <chrysler-300-club-international@xxxxxxxxxxxxxxxx> Subject: Re: how ballast resistors really work (advisory (again) 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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