BALLAST RESISTOR........WHAT GIVES?

i agree, ballast resistor is a ressistor that gets more resistant the hotter it gets. thet are delibertly like this. As apposed to a normal resistor where that behaviour is still presant but is delibertly reduced so its resistance doesn't change when its operating at the temperature range its intended to be used at. a tube radio would never have worked if all resisters in it were balast resistors the circuit specification would be different at every different temperature


Balast used in the igntion circuit so that it gets hot and is higher resistance when you are drving at 20 mph. A time when the points are closed for a long time, it limits the current more when its hot to help moderate coil temperatures, and it gets hot when current flows for long periods. Driving fast cools it down..because the coil is on and off faster and current flows through the balast for shorter and shorter periods of time which is the prefect time to allow a higher current to flow in the coil, you need to build the same magnetic field in a shorter time period, increasing the flow of charge makes sense, and thats what happens when the ballast cools a bit. its resistance to the flow of charge decreases.

the capacitor is there to sink some of the back EMF to help reduce some of the arcing at the points. it stops a big spark at the point between closed and just open. if it did this job perfectly the point contacts would never pip and hole and they'd only need replacing when the fibre foot wore out....

basically when the primary is switched off the magentic field in the coil collapses and the faster it collapses the bigger voltage and current you see at the secondary... nice big spark
but that field is also collapsing around the primary winding as well
voltage in the forward route through the primary built that filed..
so when it collapses you get a voltage the oposite way trying to push back along + wire and suck charge from the - its a back EMF and if its allowed to flow its sucking up energy from the field collapse that would be better used for making a spark on the secondary side

switching speed of points with condencer is fast enough, it works and has done for 100 years. The condencer is there to gve the points a reasonably long life

BUT
that set up is not as close to a stop-dead switch off, of the coil. As a transistor or semi conductor based switch is, becasue the points arc under their 3 amp supply when just apart, and then the condencer needs to fill with charge from the back emf, stopping an evenn bigger arc across the now bigger points gap. if the back emf is flowing in the primary its conflicting and fighting againts the flow in th secondary which is diminsihing the spark power produced by the secondary

so the mopar box providses faster switching and eliminates points but doesn't address the low current design limitations bceaue its still the same old 8volt coil
the petronix provides faster switching but doesn't address the low current design although it does avoid a big external box
the HEI with HEI coil addresses the low current design limitations, the coil can be built with low resistance and different winding ratio to really take advantance of the current
that core made of steel laminates really does hold a bigger feild and crams in more lines of flux in and around the coil

it addresse the failings of the old style igntion set up by being an excessivly large hammer to crack a reletivly small nut

doubling the current doesn't double the magentic field strength it increases exponentially its like 2 and 2/3 as big
the module switches fast and can block up to 400V worth of BACK emf before it sinks it to ground i.e OFF is OFF quicker than with points and it looks much more like totally OFF at the point when the spark starts...points can't do that becasue the condencer is empty it needs to fill up, initially while a few degrees of distributor rotor swing by to allow the points to open wide enough to avoid an arc. while its filling/chargeing up a current flows on the primary side , as it charges the condencer and that has a detrimental effect on spark power.
the spark starts later on, into the period of time it takes the feild to collapse so it wastes the first bit of that collapse.

a car with a busted condencer won't start if the foil in the condencer burns its insulator and shorts out to the inside of the can. i.e it fails with a short circuit rather than an open circuit. its just a Jelly roll /swiss roll of 2 strips of foil rolled and seperated by plastic sheet and shoved in a protective can.
not all condencers are there doing the job of a condencer. A different size of capcitor is sometimes used to suppress radio interance... which would have made a right mess of any AM station you were listening to
no real imapct on FM but might mess with digital i.e music or ecu or computerised race tools/dash....

if the radio supressor fails it can also mean your motor won't start.
a radio interferance supressor is probably more approproate when using HEI.. i have no radio and no supressor...less to go wrong

Dave