Coil manufacturers and suppliers like to quote voltage
this coil is a 50KV coil and its painted red with lightnigh bolts and stuff
but they don't back that up with anything useful
that 50KV would only be produced if the plug gap and the environmnet the plug gap was in happend to be very resistant to allowing a spark to propagate.
in the real world your plugs arc at anything from 7kv up to about 20KV
dictated by
plug gap
rotor to cap contact gap
and how many molecules and atoms are wedged between the plug contacts.
at that voltage stays more or less the same throughout the duration of the spark...once it starts the voltage doesn't get bigger
the higher the CR the more atoms and molecules you have wedged in the space betwen the plug contacts and the harder it is to rip off the outer electrons and make them flow through space
i.e you are making a plasma, a gas of atom nuclei sourrounded by a mist of oarfaned electrons.
so quoteing 50KV means nout much other than the insulation in the coil is good enough to support 50KV without breaking down
Primary resistance is key here...
old coils for points were either 1.5 ohms or more
or 0.5 ohms
you used the 1.5 ohm coil without a ballast resistor becasue it already includes a 1 ohm of resistance in the coil on top of the nominal 0.5 you get by winding half a mile of thin copper wire around a hunk of iron
the 0.5 ohm coil was a coil that ran for most of its life at 8V not 12 volts
it saw 8 volts only bacasue the ballast resistor dealt with the spare 4 volts by getting hot....
with only an 8 volt push the lower resistance of 0.5-0.8ohm was fine and the coil stayed happy, there were benefits related to frequency which is linked with RPM and some benefit to points life.
basically a coil has a different resistance at 1000 rpm to 200 rpm 4000 rpm etc due to a whole shed load of interacting stuff which gets lumped into a bucket called impeidence
modern 12 volt no balast resistor coils can have that low 0.5 ohm resistance and survive with 12 volt supply
and your switch in the circuit for this kind of coil is no longer a set of points or big transistor both of which would be destroyed if more than 3 amps flowed through them
its an HEI module which in theory will regulate the current through the primary to what it can handle
anything between 4 amps and about 6.5
thus
more current in primary= fatster magnetic flux build up in coil...so your dwell can be shorter for the same spark or produce a bigger better spark
and low resistance in primary and secondary lets that magnetic field collapse faster when the coil swicthes off.
Magentic field round the coil reaches out into the universe infinitely far when the coil is on
it collapses back into the coil making voltage and current when you switch it off less resistance makes it do this faster
its like putting a much wider plughole in the bath
back on track....
thus the rise time for the spark is reduced
and it has a larger current component
current is important
spark energy in joules is current x voltage
in watts its current x voltage x time in seconds
so you can achive the same energy with loads of current and little voltage or loads of voltage and little current
10x1 is the same as 1x10 if you catch me drift
but what you need is a voltage that easily makes a plasma for your plug gap, and combustion chamber environment, for your RPM range which we'll say will be no greater than 7000 rpm
more current in the mix makes the spark more robust
take off a nylon jumper and hear sparks of 20 KV click in your hair
very high voltage very little current. nobody got a life threatening shock off a jumper unless it was garish and the only piece of attire you wore down the pub
an arc welder is putting out couple of hundred volts at anything from 30 -200 amps
it melts steel.. if it electrocuted you it would burn through the flesh to the core of you bones and you'd be scared for life right through like blackpool in a stick of rock
a car battery at 12 volts and 240 amps can melt a 13 mm ring spanner
so getting a good whack of volts in the spark and with added bonus a bit more current
is a very good thing
HEI conversion is popular in australia on LPG converted classics
LPG cars that never run on petrol often have static CR in the 12-15:1 range. and LPG is hard to set-off
if an HEI with propely gapped plugs and a decent coil can be used for that....you'll have no problem
of course the same kind of thing can be achived with an MSD 6AL or MSD skys-the-limit, but not for so little time and money
whack it in
standard plugs
standard plug gaps
see how it goes
open plug gaps a couple of thou see how it goes
falters farts timing a mile out and runs bad at high rpm then you have your trigger wires back to front or you forgot to bypass the ballast and the module is trying to do a 12volt 7 amp job on an 8 volt supply
Dave
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