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Ignition for Old Cars

P.V. Vinod Kumar

In older carbureted cars, the con-tact-breaker (CB) point ignition system is used to fire the spark plugs. You ca

convert the ignition system of your car from CB-point-cum-condenser type into electronic using transistorise

sitching. !he circuit of the electronic ignition coil is shon in "ig. # and its electrical connections in "ig. $.

Fig. 1: Circuit diagram of ignition for old cars

In "ig. #, hen the CB point is open, both transistors !# and !$ are cut-off and no current flos through th

ignition coil. %n closing the CB point, transistors !# and !$ conduct and a very high current flos through thignition coil. &s a result, very high voltage develops in the ignition coil to drive the spark plug. & red ' ('#

glos to sho the pulsing action of the CB point. Ballast resistor *+ ($.$-ohm, #) limits current through th

ignition co

!he green ' ('$) connected in the output section lights up ith back emf and therefore it should b

connected ith reverse polarity as shon in "ig. #. se a proper heat-sink for poer transistor C//$/ (!$

In "ig. $, the ignition coil is shon along ith a condenser and 0! to spark plug1distributor connection. !h

condenser is not re2uired for electronic ignition. %ne pin of the CB point is already grounded and the other pin th

goes to the ignition coil needs to be isolated. !his pin is marked as 345 in the diagram and senses the input

electronic ignition.

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