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Back EMF from coil..
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Posted by HR on September 02, 1999 at 17:16:13 from (207.115.63.29):
All: I was busy today and missed most of the notes on were to put a resistor in a circuit earlier. I just want to add that when the coil is working there is a STRONG kick back caused by the spark arcing the plug and thus taking the secondary voltage down towards zero. This very rapid change across any coil secondary will cause a big change across the primary.. Could be a couple hundred volts kicked back across the primary and this may determine where the best place is toplace a resistor toprotect other parts like points.. This kick back from the plug firing will be only millseconds long but its enought to burn points.. So its a "hidden" problem that may not meet the eye at first glance.. There is a lot of energy being kicked around that coil just a small fractionof a second before & aftert the plug fires.. some old shops had a visual means to show this with a video display.. One could see the voltage spikes..which were very big in some units.... harvey
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