Hi Can you tekkie guys please help out I have recently fitted a electronic ignition system to my dino. It works really well but.....after about 10 miles the engine startss to miss badly. I checked all the connections and noticed the coil was really hot (57 deg c 135F). So i let it cool down and it is fine, until it gets hot again then the missing reappears. the Bosch coil which came with the kit has a primary resistance of 0.8 ohms and with a coil voltage at the + terminal of 13.9v (according to instructions no ballast resistor must be fitted) The controller is supposed to limit the current to 10amps. Tried another Bosch coil, 1.8omhs resistance and again 13.9 volts on the coil when revved to 2500rpm. Still gets really hot but no missing, did over 250 miles over the weekend and didnt miss a beat. Checked voltage regulator and it seems OK (12.75 volts on the battery @0rpm & 14.5v @2500rpm.) so no excessive spikes to worry about The coil dwell time is set at max 6.1m/s and 0.5m/s min any ideas what could be causing the coil to get this hot........Is this normal,?
Yes they came in the kit. seems like the coil is being driven too hard, but why? Is it the dwell time, resistance of the coil primary circuit, current, charging circuit too excessive for the modern electronic ignition or is it just me!!! 10amps for a TCI system seems excessive to me,so does a overactive charging rate of 14 + volts (ferrari state 14-14.2v) I have been told by the manufacturer that if the current is set to low a much reduced spark will be the end result. a coil running at 57 deg C will undoubtly fail in the short term. Kit consisted of:- 1- distributor with hall effect sensor 1- Wiring loom 1 -Controller 1- TCI Bosch coil 1 - Set HT leads 1 - Set Grommets and replacement brackets 1- Relay
Tony, you must be an engineer or think like one. Yours is a very well written, concise, and informative post. Now, let's attack the problem. If you, indeed, measure 13.9 volts at the + terminal of the coil, and you measure DC resistance of 0.8 Ohms, then you will find that the current flowing through the coil (using direct current calculations as a first approximationi) will be close to 17 amps! I understand that the CD system is designed to limit the current, but it is not accomplishing this. The voltage measured at the + terminal is the product of the resistance of the primary and the current flowing through it. Hence, 0.8 Ohms divided by 13.9 volts results in 17 amps. Now, I have made some rather gross approximations. First, this is an AC system. The impedance of the coil will result from the sum of the 0.8 Ohms and the impedance of the rather large inductor inherent in the coil of wire. What is unkown is the number of Henrys of the coil. Once known, one could model the system as a RLC (minimal capacitance) circuit and calculate the current flowing. All of this is rather academic, and unnecessary. Coils get hot. That you solved the problem by substituting another coil speaks for a defective coil on the first go-around. I would not doing anything further at this point. If the 2nd coil fails, then the Celestial Design Committee is sending you a message. Jim S.
Thanks for that jselevan, yes i am an engineer. Is clairvoyancy a specialist subject of yours!!! Thanks for your help, guess i will always carry a spare coil as i dont trust the damm thing anymore Cheers Tony
