Guest Vincent Posted February 3, 2005 Report Share Posted February 3, 2005 Hi Guys: I had this discussion on another BBS but maybe I can get more input here. My coil('58 TR3) gets amazingly hot because it is fixed with a metal bracket to the block as they all are.When I rebuilt the car I installed a top of the line sports coil and it lasted about 500 mile before it cooked.I am now running a standard after market coil similar to the original with no problems in spite of the heat. In the discussions on the previous BBS the consensus was that heat seems to be fatal to sports coils but not a problem with a std coil.I guess it should be noted that MG And Healy do not mount their coils on the engine block.I was thinking of insulating the bracket from the block.Also it is not a good idea to mount the coil to far from the distributor because you do not want too long an HT lead between them. Quote Link to post Share on other sites
jean Posted February 3, 2005 Report Share Posted February 3, 2005 Vincent, make sure you don't use a coil needing a ballast resistor, just use a 12V unballasted coil. There is no problem to mount your coil to the inner front wing just opposite side of the dizzy, that's what I did on my 3. You can eventually put 2 coils there,that's what rally people do. In case of overheating or failure you just plug the leads to the second coil When you remove the coil from the block make sure to keep the bolts in place and seal them off carefully, as far as I know the bolt holes go through the block, inside the engine and oil will be spilled if the holes remain open. Jean Quote Link to post Share on other sites
Andrew Smith Posted February 3, 2005 Report Share Posted February 3, 2005 Hello Jean I have an intermittent problem that I suspect is electrical, so I would be interested to learn of the symptoms that lead you to believe it is the coil overheating. Thanks Andrew Quote Link to post Share on other sites
rudi Posted February 4, 2005 Report Share Posted February 4, 2005 I have a Lucas sports coil fitted at some distance from the engine block. to be complete I must say I have a Luminition optronic ignition as well. The coil gets extremely hot. However, the temperature is such that it also gives me some concern. The location is in this case certainly can not be the cause (but no help eighter). I have now done about 2500 km with this set up, and in spite of the coil temp., without failure so far. Are the sports coils prone to failure or has it something to do with the combination with the optronic? I will install a standard coil next to the sports coil, to check if if there is any difference and keep you updated Quote Link to post Share on other sites
jean Posted February 4, 2005 Report Share Posted February 4, 2005 Andrew I din't say that the coil is overheating, this was Vincent. What I say is that a ballasted designed coil used without resitor will probably have a very short live due to overheating. Further I' m of the opinion that so called Sports coils do probably develop more heat than a standard coil as the sporting element on these coils is the fact that they produce a higher output. As a coil is a simple transformer the output is the relation of the primary windings to the secondary windings. Also the faster the coil has to work the more heat is generated and beside fitting it to a cooler location in the car the only agent to prevent the spools to burn out is the oil inside. Realize that the wire of the secondary spool is no more than the size of a human hair, isolation included. I think that after a certain amount of working cycles the isolation around the wires has deteriorated to such an extend that sparking develops between the wires what again will increase heating up of the coil. The first symptoms are that the coil fails when reaching a certain temperature and will work again when cooled down. To increase the heat input by fitting the coil to the engine block was maybe a practical, but not the most clever solution. Any better ideas are welcome :: Jean Quote Link to post Share on other sites
j-eichert Posted February 4, 2005 Report Share Posted February 4, 2005 Hallo all, to remind you of some basics: The coil our cars is electrically very simple: One end is connected to ground, the other end is connected to the battery with the distributor in between. As longs as the engine is not running, only the electrical resistance of the coil is acvtive because the contacts are closed. So a current is flowing through the coil, current mutliplied with voltage gives power (Watt) = Heat. ONLY when the engine is turning, the current through the coil is stoped for a small fraction of time. This induces a high voltage in the secondary winding of the coil, resulting in a high- voltage impulse -> Spark. To be able to produce enough power when revving high, the coil must recover very fast. Thats why the resistance of the sports coils must be lower -> more current -> more power ->heat So basicly the power loss of the coil ( -> its heat) is lower if the engine is turning faster ! (And just by turning the key, the battery will be drained very efficient through the coil) On the other hand (I'm working for a company producing solenoid valves), the typical design of coils is such, that surface temperature of 100°C...120°C are normal (60...80°C above enviromenment). This gives below 150°C core temperature, which is ok for the isolation of the copper windings. We get life times of several years by that, so thats no problem. Problems may come from - voltage to high: running on 13V instead of 12 V gives 17% more power -> 10..20°C more temperature - damage due to vibrations. - damage due to corrosion (water) through small cracks in the body. Mounting on the engine block maybe positive, because heat is transfered to the block if the coil is hotter then the block. As its thermal mass is higher, (water cooled position?) this may be an advantage compared to to a mounting an a light piece of sheet metal. Insulting from the block could be the worst idea -> You block heat transfer to anywhere Good ideas would be: - Sports coils only if high revs are used. - Place coil in the airstream from the radiator - Mounting cooling fins on the coil (OK, I never saw some, but its just an idea) Quote Link to post Share on other sites
marvmul Posted February 4, 2005 Report Share Posted February 4, 2005 Lumenition has two versions of the Optronic system : standard and Performance : the standard system, like most electronic systems and all contact points system, has a constant dwell angle : in terms of contact points system : the time ratio of closed and open contact points remains the same troughout the rev range. At high revs, the time that the points are closed is shorter, but there are more such times. Closed points = current through the primary coil = heat generated. The heat generated at high revs is very little less than at low revs. The Performance system of Lumenition Optronic has a variable dwell : the ratio between the time that current flows through the coil and the time that no current is flowing, rises when the revs are rising, to keep the spark strong at high revs (when the dwell angle is constant, the spark gets weaker at high revs). So the coil will get hotter at high revs with the Performance system, and in fact through the whole rev range, because the dwell angle is longer at low revs too and the current(ampèrage) through the primary coil is more square and somewhat higher. At least this is what the prospect says. And perhaps the higher temperature of the coil with the performance system is not relevant? Perhaps J Eichert is right : a very hot coil is normal. Quote Link to post Share on other sites
Nigel Lay Posted February 4, 2005 Report Share Posted February 4, 2005 On Keith Wilson's car (Tr2 that has been in family from new and never been restored) the coil is an original Lucas but painted black. I have had a close look at the car and I am sure it was black from new. Would this help with heat disipation? Nigel (with TS952) Quote Link to post Share on other sites
j-eichert Posted February 4, 2005 Report Share Posted February 4, 2005 Nigel, black paint is an advantage. A black surface sends most infrared (= heat) radiation compared to other colours, thats the reason why most heat sinks in elektronics are made from aluminium with black surface. If you add forced cooling, then the amount of heat transferred by the air stream may dominate. But thinking of still air, black surface is the best possible choice. Looking into the engine bay, i'm not sure if there is much airstream in that area. What about mounting a small ventilator (from a PC, quite cheap!) and let it blow in the direction of the coil? By the way: silver is worst.... Quote Link to post Share on other sites
Don Elliott Posted February 5, 2005 Report Share Posted February 5, 2005 My coil is the original one that came with the car 47 years ago. It is and always has been shiny aluminium colour. It has never been a problem. I have heard several stories of "LUCAS SPORTS COILS" in USA overheating and needing to be replaced every 3 or 4 years. They will work for a while, then they stop while driving on the road. When they cool down, they will re-start, but the time till the next failure gets shorter and shorter. Have we forgotten the saying, "If it ain't broke, - don't fix it" ? Don Elliott, Original Owner, 1958 TR3A, Montreal, Canada TR Register member since 1987 Quote Link to post Share on other sites
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