Spending a little time in the vast fields of the Internet, I found the website from which the “boom” of using B58 ignition coils in older/other engines has originated.
Allow me to post a copy of the image from the test results:
Note: the image above is the property of user “bahn”.
The used has serious equipment: a modern oscilloscope, FLIR thermal camera… But I will pour a few drops of tar on this topic.
a. a fundamental objection – the ignition coils are tested with different dwell times. This is FUNDAMENTALLY incorrect! Of course, a longer dwell time (till the moment when the magnetic material of the ignition coil gets saturated) increases the energy accumulated in the ignition coil. In addition, this dependence is exponential (simplified, not taking into account the resistance of the primary winding of the ignition coil); it means, for example, by increasing the dwell time by 10%, the accumulated energy increases by even 21%. Accordingly, for example, if the excellent B58 ignition coil, with its dwell time of 3.2ms (used in the test), is installed in the N54 series engine, which uses a dwell time of 2.5ms, it will indicate a much more modest gain. Dwell time will be around 28% shorter, and the accumulated energy will be around 60% lower than in the test. We see it in the test, too, for example, with the Bosch B58 ignition coil (comparing energy with 2.5/3.0/3.2ms dwell time). Dwell time (and, accordingly, energy) will be limited/defined by DME, in which the ignition coils are installed!
b. there is no such “magical” energy that is released by the ignition coil. To release larger energy, larger energy should be accumulated. Larger energy means larger (average and peak) current during dwell time. It is indicated by the test result, too. Ipeak of lower energy ignition coils is 6 .. 7A; for more powerful – reaches 15A;
c. in the test, an idealized load model is used. In real-life conditions, IGBT works in the “clamp” mode – directly after closing (and while the spark has not yet formed), Uc grows uncontrollably, reaches Uclamp, and IGBT opens repeatedly (its Overvoltage protection system is activated). This “clamp” mode SIGNIFICANTLY increases the work temperature of the IGBT. This test is NOT CORRECT – it does not reflect the actual load/temperature of the IGBT;
d. the idealized load does not take into account the maximum allowed energy/inductance/current vs. temperature (indicated in the Datasheet of the exact IGBT) in the “clamp” mode. Exactly the “clamp” mode problem poses the greatest threat – IGBT can get damaged even without overheating or not overreaching its Icmax. Regarding this and the “clamp” problem, read here;
e. in the test, the 14V voltage source is used. The onboard voltage of the BMW vehicle can reach even 15V (during colder weather and in Overrun modes, when from the alternator, a 15.XV high voltage is required). This increase is around 7%, and the increase of the accumulated energy: more than +15%. Such an overload has to be taken into account by evaluating the IGBT load;
f. in the test, the IGBT temperature reaches around 70oC, but here we have to understand: it is +50 oC against the environment temperature; it is one transistor. In the actual conditions, DME itself is in the conditions of increased temperature; 6 pieces of IGBT are placed one by another (6 times larger scattering power in a small area);
g. the author does not take into account that MSD80 and related DMEs use multi-ignition. In the range of low/average RPM is even one + FIVE sequential discharge impulses – all in “clamp” mode (read here)! In addition, the ignition coil energy is not fully released, which means – dwell time/energy will continue/partially sum up. By using “more powerful” ignition coils (with a lower inductance of the primary winding), this mode leads to saturation of the ignition coil and abnormal load to the IGBT!
h. the author sees/measures a very optimistic thermal profile of the ignition coils but does not take into account multi-ignition and the obstacle that the ignition coils are in entirely different environments (as during tests). In real conditions, the temperature of the environment of the ignition coil can be even 100 oC or more (for example, the situation with B58, read here), which means: EACH oC increase can be critical! In addition, the B58 ignition coils also indicate a very swift temperature increase (much swifter than other ignition coils). It goes without saying: in the case of a similar efficiency ratio, the more powerful ignition coil will heat up more. Unfortunately, kits do not take into account these obstacles, and no thought has even been given to cooling the ignition coils;
i. based on all this, I’m amused with the comparison of Bosch and ELDOR ignition coils. As I already found out here, Bosch is the same ELDOR, only with the Bosch label. Yes, the ELDOR codes are different, but the ignition coil (primary winding) parameters are very similar. As we see, the test confirms – the accumulated energy is practically 1:1 for both ignition coils.
I know that I won’t talk anyone out of using the B58 ignition coils in older engines. This “miraculous solution” is too tempting. The only thing I suggest – gentleman, use snubbers! What is that, and how to use it? Read here and here. Snubbers ensure that IGBT does not work in “clamp” mode:
a. reduces heating of IGBT;
b. reduces uncontrolled Upeak knockout, and the work life of the ignition coils is prolonged.
The second important nuance – install fuses for your “mega” ignition coils! Read more here.
Note: for different dwell time and ignition coil combinations, the nominal correction of the snubber elements could be necessary.