Technical Ignition Coil Secondary Spark Energy Comparison (N54/N55, B58 and PR)

bahn

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The following is an analysis between the secondary spark energy & thermals produced by various ignition coils. Secondary spark energy is the measurement of energy released from the ignition coil during the discharge event and represents energy delivered across the spark plug gap. My test setup was configured in compliance with the SAE 973-202011 standards with a modification to the measurement of secondary spark current. The modification being the use of a shunt resistor instead of a current clamp for increased accuracy of secondary spark current measurements. It is important to note that comparisons cannot be directly made between my tests and tests performed by others as conditions and component tolerances will vary. Much like a dyno, accurate comparisons can only be achieved when testing is performed with the same equipment and procedures (although I do welcome others to repeat my tests).

All tests were performed at a power supply regulated voltage of 14V with a lead acid battery inline for buffering. Dwell time was controlled by a waveform generator (simulated 8000 RPM) that is controlling a ISL9V5036S3ST IGBT as the coils tested are all “dumb” coils without igniters. The ISL9V5036S3ST is the same IGBT that is used in MSD80 DME’s and was picked to compare thermal data between the coils tested and the stock N54/N55 ignition coils. The thermal study was conducted with the IGBT in free air at room temperature (67F) with no thermal compound or heatsinking. This was done to better see the impact of certain coils and dwell times on the IGBT without having to sample data for an hour. Thermal tests concluded once the IGBT reached 160F or 260 seconds of testing. IGBT temperature was sampled every 20 seconds with a FLIR thermal imaging camera while ignition coil temperature was sampled every 20 seconds with two thermocouples.

Before getting into the data I want to mention I've found conflicting information regarding the PR coil. V8bait did a nice Primary Energy comparison between different ignition coils where it was stated the PR coil saturated at 3.7 ms and that they are rated for 118 mJ with a 3 ms dwell. I've tested these numbers and have concluded that there must have been an accident when they were published. At 3 ms dwell I get around 93 mJ from the PR coils, however at 3.7 ms I get 117 mJ. In addition I've verified the delivered dwell with an oscilloscope on my car with the PR Coil option selected. Recorded dwell times were between 4.5 ms and 4.8 ms depending on RPM which is much higher than the stated 3.7 ms. For that reason I have chosen to include PR dwell times at 3.0 ms, 3.7 ms and 4.8 ms.

There's a lot of data here to go through so we'll start off with a TLDR version before diving into it.

TLDR Version (Updated with addition of Delphi S55 & Eldor B58 01/28/2021) (Updated with addition of Audi R8, Eldor S55 & Bosch S54 02/28/2021):
TLDR.PNG


It’s no wonder there’s many high power B58’s running stock ignition coils without issue. The stock B58 coils are potent and produce significantly more energy than the OE N54/N55 coils (twice as much to be exact) and can match PR’s coils in secondary spark energy with a longer spark duration. Another consideration is the impact on IGBT temperature. The stock N54/N55 coils hit the 260 second test duration with a maximum temperature of 114-118 F. The long dwell time used by the PR coils increases the thermal load put on the IGBT with temperatures reaching 161.1 F in only 40 seconds with a 4.8 ms dwell and 164.3 F in 100 seconds with a 3.7 ms dwell. The B58 coils on the other hand provide a happy medium with IGBT temperatures reaching 160 F in 220 seconds.

I like data and colorful graphs version :hearteyes::

Inductive Secondary Spark Energy data as captured on an oscilloscope. Light blue/teal is dwell signal from the waveform generator, pink is secondary current measured at the output of the ignition coil after discharging through a zener diode load. Dark blue is primary coil current measured with an inductive current clamp. Inductive Secondary Spark Energy (mJ) is being calculated as (Spark Duration / 2) * Peak Secondary Current * Zener Diode Voltage. Spark duration is being divided by two as in most cases the decrease in secondary current is linear at a rate of 1/2. This simplification allows us to avoid having to represent the secondary current curve using calculus. Of note, the PR coils tested displayed a non-linear decrease in secondary current which will become apparent in a below graph where the B58 coil produces more energy over 3/4 of the spark event.

Bosch N54/N55 @ 2.5ms
Bosch_N54_14V_2500us.PNG


Delphi S55 @ 2.5 ms
BMW_S55_Delphi_14V_2500us.png


Eldor S55 @ 2.5 ms
BMW_S55_Eldor_14V_2500us.png


Bosch S54 @ 2.5 ms
Bosch_S54_14V_2500us.png


Audi R8 @ 2.5 ms
AUDI_R8_14V_2500us.png


Precision Raceworks N54/N55 @ 3.0 ms
BMW_PR_N54_14V_3000us.png


Precision Raceworks N54/N55 @ 3.7 ms
BMW_PR_N54_14V_3700us.png


Precision Raceworks N54/N55 @ 4.8 ms
BMW_PR_N54_14V_4800us.png


Bosch B58 @ 3.2 ms
Bosch_B58_NoR_14V_3200us.png


Eldor B58 @ 3.2 ms
Eldor_B58_14V_3200us.png

B58 (red) @ 3.2 ms vs PR N54/N55 (blue) @ 3.7 ms
B58-32_vs_PR-37.PNG


As shown above the Bosch B58 coil @ 3.2 ms dwell produces a higher peak output current, higher average current and longer spark duration than the PR coil @ 3.7 ms dwell; which is what V8Bait stated was saturation for these however it appears PR is actually using a 4.8 ms max dwell @ 14V. So what does that look like in comparison?

Inductive Secondary Spark Energy.PNG


Overlapping the secondary current for each coil allows us to visualize the difference in peak output and also energy under the curve. The PR coil (blue) with a 4.8 ms dwell generated the highest peak output energy but that energy could not be maintained and quickly decreases. The B58 (red) coil has a more linear decrease in secondary current and is able to generate a peak output energy within 12% of the PR coil (The Eldor B58 coil actually beats the PR coil for peak output energy - 01/28/2021) but is able to maintain a higher average current over 3/4 of the spark event with an increased spark duration over the PR coil.

Adding in the Eldor B58 Coil from testing on 01/28/2021
Inductive Secondary Spark Energy_Eldor.PNG


The Eldor B58 coil produces a very large initial spark current, even higher than the PR N54/N55 coils but quickly drops to output energy inline with the Bosch B58 coil as seen below.

Eldor_Bosch.PNG


Thermal Study
IGBT Temperatures sampled via FLIR thermal imaging camera.
Thermal.png


IGBT Temperatures graphed for comparison with other coils/dwell times.
Thermal_IGBT.PNG


As mentioned earlier the long dwell time on the PR coils (far left grey and yellow) creates a higher thermal load on the IGBT's than other coils at shorter dwells (even if they require higher peak current to charge the primary side of the coil). At higher dwell times the IGBT has less off-time to dissipate the heat. The B58 coil's require a shorter dwell time at higher peak current but perform better in my testing. It's important to remember the conditions of the IGBT thermal test, the IGBT is in free air without thermal compound or heatsinking (via the DME case). This test does NOT represent IGBT temperature inside the DME during normal conditions; however the temperature trend above would continue with the PR coils generating the highest IGBT temperatures of the coils tested.

Thermal_Coil.PNG


Lastly I wanted to capture temperatures of the ignition coils to see if a certain designed performed better than the other. The results were as expected with all coils following a general trend with only a few stand outs. The two standouts are from the stock N54/N55 coils at 3ms dwell and the B58 coils at 3.5ms dwell. These dwell times are above the point where the coil's core is beginning to become magnetically saturated. When the core starts to enter saturation the impedance decreases resulting in a dramatic increase in current until the coil reaches full saturation and current flatlines.

In conclusion: The B58 coil is a light, low profile coil that produces substantial spark energy over a long spark duration. The B58 coil's shorter dwell time places less load on ignition IGBT's while matching the Precision Raceworks coil in total energy delivered over the spark event.

The results of this research lead me to develop a billet aluminum bracket & components for mounting the B58 coils on the N54 & N55/S55 engines. The bracket is CNC machined in the USA from 6061 aluminum and mounts the B58 coils securely in the stock location providing ample clearance for top mount setups. Our B58 coil conversion kit (including coils) comes in at 3.5 lbs less than the Precision Raceworks kit.

To learn more about B58 coil conversion kit click here.
 

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V8bait

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Looks like you did some work! You're right about the dwell, the first scope where I gathered a lot of the data back then had some problems, dwell is closer to 4.7ms or so depending on voltage. I made a few posts about it with updates that I'm sure are lost to the ages.

I do have a few questions, namely with the heat and RPM test, the heat data looks like you were getting close to the max duty cycle. 8000rpm is 133hz but to compare to an engine you should cut it in half since it doesn't spark every rotation, not sure what you used but might help explain it. FWIW I never tested the igbt in free air (good idea though!), in car testing on the dyno at steady load/high rpm the temps were virtually identical to factory after a couple minutes. Still cool to see.

When I tested (feels like forever ago), the B58 coil was very difficult to come by. Dealers in Houston didn't even have replacements yet I think the one I tested was from an early wrecked car. Didn't do much testing on it but what I found was in essence similar to n54 OEM coils in terms of current and dwell, and since they didn't generate as much peak voltage as the R8 or PR equivalents I never tested the actual output. Unfortunately the zenners give you a set voltage load so you cant really compare peak voltage but that would only really be useful for people that like to run larger gaps. I wouldn't put much stock in spark duration, in real life the difference will be academic as loads and conditions vary. Total output IMO is king and both look great. Guess I shouldn't have written the B58 off so quickly!

If you want to torture test the coils the way I did it was not really academic but I just set them to the largest air gap they could both span (so limited by the coil with lowest peak potential) and pushed them pretty hard. I never tried the B58 but the N54 lives like 20 seconds at peak voltage before it starts shorting internally. Nice write up and great testing! Seems like PR has some competition!
 

bahn

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Looks like you did some work! You're right about the dwell, the first scope where I gathered a lot of the data back then had some problems, dwell is closer to 4.7ms or so depending on voltage. I made a few posts about it with updates that I'm sure are lost to the ages.

I do have a few questions, namely with the heat and RPM test, the heat data looks like you were getting close to the max duty cycle. 8000rpm is 133hz but to compare to an engine you should cut it in half since it doesn't spark every rotation, not sure what you used but might help explain it. FWIW I never tested the igbt in free air (good idea though!), in car testing on the dyno at steady load/high rpm the temps were virtually identical to factory after a couple minutes. Still cool to see.

When I tested (feels like forever ago), the B58 coil was very difficult to come by. Dealers in Houston didn't even have replacements yet I think the one I tested was from an early wrecked car. Didn't do much testing on it but what I found was in essence similar to n54 OEM coils in terms of current and dwell, and since they didn't generate as much peak voltage as the R8 or PR equivalents I never tested the actual output. Unfortunately the zenners give you a set voltage load so you cant really compare peak voltage but that would only really be useful for people that like to run larger gaps. I wouldn't put much stock in spark duration, in real life the difference will be academic as loads and conditions vary. Total output IMO is king and both look great. Guess I shouldn't have written the B58 off so quickly!

If you want to torture test the coils the way I did it was not really academic but I just set them to the largest air gap they could both span (so limited by the coil with lowest peak potential) and pushed them pretty hard. I never tried the B58 but the N54 lives like 20 seconds at peak voltage before it starts shorting internally. Nice write up and great testing! Seems like PR has some competition!
@V8bait Thank you for your feedback and questions, I appreciate your level of detail and great questions. As for the heat data, the test was performed at 66.66hz from my waveform generator to simulate 8000 rpm in a COP setup with the spark event occurring every 720 degrees of rotation. Like I stressed, running the IGBT in free air is certainly not comparable to the IGBT's in the DME with thermal compound and heatsinking. I did try that first though however temperature increases were slow so I figured free air would allow us to get a generalized idea of the thermal trend.

In regards to peak voltage you are 100% correct when using a zener load we're clamping the output voltage. However like you stated higher output voltage is really only useful for jumping a larger gap which isn't conducive to high boost applications anyway. Thank you for your input, I really appreciated your Primary Energy comparison post and it was very much the inspiration for this one.
 

bahn

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@CNM135i Initial testing completed for S55 and Eldor B58, I'll be performing thermal testing later tonight and post the scope captures tomorrow. S55 Delphi coil 14V @ 2.5 ms produced 89 mJ (14% increase over the Bosch & Delphi N54/N55 coils). Most interesting about the S55 coil is that it does have a bit more room in it for a slight increase in dwell time to 2.7 ms where it produced 99 mJ. Granted I have yet to perform thermal testing so we don't know the full picture of that yet. The Eldor B58 coil has a slightly higher inductance on the primary side and showed a larger increase in output energy between 3.0 ms and 3.2 ms dwell times compared to the Bosch. The slightly higher inductance meant the Eldor B58 coil produced slightly less energy than the Bosch at dwell times 3.0 ms and lower. Output from the Eldor B58 coil 14V @ 3.2 ms produced 187 mJ which puts it at a ~130% increase in output energy over the stock N54/N55 coils and a 14% increase over the PR N54/N55 coil.
 
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bahn

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Updated TLDR Results
TLDR.PNG


Updated IGBT Thermal Data
Thermal_IGBT.PNG


Updated Coil Thermal Data
Thermal_Coil.PNG


What coils would you like me to test next? I have some R8 coils on the way already. The original post of this thread will be updated with new data as I collect more.

Thank you!
 
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Blue Lightning

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The following is an analysis between the secondary spark energy & thermals produced by various ignition coils. Secondary spark energy is the measurement of energy released from the ignition coil during the discharge event and represents energy delivered across the spark plug gap. My test setup was configured in compliance with the SAE 973-202011 standards with a modification to the measurement of secondary spark current. The modification being the use of a shunt resistor instead of a current clamp for increased accuracy of secondary spark current measurements. It is important to note that comparisons cannot be directly made between my tests and tests performed by others as conditions and component tolerances will vary. Much like a dyno, accurate comparisons can only be achieved when testing is performed with the same equipment and procedures (although I do welcome others to repeat my tests).

All tests were performed at a power supply regulated voltage of 14V with a lead acid battery inline for buffering. Dwell time was controlled by a waveform generator (simulated 8000 RPM) that is controlling a ISL9V5036S3ST IGBT as the coils tested are all “dumb” coils without igniters. The ISL9V5036S3ST is the same IGBT that is used in MSD80 DME’s and was picked to compare thermal data between the coils tested and the stock N54/N55 ignition coils. The thermal study was conducted with the IGBT in free air at room temperature (67F) with no thermal compound or heatsinking. This was done to better see the impact of certain coils and dwell times on the IGBT without having to sample data for an hour. Thermal tests concluded once the IGBT reached 160F or 260 seconds of testing. IGBT temperature was sampled every 20 seconds with a FLIR thermal imaging camera while ignition coil temperature was sampled every 20 seconds with two thermocouples.

Before getting into the data I want to mention I've found conflicting information regarding the PR coil. V8bait did a nice Primary Energy comparison between different ignition coils where it was stated the PR coil saturated at 3.7 ms and that they are rated for 118 mJ with a 3 ms dwell. I've tested these numbers and have concluded that there must have been an accident when they were published. At 3 ms dwell I get around 93 mJ from the PR coils, however at 3.7 ms I get 117 mJ. In addition I've verified the delivered dwell with an oscilloscope on my car with the PR Coil option selected. Recorded dwell times were between 4.5 ms and 4.8 ms depending on RPM which is much higher than the stated 3.7 ms. For that reason I have chosen to include PR dwell times at 3.0 ms, 3.7 ms and 4.8 ms.

There's a lot of data here to go through so we'll start off with a TLDR version before diving into it.

TLDR Version (Updated with addition of Delphi S55 & Eldor B58 01/28/2021):
View attachment 48716

It’s no wonder there’s many high power B58’s running stock ignition coils without issue. The stock B58 coils are potent and produce significantly more energy than the OE N54/N55 coils (twice as much to be exact) and can match PR’s coils in secondary spark energy with a longer spark duration. Another consideration is the impact on IGBT temperature. The stock N54/N55 coils hit the 260 second test duration with a maximum temperature of 114-118 F. The long dwell time used by the PR coils increases the thermal load put on the IGBT with temperatures reaching 161.1 F in only 40 seconds with a 4.8 ms dwell and 164.3 F in 100 seconds with a 3.7 ms dwell. The B58 coils on the other hand provide a happy medium with IGBT temperatures reaching 160 F in 220 seconds.

I like data and colorful graphs version :hearteyes::

Inductive Secondary Spark Energy data as captured on an oscilloscope. Light blue/teal is dwell signal from the waveform generator, pink is secondary current measured at the output of the ignition coil after discharging through a zener diode load. Dark blue is primary coil current measured with an inductive current clamp. Inductive Secondary Spark Energy (mJ) is being calculated as (Spark Duration / 2) * Peak Secondary Current * Zener Diode Voltage. Spark duration is being divided by two as in most cases the decrease in secondary current is linear at a rate of 1/2. This simplification allows us to avoid having to represent the secondary current curve using calculus. Of note, the PR coils tested displayed a non-linear decrease in secondary current which will become apparent in a below graph where the B58 coil produces more energy over 3/4 of the spark event.

Bosch N54/N55 @ 2.5ms
View attachment 48471

Delphi S55 @ 2.5 ms
View attachment 48718

Precision Raceworks N54/N55 @ 3.0 ms
View attachment 48472

Precision Raceworks N54/N55 @ 3.7 ms
View attachment 48473

Precision Raceworks N54/N55 @ 4.8 ms
View attachment 48474

Bosch B58 @ 3.2 ms
View attachment 48475

Eldor B58 @ 3.2 ms
View attachment 48717
B58 (red) @ 3.2 ms vs PR N54/N55 (blue) @ 3.7 ms
View attachment 48476

As shown above the Bosch B58 coil @ 3.2 ms dwell produces a higher peak output current, higher average current and longer spark duration than the PR coil @ 3.7 ms dwell; which is what V8Bait stated was saturation for these however it appears PR is actually using a 4.8 ms max dwell @ 14V. So what does that look like in comparison?

View attachment 48477

Overlapping the secondary current for each coil allows us to visualize the difference in peak output and also energy under the curve. The PR coil (blue) with a 4.8 ms dwell generated the highest peak output energy but that energy could not be maintained and quickly decreases. The B58 (red) coil has a more linear decrease in secondary current and is able to generate a peak output energy within 12% of the PR coil (The Eldor B58 coil actually beats the PR coil for peak output energy - 01/28/2021) but is able to maintain a higher average current over 3/4 of the spark event with an increased spark duration over the PR coil.

Adding in the Eldor B58 Coil from testing on 01/28/2021
View attachment 48719

The Eldor B58 coil produces a very large initial spark current, even higher than the PR N54/N55 coils but quickly drops to output energy inline with the Bosch B58 coil as seen below.

View attachment 48720

Thermal Study
IGBT Temperatures sampled via FLIR thermal imaging camera.
View attachment 48478

IGBT Temperatures graphed for comparison with other coils/dwell times.
View attachment 48724

As mentioned earlier the long dwell time on the PR coils (far left grey and yellow) creates a higher thermal load on the IGBT's than other coils at shorter dwells (even if they require higher peak current to charge the primary side of the coil). At higher dwell times the IGBT has less off-time to dissipate the heat. The B58 coil's require a shorter dwell time at higher peak current but perform better in my testing. It's important to remember the conditions of the IGBT thermal test, the IGBT is in free air without thermal compound or heatsinking (via the DME case). This test does NOT represent IGBT temperature inside the DME during normal conditions; however the temperature trend above would continue with the PR coils generating the highest IGBT temperatures of the coils tested.

View attachment 48725

Lastly I wanted to capture temperatures of the ignition coils to see if a certain designed performed better than the other. The results were as expected with all coils following a general trend with only a few stand outs. The two standouts are from the stock N54/N55 coils at 3ms dwell and the B58 coils at 3.5ms dwell. These dwell times are above the point where the coil's core is beginning to become magnetically saturated. When the core starts to enter saturation the impedance decreases resulting in a dramatic increase in current until the coil reaches full saturation and current flatlines.

In conclusion: The B58 coil is a light, low profile coil that produces substantial spark energy over a long spark duration. The B58 coil's shorter dwell time places less load on ignition IGBT's while matching the Precision Raceworks coil in total energy delivered over the spark event.

The results of this research lead me to develop a billet aluminum bracket & components for mounting the B58 coils on the N54 & N55/S55 engines. The bracket is CNC machined in the USA from 6061 aluminum and mounts the B58 coils securely in the stock location providing ample clearance for top mount setups. Our B58 coil conversion kit (including coils) comes in at 3.5 lbs less than the Precision Raceworks kit.

To learn more about B58 coil conversion kit click here.
Do you know the Spark Energy for the Eldor B58 Coils at 2.5 ms ??. Also I can't tell if you are recommending the Eldor or the Bosh Coils ??.
 
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_Calle_

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I would only take the following manufacturers, because you know that you have a qualitative product.
These are also OEMs for BMW and VAG

Eldor
Bosch
Beru
Bremi
Hitachi
 

bahn

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Do you know the Spark Energy for the Eldor B58 Coils at 2.5 ms ??. Also I can't tell if you are recommending the Eldor or the Bosh Coils ??.
Yes, 132 mJ @ 2.5 ms. As for which brand, they're both very close but if I had to choose I would pick the Eldor (OE BMW) for the higher initial spark energy.
 
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V8bait

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Looking a little closer at everything the data is pretty close to what I recall seeing before in my tests, but there's a few oddities. On the secondary I'm not sure why the PR is concave like that, but you're going to get some artificially lower numbers on the output and spark duration because of it. It should be a linear decrease like the others, possibly you're getting some voltage leaking back or out of the system, could try adding a higher resistor before the zenners? Not sure.

The heat thing is what really surprises me and I still can't figure it out at those hz. The heat should be correlated to the amperage, not just the duty cycle, and from the charts it seems you're getting similar current flow but I don't think you've posted total amp draw. Otherwise, I never saw a single difference between eldor and Bosch n54/n55/s55 stuff but I didn't run output on the eldors, just primary, dwell, peak voltage, etc. Interesting, nice work.
 
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bahn

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Looking a little closer at everything the data is pretty close to what I recall seeing before in my tests, but there's a few oddities. On the secondary I'm not sure why the PR is concave like that, but you're going to get some artificially lower numbers on the output and spark duration because of it. It should be a linear decrease like the others, possibly you're getting some voltage leaking back or out of the system, could try adding a higher resistor before the zenners? Not sure.

The heat thing is what really surprises me and I still can't figure it out at those hz. The heat should be correlated to the amperage, not just the duty cycle, and from the charts it seems you're getting similar current flow but I don't think you've posted total amp draw. Otherwise, I never saw a single difference between eldor and Bosch n54/n55/s55 stuff but I didn't run output on the eldors, just primary, dwell, peak voltage, etc. Interesting, nice work.

Hey @V8bait, that concave drop on output energy was very repeatable with a sample size of 7 PR coils (I bought a brand new one recently to test the newest version). The drop is noticeable at lower dwell times as well. The calculated energy numbers are not impacted by that concave drop though as I'm representing the curve as a 1/2 linear decrease so it's actually getting the benefit of the doubt.

The IGBT temperature is related to both current and duration of pulse (dwell). It could possibly be that the IGBT has 11% longer between pulses to dissipate heat @ 3.2 ms than it does at 4.8 ms. Another possibility is a difference in fly-back voltage seen at the IGBT collector causing the clamping diodes to produce more heat or even hitting the collector to emitter breakdown voltage. I can test that shortly and record back to back videos of the IGBT thermal test between the B58 coils and the PR coils if you like.

Thanks for the feedback!
 

V8bait

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Hey @V8bait, that concave drop on output energy was very repeatable with a sample size of 7 PR coils (I bought a brand new one recently to test the newest version). The drop is noticeable at lower dwell times as well. The calculated energy numbers are not impacted by that concave drop though as I'm representing the curve as a 1/2 linear decrease so it's actually getting the benefit of the doubt.

The IGBT temperature is related to both current and duration of pulse (dwell). It could possibly be that the IGBT has 11% longer between pulses to dissipate heat @ 3.2 ms than it does at 4.8 ms. Another possibility is a difference in fly-back voltage seen at the IGBT collector causing the clamping diodes to produce more heat or even hitting the collector to emitter breakdown voltage. I can test that shortly and record back to back videos of the IGBT thermal test between the B58 coils and the PR coils if you like.

Thanks for the feedback!

Yeah I realize the calculated is getting the benefit of the doubt mathematically, but the shape suggests you're losing current outside the system so that energy isn't being accounted for. The loss is higher and more significant initially and tapers over time, but since that energy is lost it's not accounted for. Might be why I got a little higher measures at 3ms dwell by around 15-20mJ, but it's pretty trivial (could have been a hundred things lol). If there's flyback then that's possibly why the igbt is heating up and the output is below expected, the DME has a bunch of circuits to minimize flyback with resistors, capacitors, and namely diodes. 11% more time to cool isn't very much for the heat you're seeing. I think the data looks good, just thoughts on a few little things.
 

bahn

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Yeah I realize the calculated is getting the benefit of the doubt mathematically, but the shape suggests you're losing current outside the system so that energy isn't being accounted for. The loss is higher and more significant initially and tapers over time, but since that energy is lost it's not accounted for. Might be why I got a little higher measures at 3ms dwell by around 15-20mJ, but it's pretty trivial (could have been a hundred things lol). If there's flyback then that's possibly why the igbt is heating up and the output is below expected, the DME has a bunch of circuits to minimize flyback with resistors, capacitors, and namely diodes. 11% more time to cool isn't very much for the heat you're seeing. I think the data looks good, just thoughts on a few little things.
@V8bait I just want to start off by making sure you know I appreciate the feedback and questions. The test circuit (and equipment) is setup as specified in the SAE J973 standard with the modification of a shunt resistor. All coil tests are performed on the same circuit if it were a circuit issue we would expect to see the same behavior on all coils tested. I have a couple ideas as to what's going on so I'll test that along with the flyback voltage 👍. Good stuff, keep it coming!
 

rev210

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I wonder if throwing in an N54 Eldor coil might be worth a look, if you have one. As these have a following. We could see if there is more than the external differences and if the significant weight increase of the coil has something to do with internal windings or better heat management?

Excellent work by the way! 👍
 
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V8bait

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@V8bait I just want to start off by making sure you know I appreciate the feedback and questions. The test circuit (and equipment) is setup as specified in the SAE J973 standard with the modification of a shunt resistor. All coil tests are performed on the same circuit if it were a circuit issue we would expect to see the same behavior on all coils tested. I have a couple ideas as to what's going on so I'll test that along with the flyback voltage 👍. Good stuff, keep it coming!
Yeah for sure you did a great job and spent more time on this than I ever did! I seem to remember the factory coils have a diode or some components that keeps you from actually measuring secondary resistance directly, the PR do not. In testing like this where the output is constrained I wonder if that could be causing the problem. I'd need to grab one to check but if I recall it took some disassembly and special ordering to actually test the secondary resistance on the OEM coils because of it.

Looking forward to the R8 testing, that coil puts out some extreme voltages and has some high current draw at low dwells with pretty good output as well, it's a pretty impressive coil for the size honestly just not super reliable and not a great match for our DME being a smart coil. The only other popular smart coil I've seen pop up from OEM's is the GTR, may be worth a test.
 

_Calle_

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Jul 7, 2017
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Germany
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e82 135is
Found this on the Eldor side, it seams that the B58 coil is the EPT200SP and I think the N54 coil is similar to the EPT300.
If the output Energy is based of a Dwell of 2,5ms, (which is very likely) it will match with the data @bahn provide here.

B58 vs N54
Energy increase ~ 50mj / 63%
Voltage increase ~ 10kV / 28%

From my side there will be no differences if you choose Eldor, Bosch, Beru or Hitachi so long you don´t by cheap (Chinese) garbage!

In this tests only one coil is used, if you do the same test with 6 Bosch and Eldor Coils, the result should be the same due to slight fluctuations.

eldor coil.jpg
 

Blue Lightning

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Jan 23, 2021
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The following is an analysis between the secondary spark energy & thermals produced by various ignition coils. Secondary spark energy is the measurement of energy released from the ignition coil during the discharge event and represents energy delivered across the spark plug gap. My test setup was configured in compliance with the SAE 973-202011 standards with a modification to the measurement of secondary spark current. The modification being the use of a shunt resistor instead of a current clamp for increased accuracy of secondary spark current measurements. It is important to note that comparisons cannot be directly made between my tests and tests performed by others as conditions and component tolerances will vary. Much like a dyno, accurate comparisons can only be achieved when testing is performed with the same equipment and procedures (although I do welcome others to repeat my tests).

All tests were performed at a power supply regulated voltage of 14V with a lead acid battery inline for buffering. Dwell time was controlled by a waveform generator (simulated 8000 RPM) that is controlling a ISL9V5036S3ST IGBT as the coils tested are all “dumb” coils without igniters. The ISL9V5036S3ST is the same IGBT that is used in MSD80 DME’s and was picked to compare thermal data between the coils tested and the stock N54/N55 ignition coils. The thermal study was conducted with the IGBT in free air at room temperature (67F) with no thermal compound or heatsinking. This was done to better see the impact of certain coils and dwell times on the IGBT without having to sample data for an hour. Thermal tests concluded once the IGBT reached 160F or 260 seconds of testing. IGBT temperature was sampled every 20 seconds with a FLIR thermal imaging camera while ignition coil temperature was sampled every 20 seconds with two thermocouples.

Before getting into the data I want to mention I've found conflicting information regarding the PR coil. V8bait did a nice Primary Energy comparison between different ignition coils where it was stated the PR coil saturated at 3.7 ms and that they are rated for 118 mJ with a 3 ms dwell. I've tested these numbers and have concluded that there must have been an accident when they were published. At 3 ms dwell I get around 93 mJ from the PR coils, however at 3.7 ms I get 117 mJ. In addition I've verified the delivered dwell with an oscilloscope on my car with the PR Coil option selected. Recorded dwell times were between 4.5 ms and 4.8 ms depending on RPM which is much higher than the stated 3.7 ms. For that reason I have chosen to include PR dwell times at 3.0 ms, 3.7 ms and 4.8 ms.

There's a lot of data here to go through so we'll start off with a TLDR version before diving into it.

TLDR Version (Updated with addition of Delphi S55 & Eldor B58 01/28/2021):
View attachment 48716

It’s no wonder there’s many high power B58’s running stock ignition coils without issue. The stock B58 coils are potent and produce significantly more energy than the OE N54/N55 coils (twice as much to be exact) and can match PR’s coils in secondary spark energy with a longer spark duration. Another consideration is the impact on IGBT temperature. The stock N54/N55 coils hit the 260 second test duration with a maximum temperature of 114-118 F. The long dwell time used by the PR coils increases the thermal load put on the IGBT with temperatures reaching 161.1 F in only 40 seconds with a 4.8 ms dwell and 164.3 F in 100 seconds with a 3.7 ms dwell. The B58 coils on the other hand provide a happy medium with IGBT temperatures reaching 160 F in 220 seconds.

I like data and colorful graphs version :hearteyes::

Inductive Secondary Spark Energy data as captured on an oscilloscope. Light blue/teal is dwell signal from the waveform generator, pink is secondary current measured at the output of the ignition coil after discharging through a zener diode load. Dark blue is primary coil current measured with an inductive current clamp. Inductive Secondary Spark Energy (mJ) is being calculated as (Spark Duration / 2) * Peak Secondary Current * Zener Diode Voltage. Spark duration is being divided by two as in most cases the decrease in secondary current is linear at a rate of 1/2. This simplification allows us to avoid having to represent the secondary current curve using calculus. Of note, the PR coils tested displayed a non-linear decrease in secondary current which will become apparent in a below graph where the B58 coil produces more energy over 3/4 of the spark event.

Bosch N54/N55 @ 2.5ms
View attachment 48471

Delphi S55 @ 2.5 ms
View attachment 48718

Precision Raceworks N54/N55 @ 3.0 ms
View attachment 48472

Precision Raceworks N54/N55 @ 3.7 ms
View attachment 48473

Precision Raceworks N54/N55 @ 4.8 ms
View attachment 48474

Bosch B58 @ 3.2 ms
View attachment 48475

Eldor B58 @ 3.2 ms
View attachment 48717
B58 (red) @ 3.2 ms vs PR N54/N55 (blue) @ 3.7 ms
View attachment 48476

As shown above the Bosch B58 coil @ 3.2 ms dwell produces a higher peak output current, higher average current and longer spark duration than the PR coil @ 3.7 ms dwell; which is what V8Bait stated was saturation for these however it appears PR is actually using a 4.8 ms max dwell @ 14V. So what does that look like in comparison?

View attachment 48477

Overlapping the secondary current for each coil allows us to visualize the difference in peak output and also energy under the curve. The PR coil (blue) with a 4.8 ms dwell generated the highest peak output energy but that energy could not be maintained and quickly decreases. The B58 (red) coil has a more linear decrease in secondary current and is able to generate a peak output energy within 12% of the PR coil (The Eldor B58 coil actually beats the PR coil for peak output energy - 01/28/2021) but is able to maintain a higher average current over 3/4 of the spark event with an increased spark duration over the PR coil.

Adding in the Eldor B58 Coil from testing on 01/28/2021
View attachment 48719

The Eldor B58 coil produces a very large initial spark current, even higher than the PR N54/N55 coils but quickly drops to output energy inline with the Bosch B58 coil as seen below.

View attachment 48720

Thermal Study
IGBT Temperatures sampled via FLIR thermal imaging camera.
View attachment 48478

IGBT Temperatures graphed for comparison with other coils/dwell times.
View attachment 48724

As mentioned earlier the long dwell time on the PR coils (far left grey and yellow) creates a higher thermal load on the IGBT's than other coils at shorter dwells (even if they require higher peak current to charge the primary side of the coil). At higher dwell times the IGBT has less off-time to dissipate the heat. The B58 coil's require a shorter dwell time at higher peak current but perform better in my testing. It's important to remember the conditions of the IGBT thermal test, the IGBT is in free air without thermal compound or heatsinking (via the DME case). This test does NOT represent IGBT temperature inside the DME during normal conditions; however the temperature trend above would continue with the PR coils generating the highest IGBT temperatures of the coils tested.

View attachment 48725

Lastly I wanted to capture temperatures of the ignition coils to see if a certain designed performed better than the other. The results were as expected with all coils following a general trend with only a few stand outs. The two standouts are from the stock N54/N55 coils at 3ms dwell and the B58 coils at 3.5ms dwell. These dwell times are above the point where the coil's core is beginning to become magnetically saturated. When the core starts to enter saturation the impedance decreases resulting in a dramatic increase in current until the coil reaches full saturation and current flatlines.

In conclusion: The B58 coil is a light, low profile coil that produces substantial spark energy over a long spark duration. The B58 coil's shorter dwell time places less load on ignition IGBT's while matching the Precision Raceworks coil in total energy delivered over the spark event.

The results of this research lead me to develop a billet aluminum bracket & components for mounting the B58 coils on the N54 & N55/S55 engines. The bracket is CNC machined in the USA from 6061 aluminum and mounts the B58 coils securely in the stock location providing ample clearance for top mount setups. Our B58 coil conversion kit (including coils) comes in at 3.5 lbs less than the Precision Raceworks kit.

To learn more about B58 coil conversion kit click here.


I'm still not seeing a 2.5 ms test for the Eldor coils....... Are these coils simply unable to operate with that short of a Dwell ??