Follow up to my previous thread examining how the OEM ignition system works, this thread will be a comparison of different coil packs; dwell time, saturation points, current draw, and energy output (coming soon) are examined.
Note- Current draw values are fixed from the previous thread, scope channel scaling ranged for comparative purposes not calculations other than those provided.
***Disclaimer- I have been helping develop a coil solution for the N54/N55 with Precision Raceworks, but I like sharing stuff. I made it a point to stick to the data and unbiased analysis for educational purposes and the betterment of the community and will be updating this thread with complete dwell maps for any coils tested. Apologies for any errors I’m a Chem. E. not an E.E. but I can solder preety gud***
Background:
Voltage: The force pushing electrons forward, the electrical "pressure" of a system.
Current: Measurement of the flow rate of electrons in a circuit, and is measured in Coulombs per Second (C/s), a.k.a. Amps (A). In a river, this is how much water is flowing in a given time.
Resistance: Deals with the opposition to the flow of current, and is measured in Ohms. In a river, this is the dam that slows the current.
Inductance: Property of a circuit's magnetic field to resist change in current without opposing that current directly, measured in Henry. As a circuit is induced by flowing electrons, it builds a charge, this charge dissipates all at once if current stops flowing across the magnetic field. This is a boat in the river, being sped up by the current, when the current stops the boat crashes into a rock releasing stored energy.
Power and energy: Power is a calculated value obtained by multiplying voltage times current, measured in Watts. For example, a 12V car battery driving an audio system with 10 amps is 120 Watts. Energy, however, is power delivered over a period of time. If you check your power bill, you'll notice it's in kW/hr, or killowatt-hours, this means how much power over how long. In ignition coils, the values are MUCH smaller, so we use milliamps (mA) and millijoules (mJ) for the energy.
When looking at the following graphs:
Channel 1 (yellow) - Current draw through primary in amps
Channel 2 (blue) – High voltage at secondary (attenuated values not to scale)
Channel 3 (green) – regulated power supply voltage
Channel 4 (purple) – function generator dwell signal
Data:
First, we determined saturation points for the coils at 14V, that was covered in the prior thread however the amperage was off so it was repeated. Saturation time didn’t change only amp scale. Here’s an example for BMW, increasing dwell over stock 2.4ms doesn’t net much, they saturate around 2.5-2.7ms, on the zoomed picture you can see how it’s just flat past 2.5ms. To build a proper dwell map, this must be done at multiple voltages.
Current draw data like this allows us to reconcile the coils for the overall design of the ignition system; transistors to wiring gauge to fuse sizes etc. It also gives us an idea of coil output. Basically, there’s two ways to charge a coil. High current/low inductance and let the current quickly charge it, or low current/high inductance and lean on the inductance over a lengthy dwell.
Below is a Lamborghini ignition coil at 2.5ms dwell drawing 14A current, compared to a LS Truck coil at 6.5ms dwell drawing 15A current. Both are drawing similar amperage, but the LS coil has much higher stored energy in the primary after the lengthy dwell:
So, why not just make high induction coils for everyone, because they are awesome right! Well, no, not always. The LS was driven way past safety at 6.5ms dwell to get the current up that high. (See the raw data for what happens at 7ms, the coil prematurely fires!! BAD!!) When dwell was lowered to 4.5ms (where they are actually driven IRL), stored energy was closer to the Lambo pencil coil as you can see in the figure comparing them all a few lines down.
So if high inductance, long dwelling coils isn't the answer, lets just use the low resistance Lambo coils for every! Because lambo! Again, no, this isn't always better. The data below shows how just because the primary energy is similar when measured at saturation between some of these high power coils, the current required to get there varies as well as spark duration. High inductance coils have the benefit of longer sparks, while low resistance coils have the benefit of short dwell. Here is the data on all of the coils tested at saturation point for current and energy:
Summary of some of tested values at 14V with known specs of tested coils:
Raw data images and excel file:
https://drive.google.com/file/d/0By-fFLRvLQQxOVN2YlhGM2JWUm8/view?usp=sharing
Results:
-BMW Coil: Pros- Fits well into the N54 head; good/average output for a pencil coil; cars make over 800whp with them. Cons- Very short spark duration; runs warm in testing; known to be failure prone; killed 3 in testing.
-LS Truck coil: Pros- Ran cold in all tests; substantial primary energy and strong spark with long dwell periods; stronger than BMW even at short dwell periods, longest tested spark duration. Cons- Long dwell requirement compromises high RPM functionality; smart coil so cannot be driven directly by DME; requires plug wires and coil mounting.
-Lamborghini coil: Pros- Powerful at very short dwell; capable of 10,000+ RPM without a CDI; possibly highest power pencil coil on the market; highest initiating secondary voltage tested; fits into N54 head directly. Cons- Short dwell means high amperage and low inductance; warm to the touch after use; smart coil so cannot be driven directly by DME; reported failure prone (fixed?).
-Precision Raceworks coil: Pros- Higher primary energy than LS Truck coil below 4.5ms dwell; similar current draw characteristics to BMW; matches Lamborghini primary energy with lower current; matches LS coil spark duration. Cons- requires plug wires and coil mounting.
Conclusion:
Keep in mind this is experiment tested energy on the primary coil only, which is the side that places demand on wiring and electronics. What happens when this energy is transferred to the secondary coil and spit out as spark is directly related to this however. Secondary resistance, twist ratio, and inductance are key variables for determining secondary coil energy mathematically, however not all of these specifications are available. As such, spark duration was the only way to monitor secondary coil output at this time. However, since voltage cannot be accurately measured on the secondary it is impossible to say the actual secondary energy output. Future studies may look at measuring secondary output though a set load voltage, but for now we just used a simple air gap to visualize the spark, and every coil tested destroyed the BMW. In fact 3 BMW coils self-destructed in the process!
Note- Current draw values are fixed from the previous thread, scope channel scaling ranged for comparative purposes not calculations other than those provided.
***Disclaimer- I have been helping develop a coil solution for the N54/N55 with Precision Raceworks, but I like sharing stuff. I made it a point to stick to the data and unbiased analysis for educational purposes and the betterment of the community and will be updating this thread with complete dwell maps for any coils tested. Apologies for any errors I’m a Chem. E. not an E.E. but I can solder preety gud***
Background:
Voltage: The force pushing electrons forward, the electrical "pressure" of a system.
Current: Measurement of the flow rate of electrons in a circuit, and is measured in Coulombs per Second (C/s), a.k.a. Amps (A). In a river, this is how much water is flowing in a given time.
Resistance: Deals with the opposition to the flow of current, and is measured in Ohms. In a river, this is the dam that slows the current.
Inductance: Property of a circuit's magnetic field to resist change in current without opposing that current directly, measured in Henry. As a circuit is induced by flowing electrons, it builds a charge, this charge dissipates all at once if current stops flowing across the magnetic field. This is a boat in the river, being sped up by the current, when the current stops the boat crashes into a rock releasing stored energy.
Power and energy: Power is a calculated value obtained by multiplying voltage times current, measured in Watts. For example, a 12V car battery driving an audio system with 10 amps is 120 Watts. Energy, however, is power delivered over a period of time. If you check your power bill, you'll notice it's in kW/hr, or killowatt-hours, this means how much power over how long. In ignition coils, the values are MUCH smaller, so we use milliamps (mA) and millijoules (mJ) for the energy.
When looking at the following graphs:
Channel 1 (yellow) - Current draw through primary in amps
Channel 2 (blue) – High voltage at secondary (attenuated values not to scale)
Channel 3 (green) – regulated power supply voltage
Channel 4 (purple) – function generator dwell signal
Data:
First, we determined saturation points for the coils at 14V, that was covered in the prior thread however the amperage was off so it was repeated. Saturation time didn’t change only amp scale. Here’s an example for BMW, increasing dwell over stock 2.4ms doesn’t net much, they saturate around 2.5-2.7ms, on the zoomed picture you can see how it’s just flat past 2.5ms. To build a proper dwell map, this must be done at multiple voltages.
Current draw data like this allows us to reconcile the coils for the overall design of the ignition system; transistors to wiring gauge to fuse sizes etc. It also gives us an idea of coil output. Basically, there’s two ways to charge a coil. High current/low inductance and let the current quickly charge it, or low current/high inductance and lean on the inductance over a lengthy dwell.
Below is a Lamborghini ignition coil at 2.5ms dwell drawing 14A current, compared to a LS Truck coil at 6.5ms dwell drawing 15A current. Both are drawing similar amperage, but the LS coil has much higher stored energy in the primary after the lengthy dwell:
So, why not just make high induction coils for everyone, because they are awesome right! Well, no, not always. The LS was driven way past safety at 6.5ms dwell to get the current up that high. (See the raw data for what happens at 7ms, the coil prematurely fires!! BAD!!) When dwell was lowered to 4.5ms (where they are actually driven IRL), stored energy was closer to the Lambo pencil coil as you can see in the figure comparing them all a few lines down.
So if high inductance, long dwelling coils isn't the answer, lets just use the low resistance Lambo coils for every! Because lambo! Again, no, this isn't always better. The data below shows how just because the primary energy is similar when measured at saturation between some of these high power coils, the current required to get there varies as well as spark duration. High inductance coils have the benefit of longer sparks, while low resistance coils have the benefit of short dwell. Here is the data on all of the coils tested at saturation point for current and energy:
Summary of some of tested values at 14V with known specs of tested coils:
Raw data images and excel file:
https://drive.google.com/file/d/0By-fFLRvLQQxOVN2YlhGM2JWUm8/view?usp=sharing
Results:
-BMW Coil: Pros- Fits well into the N54 head; good/average output for a pencil coil; cars make over 800whp with them. Cons- Very short spark duration; runs warm in testing; known to be failure prone; killed 3 in testing.
-LS Truck coil: Pros- Ran cold in all tests; substantial primary energy and strong spark with long dwell periods; stronger than BMW even at short dwell periods, longest tested spark duration. Cons- Long dwell requirement compromises high RPM functionality; smart coil so cannot be driven directly by DME; requires plug wires and coil mounting.
-Lamborghini coil: Pros- Powerful at very short dwell; capable of 10,000+ RPM without a CDI; possibly highest power pencil coil on the market; highest initiating secondary voltage tested; fits into N54 head directly. Cons- Short dwell means high amperage and low inductance; warm to the touch after use; smart coil so cannot be driven directly by DME; reported failure prone (fixed?).
-Precision Raceworks coil: Pros- Higher primary energy than LS Truck coil below 4.5ms dwell; similar current draw characteristics to BMW; matches Lamborghini primary energy with lower current; matches LS coil spark duration. Cons- requires plug wires and coil mounting.
Conclusion:
Keep in mind this is experiment tested energy on the primary coil only, which is the side that places demand on wiring and electronics. What happens when this energy is transferred to the secondary coil and spit out as spark is directly related to this however. Secondary resistance, twist ratio, and inductance are key variables for determining secondary coil energy mathematically, however not all of these specifications are available. As such, spark duration was the only way to monitor secondary coil output at this time. However, since voltage cannot be accurately measured on the secondary it is impossible to say the actual secondary energy output. Future studies may look at measuring secondary output though a set load voltage, but for now we just used a simple air gap to visualize the spark, and every coil tested destroyed the BMW. In fact 3 BMW coils self-destructed in the process!
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