General > General Technical Chat
Ignition systems
langwadt:
here's an interesting way of doing CDI, https://electrooptical.net/static/oldsite/www.analog-innovations.com/SED/CD-Ignition-Basic.pdf
NiHaoMike:
--- Quote from: Circlotron on October 01, 2021, 07:44:16 am ---One of the most overlooked issues with a capacitor discharge ignition is it's woefully low efficiency, at least when using conventional coils. The short answer is - a 1uF capacitor charged to 450VDC has 100mJ of energy. Discharge it into a coil primary, and once the spark in a running engine has begun it takes about 1500V to maintain the spark. Under these conditions a modern E-core coil will send about 35mJ to the spark gap. An older points type canister coil delivers about 25mJ. if you ignore plug lead resistance the majority of the losses are in the coil secondary. with a 1uF 450V CDI the coil secondary current will be close to 400mA peak. If the coil secondary resistance is say 6000 ohms then there will be 1500V across the spark gap and 2400V lost in the coil secondary resistance. So right way we can see the efficiency would be only 38.5%. One particular inductive ignition I make delivers a measured 150mJ to the spark gap. This is a huge jump compared to a CDI.
--- End quote ---
100mJ per spark (as measured on the primary side) is only about 7W for a 4 cylinder engine running at 2000RPM. There's much, much greater energy savings elsewhere in the engine.
Circlotron:
--- Quote from: NiHaoMike on October 03, 2021, 01:36:53 am ---100mJ per spark (as measured on the primary side) is only about 7W for a 4 cylinder engine running at 2000RPM. There's much, much greater energy savings elsewhere in the engine.
--- End quote ---
The point was no so much wasted energy as the discrepancy between advertised spark energy and what is actually delivered to the plug gap. As an example, using my standard test gap (pictured) a 100mJ measured-at-the-secondary inductive setup can eventually make the ceramic insulator glow bright yellow at a high spark rate but a "100mJ" CDI hasn't got a hope in the world. That's gotta be the lowest tech method of observing the amount of energy delivered.
paulca:
--- Quote from: David Hess on October 02, 2021, 11:52:12 pm ---In principle the capacitor should be replaced with a lumped element transmission line used as a charge line so the peak to nominal discharge current is lowered increasing efficiency, but I have never seen or read of a capacitive discharge ignition which did this and now high frequency high voltage solid state switches allow even better ways.
--- End quote ---
On a 2021 motorcycle the ignition system is called "Computer controlled digital transistorized with electronic advance"
Which is Honda speak for a "digital" CDI unit using a SCR under computer control.
The unit is usually a box about the size of a cigarette packet, fully potted, the coil is embedded at the base of the HT lead.
Hard to find the actual unit on this bike, I expect it's contained in the FGM-TI fuel injection black box or similar.
https://www.bike-parts-honda.com/honda-motorcycle/750-MOTO/NC/2021/NC750XAM/Frame/IGNITION-COIL/103806/F_38_20/2/42369
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