Author Topic: Ignition systems  (Read 6104 times)

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Offline paulcaTopic starter

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Re: Ignition systems
« Reply #50 on: October 02, 2021, 04:16:45 pm »
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On coils....  however they claimed that on some bikes at least, they use different sized coils and power different things from each coil.

I'm just not sure how true this is or how common it is.
don't know about modern bikes,but it was certainly true on the  some of the bikes  i had in the past.

I figured it would be the only way to do it without a battery.  And a lot of bikes didn't have batteries or electric starters "back in the days".

But thinking back I have had bikes which will not run their head light off the battery.  Tail light, side lights, indicators, dash lights, yes, head light no.  (I found this out the hardway when I accidentally hit the kill switch while riding through pitch black night, instinctively pulled the clutch and the headlight went out.... at 50mph.
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Offline Benta

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Re: Ignition systems
« Reply #51 on: October 02, 2021, 04:34:07 pm »
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Your magneto was on the cam shaft? What kind of bike was this? The ones I know of have it on the crank shaft
no,the cam bearing was worn,causing the timing  chain  that drove the points to go slack ,putting more load on the engine, by turning on the headlights , took enough slack out to get me home.I discovered the "cure" when i hit the indicators to pull over as the engine was dying and dam thing started running again,turning  off the indicators  and the engine started to die.

That still makes no sense to me. But never mind, I don't care about bikes anyway.

 

Offline Nusa

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Re: Ignition systems
« Reply #52 on: October 02, 2021, 06:44:40 pm »
I once had a 1980 Datsun truck that had two coils, 2 plugs per cylinder and a 10-wire distributor (2 in, 8 out). My understanding is both plugs were fired at the same time with the aim of faster and more complete combustion in the cylinder. I passed that truck to family in 1993 when I moved to California. Sitting in a cousins barn in Ohio, last I knew.
 

Offline Stray Electron

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Re: Ignition systems
« Reply #53 on: October 02, 2021, 07:59:09 pm »
  I had an 1985 Nissan truck that also had the dual spark plug per cylinder setup. IIRC the spark plugs were actually timed to fire about 5 (?) degrees apart.
 

Offline David Hess

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Re: Ignition systems
« Reply #54 on: October 02, 2021, 11:52:12 pm »
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.

You are absolutely right that the constant current out with variable compliance from an inductive source is more ideal.  I suspect in the past capacitive discharge systems did better simply because commonly available Kettering systems were marginal for higher compression engines when only points were available.

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.
 

Online langwadt

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Re: Ignition systems
« Reply #55 on: October 02, 2021, 11:59:54 pm »
 

Online NiHaoMike

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Re: Ignition systems
« Reply #56 on: October 03, 2021, 01:36:53 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.
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.
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Online Circlotron

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Re: Ignition systems
« Reply #57 on: October 03, 2021, 02:40:04 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.
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.

« Last Edit: October 03, 2021, 02:41:43 am by Circlotron »
 

Offline paulcaTopic starter

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Re: Ignition systems
« Reply #58 on: October 03, 2021, 08:58:01 am »
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.

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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