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Ignition systems

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paulca:

--- Quote from: themadhippy on October 02, 2021, 01:11:14 pm ---
--- Quote ---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.
--- End quote ---
don't know about modern bikes,but it was certainly true on the  some of the bikes  i had in the past.

--- End quote ---

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.

Benta:

--- Quote from: themadhippy on October 02, 2021, 03:58:50 pm ---
--- Quote ---Your magneto was on the cam shaft? What kind of bike was this? The ones I know of have it on the crank shaft
--- End quote ---
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.

--- End quote ---

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

Nusa:
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.

Stray Electron:
  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.

David Hess:

--- 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 ---

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.

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