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Coiled ignition systems

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1rv4

Joined: 11 Sep 2006
Posts: 20

Posted: Fri Oct 21, 2016 8:32 am Post subject: Coiled ignition systems

Hi All  

 I have finished wiring a very simple single  place biplane with a VW engine. The engine has single ignition, automotive style  with coil and breaker points. I used a master switch to turn off all power at  the contactor which is next to the battery behind the seat. There is also a key  ignition switch that is used to start the engine it powers the starter and  coil.

 So in order to start the plane the   master has to be on and then the ignition switch provides power for the starter  and ignition. I know this is a two point failure set up, but the alternative is  to have the pilot remember to turn off both master and ignition switch in case  of emergency, something that probably wouldn't happen in a  stressful  situation.

 Is there a better way to  handle coiled  ignition systems?

  

           Thanks

                   Chris

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sat Oct 22, 2016 5:53 am Post subject: Re: Coiled ignition systems

If a forced landing is immanent, all electrical power should be shut off to prevent ignition of leaking fuel.  A master switch that shuts off everything including the engine is good for that scenario.  However, smoke in the cockpit is an emergency that may require shutting off all electrical loads except the engine.   In that case, engine ignition needs to be independent of the master switch.  The most reliable ignition circuit is less complicated and has fewer components.  If it were my plane, I would power the ignition system from the battery, independent of the master switch.  The engine starter circuit should be disabled when the master switch is off.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Oct 22, 2016 10:03 am Post subject: Coiled ignition systems

At 08:53 AM 10/22/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 If a forced landing is immanent, all electrical power should be shut off to prevent ignition of leaking fuel.  A master switch that shuts off everything including the engine is good for that scenario.  However, smoke in the cockpit is an emergency that may require shutting off all electrical loads except the engine.   In that case, engine ignition needs to be independent of the master switch.  The most reliable ignition circuit is less complicated and has fewer components.  If it were my plane, I would power the ignition system from the battery, independent of the master switch.  The engine starter circuit should be disabled when the master switch is off. 	


    Agreed . . . 



    Since your ignition system will run nicely

    on 7A or less, I too would recommend you

    run the ignition directly from the battery

    through a 7A fuse. Power the starter from

    the bus powered through the master contactor.



    The ignition circuit is low risk for post-crash

    ignition source . . . so even if you don't

    get the engine killed before anticipated

    contact the primary risk is to the engine

    having a powered prop strike.



    Taking everything else through the battery

    master is the conventional philosophy.



 



 

 

   Bob . . .

yellowduckduo(at)gmail.co
Guest

Posted: Sat Oct 22, 2016 11:39 am Post subject: Coiled ignition systems

A 7 amp CB seems reasonable but a 7 amp fuse makes me a bit nervous. I 

seem to recall that when I looked at ignition currents I noted that they 

went up at high rpm, at high temperatures, and in some rare cases when 

the engine was not turning.  I did not notice any automotive systems 

that lightly fused the ignition circuits.  So while I've never measured 

over 5 amps on my soob units, my personal recommendation is a minimum 10 

amp fuse on ignition circuits that feed multiple cylinders even if they 

are solid state.  It may be that the peak currents as seen on a scope 

caught my attention or that I just like more headroom on critical fuses. 

I think part of my thought process might have been that on my system if 

one solid state coil driver shorted full on it would not necessarily 

take out the system fuse. I don't have any idea what the tolerance is on 

an ATC fuse. I have 700 hours on the original 10 amp fuses that feed the 

4 cylinder soob. I've had two cases of one cylinder losing power due to 

a partial coil failure. Once during initial ground testing and once at 

around 500 hours. These are DIS coils that each feed two cylinders but 

in both cases only one cylinder lost power.

Ken



On 22/10/2016 2:02 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   At 08:53 AM 10/22/2016, you wrote:

> 

>

> If a forced landing is immanent, all electrical power should be shut 

> off to prevent ignition of leaking fuel.  A master switch that shuts 

> off everything including the engine is good for that scenario. 

> However, smoke in the cockpit is an emergency that may require 

> shutting off all electrical loads except the engine.   In that case, 

> engine ignition needs to be independent of the master switch.  The 

> most reliable ignition circuit is less complicated and has fewer 

> components.  If it were my plane, I would power the ignition system 

> from the battery, independent of the master switch.  The engine 

> starter circuit should be disabled when the master switch is off.



    Agreed . . .



    Since your ignition system will run nicely

    on 7A or less, I too would recommend you

    run the ignition directly from the battery

    through a 7A fuse. Power the starter from

    the bus powered through the master contactor.



    The ignition circuit is low risk for post-crash

    ignition source . . . so even if you don't

    get the engine killed before anticipated

    contact the primary risk is to the engine

    having a powered prop strike.



    Taking everything else through the battery

    master is the conventional philosophy.





   Bob . . .

ceengland7(at)gmail.com
Guest

Posted: Sat Oct 22, 2016 12:54 pm Post subject: Coiled ignition systems

Ken brings up an easy redundancy opportunity. Some (most?) automotive 

style engine controllers switch the ground side of the coils and the 

injectors. To limit the impact of such failures, I chose to 

independently fuse each coil. Might be worth a look if running an auto 

style engine controller.

Charlie

On 10/22/2016 2:37 PM, C&K wrote:

 	  Quote: 	

 A 7 amp CB seems reasonable but a 7 amp fuse makes me a bit nervous. I 

 seem to recall that when I looked at ignition currents I noted that 

 they went up at high rpm, at high temperatures, and in some rare cases 

 when the engine was not turning.  I did not notice any automotive 

 systems that lightly fused the ignition circuits.  So while I've never 

 measured over 5 amps on my soob units, my personal recommendation is a 

 minimum 10 amp fuse on ignition circuits that feed multiple cylinders 

 even if they are solid state.  It may be that the peak currents as 

 seen on a scope caught my attention or that I just like more headroom 

 on critical fuses. I think part of my thought process might have been 

 that on my system if one solid state coil driver shorted full on it 

 would not necessarily take out the system fuse. I don't have any idea 

 what the tolerance is on an ATC fuse. I have 700 hours on the original 

 10 amp fuses that feed the 4 cylinder soob. I've had two cases of one 

 cylinder losing power due to a partial coil failure. Once during 

 initial ground testing and once at around 500 hours. These are DIS 

 coils that each feed two cylinders but in both cases only one cylinder 

 lost power.

 Ken

 On 22/10/2016 2:02 PM, Robert L. Nuckolls, III wrote:

> At 08:53 AM 10/22/2016, you wrote:

>> 

>>

>> If a forced landing is immanent, all electrical power should be shut 

>> off to prevent ignition of leaking fuel.  A master switch that shuts 

>> off everything including the engine is good for that scenario. 

>> However, smoke in the cockpit is an emergency that may require 

>> shutting off all electrical loads except the engine.   In that case, 

>> engine ignition needs to be independent of the master switch.  The 

>> most reliable ignition circuit is less complicated and has fewer 

>> components.  If it were my plane, I would power the ignition system 

>> from the battery, independent of the master switch.  The engine 

>> starter circuit should be disabled when the master switch is off.

>

>    Agreed . . .

>

>    Since your ignition system will run nicely

>    on 7A or less, I too would recommend you

>    run the ignition directly from the battery

>    through a 7A fuse. Power the starter from

>    the bus powered through the master contactor.

>

>    The ignition circuit is low risk for post-crash

>    ignition source . . . so even if you don't

>    get the engine killed before anticipated

>    contact the primary risk is to the engine

>    having a powered prop strike.

>

>    Taking everything else through the battery

>    master is the conventional philosophy.

>

>

>   Bob . . .

>

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Oct 23, 2016 4:51 am Post subject: Coiled ignition systems

At 02:37 PM 10/22/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: C&K <yellowduckduo(at)gmail.com>



 A 7 amp CB seems reasonable but a 7 amp fuse makes me a bit nervous. I seem to recall that when I looked at ignition currents I noted that they went up at high rpm, at high temperatures, and in some rare cases when the engine was not turning. 	


    The Kettering-coil style ignition system

    draws the most with engine stopped and points

    closed. Current goes down after engine starts

    and slightly less at higher rpm.



  	  Quote: 	
		  I did not notice any automotive systems that lightly fused the ignition circuits. 	


    No rational for doing it in cars . . . all fused

    feeders are relatively robust with respect to

    their loads. In the case of an always-hot

    battery feed, the AVIATION rational is 5A

    max breakered, 7A max fused. For a Kettering

    coil/points system, 7A fusing is very robust.



  	  Quote: 	
		    So while I've never measured over 5 amps on my soob units, my personal recommendation is a minimum 10 amp fuse on ignition circuits that feed multiple cylinders even if they are solid state. 	


    Those are CDI or other more modern techology

    and DO behave differently from the Kettering

    coil/points system.



  	  Quote: 	
		    It may be that the peak currents as seen on a scope caught my attention or that I just like more headroom on critical fuses. I think part of my thought process might have been that on my system if one solid state coil driver shorted full on it would not necessarily take out the system fuse. I don't have any idea what the tolerance is on an ATC fuse. I have 700 hours on the original 10 amp fuses that feed the 4 cylinder soob. I've had two cases of one cylinder losing power due to a partial coil failure. Once during initial ground testing and once at around 500 hours. These are DIS coils that each feed two cylinders but in both cases only one cylinder lost power. 	


    Understand . . . but that's a different

    breed of cat . . .



    Even so, even real beastly electronic CDI

    systems (Lightspeed comes to mind) only

    draw 2.5A at 28V into a constant-power

    switchmode power supply . . . so 5A at 14V

    for a 6 cylinder engine at red-line rpm.

    That's a LOT of watts. Waaayyyy more than

    necessary but I think Klaus's engines are expected to

    run on spark-power alone (just kidding).



    But consider a 10A feeder in an automobile:

    7A continuous is a reasonable load factor for

    a 10A fuse. In a 14v system 7A is 100 watts.

    There's just no reason that the ignition

    system should use such power. Consider the

    ignition excitation system on a Rotax that

    a gets fly-by of a single magnet once every

    crankshaft revolution . . . compare that with

    the array of magnets, windings and cores on

    the same flywheel designed to 18A at 14 volts

    or 250 watts . . . a huge difference in energy

    budgets/requirements.



    But your point is well taken and the caveat

    here is to KNOW the requirements your particular

    system. When in doubt measure it. 



 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sun Oct 23, 2016 6:22 am Post subject: Re: Coiled ignition systems

This discussion reminds me of the electric fire pump motor at work.  I can not remember the size, but it was a big motor, 50 or 100 HP, 3 phase, 480 volts.  There was no circuit protection, just a disconnect switch.  The reasoning is that it is more important to save the factory from fire than to protect the fire pump motor or wiring.  If anyone is interested, you can read about fire pump requirements:

http://ecmweb.com/code-basics/power-pump

Some aircraft builders might apply the same reasoning to their engine ignition system by using an oversize fuse.  They would rather have the wires and coils burn up than take a chance on a fuse blowing and the engine quitting.  Of course smoking components should be on the engine side of the firewall.

  I am not recommending a fuse size that would actually allow wires to smoke, just saying that a fuse could be one or two sizes bigger for a critical application.

_________________
Joe Gores

rnjcurtis(at)charter.net
Guest

Posted: Sun Oct 23, 2016 7:39 am Post subject: Coiled ignition systems

This discussion reminds me of the electric fire pump motor at work.  I can not remember the size, but it was a big motor, 50 or 100 HP, 3 phase, 480 volts.  There was no circuit protection, just a disconnect switch.  The reasoning is that it is more important to save the factory from fire than to protect the fire pump motor or wiring.  If anyone is interested, you can read about fire pump requirements:

http://ecmweb.com/code-basics/power-pump

Some aircraft builders might apply the same reasoning to their engine ignition system by using an oversize fuse.  They would rather have the wires and coils burn up than take a chance on a fuse blowing and the engine quitting.  Of course smoking components should be on the engine side of the firewall.

  I am not recommending a fuse size that would actually allow wires to smoke, just saying that a fuse could be one or two sizes bigger for a critical application.

 

               I would (ass u me) that the manufacturer’s specs on installation of an electronic ignition would spec wires to handle the maximum current draw of the unit under all operating conditions.  If one were to fuse it to these specs, then there should be no wire burning, and the fuse will not blow unless there is a failure causing more than the maximum current flow.  This might mean that if you have a “current hungry” device, the fuse could possibly be a bit larger than the 7 amp max normally specified on production aircraft.  If you have a problem with using a larger fuse, even though it is protecting your wiring, then I would suggest that the alternative is to purchase and install an ignition system with a current draw that is within your comfort zone.

 

               Roger

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 24, 2016 9:24 am Post subject: Coiled ignition systems

I would (ass u me) that the manufacturer's specs on installation of an electronic ignition would spec wires to handle the maximum current draw of the unit under all operating conditions.



   Actually, the manufacture should be silent on

   the matter of wire sizes and protection OUTSIDE

   their product's boundaries.



   The classic interface specification for aircraft

   hardware speaks to a 'box' . . . some kind of device

   or collection of devices with goesintas and goesoutas.



   I.e. you supply operating energy and control command

   inputs to effect the specified result whether that's sparks,

   noises from the headphones, or fluid flows to the engine

   as outputs.



   You also list limits for which the product is designed

   and tested to tolerate which included but are not

   limited to performance, extraordinary demands, environment,

   etc.



   This philosophy offers a set of conditions that are

   easily verified during qualification and manufacturing

   in the laboratory environment. This is how we get the

   'good housekeeping seal of approval' on the various

   mechno and electro-whizzies totally independent of

   the products ultimate application.



   It is up to the system designer to evaluate capabilities

   and limits for the sub-system for suitability to task

   in the super-system. This would include a failure mode

   effects analysis and characterizing the risks to

   aluminum and body parts should expectations not

   be realized.



   The fire-fighting pump narrative is interesting . . .

   it was probably the sum total of regulatory effects

   for two or more committees . . . who don't talk

   to each other . . . never had to fight a fire . . .

   and don't do system integration tasks aided by

   thoughtful FMEA.



   In the case of our single Kettering ignition system,

   exactly what kind of fault might we suppose would

   demand an extra-ordinary amount of energy yet

   have no effect on normal or even crippled

   operation of the ignition system?

   Get out your hammers, picks, soldering irons . . .

   any tool of your choice and create a fault within

   the system that falls within the scenario of

   concern.



   In the case of single, battery-powered Kettering

   (or even more modern automotive) ignition systems,

   we're evaluating the same risks tackled by 

   all auto-conversion configurations since

   the DH Pietenpol bolted the model A engine

   into the Air Camper. 



  http://tinyurl.com/jxctbso



  http://tinyurl.com/z5syrtf

   

   Interestingly enough, the model T engine was

   wwaayyyy ahead of its time. Like modern automobiles,

   each spark plug enjoyed its own, dedicated ignition

   coil. This offered some level of failure tolerance

   for the coils each of which behaved much like the

   'shower of sparks' system and featured its

   own set of vibrator points and 'condenser'.



 [img]cid:.0[/img]



   The fundamentals for storing energy on an

   inductor, using 'transformer action' of a

   high ratio secondary, periodic charging

   and release of the energy through a switch

   and value of adding a capacitor across that

   switch to improve spark performance and

   switch life were well understood. The Ford

   system described above illustrates application

   of those principals. 



   Tesla knew these things too as illustrated

   in his patent of 1893.



  http://tinyurl.com/gro5ruq



   But Kettering took those simple ideas and

   distilled them down to the simplest, most

   robust configuration that was also manufacture

   friendly. Not that in the Kettering patent,

   the system steil featured the 'buzzer', 'vibrator'

   or 'tembler' to provide multiple sparks per timing

   intervale. 



   Later all the car manufactures capitalized on A.

   Kent's improved ignition coil ideas such that

   multiple sparking was no longer necessary. The

   vibrator went away (but was still use to boost

   magneto cranking performance aka "shower of sparks").



   Yes, engine operation is real important for

   staying airborne. Assuming one chooses

   to fly with a single, battery powered ignition

   system, what value is secured by making the

   power feeder to that system extra robust with

   respect to current draw?



   Further, what's the demonstrated history of

   the Kettering style system. I've driven hundreds

   of thousands of miles behind such systems with

   nary a single engine-crippling failure of the

   ignition system.



   The factor germane this thread becomes clear

   with understanding how the various systems

   work . . . after knowing everything there is

   to know . . . exactly what condition MIGHT

   arise in the field to produce a system that

   draws too much current but still functioning?



   This question is tsame whether you're contemplating

   a Model A engine with a stock Ford ignition in a

   Pietenpol or a I0-540 with Light Speed's spark

   plug blaster



   Recall that the overwhelming majority of engine

   failures in airplanes are the result of fuel

   exhaustion. Mechanical failures come next.

   Given our understanding and experience with

   the Kettering system, what are the real risks

   loss of the ignition due to component wear-out

   or gross failure?



   It would be interesting to talk to the Corvair

   jockies. But I'd beet a case of beer to a pack

   of chewing gum that any ignition failures they

   have experienced were borne of poor maintenance

   or craftsmanship as opposed to unexpected 

   component failure.



   Bottom line is that there is little 'comfort'

   to be secured with fatter fuses and wires . . .

   and much comfort to knowing the system's

   performance and limits and then doing the FMEA

   drives risks to acceptably low levels. I suggest

   further that the fire water pump analogy is

   not particularly meaningful in the well crafted

   heavier than air flying machine. 

  



 



 

   Bob . . .

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lm4(at)juno.com
Guest

Posted: Mon Oct 24, 2016 12:03 pm Post subject: Coiled ignition systems

On Oct 24, 2016, at 1:22 PM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		  I suspect the fire fighting pump story could br referenced to 

that part of the NEC wheras one is forbidden to fuse or 

breaker conductors when the failure of the equipment will 

put lives at risk.



	
									Larry



 	  Quote: 	
		     The fire-fighting pump narrative is interesting . . .

   it was probably the sum total of regulatory effects

   for two or more committees . . . who don't talk

   to each other . . . never had to fight a fire . . .

   and don't do system integration tasks aided by

   thoughtful FMEA.

 

	


  



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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 24, 2016 4:04 pm Post subject: Coiled ignition systems

At 03:02 PM 10/24/2016, you wrote:



  	  Quote: 	
		  On Oct 24, 2016, at 1:22 PM, Robert L. Nuckolls, III wrote:

  	  Quote: 	
		  I suspect the fire fighting pump story could br referenced to 

 that part of the NEC wheras one is forbidden to fuse or 

 breaker conductors when the failure of the equipment will 

 put lives at risk. 	
	


   Does it really read that way? the whole idea

   behind conductor protection is to (1) prevent

   catastrophic failure of the conductor with

   the attendant risk of smoke, fire and propagation

   of the failure event to other conductors and

   their systems.  And (2) prevent

   a failure from propagating upstream . . . the

   i(squared)*t constant for the upstream protection

   must be some large factor greater than any

   single protection . . . lest a short in your

   toaster turn out the neighborhood lights.



   I've demonstrated that a 22AWG wire, normally

   loaded to less than 5A, is not at serious

   risk for failure at loads up to 20A.



  http://tinyurl.com/h3zlpta



   Current limiters in airplanes (while they

   have the general appearance of fuses) have

   very robust I^2*T numbers. they protect

   wires from hard faults while avoiding nuisance

   trips due to opening transients due to

   operation of a downstream protector.



   There are fuses and breakers, then there

   are FUSES and BREAKERS. I suggest there are

   NO situations where feeders for any device

   cannot be selected to meet design/risk goals

   without making vague blanket statements about

   'putting lives at risk'.



   Circuit protection has always been about avoinding

   risk to folks and hardware . . . it's just a matter

   of picking the right protection. 



 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Mon Oct 24, 2016 4:30 pm Post subject: Re: Coiled ignition systems

 	  Quote: 	
		  Overcurrent protection [695.6(D)]. Overcurrent protection devices (OCPDs) must be sized to carry the sum of the locked-rotor current of the fire pump and pressure maintenance pump motor(s) indefinitely, and 100% of the ampere rating of the fire pump's accessory equipment. 	


In other words, there is no over current protection, but there is short circuit protection.

_________________
Joe Gores

lm4(at)juno.com
Guest

Posted: Mon Oct 24, 2016 4:40 pm Post subject: Coiled ignition systems

On Oct 24, 2016, at 8:03 PM, Robert L. Nuckolls, III wrote:



 	  Quote: 	
		   At 03:02 PM 10/24/2016, you wrote:


	


 	  Quote: 	
		   It doesn't read exactly that way and I have forgotten how exactly how it does read.

But, I do remember that there was a main breaker, fused, for much more than the wire 
	


would need for protection. The conductors were kept in their own conduit and the 

overload protection on the motor of the gantry crane had to be removed. 

That sounds a lot like the fire protection motor. At least it does to me

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