Ignition question

[Gordon]

I am currently building an Upshur twin cylinder engine. Plans call for a distributor. There has been some discussion in another thread about using a single ignition module with a wasted spark. My thought is to use one module with a COP coil with two high tension wires off from the coil. I have used that successfully with a single cylinder engine. Has anyone done that? Would it work better to use two coils from a common module? Any time that the engine fires one plug is under compression and the other is exhausting. I am not worried about battery life. These engines never run for more than 15 minutes.

Gordon

 

[Charles Lamont]

Use a Minimag Novus-2 coil? - designed for waster spark.

 

[Gordon]

Use a Minimag Novus-2 coil? - designed for waster spark.

I have never heard of them but that is quite expensive and in UK and I am in US so that makes it difficult. It actually would be cheaper to use two separate systems. The COP coils are pretty cheap.

 

[Longboy]

These type of coil systems are like ........inches tall. Seems outta place sticking up from a model engine. What's the issue avoiding a distributor and single lead coil?

 

[Gordon]

These type of coil systems are like ........inches tall. Seems outta place sticking up from a model engine. What's the issue avoiding a distributor and single lead coil?

The coil itself is about 1 3/4 dia x 2" long. The long extension can be removed. The ones I have been using are for a Ford engine and they are available on eBay for about $30 for a set of eight.

I have been looking and there are apparently wasted spark ignition coils available. These are automotive and motorcycle so I am not sure if they would work. I am still trying to figure it out but it seems like the plugs change polarity as each one is fired. It is not my area of expertise so I am trying to comprehend what is happening. If the polarity is indeed changing it would not work with a hall sensor because the wrong polarity burns them out immediately.

I have also discovered that I have a MJN Exciter coil which I have never used with two leads. If I recall it needs a resistor in order to work.

Gordon

 

[propclock]

I have done this many times . Use 2 coil over plugs with primary's in series.
They have VERY low primary resistance so this actually helps that a bit.
I use dg508 coils from ebay about 5$ each. I use the Dave Sage
coil driver circuit. I even made a V8 this way no distributor. 8 coils. 4 drivers.
It was a Shilling V8 made for glow fuel , converted to spark/gas.

 

[Longboy]

.......I have been looking and there are apparently wasted spark ignition coils available.........
I have also discovered that I have a MJN Exciter coil which I have never used with two leads. If I recall it needs a resistor in order to work.
Gordon

Wasted spark coils are not a type of ign. coil but just an effect presented in 4 stroke timing sequence where it's second lead is on an exhausting cylinder. Motorcycle dual lead coils need just one points set or electronic module to fire. My best guess is your MJN being more compact yet is the way to go. I have this classic Smith dual fire coil on a distributor-less 2 cyl. model. Does well.

 

[propclock]

Did you ever wonder why you don't see a distributor on all those
4 cylinder motorcycles? wasted spark. Honda's have single primary and a dual
secondary that goes to 2 plugs one with + spark one with - spark.
The coil has to jump 2 spark gaps though.
So if you can find a motorcycle dual out put coil , and some cars
used dual output coils you are good to go. But 2 coil over plug coils
are readily available. and cheep.

 

[Gordon]

OK Thanks. It looks like two COP coils are the best way to go. I have tried using the MJN coil in the past and did not have any luck. I am not sure if the coil is defective or I had it wired wrong. I will probably try the MJN coil first and if I cannot get that to work I will go to the COP coils. I already have those because I have used them on several other single cylinder engines. My plan is to try using the Howell buzz coil module which I also already have.

Gordon

 

[TonyM]

I get that a wasted spark on a single works because the wasted spark occurs on the exhaust. On a twin though, one cylinder on exhaust one cylinder on compression wouldn't the wasted spark on the exhaust cylinder stop the spark occuring on the compressed cylinder as the resistance is lower on the exhaust cylinder?

 

[bobden72]

OK what do the acronyms COP and MJN mean please.

 

[tornitore45]

If a single coil feeds two plugs (in parallel) the plug in the exhausting cylinder has a lower spark voltage (lower pressure) and will fire first lowering the voltage to both plugs. The plug in the compressing cylinder may have insufficient voltage to fire.
Regular coils have one lead of the HV secondary internally tied to the points or GND.

A wasted spark system either use 2 coils ore one coil where both ends of the HV secondary are available and well insulated. Each end of the secondary goes to one plug. The two plugs gaps are effectively in series with the middle point going to chassis. Since the voltage drop on the exhausting cylinder is minimal it does not subtract substantially from the voltage available to the firing cylinder.

 

[stevehuckss396]

COP is "Coil on plug"
MJN is "Mike J Neal" Mike Neal was a supplier of ignition parts. I started building engines in 2006 and he was already out of the business or close to it.

 

[rsholl]

Gordon,

email me at rsholl@cncengines, I am still building CDI units and do a twin/waste fire CDI. Efficient and runs on 4.5-5 volts.

 

[Ken I]

A wasted spark system uses two coils or a duplex coil (one primary and two secondary's) - they both fire together, once per revolution so each plug fires once at the end of the compression stroke and again at the end of the exhaust stroke - this is the "wasted spark".

Using a single coil to fire two plugs in parallel will only end in tears. Similarly using a single coil to fire through both plugs in series means the cylinder block cannot be grounded and has "float" to such high above ground voltages that it will strike to earth via other point or hall effect sensor wiring resulting in a single cylinder only firing - not to mention damage to electronics etc. etc. Don't even think of attempting either of these methods.

There are plenty of motorbike and car engines that use duplex coil systems - some with a built in trigger system - look for three wire terminals - pos. neg & fire but you need to dope out the system there are a number of variants. Typically the "fire" signal needs to be a transient signal as the internals short out the pos. & neg. during firing - some have ballast resistors, some rely on the wiring resistance alone.

I tried driving one off a square wave generator and it rapidly overheated as the "short" was present 50% of the time - inserting a filter capacitor (which produced a transient from the square wave) sorted that out.

Regards, Ken

 

[tornitore45]

Similarly using a single coil to fire through both plugs in series means the cylinder block cannot be grounded and has "float" to such high above ground voltages that it will strike to earth via other point

Not true and WRONG. The "floating" block as you call it is the reference point is no more floating that the block of an 8 cylinder with standard ignition. When the exhaust plug fire fist there is short to chassis and it behave exactly like a normal ignition. The next cycle the same happens at the other plug.

I built an Upshure twin Boxer engine that run just fine with the plugs in series.
I can put mi tongue on the chassis with no danger of shock.
As everything in science and engineering, one counterexample disprove a million people insisting on a wrong theory.

Damage to electronic is always the result of poor wiring sequence in the GND network. There is a correct way to sequence all the nodes connected to common/GND. Just bungling them all together randomly has a good chance of missing the correct topology.

 

[Ken I]

Mauro, It works only as long as the coil is not grounded - something has to float - but I'm not sure I'd risk my tongue on it.

Regards, Ken

 

[tornitore45]

Of course. The HV secondary is not grounded and well insulated from it at both sides.
The primary is tied to battery and grounded by the points periodically.

I took a job with a company that was developing power IC for the first time after a lifetime of developing low voltage circuits.
The culture there was very afraid (rightly so) of the 400VDC the new development dealt with.
One day in the lab, the technician was worried about the wire insulation, whether it was adequate for 400V. He would not touch the wires with the circuit energized. I told him Look and I gave a long French kiss to the wire. I knew what I was doing.
That became the news of the day... Mauro licked the wire, everybody was told. People were less afraid since then.
Is not a matter of being afraid or bold. Real danger needs to be respected. But knowledge can be the difference between safe and dead.

 

[Steamchick]

Hi Mauro. As you appreciate, but maybe it doesn't come across so clearly: It's not "volts" that kill, nor Amps, but the combination - and whether DC or AC, and where applied.
They say that when the electric chair was powered-up, the lights used to "Dim" a bit.... due to the power taken by the occupant. No so, as you can kill at relatively low power given the right circuit to stop the heart....
In fact putting it simply: 12V cars are safe for the 12V circuit. Ignition circuits are safe at 2~5kV - unless you apply it from one finger to the opposite arm and continuously for more than a few seconds. Then it can cause the heart to fibrillate - which can be deadly.
Single bolts of lightning - at 50,000kV usually don't kill, but cause nasty burns on the skin.
Telephones were powered by 50V DC for decades... and were reputed to have never killed anyone.
Yet a 1500V DC third rail on the railway WILL kill, just as easily as the 110V, 240V or whatever you have in the house....
Yet with trained Electricians perform "live-line" working on overhead lines at 33kV and above. But they have the training, understand equipment and safety measures to "make it work safely".
Edison killed elephants with AC current to try and frighten people from wanting Tesla's AC systems. Yet if he had used the same power (voltage and current) DC, then the elephants would be just as dead.
Don't be frightened of electricity, just respectful and careful.
It's not the voltage, but current across the heart or brain that kills, but to get the current you need more than 50V applied in the right way.
The single HT circuit coil winding discussed above does NOT connect to earth anywhere on the HT circuit - except between cylinders. So the ends of the coil "float" instantaneously at whatever voltage is across the nearest spark gap. Assuming a 3kV coil, the end adjacent to the "exhaust" spark will be at around 300V to generate that spark, whereas the end of the coil at the "firing cylinder end" will be at around 2700V. (Voltage relative to the engine block). And on the next firing stroke, the voltages will be the equivalent - but the coil will see it the other way around. It's the coil that does does the "clever" bit (effectively floating...), as the engine block stays at "earth" - because the primary winding keeps it there. So only the voltage in the coil and HT cables to spark plugs ever sees "high voltage".
It puzzles me that we (non-electricians) want "clever electronics" to power our "Victorian technology" engines, as simple coil and contact ignition was very successful for around 100 years... After all, we are doing it "just for fun", and "remembering" classic engines. So maybe we should be using some "Classic" ignition technology?
I'll shut-up now.
K2

 

[Gordon]

I did not take long for this to go way over my head. Seems like some folks have had success with setups others say cannot work. Ignition systems are not my area of expertise.