Simple Test for Coil On "Wasted Spark" 2 Cylinder Engine

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Ian Field wrote:

> All the "wasted spark" coils I've seen are strung between the 2
> plugs and have no chassis connection anywhere between the 2 HT
> leads emerging from the unit.


Except for the engine block metal in between the two plugs. That is
part of the series circuit.....

'coil end 1'...plug...metal...plug...'coil end 2'



mike






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"m II" <C@in.the.hat> wrote in message news:jq97de$i3p$1@dont-email.me...
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>
> Ian Field wrote:
>
>> All the "wasted spark" coils I've seen are strung between the 2
>> plugs and have no chassis connection anywhere between the 2 HT
>> leads emerging from the unit.
>
>
> Except for the engine block metal in between the two plugs. That is
> part of the series circuit.....
>
> 'coil end 1'...plug...metal...plug...'coil end 2'


I assumed that would be obvious to all but the very thickest of dumbasses. 

On Wed, 30 May 2012 16:26:17 -0700 (PDT), Bret Cahill
<BretCahill@peoplepc.com> wrote:

>I meant "does doubling the voltage in the primary double the voltage
>in the secondary?"

Not in the standard Kettering, or any system that depends on the
collapsing magnetic field to produce the voltage spike.  

With more voltage you could saturate the iron faster so the "dwell"
time could be less (translates to a hotter high RPM spark).
Eventually you run up against iron saturation as the limiting factor.
Higher voltage increases the ampere-turns and magnetic field strength.

You are thinking transformers and applying that to induction coils -
two different animals.

Now something like a CDI where you operate the coil like a pulse
transformer would seem to benefit from increased primary voltage.

>>the bike would die if the brake light
>> filament burned out and you used the brakes. &#4294967295;(one of its many
>> endearing idiosyncrasies)

>Sounds like a good safety feature got dove tailed in there.

As far as letting you know the light is out  - a resounding YES, but
it wasn't easy, or safe,  to drive very far that way, particularly in
traffic on hills.  

>> Johnson and Evinrude both use energy transfer magneto systems with
>> dual secondary coils. Or my three outboards do (circa 1987 and
>> earlier) &#4294967295;If you need a coil like that - try a junked outboard.
>
>It might not fit physically but would it work electronically?
>
>I just read where the CDI coil for a Honda 100 outboard was only 9K
>ohms between the two spark plug wires.
>
>The coil I have is 30K ohms between the two spark plug wires.  If
>higher resistance => higher voltage in the secondary this would seem
>to be closer to what an energy transfer system might require.

I don't think you can put too much trust in DC resistance values.  A
high secondary resistance might suggest a lot of  turns of very fine
wire, and that would probably be a Kettering system coil where
inductive collapse is the means of producing high voltage.  If the
system is run as a pulse transformer, turns ratio  would seem to count
for more - that is a relatively few turns in the primary and lot in
the secondary (something all systems have but I'm talking an order of
magnitude fewer primary turns, so they might use larger diameter
secondary wire with fewer turns)

When all is said and done, it is the energy in the spark that
initiates ignition, not the voltage.  A high current spark of 4,000
volts may outshine a low current 30 KV spark.

Did you also measure from the coil secondaries to ground?  My Honda
coils have a bare wire that runs from the molded epoxy housing to the
core iron and it is painted black along with the iron - secondary is
center tapped to ground (at least when bolted to the frame).

And Honda calls it "CDI" but it runs from the battery and the modules
that do the switching aren't very large - they are ~1" X 1-1/4" X 3/8"
and it is obvious that most of the room inside the things are potting
epoxy and large diameter wires (relative to the size of the module).
It seems way too small to actually step up voltage to charge a cap to
fire the coils.

Here is a url for a site that may help a little...
http://gardentractorpullingtips.com/ignition.htm


http://www.cx500.50webs.com/
"How to Build a 1980 Honda CX500C CDI Module"

with schematic

On Thu, 31 May 2012 20:20:34 +0100, "Ian Field"
<gangprobing.alien@ntlworld.com> wrote:

>
><default> wrote in message 
>news:cun6s7lvv6u9jp8oik2cg5d90td51b4c0u@4ax.com...
>> On Fri, 25 May 2012 16:40:43 -0700 (PDT), Bret Cahill
>> <Bret_E_Cahill@yahoo.com> wrote:
>>
>>>I suspected a CDI coil wouldn't put out enough voltage for the "energy
>>>transfer" -- the worst misnomer ever -- system and suggested shorting
>>>out the spark plug electrode on one of the 2 cylinders by pounding the
>>>gap shut or stuffing it with a bit of foil.
>>>
>>>The theory was instead of jumping two gaps it would only need to jump
>>>one.  The lower effective resistance would give a better spark on the
>>>remaining firing cylinder.  The al foil trick worked.  It ran on one
>>>cylinder which seems to confirm my suspicions about the coil as well
>>>as my test, which may or may not be original.  Googling is hard work.
>>>
>>>Anyway the engine has two magnetos opposite each other, one for the
>>>ignition and one for charging the battery.  The four magnets are
>>>equally spaced on the flywheel.
>>>
>>>The 2 low voltage magneto coils look about the same and both seem to
>>>do the same thing to a volt meter when cranked -- admittedly not a
>>>very scientific indicator.
>>>
>>>It seems like it would be possible to just forget about charging a
>>>battery and wire another CDI coil to the charger coil.
>>>
>>>Even simpler would be to tap the plug gaps to half that recommended in
>>>the specs.
>>>
>>>Maybe the fuel efficiency would drop by 20%?  Maybe it wouldn't fire
>>>at all?
>>>
>>>
>>>Bret Cahill
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>> The wasted spark is derived from two series connected coils (connected
>> at the low voltage side in series) or one coil with two secondary
>> windings;  the spark plugs themselves aren't in series.  Think about
>> it - that would take an engine block operating ~20 KV above ground
>> unless you had spark plugs with two insulated electrodes.
>
>
>You'd be better off confining your replies to topics where you know what 
>you're talking about.
>
>All the "wasted spark" coils I've seen are strung between the 2 plugs and 
>have no chassis connection anywhere between the 2 HT leads emerging from the 
>unit.

Obviously you've never seen a BMW motorcycle ignition or a Honda with
a grounded twin secondary coil?  Pull one coil wire loose and the four
cylinder engine runs on three cylinders - not two.
>
>If you had 2 HT coils sharing the core with the same LT winding; the one 
>feeding the narrowest gap (inequality can happen no matter how good you are 
>with feeler guages) would effectively clamp the spark voltage - one plug 
>would have a good spark (sort of), the other plug would have a very weak or 
>no spark! 
>

On Fri, 01 Jun 2012 12:38:32 -0400, default wrote:

>
>
>http://www.cx500.50webs.com/
>"How to Build a 1980 Honda CX500C CDI Module"
>
>with schematic

After looking at it ...  I'm wondering if they are using the inductive
kick of the coil primary to charge the capacitor to a higher than
battery voltage.

> >http://www.cx500.50webs.com/
> >"How to Build a 1980 Honda CX500C CDI Module"
>
> >with schematic
>
> After looking at it ... =A0I'm wondering if they are using the inductive
> kick of the coil primary to charge the capacitor to a higher than
> battery voltage.

At least some CDIs step up from 12 V to 400 V in the CDI module.  If
it's 12 V DC then there's an inverter as well which is why DC CDIs are
often larger than AC CDIs.

The coil we're using is only slightly small than the original and
there 30K ohms between the two plug wires.  A CDI coil might be
significantly smaller and have lower resistance.

Is there any difference between a "pulsar" and a low voltage magneto?
It might be easier to omit the points and go to CDI.


Bret Cahill

default wrote:

> On Wed, 30 May 2012 16:26:17 -0700 (PDT), Bret Cahill
> <BretCahill@peoplepc.com> wrote:
> 
> 
>>I meant "does doubling the voltage in the primary double the voltage
>>in the secondary?"
> 
> 
> Not in the standard Kettering, or any system that depends on the
> collapsing magnetic field to produce the voltage spike.  
> 
> With more voltage you could saturate the iron faster so the "dwell"
> time could be less (translates to a hotter high RPM spark).
> Eventually you run up against iron saturation as the limiting factor.
> Higher voltage increases the ampere-turns and magnetic field strength.
> 
> You are thinking transformers and applying that to induction coils -
> two different animals.
> 
> Now something like a CDI where you operate the coil like a pulse
> transformer would seem to benefit from increased primary voltage.
> 
> 
>>>the bike would die if the brake light
>>>filament burned out and you used the brakes.  (one of its many
>>>endearing idiosyncrasies)
> 
> 
>>Sounds like a good safety feature got dove tailed in there.
> 
> 
> As far as letting you know the light is out  - a resounding YES, but
> it wasn't easy, or safe,  to drive very far that way, particularly in
> traffic on hills.  
> 
> 
>>>Johnson and Evinrude both use energy transfer magneto systems with
>>>dual secondary coils. Or my three outboards do (circa 1987 and
>>>earlier)  If you need a coil like that - try a junked outboard.
>>
>>It might not fit physically but would it work electronically?
>>
>>I just read where the CDI coil for a Honda 100 outboard was only 9K
>>ohms between the two spark plug wires.
>>
>>The coil I have is 30K ohms between the two spark plug wires.  If
>>higher resistance => higher voltage in the secondary this would seem
>>to be closer to what an energy transfer system might require.
> 
> 
> I don't think you can put too much trust in DC resistance values.  A
> high secondary resistance might suggest a lot of  turns of very fine
> wire, and that would probably be a Kettering system coil where
> inductive collapse is the means of producing high voltage.  If the
> system is run as a pulse transformer, turns ratio  would seem to count
> for more - that is a relatively few turns in the primary and lot in
> the secondary (something all systems have but I'm talking an order of
> magnitude fewer primary turns, so they might use larger diameter
> secondary wire with fewer turns)
> 
> When all is said and done, it is the energy in the spark that
> initiates ignition, not the voltage.  A high current spark of 4,000
> volts may outshine a low current 30 KV spark.
> 
> Did you also measure from the coil secondaries to ground?  My Honda
> coils have a bare wire that runs from the molded epoxy housing to the
> core iron and it is painted black along with the iron - secondary is
> center tapped to ground (at least when bolted to the frame).
> 
> And Honda calls it "CDI" but it runs from the battery and the modules
> that do the switching aren't very large - they are ~1" X 1-1/4" X 3/8"
> and it is obvious that most of the room inside the things are potting
> epoxy and large diameter wires (relative to the size of the module).
> It seems way too small to actually step up voltage to charge a cap to
> fire the coils.
> 
> Here is a url for a site that may help a little...
> http://gardentractorpullingtips.com/ignition.htm
> 
> 
> http://www.cx500.50webs.com/
> "How to Build a 1980 Honda CX500C CDI Module"
> 
> with schematic
Interesting blog here.

   A few years ago, I assisted a person that was restoring an old car.

  I gave him a circuit that involved using a 555 timer with a few other 
components to current sense and trigger the coil. He was using the 
standard auto transformer style of collapsing the field. If you monitor
the current (Dwell Time) in the circuit, you can pretty much dictate the
level of spark you need. Putting in a PTC also helped to lower the spark
level when the engine was hot.

   Monitoring the current in the primary side of the coil will allow you 
to adjust your dwell time and thus when design properly will also give
you timing control, all in one..

Jamie

On Fri, 1 Jun 2012 10:19:29 -0700 (PDT), Bret Cahill
<BretCahill@peoplepc.com> wrote:

>> >http://www.cx500.50webs.com/
>> >"How to Build a 1980 Honda CX500C CDI Module"
>>
>> >with schematic
>>
>> After looking at it ... &#4294967295;I'm wondering if they are using the inductive
>> kick of the coil primary to charge the capacitor to a higher than
>> battery voltage.
>
>At least some CDIs step up from 12 V to 400 V in the CDI module.  If
>it's 12 V DC then there's an inverter as well which is why DC CDIs are
>often larger than AC CDIs.
>
>The coil we're using is only slightly small than the original and
>there 30K ohms between the two plug wires.  A CDI coil might be
>significantly smaller and have lower resistance.
>
>Is there any difference between a "pulsar" and a low voltage magneto?
>It might be easier to omit the points and go to CDI.
>
>
>Bret Cahill

I don't know what a pulsar is - some manufacturer's name for
something?

If you read that URL for small engines he shows how to adapt various
car type solid state ignitions with pickup coils to old points type
small engines.  Nothing looks too easy (to me) but that might all
depend on what type engine you have.

Briggs and Stratton did, and probably still do, have a retro-fit for
magneto coils so that the points are solid state.  I haven't messed
with it myself.

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message 
news:kr7yr.30447$x11.25507@newsfe21.iad...
> default wrote:
>
>> On Wed, 30 May 2012 16:26:17 -0700 (PDT), Bret Cahill
>> <BretCahill@peoplepc.com> wrote:
>>
>>
>>>I meant "does doubling the voltage in the primary double the voltage
>>>in the secondary?"
>>
>>
>> Not in the standard Kettering, or any system that depends on the
>> collapsing magnetic field to produce the voltage spike.  With more 
>> voltage you could saturate the iron faster so the "dwell"
>> time could be less (translates to a hotter high RPM spark).
>> Eventually you run up against iron saturation as the limiting factor.
>> Higher voltage increases the ampere-turns and magnetic field strength.
>>
>> You are thinking transformers and applying that to induction coils -
>> two different animals.
>>
>> Now something like a CDI where you operate the coil like a pulse
>> transformer would seem to benefit from increased primary voltage.
>>
>>
>>>>the bike would die if the brake light
>>>>filament burned out and you used the brakes.  (one of its many
>>>>endearing idiosyncrasies)
>>
>>
>>>Sounds like a good safety feature got dove tailed in there.
>>
>>
>> As far as letting you know the light is out  - a resounding YES, but
>> it wasn't easy, or safe,  to drive very far that way, particularly in
>> traffic on hills.
>>>>Johnson and Evinrude both use energy transfer magneto systems with
>>>>dual secondary coils. Or my three outboards do (circa 1987 and
>>>>earlier)  If you need a coil like that - try a junked outboard.
>>>
>>>It might not fit physically but would it work electronically?
>>>
>>>I just read where the CDI coil for a Honda 100 outboard was only 9K
>>>ohms between the two spark plug wires.
>>>
>>>The coil I have is 30K ohms between the two spark plug wires.  If
>>>higher resistance => higher voltage in the secondary this would seem
>>>to be closer to what an energy transfer system might require.
>>
>>
>> I don't think you can put too much trust in DC resistance values.  A
>> high secondary resistance might suggest a lot of  turns of very fine
>> wire, and that would probably be a Kettering system coil where
>> inductive collapse is the means of producing high voltage.  If the
>> system is run as a pulse transformer, turns ratio  would seem to count
>> for more - that is a relatively few turns in the primary and lot in
>> the secondary (something all systems have but I'm talking an order of
>> magnitude fewer primary turns, so they might use larger diameter
>> secondary wire with fewer turns)
>>
>> When all is said and done, it is the energy in the spark that
>> initiates ignition, not the voltage.  A high current spark of 4,000
>> volts may outshine a low current 30 KV spark.
>>
>> Did you also measure from the coil secondaries to ground?  My Honda
>> coils have a bare wire that runs from the molded epoxy housing to the
>> core iron and it is painted black along with the iron - secondary is
>> center tapped to ground (at least when bolted to the frame).
>>
>> And Honda calls it "CDI" but it runs from the battery and the modules
>> that do the switching aren't very large - they are ~1" X 1-1/4" X 3/8"
>> and it is obvious that most of the room inside the things are potting
>> epoxy and large diameter wires (relative to the size of the module).
>> It seems way too small to actually step up voltage to charge a cap to
>> fire the coils.
>>
>> Here is a url for a site that may help a little...
>> http://gardentractorpullingtips.com/ignition.htm
>>
>>
>> http://www.cx500.50webs.com/
>> "How to Build a 1980 Honda CX500C CDI Module"
>>
>> with schematic
> Interesting blog here.
>
>   A few years ago, I assisted a person that was restoring an old car.
>
>  I gave him a circuit that involved using a 555 timer with a few other 
> components to current sense and trigger the coil. He was using the 
> standard auto transformer style of collapsing the field. If you monitor
> the current (Dwell Time) in the circuit, you can pretty much dictate the
> level of spark you need. Putting in a PTC also helped to lower the spark
> level when the engine was hot.
>
>   Monitoring the current in the primary side of the coil will allow you to 
> adjust your dwell time and thus when design properly will also give
> you timing control, all in one..
>
> Jamie


At various times I've tried all kinds of circuits for transistor assisted 
contactor - every single one failed due to the lack of "wetting current", 
oxide, tarnish or whtever insulated the points faces before I got as far as 
the end of the road.

The most successful version to date used a high voltage MOSFET (from flyback 
switcher PSU in 19" monitor) used in basically grounded base mode.

The coil lead was removed from the points abd connected to drain, the gate 
was connected to +12V and the source connected to the points. A suitable 
capacitor was found to put directly in parallel with the LT winding and a 
zener was added to clamp the G/S voltage.

With the conventional coil/points arrangement, the points capacitor slows 
the Dv/Dt so the spark quenches sooner as the points part, but the spark 
still lasts long enough to waste significant energy - with the grounded gate 
MOSFET the points voltage never exceeds 12V. Grounded gate is the fastest 
configuration so the coil current is interrupted orders of magnitude faster 
(you do need that capacitor!).

Not sure what the usual practice elsewhere, but on kettering ign honda 
motorcycles, they usually wind the LT coil with wire having a strong PTC. A 
sample coil drew 8A when connected to a 12V battery, but the reading sank 
steadily untill it levelled out at 4A as the coil became warm - where 
motorcycle coils are mounted gets a good airflow once underway, so they're 
well cooled at normal commuting speeds. 

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Ian Field wrote:

> I assumed that would be obvious to all but the very thickest of
> dumbasses.


I should have realized this was just another of your many, ill-formed
personalities. Feel the pity.

mike










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