Dear Experts,
I have a specific need to improvise a circuit for sparking a Spark Plug (a Vehicle Spark Plug) outside the vehicle set up. On a table top.

So I searched and came across this circuit design where it requires one to connect a battery to Ignition Coil thru a ballast resistor and the output of ignition coil connects to the spark plug. (Image attached)

I didnt use the distributor cam etc., but just used a contactor to break open the primary coil voltage from battery to see if the plug sparks.

It does spark, but the issue is that the spark is too feeble. Visible but feeble. Also, its not repetitive.

Now I am using standard automobile components so I don't wanna doubt them.

My questions:
1) Is this circuit, as it is, implemented in an automobile? Or its only an indicative one, with other spark intensity enhancing features added in real world design.

2) The secondary side of coil would require to spark the plug every fraction of second, given the speed of movement of piston etc. When I am repeatedly making and breaking the contacts, the spark seems to get more and more feeble and fails very frequently. So what is it that I am missing.

3) In the circuit it shows that the return of both Primary and Secondary side is connected to the return of Battery. Is it right? Doesnt it mix up the isolation between the two sides of the induction coil?

My aim is to get a healthy spark that is capable of igniting a predominantly methane gas mixture, under controlled conditions.

Looking forward to some insights on this.

Thanks in advance and regards,
Rahul

 

1) Yes. This is the general setup.
2) What is your "battery" ? If it is not a normal car battery, it may not be able to feed sufficient power to sustain the sparks.
3) Yes. It is ok. There is no need for Isolation between the Primary and Secondary.

In your case, you don't need the "Contact breaker/Distributor" setup. That is only if you need to distribute the spark across multiple spark plugs.

 

Have you connected the body of the sparking plug to 0V?

 

In an automobile, the contact points have a condensor connected across the contact points to dampen the back emf generated by the collapsing magnetic field.
Without this condensor you will experience a weak voltage at the ignition coil's secondary.

 

Hi Rahul,

Here's the schematic.



A standard electromagnetic relay, with its 'NC' contact connected in series with its coil, is used as an interrupter for the primary current.

When the push button switch is actuated, the continuous chatter of the relay contact will produce continuous sparking across the spark gap.

Using a breaker to break the primary current will produce only a single spark.

Nandu.

 

1) Yes. This is the general setup.
2) What is your "battery" ? If it is not a normal car battery, it may not be able to feed sufficient power to sustain the sparks.
3) Yes. It is ok. There is no need for Isolation between the Primary and Secondary.

In your case, you don't need the "Contact breaker/Distributor" setup. That is only if you need to distribute the spark across multiple spark plugs.

Battery is a standard car battery. But once the system works on 'table-top', we plan to source 12VDC from an electronic power supply.

I am using a contact breaker on the primary side to disconnect the primary from the battery, so that the magnetic field collapses and causes the spark to occur. Or that's what I have understood from what I read. That first you power up the primary so that the magnetic field saturates inside the coil.

And when you suddenly break the primary coil voltage (disconnect the battery), the magnetic field would collapse and this would cause di/dt to rise on the secondary and induce high voltage to cause a spark...!!

Hope I am doing it right...

 

Have you connected the body of the sparking plug to 0V?

Yes. The body of spark plug is wired to battery ground (negative).

 

As noted by DbLoud120 and vu2nan, the weak spark is likely because you omitted the necessary capacitor across the contacts.
Without the capacitor, much of the energy is lost in the spark across the opening contacts.
The capacitor allows the contacts to open with virtually no spark, so all the coil inductive energy can then generate the output spark

 

1) Yes. This is the general setup.
2) What is your "battery" ? If it is not a normal car battery, it may not be able to feed sufficient power to sustain the sparks.
3) Yes. It is ok. There is no need for Isolation between the Primary and Secondary.

In your case, you don't need the "Contact breaker/Distributor" setup. That is only if you need to distribute the spark across multiple spark plugs.

Also wondering if 24VDC would better the performance or destroy the coil...??

 

As noted by DbLoud120 and vu2nan, the weak spark is likely because you omitted the necessary capacitor across the contacts.
Without the capacitor, much of the energy is lost in the spark across the opening contacts.
The capacitor allows the contacts to open with virtually no spark, so all the coil inductive energy can then generate the output spark

Thanks indeed... I shall make the next attempt with a capacitor across the primary side interrupter and post...!!

Regards,
Rahul

 

Is this circuit, as it is, implemented in an automobile?

Not quite. It is missing the capacitor (condenser) across the switch contacts.
See: https://www.themagnetoguys.co.uk/condensers-theory

 

What resistor do you have in series? Did you try reducing it?

 

What resistor do you have in series? Did you try reducing it?

Its ~5 Ohms.

I didn't attempt at modifying any standard component that came along from a reputed automobile vendor. The ignition coil itself came with this resistor tied on its body. ( Buy Ignition Coil Online - GoMechanic )

Yes, I didn't use a distributor and directly connected the output of the Ignition coil to spark plug.

 

Also wondering if 24VDC would better the performance or destroy the coil...??

No, as the coil core will likely saturate, giving no increase in spark voltage.
It likely won't destroy the coil unless you leave the switch on for more than a few seconds.

 

How long do you plan on making these sparks, time wise? If it is only going to be for a small time period don't use the ballast resistor. when a points ignition engine is first trying to start the resistor is not in the circuit. It gets by past by the starter solenoid. After the engine is running the resistor is put back in the circuit, to prevent the coil from burning out. For just manually sparking the coil, you can do it for quite a long time and not worry about damaging the coil.

 

How long do you plan on making these sparks, time wise? If it is only going to be for a small time period don't use the ballast resistor. when a points ignition engine is first trying to start the resistor is not in the circuit. It gets by past by the starter solenoid. After the engine is running the resistor is put back in the circuit, to prevent the coil from burning out. For just manually sparking the coil, you can do it for quite a long time and not worry about damaging the coil.

Intend to use this set up to light a pilot flame by igniting Methane Gas flowing thru a very tiny orifice near the spark plug...!!

In that sense, the sequence would be as follows:

A start push button would set a relay to turn on, to connect the battery to primary coil.

Wait for a few secs

Then break the primary side to cause the spark plug to spark while methane gas is flowing over it

Wait for pilot flame

If it doesnt light, then connect primary side again to battery thru relay contacts

wait a few secs

again break the contact for spark to occur


Ofcourse the above is an approx sequence. We intend to first establish a good spark before attempting the other things.

 

For safety, cost, size, convenience get a piezo igniter like used in gas grills. No power required. Push the button and it creates a spark.

 

No, as the coil core will likely saturate, giving no increase in spark voltage.
It likely won't destroy the coil unless you leave the switch on for more than a few seconds.

The coil is probably already in saturation with it being switched so slowly by manual operation. On an engine the contacts would only be closed for milliseconds.

 

the contacts would only be closed for milliseconds.

True.
But the time-constant for a typical 8mH coil charging to a 6A maximum from a 12V source is only 4ms, so for normal engine speeds the coil reaches its maximum current between sparks.

 

The coil is probably already in saturation with it being switched so slowly by manual operation. On an engine the contacts would only be closed for milliseconds.

It has to produce a good spark at cranking speed at which time the resistor is shorted out.