interfering to ignition system

Hello,i want to interfere to an ignition coil system to be able to cut ignition for a short time.The ignition controller use sink pulses while the other end of the coil is connected permantly to 12volts to charge and discharge it.I already have a mechanic relay which I control with Arduino.I have connected the sink pulse signal from controller to NC of the relay and I trigger the relay to cut the ignition when I need.What I want is to replace the relay with a faster and more reliable part since relays wear our.I am thinking of a power mosfet or an igbt.Can anyone suggest me which part to use and how to connect it properly.Thank's in advance

"interfering to ignition system" should be "Interfacing to ignition system"

You are best using an SCR as they have a much higher voltage than a FET. Mind you you still have to get a high voltage one. Also once triggered you get the full discharge, which you won't get with a FET.

Finally note the Arduino processor data sheet says this:-

Atmel products are not designed nor intended for use in automotive applications unless specifically designated by Atmel as automotive-grade.

Grumpy_Mike:
"interfering to ignition system" should be "Interfacing to ignition system"

You are best using an SCR as they have a much higher voltage than a FET. Mind you you still have to get a high voltage one. Also once triggered you get the full discharge, which you won't get with a FET.

Finally note the Arduino processor data sheet says this:-

Thank's for your reply.Can you explain me how it will be connected I have never used one before.I want to control the pulses line and not the permanent 12 volt supply of coil.

.Can you explain me how it will be connected

Well I can but if you have to ask then you have not yet developed the skills to design the system, especially as the engine could be damaged if you get it wrong.

It is not a trivial project although the basic design is simple. The anode of the SCR is connected to the end of the coil that is normally grounded through the contacts, with the other end to ground. The gate has a series resistor with an Arduino output pin. Putting the pin high fires the SCR.

Read about the SCR here.

I would suggest you take a year out learning about electronics before you attempt this.

Grumpy_Mike:
Well I can but if you have to ask then you have not yet developed the skills to design the system, especially as the engine could be damaged if you get it wrong.

It is not a trivial project although the basic design is simple. The anode of the SCR is connected to the end of the coil that is normally grounded through the contacts, with the other end to ground. The gate has a series resistor with an Arduino output pin. Putting the pin high fires the SCR.

Read about the SCR here.

I would suggest you take a year out learning about electronics before you attempt this.

I attach an image.If we remove R2 and U1 the circuit is how it works under normal conditions.the bc547 probably is not the correct one because its inside my ECU and I cant see it I just used it to make the circuit.Will this connection works?If I keep U1 gate high all the time so the coil charge and discharge following the ecu pulses and set it low when I need to stop the ignition?The coil can be charged and discharged up to 250 times per second since the rpm goes up to 15000.

I attach an image

No you don't.

Grumpy_Mike:
No you don't.

I did now sorry

Is there a zener diode across the BC547, the back EMF off that coil must be horrendous and if you put a diode across the coil you short out the flyback transformer action ( it is an ignition coil, isn’t it). I know the BC547 has a Vceo of 45v but I would not have thought that that was enough.
Please tell me there is, otherwise my years of experience in electronics has been for nought.

Dead_Ard

Dead_Ard:
Is there a zener diode across the BC547, the back EMF off that coil must be horrendous and if you put a diode across the coil you short out the flyback transformer action ( it is an ignition coil, isn't it). I know the BC547 has a Vceo of 45v but I would not have thought that that was enough.
Please tell me there is, otherwise my years of experience in electronics has been for nought.

Dead_Ard

the bc547 is placed in the diagram just to create it.I don't know what transistor/igbt etc is used to drive the ignition coil because it is inside my ecu and its in a waterproof case which I don't want to open.I can only see the one pair cable that ends to my ignition coil.It is confirmed that when I turn on the key 12volts are permantly supplied to one end of the ignition coil and the other end is driver with ground pulses coming from ecu.Now I am using a relay at the pulses line to cut the ignition when I need to.My question is what is the best way to replace the relay with something faster and more reliable and how it has to be connected?

Not that easy.

An inductive discharge system as used on modern vehicles has to deal with several 100’s of volts when the coil primary is switched ‘off’ to generate the spark. And the coils are of very low impedance, driven by a short pulse - if you left them permanently connected across 12v they would burn out very quickly.

A SCR across the primary and ground would do this… and won’t switch off.

Maybe a relay in series with the coil is the only safe ( though not perfect) solution…

Allan

allanhurst:
Not that easy.

An inductive discharge system as used on modern vehicles has to deal with several 100's of volts when the coil primary is switched 'off' to generate the spark. And the coils are of very low impedance, driven by a short pulse - if you left them permanently connected across 12v they would burn out very quickly.

A SCR across the primary and ground would do this.. and won't switch off.

Maybe a relay in series with the coil is the only safe ( though not perfect) solution.....

Allan

I know its not that easy that's why i asked help.i tried some different ways to do it but the only one that worked was the relay.since you look familiar with ignition coils do you think that a dc solid state relay at positive side of ignition coil to cut 12volt and leave the pulse side connected as is will do the job?

It's decent idea, and might work... but suppose it operates part way through the 'on' part of the pulse - then it has to deal with the many hundreds of volts switching pulse......

Actually a 4-quadrant triac of suitable current and voltage rating in the +ve feed side of the coil might be ok - the ecu turns off the current so it doesn't latch , and you can switch it with an active 'low"...... but they're slow.

could you do it with an SCR? I'll have to think about it...... they need a +ve voltage compared to their cathode to work....

pondering ..

Allan

allanhurst:
It's decent idea, and might work... but suppose it operates part way through the 'on' part of the pulse - then it has to deal with the many hundreds of volts switching pulse......

Actually a 4-quadrant triac of suitable current and voltage rating in the +ve feed side of the coil might be ok - the ecu turns off the current so it doesn't latch , and you can switch it with an active 'low"...... but they're slow.

could you do it with an SCR? I'll have to think about it...... they need a +ve voltage compared to their cathode to work....

pondering ..

Allan

thank's for your advice.if you have time to think about it and post me a solution i would be grateful.

Perhaps something like this might work…

Allan

ign kill.pdf (20.3 KB)

allanhurst:
Perhaps something like this might work...

Allan

I will test the next days and post back the result.thank's for your help

nixtas:
I will test the next days and post back the result.thank's for your help

Ok i test the circuit you posted.It works but only without the diode.If the diode is placed there are no sparks generated.

A 'high' on the arduino output should enable sparks - a 'low' => no sparks....

You presumably mean D1 ... did you use a zener? It's only there for overvoltage protection of Q2.

Is it the right way round?

Allan

allanhurst:
A 'high' on the arduino output should enable sparks - a 'low' => no sparks....

You presumably mean D1 ... did you use a zener? It's only there for overvoltage protection of Q2.

Is it the right way round?

Allan

Hello again,i found some free time and tried your circuit on my motorcycle but it doesn't seem to work.I tried a different circuit driving an igbt with the ecu pulses to keep the bike running and turn of the igbt when I need to cut the ignition.The bike is running fine but the check engine lights after about 10 seconds and I guess it cuts the fuel.The fault says that the igniton coil cable is disconnected.I guess it happens because the negative pulses isn't directly connected to the coil.Do you have any idea how ecu checks if coil is connected or not?

Can you please tell us why you are trying to turn your motorcycle's ignition coil off and on? Maybe to make a loud backfire (after-fire) or to create a exhaust flamethrower? Otherwise, I do not understand.

ty_ger07:
Can you please tell us why you are trying to turn your motorcycle's coil off and on? Maybe to make a loud backfire or flamethrower? Otherwise, I do not understand.

to reduce power for short time