Ignition coil supply switching with MOSFET (is it acceptable)?

Thread Starter

dimkipa

Joined Jan 26, 2016
17
My point exactly is this!
I have an inductive sensor giving the signal and I want to make flat foot shifting. The car is only for racing so catalytic converters etc are out of the equation :)
The injectors will be dumping fuel for a very short time (about 60ms) and a small backfire will be the "music" that we be heard.
Will the MOSFET handle all this amperage? I know this it is rated for 60A but I don't know the actual amperage. In my bench I saw about 2A which is quite low I think...
Interrupting the supply would be ideal for me as long as I don't have issues on the future (mosfet or the ignition coil failure).

What do you think?
 

shortbus

Joined Sep 30, 2009
10,049
I made a post on Saturday that seems to be disappeared.:( I'm asumming that the area in the schematic you last posted is a connector. To test if it is the correct place to shut down the ignition, try unplugging it and see if the motor runs. If it is the ignition connector, buy another set of those connectors (auto wrecking yard). This will allow you to add the 'new' circuit. Then you can run wires from the new connector to a double pole single throw switch, a normally closed push button type. Mount this switch on you shift lever, and when you want to shift, push the switch and change gears and then release the button. Nothing electronic involved. They do this type of thing for a "line lock" on drag cars.
http://www.jegs.com/i/JEGS-Performance-Products/555/10332/10002/-1?parentProductId=751020
 

Thread Starter

dimkipa

Joined Jan 26, 2016
17
Hello!
I made some test on Saturday and I have some very interesting results..I used the ecu from a friend that has a cut off capability. The measurements are shown in the picture below.
ignition pulse test.jpg

When I have the signal of the sensor the ecu "interrupts" the pulse, by keeping it high for a specific amount of time.
All good until now. I want to use a N-channel mosfet...I am a little confused about the circuit connection..
I will connect the pulse (from ecu) to the Drain and the Source to ground (in order to act as a low side switch), and I will have the cable going to the ignition to the Drain side. How can I keep this to 5v?

I think that I need two MOSFETs cascading in order to send the 5v to the ignition coil...
:confused::confused::confused::confused::confused:

Now I am lost.
 

shortbus

Joined Sep 30, 2009
10,049
Don't know what sensor your taking about? I'm not familiar with the car your talking about though. Most American cars source the 5V from the ECM to the sensor the the sensor sends a modified signal back to the ECM. Or in the case of fuel injectors or ignition coils back to the ECM to be grounded by a low side switch internal to the ECM.

Could you post a PDF of the complete engine wiring schematic? Using the "upload a file" button. Maybe then the circuit will make more sense.
 

Thread Starter

dimkipa

Joined Jan 26, 2016
17
I attach a file showing the schematic.
The wires labeles "110-111" are the two pulses that go to the ignition coil (the pulses are shown in the diagram I uploaded before).
When i say "sensor" I mean the inductive sensor that I will be using that will trigger the ignition cut!

Kind Regards.
 

Attachments

cork_ie

Joined Oct 8, 2011
428
Hello again,
My goal is the following.
I want to "interrupt" ignition at a specific time (when I have a specific trigger from an inductive sensor). I want to create a "flat-foot' shifting circuit.
The ignition coil that I have has got a 4-wire connector.
1--> + 12v
2--> ground
3--> firing pulse (1/3 cylinders)
4--> firing pulse (2/4 cylinders)
The way to go is to pass the pulses through two mosfets (for each wire) and stop 'firing'.
If I isolate/interrupt the supply (or ground) the outcome will be the same BUT what are the effects on the coil? Will it be affected long term?

Thank in advance for your time!
1) First of all, you have a separate ground and +12V going to the ignition coil, so you will need to confirm whether final amplification is in the coil or the engine ECU. The Peugeot 106 is a fairly old model so I suspect the latter. This is going to have a big impact on the type of circuit you need. You will be switching approximately 10A or 10 mA twice for every engine revolution . I don't think speed is going to be an issue, because even at 7,200 RPM, which would probably blow your engine, that is still only 120 pulses per second i.e. 120 HZ and most transistors will handle many multiples of that figure
2) I assume when you say firing pulse (1/3 cylinders) you meant (cylinders 1/4) & firing pulse (2/4 cylinders) you meant (cylinders 2/3)
3) IGBT's are the best type of transistor for switching ignition coils
3) If the final coil driver is internal in the ECU , then the cheapest and most reliable option is to try and intercept the signal before the final driver transistors internal in the ECU as they are properly heatsinked and you won't affect EMC emissions etc.

I still don't quite understand what you are trying to achieve , other than make your exhaust bang
 
Last edited:

Thread Starter

dimkipa

Joined Jan 26, 2016
17
Hello and thanks for the response!
I apologize for the mistake regarding the cylinders, I have corrected it in the original post.
Tomorrow I will measure the amperage of the pulse and come back with the results. The point that I want to "interrupt" the pulse is after the amplifier (and right before the ignition coil). I don't think that it will in the range of amperes...hopefully.

My engine goes at about 8500 rpm but again the switching time is ok.

My goal is to switch off the ignition for some time (few ms) while the gear change will taking place without lifting my foot of the gas pedal (aka flat foot shifting). Some aftermarket ECUs have it built in as a choice. The measurements of the pulse (after the amplifier) I uploaded above are taken while using an aftermarket ECU with this capability. What I want to do is make a circuit that will behave like that!
When the inductive sensor (indicates gear change) --> cut the ignition for a specific time (controlled by a microcontroller).

Kind Regards
:rolleyes::rolleyes::rolleyes::rolleyes:
 

shortbus

Joined Sep 30, 2009
10,049
I have another question, about the 'inductive sensor'. What and where is it going in your flat shift modification? I'm looking to find more about the Bosch ECM.
 

Thread Starter

dimkipa

Joined Jan 26, 2016
17
I have another question, about the 'inductive sensor'. What and where is it going in your flat shift modification? I'm looking to find more about the Bosch ECM.
the inductive sensor is seeing the mechanical movement for the gear change and triggers the procedure of the cut off.
I measured the amperage of the wires (110-111 on the schematic) leading to the ignition coil (the two wires that I will use to cut the ignition) and are as follows:
1000 rpm --> 0.3A
8000 rpm --> 0.9A

hope i gave you an understanding...
 

shortbus

Joined Sep 30, 2009
10,049
I have my doubts that your sensor and the mosfet will work fast enough to be effective for what your doing. Triggering the cut off needs to happen before the shifting takes place. Cutting the engine power allows the torque to drop so the synchronizers free up to allow shifting, like pushing in the clutch. Drag racers do this for racing.

So now we get back to the question I asked last week. Is the 110 and 111 terminal grounding or sourcing voltage?
 

Thread Starter

dimkipa

Joined Jan 26, 2016
17
These two wires are sourcing voltage. These are the pulses that drive the ignition coil...
On a diagram I uploaded the two pulses are shown.
Kind regards.
 

shortbus

Joined Sep 30, 2009
10,049
The Bosch system in use doesn't seem to have much of a shared knowledge base out there. Thinking about your problem, I would put the ignition "break" in the wire feeding the coil pack. This then only need one 'switch' to cut the ignition. In your wiring diagram it would be wire #1225, the one you marked as 12V, coming from relay block #5.

I still don't understand where your getting an "inductance sensor" signal from. The type of inductance sensor I,m familiar with is like a crank position or cam position sensor. The work by a moving ferrous metal object passing the sensor. Also the ignition shift cut off circuits I'm familiar with are for clutchless shifting. They cut engine output to allow a shift to be made. This said, if you induction sensor is on the shift mechanism, the shift lever would need to be in motion for it to put out a signal. This would mean that the ignition cut out would happen after the shift, not during the shift. Am I wrong on what your trying to do?

Back to the cut off. I would use a DC-DC solid state relay. These allow a low voltage and amperage to switch a higher voltage and amperage. It has to be a DC-DC SSR, they use mosfets internally to do the switching. All in one ready made off the shelf, sealed package. Here is a link that tells how to chose one to do what you are wanting, raed the part abou DC-DC. - http://www.phidgets.com/docs/Solid_State_Relay_Primer#DC_SSRs
 

Thread Starter

dimkipa

Joined Jan 26, 2016
17
Thanks for the response.

You have understood exactly what I am trying to do. The mechanical movement (we have put the sensor on the gearbox) is sensed by the inductive sensor. It works fine with the ECU's cut off option so the timing of the movement and the the ignition cut is ok.

I will try the solid state relay and get back to you with the results!

Kind Regards!
 

Thread Starter

dimkipa

Joined Jan 26, 2016
17
Hi everybody,

thanks for all the help. I managed to solve the issue by using a mosfet and interrupting the signals to the coil.

Again thanks for all the help!
Kind Regards!
 

kostral

Joined Nov 24, 2019
1
Hello to all,

It's an old thread but it's exactly what I am looking for. Dimitri I want to built a device which interprets the ecu ignition signal. My car also uses a "wasted spark" ignition system. I have some questions concerning the MOSFET connection. I would appreciate your help.

Thanks in advance.
 
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