Background: I have a PCM with internal coil ignitors. An Ignitor is an IGBT transistor for increasing current capacity of standard triggering for igniting inductive ignition coils. The problem is, I now have double the coil count. The original configuration used wasted spark double-coils, the new configuration uses individual coils. Obviously I cannot connect the pairs in parallel or I will overload the original ignitors. The solution is to use double the number of ignitors externally, and put the parallel connection on the control side of the ignitor array, not on the loaded side. The problem is that the new ignitors use a 5-15V trigger signal firing on the falling edge, and the original ignitors only supply a controlled ground signal, which would normally fire on the rising edge/control off.
Problem: I currently have an active ground signal that I need to convert into a +12V signal, and the form needs to be Ground Active = 12V, Ground Inactive = 0V. This signal is High Speed Switched, no electro-mechanical solutions need apply.
Problem Limitations: Extreme reliability, minimalist approach, smallest packaging.
Proposed solution(s):
1a. Utilize a 3K ohm Pull-Up resistor to pull the Ground to 12V when not active, producing a square wave output in the inverted form.
1b. Utilize a form of “Inverting Amplifier” to invert the signal by way of a few resistors and a BCX58 Transistor.
RISKY option: Disassemble the engine controller, remove the IGBT transistors, and re-wire in order to use the original IGBT control signal as an “output” rather than the control for the IGBT.
Curious to hear thoughts and if anyone has any other ideas?
Sounds like #3. If you know where on the PCM PCB to re-wire the “Output” for the IGBT I would do that. What’s the risk? Do you not know how to re-configure it?
I would be more cautious about adding a pull-up resistor in place. Will “breaking” the ground throw a code?
Instead of “overloading” the single coil can you replace it with a high uH coil? If you know the specs on what the original one is you can get a new coil spun if a commercial one is not readily available. It won’t need to be exact either if you can find one close enough.
The risk is getting the PCM apart, they are not easy. The front cover of the PCM, where the socket is, is a “pull through” type, and soldered to the board. I cannot remember for the life of me of the IGBT’s are located on the front or back of the board, so they may or may not be easily accessible.
No problem there, I can re-flash the PCM to ignore any IGBT feedback issues. I do this all the time on stand-alone cars where I wire in a resistor array to prevent long term damage to the IGBT’s. The current wont peak high enough to pass the internal tests, but it at least prevents damage from floating.
It is not the coils that will be overloaded, it is the IGBT’s. The Stock double coils are 0.7 Ohm, while the new single coils are 0.6 Ohm, and when wired in parallel, they are only 0.3 Ohm. That is WAAAAAAAY too much current for an ignitor. Since I only have 5 ignitors in the OE PCM, I made an external 10 ignitor array [one for each coil @ 0.6 Ohm], where I can pair the coils on the trigger side rather than the load side of the ignitor. The problem is- those ignitors [IGBT’s] require an active input, not a ground control like the OE ignitors offer. This wouldn’t be a problem on a stand-alone with 10 IGBT’s which could control the coils individually or 5/10 TTL outputs that have the correct control format as they are basically the same as what the IGBT control signal would be upstream… but I am stuck with the one pain in the ass configuration.
To confirm what I think you know is the best way to do it… #1.
My thoughts were of Luke’s in the most difficult up front, but probably the “best” relatively speaking. But #1 with the pullup is the KISS method for sure.
There should be a removable access cover. Most of these are made to be taken apart for trouble shooting at a minimum. Even if the connector is holding the PCB in place to the housing it should be able to be removed without much trouble. It is just a lot of de-soldering, probably close to 100 pins. I would bet that the cover is screwed to the “housing” and the PCB with the connector can be removed internally. Provided it is not encapsulated with RTV, which it might be, you should be able to take it apart no problem.
If you do need to drill/remove the swaged (pull thorugh) standoff’s you can replace them failry easily. Just a rough guess: McMaster-Carr: 93500A125 (McMaster-Carr)
I rework “complex” inverters and avionics supplies if you want me to try for you.
I’m with you now…this is above my circuit design capabilities.