TCI & CDI ignition systems.

[Graham Woolnough]

Dear Tech Folk, I have a horizontally opposed 2 cylinder 2 stroke .It fires the ignition on both cylinders @ the same time.At present has a TCI system with 2 internal coils 180 degrees opposed with 2 magnets in the flywheel opposite one another.This engine is going into an ultralight so for reliability & safety I wish to convert to dual ignition. Being technically challenged my question is can I utilise the TCI system to achieve this or will I have to convert to CDI. The engine has no charging system but plane will be equiped with a 12 volt battery. I have doubled up on a CDI system in the past so have no real problems with the mechanical issues. I would be most great full if someone could give me a solution & a list of components I need, Looking forward to a solution. Regards Graham.

 

[dr pepper]

Welcome.
I need more info, you say Tci, and opposed coils with 2 magnets, are these coils just pickup coils going to an ignitor box, or are they generating the spark voltage directly? (if so that would be a magneto ignition).
If the coils you mention are pickups for an ignitor then yes its possible to use them on another ignition system, so long as said system has a way to adjust the angle the pickup is located at with respect to tdc, aftermarket systems tend to have this feature so they can be fitted to various engines.
It would probably be better though to replace the entire system and use a optical or Vr sensors.
Then if the craft is going to be in the air for anything other than a very short time you'll need some kind of charging system.

Some interesting info:
https://www.sportdevices.com/ignition/ignition.htm

 

[Graham Woolnough]

Thanks for the reply Dr Pepper, I believe TCI stands for transistor controlled ignition.The coils under the flywheel are the spark producing coils,the only other components being the high tension leads & two little transistor boxes attached to each coil,they are external.A pretty simple system, but can I double up somehow? I will machine heads for extra plugs.Hope that explains a bit better.Cheers Graham.

 

[alec_t]

At present has a TCI system with 2 internal coils 180 degrees opposed with 2 magnets in the flywheel opposite one another.

Do both coils fire one cylinder, or is it one coil per cylinder only?

for reliability & safety I wish to convert to dual ignition.

Good idea. However, a weak link seems to be the internal coils in the flywheel. Is there space to duplicate those? If not, having to share the coils between the TCI and CDI systems may not add much to the overall reliability.

 

[Graham Woolnough]

Dear Dr Pepper, Both cylinders fire together so I presume there is one coil per cylinder. No room for extra coils & if there was they would be 90 degrees out of timing.My thought would be to throw away the TCI system, replace the coils with CDI triggers where the coils were,fit 2 DC CDI modules with 2 twin coils which will give me 4 HT leads .these leads would be crossed over so if one system failed the other would fire both cylinders. What do you think? There are plenty of components on the market so should not be too difficult to get. Looking forward to your reply Cheers Graham.

 

[alec_t]

Do you have any figures for the relative reliability of the TCI and CDI systems you intend to use? Would these systems have to be officially certified for aircraft use?
With dual ignition systems powered by one battery the running time will obviously be halved (or worse, depending on the battery characteristics). Pity there's no onboard charger.

 

[Graham Woolnough]

Dear Dr Pepper, Both systems are reasonably reliable,but it's always nice to have the back up Being the class of aircraft that it is,even though the engines are designed for there use ,even the manufacturers do not guarantee the engines,so improving the reliability is not an issue. Regards Graham.

 

[dr pepper]

I'm not sure of the terminology however the existing setup sounds like what I recognize as a low voltage magneto, the pick up coils generate both low voltage for the electronics and high voltage for the spark, the electronics controlling when the spark occurs over a range of firing angles, does this sound like yours?

You could probably use the low voltage side of the coils as trigger pickups for your system, if the high voltage side isnt dis connectable then you'll need some kind of load to keep the high voltage from going wild and flashing over inside the coil if your using other coils to fire the plugs.
Connecting the high voltage side of 2 coils together in parallel is not advice-able, long term reliability issues might result, you'd need specially made coils for that.
If you are machining heads yourself maybe you could consider 2 spark plugs per cylinder and 2 seperate systems with 2 dual ended coils, then you would need some means to detect when one of the systems isnt working, otherwise you wouldnt know till both fail.

 

[Graham Woolnough]

Dear Dr Pepper, I agree with what you are saying as regards the TCI system.if one was to splice the high tension leads I guess you would only get half the voltage to each plug. A lot of vehicles are now using coils that fit on the spark plugs. Do you think these could be utilised in some way with the TCI system if the leads were spliced.As the system is at present the coils have to be switched with seperate earth switches. Graham.

 

[Graham Woolnough]

Dear Dr Pepper. Normal pre flight checks include testing both ignition systems.If one is faulty you stay on the ground until it is fixed. I have been giving some thought to COP coils (coil on plug). Could I leave the old system in place & use the low voltage side of the pick up to fire 2 COP coils on seperate plugs. Research shows me that the coils have 4 terminals 1 for earth ,1 for 12 volt supply,1 for trigger & 1 that sends a message back to the ECM for limp home mode on cars.that one would not be required. As it is usually the high voltage side of the coil that normally fails I don't think the triggers would cause a problem. What do you think .Cheers Graham.

 

[dr pepper]

Testing both ignitions is your means of checking both work then, that sounds acceptable, you wouldnt know if one failed during flight, but you'd notice at the next pre flight check so that might be Ok for a small craft.

Yes you might be able to use a cop system, there are 2 things to consider, there is some 'smart' circuitry in these, there might well be some voltage measuring circuitry meaning if you dont have a charging system they might not work properly due to the power supply being <13.8v.
Secondly and more complex is these units tend to be constant energy spark coils, meaning that the trigger pulse supplied needs to be a constant length irrespective of engine speed, so you need a processor to calculate when to fire the coil and provide the same length trigger pulse independent of crank Rpm.
The existing low voltage coils could be used you are correct, probably the best thing to do is process the signal from these using a dedicated pickup coil amplifier ic.
You might be able to get the whole lot working with an arduino, or 2 for redundancy, you might need a leonardo to get enough speed depending on max crank rpm, I'm guessing a smaller motor might well get to screaming revs.

The 4th wire on a toyota cop is a signal back to the ecu to tell it that the spark was actually successful, if there was no spark then there would be no pulse, you could use this for a on board diagnostic system to detect a fouled plug/broken lead/other fault.
Other systems might have a different function.

 

[Graham Woolnough]

Dear Dr Pepper.

 

[Graham Woolnough]

Dear Dr Pepper, I am posting 3 images ,should have done that in the first place. They show the complete system apart from the plugs.You can see the HT leads coming out behind the transistor boxes.they have a white covering.The motor revs to about 5700 rpm .If needed I don't think it would be hard to put on a small alternator.I think this system could work if set up correctly. It is possible to get a 3 wire COP coil eliminating the wire back to the ECM. As I said before when it comes to this sort of stuff I am technically challenged. I understand a dedicated pick up coil amplifier, but what is an Arduino & a Leonardo. I would be most greatefull if you could send me a schematic showing where & what to use.We have good stores out here to buy electronic bits Cheers Graham

 

[dr pepper]

OK, an arduino is a pcb with a microcontroller on board, you can program it from windows with free software.
If your new to micrcontrollers then programming an ignition system probably isnt a good first project.
You could use a 3 or 4 wire cop, the 4th wire on the 4 wire cop could just be left disconnected.

You might be able to suss out a project allready on the net, heres one that uses cop ignition modules:

https://www.spaco.org/Computing/arduino.htm