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TCI / CDI IGNITION SYSYEMS - TESTING

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THUNDERBOLT

Aug 29, 2010
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I wonder if I should be posting this in a different area of this forum. If so, could the relevant person please shift it or advise where I should have put it. Thanks

Anyway, the question I have is regarding the triggering of a TCI motorcycle ignition. I wish to test the module which contains the transistors.

Having looked at the wiring diagram, it is pretty simple to supply the relevant inputs that the module should be supplied with, and therefore enable the study of the output.

It is my aim to test the module remotely, i.e. not attached to the motorcycle.

So, there are 5 wires going to the module.

1 = 12v supply
2 = GND
3+4 = sine wave input pulse from pulse triggering coil
5 = the path to earth (via the tansistors inside), which causes the collapse of the ignition coil, hence inducing the spark.

I think my question is a pretty simple one, but maybe the answer isn't.

The 12v and GND I can easily supply, and I can easily attach a known good ignition coil and sparkplug to the circuit, however my question is regarding the triggering pulse.

I was consider just creating a small circuit to produce an intermittent sine wave, which is generally what I believe these VR type pickups output.

My question therefore is, does anyone know what tolerance these ignition modules have, regarding the required pulse voltage, and what actual POWER the pulser sine wave should have. I hope that makes sense.

I possibly don't use the correct term when I said POWER, but I'm just worried that, 1, if I create a sinewave circuit, it won't have enough POWER? (V*I) to do the business inside the ignition module, even although I have the correct peak to peak voltage (found by trial and error hopefully), and 2, if I supply a peak to peak voltage which is too great while trying to establish what is the required peak to peak voltage, am I likely to destroy the module?

Thanks for any advice.
 

Resqueline

Jul 31, 2009
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I'm not quite sure how large the signal from the trigger coil is on motorbikes, but it seems a common value for vehicle pickups is several volts (1-10). It'll vary with speed.
The circuit is no doubt very adaptive. If you use a resistor of at least 100 Ohms in series with the signal then I'm confident that nothing will be damaged no matter what.
 

THUNDERBOLT

Aug 29, 2010
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resqueline: Good news. I will probably be able to do a trial in the next day or two, so I will post a reply then. Thanks for your reply
 

Resqueline

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Initially I would have guessed at some milliVolt signal, but there are no parts I'm aware of that can't stand 5V & 20mA (250 Ohms) so if you stay within that it's safe.
 

Militoy

Aug 24, 2010
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I'm interested in the results of the "trigger test". I play around with CD ignitions (MK10B; Tiger 2; Tiger 600 etc) on my play vehicles occasionally. I picked up a TCI module at one time - but sold it before getting the chance to fire it up. Is it designed to trigger off the OEM ignition magneto on the bike? Or - does it come with its own trigger coil and magnet?
 
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THUNDERBOLT

Aug 29, 2010
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I'm interested in the results of the "trigger test". I play around with CD ignitions (MK10B; Tiger 2; Tiger 600 etc) on my play vehicles occasionally. I picked up a TCI module at one time - but sold it before getting the chance to fire it up. Is it designed to trigger off the OEM ignition magneto on the bike? Or - does it come with its own trigger coil and magnet?


Well, I know you're the expert on here, but just so that we are speaking the same language I think its good to clarify at the outset that CDI and TCI are quite different. You are probably well aware of that, but it seems many people use the terms loosley, so that people think they are the same.

CDI systems dump a charged capacitor through the ignition coil at the instance a spark is required, while TCI uses a transistor to cut off the circuit of an already saturated primary winding, when a spark is required.

So, on any motorcycles I have been working at, there is always a pick up sensor which is usually called a trigger coil, a pulse coil, pick up coil or something similar. This is usually just attached close to the OEM flywheel on the crankshaft. A raised portion on the flywheel passes close to the pickup and creates a sinewave pulse, which is then fed directly to the TCI or CDI box where it is shaped to suit the triggering characteristics required. Some use the sinewaves waveform variation with respect to speed, as a means to apply spark advance/retard as required. For anyone interested, there is an excellent Motorcycle Electrical Manual by Tony Tranter.

I realised I was going to need some means of creating a sinewave to mimic the trigger coil, so I salvaged a small tachometer from a washing machine. It is basically a 10 pole sensor, so that for one revolution of the washing machine drum, there are 10 sinewaves output.

When I tried this sensor (spun up using my hand drill) it created pulses of 2 volts peak to peak (at the speed my drill could achieve). Although when I flicked it quickly with my fingers, I could achieve 5 volts peak to peak due to the higher acceleration of the magnet.

Anyhow, when I then used this washing machine tacho as my triggering pulse, i.e. I connected it to my TCI box, no triggering took place. Next I thought perhaps this gentle sinewave wasn't instantaneous enough, so I decided to simply attach a small function generator bought from Maplin for £12. When I attached it, once again no triggering took place, but once I switched it to a square wave rather than a sinewave, the sparkplug came to life. The output on the function generator is 0 -5 v The generator lets me sweep through a huge range of "RPM" frequencies so its really good for £12 (although you have to solder it together yourself).
 

Militoy

Aug 24, 2010
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....So, on any motorcycles I have been working at, there is always a pick up sensor which is usually called a trigger coil, a pulse coil, pick up coil or something similar. This is usually just attached close to the OEM flywheel on the crankshaft. A raised portion on the flywheel passes close to the pickup and creates a sinewave pulse, which is then fed directly to the TCI or CDI box where it is shaped to suit the triggering characteristics required. Some use the sinewaves waveform variation with respect to speed, as a means to apply spark advance/retard as required. For anyone interested, there is an excellent Motorcycle Electrical Manual by Tony Tranter....

Oops - I didn't intend to muddle the two technologies - I've played around more with the CD units though, than the TCI or magamp types. The induction pickup sounds similar to the kind we're using on our diesel robot for tach and speedo feedback in the chassis monitoring system. Those ones put out a sine output at around 30V peak. A pretty good older book that covers various types of aftermarket ignition systems is "Solid State Ignition Systems" by R.F. Graf and G.J. Whalen.
 

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Resqueline

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The sinewave output from the pickups lasts only for a degree or two for each revolution (1-2 cyl.) so it has rather steep flanks. The square wave mimics these flanks.
 

Militoy

Aug 24, 2010
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The sinewave output from the pickups lasts only for a degree or two for each revolution (1-2 cyl.) so it has rather steep flanks. The square wave mimics these flanks.

Seems like you could match the natural rise time by kicking up the frequency of the sine wave - but maybe the trigger is current-related - and the square wave is providing something the sine isn't capable of in that particular instrument (???)
 

THUNDERBOLT

Aug 29, 2010
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I just ran the sinewave at a period of 0.0005 seconds per cycle, and the sinewave still isn't capable of triggering this TCI box. The square wave still does the trick though, at this 120,000 rpm equivalent. I realise the coil is sparking pretty quickly, but probably not at 2000 times per second. I imagine it is just sparking as quick as it can, while many of the 2000 trigger pulses are actually redundant. I'm not very confident regarding testing the HT side of the ignition coil on my scope. I remember our electronics blokes in work had big whopper probes for working with HT voltages. I don't know why they where so big physically, so I don't want to risk blowing up my scope.
 

Resqueline

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You can't run a continuous sine to the trigger input. It needs a substantial pause between each sinewave in order for the trigger circuit to be able to trig on it.
Yes, 20-30kV really does need a physically big probe (due to breakdown voltages & capacitance). They're expensive.
The primary HT side though "only" employs 300-400V pulses, but even that may be too much for ordinay probes - that may be rated for max 200V peak (to peak).
 

THUNDERBOLT

Aug 29, 2010
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You can't run a continuous sine to the trigger input. It needs a substantial pause between each sinewave in order for the trigger circuit to be able to trig on it.

Thanks.

That is what I had presumed, hence I initially used the washing machine tacho, since I presumed it was producing a flat line between pulses, but when it didn't work, I just thought, I'm going to try this sine wave from the function generator just out of curiosity, so I wasn't surprised when it didn't work. While I had the function generator connected I was just curious again if the square wave would do the business, so I tried it and it worked okay.

Is it possible to buy a function generator that would create thte intermittent pulse that would simulate the reality of the intermittent trigger coil pulse, or is that a circuit that I would need to create myself? If so, do you know any such circuit?

I suppose to do it so that it mimics a real trigger pulse, the pulse might need to have a very small curve from flat line to the flank, as opposed to a sharp switching edge like a square wave has. I suppose that would make it even more dificult to mimic. The reason I am thinking that, is because if I create a circuit that produces a one shot sine wave, then reset it every time I want another sinewave, I'm probably not going to get that little "fillet " radius where it changes from a flat line to a sine wave, in reality. As the trigger bar approaches the trigger coil, I'm presuming in reality there must be a little fillet. I will soon have the chance to put the trigger coil on to my scope and see what it does look like in practice.


Thankyou
 
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