TCI (or CDI) IGNITION TRIGGERING PULSE TOLERANCE

[MRSSPOCK]

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.

 

[jbkettler]

Although the VR sensor generates a voltage, it is not used to power anything inside the control module. It is used as a signal which is interpreted and decisions are made based on it. The module has power and ground so it can work. THe analog (sine wave) signal goes into the control module and is viewed and digitized by an a/d convertor (control modules are digital monsters - they can do nothing with analog information). The analog signal will have both an increasing amplitude and frequency with increasing rpm - it is still just a signal and does not power anything. Most modules have over voltage and over current protection built in. You could always use a lab scope on the bikes rpm sensor to see what it generates during cranking and have a signal generator mimick that.

 

[dgallup]

One of the ones we make puts out 1.7V peak to peak into a 20kohm load at .07" gap with a surface speed of 42 in/sec. That is a low speed, voltage will increase with speed.

 

[MRSSPOCK]

jbkettler: Thanks, that's really useful to know. As you can gather I'm just learning about these things, so anything I can glean is appreciated. Just one question reagarding the A-D convertor. Would I be right to suppose the A-D convertor can recognise changes in the sine wave as engine speed increases, so calculates a different DIGITAL value as the ANALOGUE waveform is changing. (Maybe theres no need for that since the interval between pulses is already providing the indication of RPM?).

dgallup: Thanks to you too. I have just salvaged a tacho sensor from a washing machine and am about to run it up on my powerdrill to see what voltage it registers on my oscilloscope. If it is in the ball park that you mention I can maybe use it in my test rig. I'm presuming the "gap" you refer to is the air gap between the sensor and the passing lump of metal?

Thanks again.

 

[theoldwizard1]

I disagree with what jbkettler has stated. "The analog (sine wave) signal goes into the control module and is viewed and digitized by an a/d convertor ,,,"

On all of the ECM/electronic ignition system I have worked
on, the VR signal is "squared up" by a zero crossing detector circuit and a one shot "pulse stretcher". This is then feed to a DIGITAL input on the microprocessor.

Because a VR sensors output varies considerably with the speed of triggering wheel (from mV to over 100V) low speed/low voltage detection is hard to differentiate from noise. High voltages can be easily clamped because current is very low.

Here is another tip. If you plan on hooking the DUT to a real ignition coil, besides generating a high voltage out of the coil, which you need to manage, there are some terrific "back EMF" voltages created by the coil. Depending on how well the ignition module handles these negative voltage spikes, your test equipment may have a problem.

One ignition module we were testing would trip out and power supply were were using. The solution was to use a real lead acid battery to power it.