Motorcycle CDI Pulse output

Hi Max, just a bit of ETO information:

if you want to quote a post just click 'Quote' at the lower right of that post and that post will appear in your new post window with opening and closing tags. You can insert as many opening and closing tags as you like to chop up an original post into manageable chunks for responses for, example.

spec

If you want to quote only part of a post it is easier just to click-and-drag select the part, then click the 'Quote' button.

alec_t said:

If you want to quote only part of a post it is easier just to click-and-drag select the part, then click the 'Quote' button.

Click to expand...

I must be doing this wrong. I highlight (hold down left button and trace the words) and a black "quote" balloon shows, then you click on that.

Hi Max,
I was taking you comment in post #37 literally when you said two wires from the charge coil. From post #40 it seems that one wire was the charge coil and one the trigger coil. It can't be two ends of the same coil as the pulses occure at different times. You will need to correct your readings as your potential divider does not divide by 10. The top resistor is 8.4 meg (7 x 1.2) and the bottom resistor is 1.3 meg (1.2 Meg + 100K) As your scope probe presents a 10 meg load it is in parallel with the bottom 1.3 meg resistor which changes the value to 1.3 x 10/(1.3 + 10) = 13/11.3 = 1.15 meg.so the ratio of your divider is (8.4 + 1.15)/1.15 = 9.55/1.15 = 8.3 So the actual voltage is 8.3 times of that on the input of your divide by 10 probe. (Or 83 times the voltage at the input of your scope)

Les.

Les, we seem to be mis-understanding each other.
Associated with the CDI for charging and triggering, there is only one coil, the one I've been calling the "Charge/Trigger" coil, each end of this coil has a wire going to the CDI. (so two wires) Neither of these two wires are earthed. After the CDI does its trickery, the CDI also has a power wire and ground wire going to the High Tension coil (which is mounted on and earthed to the bike frame) whose output is to the Spark Plug.
The Charge/Trigger coil is wound on the original stator (inside the flywheel) but has no electrical connection to that stator core or earth. Also wound on that stator are separate lighting generator coils, but they have no electrical connection to the Charge/Trigger coil.

Regards, Max.

POST ISSUE 03 of 2017_01_06

Hi Max and Les,

below is a sketch for a suggested CDI control circuit (every time I start putting it in EAGLE something happens and I get distracted so here it is in the raw). The circuit uses the Hall sensor recommended by Les.

spec

DATASHEETS
(1) **broken link removed**
(2) https://www.mouser.com/ds/2/149/cd4538bc-294672.pdf

CIRCUIT DESCRIPTION
(1) When the hall effect sensor detects a gap in the flywheel (don't worry about the practical aspects of this for the time being), the hall effect sensor outputs a negative pulse.
(2) The negative pulse form the hall effect sensor triggers two monostable timers, N2A and N2B.
(3) When the monostable timers receive a negative input pulse they immediately produce a positive level (12V) at their Q outputs and a negative level (0V) at their /Q outputs.
(4) The monostable timers will maintain these levels for a time defined by the resistor and capacitor shown at the top of each monostable timer.
(5) Once this time is reached the Q output will return to 0V and the /Q output will return to 12V.
(6) The monostable timers will then be ready to receive another negative trigger pulse from the hall effect sensor.
(7) The lower monostable timer /Q output connects to an NMOSFET which provides a high current negative pulse to trigger the CDI SCR and generate the spark.
(8) The upper monostable timer /Q output also connects to the gate of an NMOSFET which in turn connects to the gate of a PMOSFET.
(9) The PMOSFET acts like a switch and turns off the 200V supply to the CDI to prevent SCR latching.
(10) The period of N2A is longer than N2B to give sufficient time for the CDI to turn off before the 200V is applied again to the CDI.
(11) The 200V is produced by a standard step up switch mode converter which is powere from the battery and/or the generator.
(12) The 200V inverter runs continuously.

And that is all there is to it.

G'day Gents, Thank you for the sketch above Spec. I can't say I understand its operation yet, guess I need more study.

While away on the other side of the country last week, I visited a well known professional motorcycle electrics fellow I know.
I can now confirm some information.

He confirmed what Les has been saying, that the output of the Charge/Trigger coil would be around 3oo ish volts. He suggested I must be picking up some kind of stray field, to measure +2000 volts.

When I re-measured using his method, (at the kill switch) I get greatly reduced voltages. (makes more sense)

I also re-measured using my loom breakout connection, (without voltage divider) but this time routed the wires much further away from the High Tension spark plug lead, and I obtained similar readings as at the kill switch.

The positive 12.8 volts peak is on the charge/trigger wire and the 278v on the other wire to the CDI. These measurements were taken with the engine running at a bit over 2,000 rpm.

He showed me the circuit diagram of the inside of the CDI and confirmed only one of the wires does both the charging (North Pole/Pos. cycle) and the triggering (South Pole/Neg. cycle). This is the wire showing about 11v in the first attached pic of traces, where the voltage first has a positive peak, capacitor charging, then goes a little negative as the scr is triggered.

The second pic is from the other end of the charge/trigger coil, into the cdi.

The third pic is at the Kill switch.

To answer a previous question Les asked about which voltage does my scope display. I did some checking and the answer is the voltage of the circuit the probe touches, when the divide ratio on the scope panel is set to correspond with the probe ratio. ie; 1:1, 10:1 etc.

In the below pics, the panel and probe settings were at 10:1.


So hopefully this makes things a little easier, not needing such high voltages.






Power on regardless.

G'day Spec, Am I asking too much to ask for an explanation of how your circuit functions and what the various components are ?

MaxD said:

G'day Spec, Am I asking too much to ask for an explanation of how your circuit functions and what the various components are ?

Click to expand...

Hi Max,

Nice to see you back on ETO.

Hope you had a good Xmas and all the best for 2017.

An explanation of the schematic of post #46 would be no problem.

spec

Hi again Max,

Circuit description now added to post #46.

If you have any questions just fire away.

spec

Hi Max,
As you have seen the internal schematic of the CDI unit can you explain how it seperates the charge and trigger parts of the waveform from the pickup coil ? Having hard facts rather than just guesswork will make the design more likely to work.

Les.