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Ämne: Requesting DI information

  1. #1
    Sugmotor
    Reg.datum
    mar 2006
    Ort
    Chicago, USA
    Inlägg
    6

    Requesting DI information

    Hi group. Sorry, I can't post in swedish. Hope this does not offend.

    I am trying to figure out some stuff on the DI. Looking at having MegaSquirt drive a DI cassette on my '91 C900 Aero. I know how I can get dual wheels to get sequential spark signals (crank trigger and cam trigger). What I am really trying to figure out is what the signal looks like to the spark triggers. I know it is a 'ground' that fires the spark. Is it just a 50% duty cycle pulse train that it needs or does it need dwell to be calculated as well? Any information appreciated.

    Regards,

    KeithG

  2. #2
    Steg 6
    Reg.datum
    jan 2003
    Ort
    Trollhättan
    Inlägg
    6 865
    Hej !

    Just pull down the trigg lead(s) for 1 ms or so.
    The spark will fire at the beginning of the pulse.
    As it's a capacitive discharge system, so don't worry about dwell.
    B235R, B234R+, 318-3, S4, A35, 51J, 2G40, 4/3, G50, FM100, Meteor Mk 4B/2, B80 Mk 5 P, ЗВЕЗДА M50 F6-L + lite till....

  3. #3
    Sugmotor
    Reg.datum
    mar 2006
    Ort
    Chicago, USA
    Inlägg
    6
    I received this from Lars in Amal:

    I have attached a file for the pin out of the Ignition cassette. Nr. 4
    cylinder is the one closest to the connector. Pin number 1 is used for
    monitoring the charge voltage to the capacitor (1/100 of the charge
    voltage gives about 0-4V)

    The voltage on the trigger pins is 12V and it triggers on the falling
    flank when grounded (500mA peak). The trigger must at least be held
    low for the discharge time of the coil which is about 500us. There
    must be 2.5ms charge time between triggers to avoid damage to the
    cassette. The recharge of the capacitor starts directly when the
    trigger goes high again and the charge time is 2.5ms at 12V battery
    voltage. It's important to minimize voltage drop in the harness as the
    charge time will rapidly increase with lower voltage (3ms at 9V).
    Charge voltage can be monitored the on pin 1.

    The misfire signal is a square wave signal 0-12V. There are 2 lines
    for this, one is for cyl. 1&2 and the other is cyl.3&4. SAAB also use
    this signal during cranking to find the which cylinder is in the
    compression stroke and which is in the exhaust stroke. The SAAB
    Trionic trigs both partner cylinders until it can detect a combustion
    in one of the cylinders, during this time these two coils get half
    each of the stored energy in the Cap. You will have a signal some
    microseconds after a trigger if you have a combustion. This signal is
    only for combustion detect and has nothing to do with knock.
    It looks like it needs a 2.5 ms dwell if this information is correct.

    KeithG

  4. #4
    Steg 3
    Reg.datum
    jan 2003
    Ort
    Norrköping
    Inlägg
    3 766
    Medlem#
    10798
    Citat Ursprungligen postat av keithg
    I received this from Lars in Amal:

    I have attached a file for the pin out of the Ignition cassette. Nr. 4
    cylinder is the one closest to the connector. Pin number 1 is used for
    monitoring the charge voltage to the capacitor (1/100 of the charge
    voltage gives about 0-4V)

    The voltage on the trigger pins is 12V and it triggers on the falling
    flank when grounded (500mA peak). The trigger must at least be held
    low for the discharge time of the coil which is about 500us. There
    must be 2.5ms charge time between triggers to avoid damage to the
    cassette. The recharge of the capacitor starts directly when the
    trigger goes high again and the charge time is 2.5ms at 12V battery
    voltage. It's important to minimize voltage drop in the harness as the
    charge time will rapidly increase with lower voltage (3ms at 9V).
    Charge voltage can be monitored the on pin 1.

    The misfire signal is a square wave signal 0-12V. There are 2 lines
    for this, one is for cyl. 1&2 and the other is cyl.3&4. SAAB also use
    this signal during cranking to find the which cylinder is in the
    compression stroke and which is in the exhaust stroke. The SAAB
    Trionic trigs both partner cylinders until it can detect a combustion
    in one of the cylinders, during this time these two coils get half
    each of the stored energy in the Cap. You will have a signal some
    microseconds after a trigger if you have a combustion. This signal is
    only for combustion detect and has nothing to do with knock.
    It looks like it needs a 2.5 ms dwell if this information is correct.

    KeithG
    As I understand it, he only means that the system needs 2.5ms of recharge between trigs to avoid damage to the cassette, not that it needs a 2.5ms dwell.

  5. #5
    Sugmotor
    Reg.datum
    mar 2006
    Ort
    Chicago, USA
    Inlägg
    6
    To my understanding, is it not, effectively, the same thing as dwell on a RL circuit? He says it is 12V and it sparks when the input goes from 12V to gnd (high to low) and the circuit starts charging when the trigger line goes back to 12V. So, with a square wave the time it is at 12V (high) would be the dwell time recuired to charge the circuit, wouldn't it?

    In a standard RL circuit, there needs to be 12V on the output to charge the coil and the time it is held at 12V is the dwell time. It discharges the coil when it goes low and it is held low until the dwell period before the next spark starts then it goes high to charge the coil.

    So, for a standard coil, this is about 4ms and the DI cassette would be 2.5ms which illustrates the advantage of the capacitive discharge system and its short time constant.

    Do I have this mixed up or is this correct? My goal is to properly drive the DI cassette with Megasquirt with 2 trigger inputs (crank and cam).

    KeithG

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