megasquirt MS3 MS3X direkt ac cdi control

[MS2tester]

if one were to build a circuit to let the megasquirt MS3 control alternating current ac cdi capacitive discharge ignition through the ms3X board the thyristor gate,s
of an original cdi ignition
how would this look like ?
it might be necessary to use 12 volts

[dontz125]

Without more information, I would suggest the MS3X spark outputs would be capable of driving the thyristor / SCR gates directly with no additional circuitry. Triggering the MS will be more interesting; since this seems to be a wasted-spark 4-stroke, it should be possible to treat it as an inline 3-cyl. Wiring 2 of the 3 pickup coils to a suitable filter circuit (leaving the third coil disconnected) should give the equivalent of a 3-1 wheel; I came up with this circuit for a fellow using a Dual Trigger set-up, but should work well with this arrangement as well.

Dual Edge Trigger.jpg

The output would be fed to the Opto circuit. The spark advance arm would need to be fixed, much like the advance mechanism of a distributor.

Note that a MS2 would be able to handle this with little difficulty, driving off the LEDs. Since you don't have enough info to run sequential injection, you have enough spark and injection channels (with Jean's card mods) for wasted spark and semi-sequential injection.

[MS2tester]

thank you for the reply
triggering the MS3 will not be a problem
i have already a 36-1 tooth pattern in the starter ring machined
so missing tooth 36-1 with V6 two stroke should work
i guess will just have to hook it up and see if it works

[piledriver]

If you need a more "narrow" sensor, the early MK4 VW/Bosch unit has about a 3mm tip. (VR, 3 wire, one pin is shield) TDI.
I suspect the gas Mk4s have a similar active area but I know the TDi unit has a small effective area.

It might prove interesting trying to ignore those magnets and the flywheel teeth.

[MS2tester]

Thank you for yhe information
But i have little space where i want to put it
I have use the digital sensor wich works
Until an ignition coil is wired in the system
Then rpm is all over the place
I have used thr VR sensor with great succes http://m.youtube.com/watch?v=0Bvj8llGC6g#

[old-colt]

If this were my setup I would change the coils to some designed to run on 12V rather than the CDI coils.
I expect you want to eliminate the sparkboxs to rid yourself of their known failures and run the MS3X direct to the coils.
For coils it may be easiest to select something as the GM LS1 coils with built in triggers which are what the MS3X was designed to run. These are a coil near plug so mounting to the engine should be similar to the original setup.

[MS2tester]

The idea is to keep it as close to stock as is
And the CDI ignition does not foul the spark plugs as fast as induction ignition
Altough the latest series of X engines and XS engines ( direkt injection) use the induction coils
If this does not work out that will be the way to go
But not giving up just yet

[old-colt]

Keep in mind with that intake the center cylinders get a stronger charge and are prone to a mixture variation. Keep that in mind as you develop this when it comes to timing and mixture settings.

[MS2tester]

ok tried the original switch boxes
but don,t get any spark
now i came across this shematic
could it be possible to repeat this 6 times for the 6 cylinder
as per attached revised shematic ?
need some help with this as i am no electronics engineer
this way all the electronics components are know and have direk access to

[old guy]

That circuit looks very similar to the early 80s YZ80. It will most likely retard the ignition as rpm's increase which is what most 2 stroke cdi's do. You will be fighting the retard in the box with the ignition map in the MS. I know you are set on using the cdi because of the spark plug fouling but you would be surprised at the output of the LS1 coils.It would be a lot easier to use them instead of trying to of trying to mix and match a bunch of unknown electrical components.
Also be aware that a 2stroke ignition map is going to be much different than a 4 stroke one.Is there any way you can find out what the ignition curve is for your engine?
Just my .02 cents worth.

[old-colt]

Keep in mind you have 3 trigger coils for 6 cyl. The original spark boxes read both + and - pulses from the triggers to determine which cylinder is to fire and depending what year your engine is "I have not paid attention" you may have high speed and low speed triggers as well.
The factory CDI trigger coils put out the better part of 250 to 400 volts as well.

[slow_hemi6]

For simplicity I would be going for the Mercury IGN-1A coils with the self contained ignitors. Pretty sure DIY sell those coils also.

[dontz125]

I'm going to agree with the OP on one aspect - CDI is generally better at resisting fouling in the oily 2-stroke environment than a TCI ignition.

Old-colt: trigger coils =/= charging coils; not sure which you meant.

[MS2tester]

The original engine has an advance curve of 0 to 25 btdc can you explain why the new circuit would retard timing
Since timing (controlling firing of the SCR) would be under complete control of the mcu and based upon the 36-1 wheel
It would be not that different than in the attached freescale document

[dontz125]

Stroker ignitions advance the spark as revs climb, but once you go past the tuned pipe rpm, the timing is retarded back. This increases the heat going into the pipe, which increases the pulse velocity and keeping the engine 'on the pipe' that much longer.

[MS2tester]

Ok but that is not an issue here the original engine has a curve from 0 to 25 by fisically moving the timer base (pulser coils ) non of these parts will be used!
So to get back at the original quistion would you see any problem with the shematic as i modified it
I think the 1 Kohm pull dow resistor would have to be subsitituted for a 100 ohm to get a 1.1 voltage on the scr gate?

[old-colt]

I'm going to agree with the OP on one aspect - CDI is generally better at resisting fouling in the oily 2-stroke environment than a TCI ignition.

Old-colt: trigger coils =/= charging coils; not sure which you meant.

My post has the trigger coils as + "plus" and a - "minus" not an =/=. Maybe this shows up differently in different browsers.
The trigger coils are a wire wound coil that put out an AC current at a low frequency. A big wide VR sensor if you like.
The CDI units are wired such that one would be triggered by the positive and one by the negative side of the trigger much as we would be looking at the rising or falling side of a sensor.
In an outboard this sets the timing and which cylinder fires of the 3 pairs of ignitions,

There was a question of timing curve of the engine.
In most early outboards the timing is set manually with a cam controlling the carb opening in relation to rotation of the mounting of the stator as the throttle is moved.
Even as factory fuel injection came to outboards in the '80s&90s they still triggered and timed the engines manually for a number of years. Basically they used fuel only injection as many cars had.

[MS2tester]

I'm going to agree with the OP on one aspect - CDI is generally better at resisting fouling in the oily 2-stroke environment than a TCI ignition.

Old-colt: trigger coils =/= charging coils; not sure which you meant.

The CDI units are wired such that one would be triggered by the positive and one by the negative side of the trigger much as we would be looking at the rising or falling side of a sensor.
In an outboard this sets the timing and which cylinder fires of the 3 pairs of ignitions,

There was a question of timing curve of the engine.
In most early outboards the timing is set manually with a cam controlling the carb opening in relation to rotation of the mounting of the stator as the throttle is moved.
Even as factory fuel injection came to outboards in the '80s&90s they still triggered and timed the engines manually for a number of years. Basically they used fuel only injection as many cars had.

this is not exactly the case
if i may point your attention to the second drawing from the first post
and then specifically the note: switch boxes respond only to positive voltage on trigger terminals

which is logical as Cyl 1 terminal sees a positive wave
cyl 4 terminal ( 180 dgr opposite ) sees a negative wave but does not trigger at least not on this system
that comes when the AC wave is reversed
this particular system uses 2 trigger magnets with north and south mounted horizontally but reversed as the trigger coils are mounted vertically
so one AC wave across 360 dgr crank rotation
they made some kind of provision in the switch box to keep the ign timing stationary as rpm,s increased so that only fisically moving the timer base advances spark
which is probably making it impossible to trigger the switch boxes directly

OMC evinrude uses a trigger/timer coil per cylinder which would probably make life a lot easier

[old-colt]

Yes you are wording this better than I did, I did not have my coffee yet this morning when I wrote that. Yes the coils put out an AC current which obviously reverses and triggers the cylinders as appropriate on the positive pulse.

[old guy]

The original engine has an advance curve of 0 to 25 btdc can you explain why the new circuit would retard timing
Since timing (controlling firing of the SCR) would be under complete control of the mcu and based upon the 36-1 wheel
It would be not that different than in the attached freescale document

The timing retards because C2 and R2 put a delay in the trigger pulse, so as engine speed increases the timing retards.
In your diagram of how you would wire it you eliminated C2 , so there is a possibility that it would not retard.
Trust me I built a bunch of very similar CDI's back in the old Honda Odyssey days and they definitely retard as the engine speed increases.
On a 250 Odyssey this ignition made a 3HP improvement on the dyno compared to the stock ignition which had fixed timing.
One question, do these engines still use the deflector type pistons or are they now a loop scavenged design. I am sure this would have some influence on what he timing curve would be.