megasquirt MS3 MS3X direkt ac cdi control

[MS2tester]

all the big outboards from 1990 and on are loop scavenged
and if anything over the years they actually been running more advance
the old 2.5 ltr racing engine is normally set for 25 BTDC
the engine pictured above is a later one wich runs 28 drg BTDC as do the 3 ltr 300 Hp engines from mercury

would you want an extra piece in your electronics wich may or may not move your ignition timing around
i would want that what i read in my ignition advance map is wat is happening in real life on the engine
the timing is not the issue

the question is do the charging circuits properly charge the Capacitor as in the schematic?
and does the MS3X output properly fire the SCR ( thyristor ) as pictured in the schematic?

[slow_hemi6]

If you are talking about the china bike ignition then depending on the I gate to turn on the SCR it could require a minimum of about 10V for a positive trigger to fire the SCR. Would have to test to be sure.

[MS2tester]

the components i think off would be
6 for 6 cyl BT151 SCR turn on gate voltage 0,6 volts maximum gate 1,7 volts
6 for 6 cyl polypropylene 400v 1uf ignition charge capacitor
diodes =1n4007
33o ohm MS3X output to gate SCR
100 ohm gate SCR to ground
basicly a repeat of the image minus the trigger part

[slow_hemi6]

When SCR's turn on they remain conducting until the current drops to the level required for turn off. They only require a 1 shot trigger. The components in between the trigger wire and the SCR gate are a filter that reduces and limits the trigger voltage generated by the trigger winding and magnets found on those dirt bikes. The trigger windings generate higher voltages the faster the magnets pass them. Thus the input filter tends to have a minimum voltage requirement to fire the scr and also the ability to limit/filter excessive voltage when generated by the trigger coil. I am no EE but this is how I see the input working. The first diode only allows passage of the positive 1/2 cycle from the trigger coil. The 330 ohm resistor pretty much sets the minimum voltage required as voltages lower will not provide the SCR with the turn on current required. The capacitor initially behaves as a short circuit but as it charges it and the other 2 resisters become the filter.

[old guy]

Most of these ignition boxes used sensitive gate SCR's which if I recall required less than a 1 volt to trigger. I am no EE but as i know from experience the resistor and the cap cause the ignition to retard.

In reply to MS2tester, I didn't say to put the cap in your circuit. I said that if you left the cap out the circuit it would probably follow the curve of the ECU and not retard on it's own.
If it was me I would build a test stand. Mount the flywheel on an electric moter with a speed control , make a suitable mount for your trigger coils and have at it . I did this when I was building a lot of two stroke motorcycle engines and it worked great. Better than free revving your high dollar engine to high rpm's to test an advance curve.
I think 24C here on the forum built one and can probably also attest to how handy it is if you are doing any ignition development.

[MS2tester]

i,m already very happy if i can get the thing to spark
i actually have an land and sea dyno so i can test the engine under load in a test bassin
together with an HD camera and timing light
i should be able to keep an eye on the ign timing
here it is with a different ecu set up
http://www.youtube.com/watch?v=Zj7aO2DFvE8

[MS2tester]

well this is sorta i came up with

[MS2tester]

wondering if i,m going to need a snubber circuit ?
and btw maybe some fun reading for diy elvers

[MS2tester]

after contacted thierry of transmic http://www.transmic.net/en/home.htm
we came up with a revised circuit
and am pleased to announce we have a spark
unfortunately the crank wheel sensor i am using gives a rather weak signal (unstable rpm )
in the process of replacing!

[MS2tester]

well have it running
i started with fixed duty 15 % going high
https://www.youtube.com/watch?v=PRNNY_z ... DHeMuBGWVg

but i felt there was a lot of drift in the ignition timing
this is with 10 dgr fixed timing
second i reversed the signal and set it to
fixed duty 80% going low
https://www.youtube.com/watch?v=hy_UVLH ... DHeMuBGWVg
this seems to get the timing more stable

the only thing is i can,t get it to idle now it will die
is there some max dwell duty goign on preventing me from charging my capacitors ?
and unfortunately my C16 capacitor took a permanent vacation

[old-colt]

C16 is in the power supply and is between the +12 in and ground, well used to be in your case.
Where C16 is before the regulator C17 is after the regulator and in the +5V circuit. Any chance it might have been installed backwards?

[MS2tester]

very highly unlikely as i triple check each component number type orientation enz
befor i solder it
if it was how long would it take to blow ?
and this is not my first MS i put together
there never was a voltage spike at-least that shows up in the log

but any way will try to get a new one
there is no physical damage that can be viewed to MOV1 or D10 anything else to check?

and i guess i will put in a 1.0 Ohm 1. Watt resistor in series with 12 volt on the megasquirt

data log of the entire running time

[old-colt]

The fact that C16 is between the 12V input and ground as are many other components including MOV1 I personally would not see what on the board could cause this to fail. D10 is there to reduce chances of damage in the event of reverse voltage, otherwise has not limiting of input here.
If it had been backwards I would expect C17 might have been as well and might be readable still.
I would presume MOV1 would drain any serious power spikes if they had been there at startup. And yes the log should have shown a spike.
I do not have any answer other than those thoughts.

[MS2tester]

the log is actual 4 times larger
i had it running the entire time
and it did not show a value higher than 14.4 volt
so i,m a bit puzzled to
it blew after over an hour of running time
if it was installed backwards you would expect it to blow immediately or very soon after!

and it seems to happen more often

[MS2tester]

did a bench test with my MS2
80% dwell fixed duty
the only difference between the 2 is the overdwell protection on and off
wich you can turn off with the MS2 code
i can,t do this with the MS3 code
unless it,s somewhere else where i can,t seem to find it

so is there some back ground overdwell protection in the MS3 code?
because it would be nice to be able to turn it off
and see where that gets me

[Reverant]

The C16 problem is a common one. You need to upgrade to a 35V part, 25V is too low.

[MS2tester]

upgraded to a 35V part for both c16 and c17
and for good measure a 1 Ohm 1 watt resistor in the 12 volt wire to MS3
so hopefully avoiding another campfire
and whe can say there is no over dwell control visible with fixed duty

[MS2tester]

final start up
after some fresh spark plugs and readjusting the throttle idle
we now have a sort of stable idle about as much as you can have without the back pressure of water when the engine is submersed
https://www.youtube.com/watch?v=nfRZIck ... DHeMuBGWVg

guess we are ready for the dyno

it,s not the pretty,s build but wat can you do

[MS2tester]

Megasquirt_CDI_schematic.pdf

the latest schematic with as much of the parts on it
but you can take a look at http://www.transmic.net for proper parts listings there

[MS2tester]

well i guess we can say autotune from tunerstudio can also handle a V6 2 stroke
a shame i was not able to break the engine at higher rpm due dyno supply issues
https://www.youtube.com/watch?v=xcv5esY ... DHeMuBGWVg