I was surprised at the size of the capacitors
 so that added a bit of square inches to the
 PC board. Back in the old days (60's) we used
 large metal can capacitors that were oil filled
 for our CD systems and vac tubes of course.

 Those caps store the spark energy instead of
 being stored in the coils. CD coils
 run cool as they are simply used as pulse
 transformers.

 Boards cost about 65 cents per square inch
 Plus a fixed cost of $55 for tooling.

 The caps are the 4 big boxes in the center of the PC
 Board. I'll use my favorite heat sink and
 TV connector for the output to the coil.
 This is for one spark plug on one rotor.
 The trailing plug does not need it and
 and any back up ignition can be used on the
 trailing rotor.

 This requires 4 Hall Effect devices
 per plug to trigger every 10 degrees for
 40 degrees after 22 degrees BTDC.
 In other words 20 BTDC, 10 BTDC, TDC and
 10 degrees after TDC with no RPM limit
 such as MSD's have problems with.
 One cap for each spark.

 The whole idea here is to see if it will
 cut the fuel burn.

 I'll see if I can get Mazdatrix to test it on
 the dyno. I'll loan it to them for use on
 what ever engine they are fooling with at
 the moment.

 It uses one 400 watt 220 Volt AC off the shelf 12 V power
 supply for up to 6 PC boards if you want to implement
 that many on a 3 rotor.

 Paul Lamar

 It would appear that isolation devices are needed between the four
 2mfd caps
 and the coil.  When trigger is low, there is a low impedance to ground
 thru
 the lower FET of the half-bridge, essentially putting the caps of the
 untriggered drivers in parallel with the coil.

 Victor Roberts,

 Yes I see what you are saying. It is helpful I have other engineers
 looking
 over my shoulder.

 I need some more switches in there.
 Thanks Victor. Do you have any suggested circuits?

 Paul Lamar

 The current configuration still leaves the 3 untriggered caps with one
 lead
 open. This does not put them in parallel with the coil or am I missing
 something?
 Dick Handverger


 Thanks Dick.
 First condition.  All caps are fully charged through the coil.
 This group is in series with the coil. The problem Victor pointed out was
 when any lower gate closed all caps now in parallel would be discharged
 through that gate bypassing the coil as that would be the path of
 least resistance. The coil would see no current flow.

 I think I need Triac's in series with all caps to prevent that from
 happening so only the coil sees the sudden increase in current.

 Triacs are bidirectional switches unlike most semiconductors.
 They look like a relay contacts. Relays contacts don't care
 which way the current flows.

 All Triacs need to be on when no trigger pulse is occurring so
 the caps can charge through the coils. Only the Triac that
 is associated with the trigger pulse stays on when the trigger
 occurs.

 I have yet to figure out the logic on how to do that
 short of a computer. Any suggestions?

 Here is an incremented schematic.

 ---------------------------------------------

 Here is the truth table. Output refers to the triac.
 0 is off and a 1 is on.

 Looks like I will need a programmable logic chip
 with 4 inputs and 4 outputs unless somebody can
 come up with a better idea.

 The all triggers on condition never happens.
 In that case there is an error so all triacs
 should be off.

 Paul Lamar
 I believe that if you are using a positive trigger that all outputs
 are low until trigger, then output goes high, charging the cap between
 supply and ground through the coil. This probably means it is a
 capacitive-charge rather than discharge system but since the caps are
 not electrolytic charge and discharge should be symmetrical.

 In order for trigger 2 to deliver full potential, trigger 1 should
be short enough that the voltage at the coil has returned to near zero
before trigger 2 begins.  Some experimentation with the cap and coil
should reveal the duration of the spark. As soon as the spark ends, the
trigger should go low to "clear the deck" for the next pulse as there is
no benefit from continuing  the connection once the current has decayed
below the level required to sustain spark  If I recall correctly, I
think one of your earlier posts showed the typical duration of a CD
spark as being around 100 microseconds. At 8 ms per rev, 10 degrees=220
microseconds. So, a 100 microsecond trigger gives 120 microseconds to
recover.

Victor


The caps are supposed to charge during the other 320 degrees of E-shaft
rotation. That means the upper gate should be on during that time.

The output impedance of the high voltage power supply is finite
so even though the cap is grounded on one side by the coil
and connected to 220 volts on the other side by the upper gate
the internal resistance of the power supply, the coil DC resistance
and the upper gate resistance restricts the speed at which the
caps can recharge.

If I could be sure the cap could recharge in 10 degrees at 7500
RPM I could use only one section and one cap.  I would use
4 hall effect sensors and a 4 input nand gate to trigger
the system ten degrees apart.

7500 RPM is 125 pps. The time it takes between pulses
is .008 seconds or 8 ms. 10 degrees at 7500 RPM is .00022221 seconds
I think or 222 micro seconds if my arithmetic is correct. Hopefully
the capacitor can recharge in 222 micro seconds.

That is why I am using  separate caps for each spark.


I am going to bread board this shortly with only one section
to keep it simple at first. Then  I'll pulse it 36 times per rev
or 4500 PPS and see if the system can keep up.

Here is another idea for isolating the coil.

Here too are a bunch of pictures with Craig's function
generator pumping 12 volts  into a Mazda 2nd gen
coil through a 1 Mfd cap. The screen readouts
will tell you what is going on frequency wise. The upper trace
is out of the function generator and the lower
trace is across the coil. This is only about 12 volts
so heaven elp us  at 250 Volts.

Paul Lamar