I cut the voltage to 420 from 560 because I have not received the 650
Volt 1 mF capacitors yet. This is about 1000 RPM. Watch the movie and
you can see the blue flashes in the middle of the screen. The circuit
is basically the same as the outboard/Vespa circuit but the high
voltage power supply works off a 110 volt wall socket instead of a
charging coil. I am using the latest hi tech solid state switch
called an IGBT instead of an SCR shown in the outboard schematic.
IGBT Insulated-gate bipolar transistor is a three-terminal power
semiconductor device primarily forming an electronic switch and in
newer devices is noted for combining high efficiency and fast
switching. It will dump up to 50 amps through the coil primary
winding in less than a microsecond. The coil is basically used as a
pulse transformer so it runs much cooler than when used in an
inductive mode. It also fires immediately so there is no dwell time
needed. In this set up I am using a stock 2nd gen Mazda coil with out
the igniter.
The 1 mF 450 Volt cap is charging through a 1.5 K resistor hence the
visible charging curve you see on the O-scope. This high value
resistor may not work at the higher RPM's but prevents the IGBT from
shorting the high voltage supply. I plan to experiment with a choke
instead.
Paul Lamar
Congratulations on the spark!
Henry
Thanks henry. What do you think of putting a diode across the coil to
aglow the coil to ring?
Paul Lamar
Paul,
I assume that you are using a circuit similar to the Mariner
Ignition. I also assume that you are thinking about back emf,
creating a high voltage spike at the end of the discharge cycle. I
would say that you can add a diode to prevent high voltage on the
cap, but I don't think you have too much of a problem as capacitors
can discharge most of its energy rather quickly. Once the energy is
discharged, and used up immediately as a spark on the secondary side,
the remaining voltage, and current, if any, from the capacitor should
be limited, and it can be dissipated through the primary winding to
the ground rather quickly. Especially when you notice that there is
not much heat building up on the coil.
So my two cents: The ringing is most likely a minor issue, but it
does not hurt to add a diode there.
Henry
Yes on the Mariner circuit. Here it is. IGBT instead of SCR.
Paul Lamar --
Paul,
You are still sending the Mariner circuit. :) Don't worry, I think my
conclusion is still valid. Even if there is ringing induced voltage,
the path to ground via the coil should still take care of it.
Henry
That is what I am using except for the charging coil.
I am slowly coming to the conclusion that a power resistor in series
with the high voltage supply is a good thing. About 1.5 K seems about
right for 8,000 RPM. Allows the 1 mF caps to charge but stops shorting
the HV supply to ground.
Paul Lamar
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