Deciphering the igniter...

Wow, what a response!

With the knowledge amply herein exhibited, maybe this group ought to be
called rec.autos.makers.honda.electronics! I'm impressed. This is the sort
of thing that makes a good FAQ possible. Thank you.

I'm responding in this particular message only because my original post has
been pushed off the stack by my news provider.

With the wealth or information in everybody's responses, I've saved them
all and will have to review them. I will post a draft once I figure I
understand all this.

For a picture of the insides of an igniter, see here:
http://www.gcw.org.uk/rover/igniter.htm#userreport
(you'll have to scroll up a bit)

For more pics:
http://www.markl.f9.co.uk/howto/electrical/igniter/igniter.htm

More questions:
1) Can anyone tell from the foregoing pics what kind of transistor is in
the igniter pictured?
2) What's this thing about the attachment of a heat sink by "wires"? I must
be dense or something, because I thought heat sinks were firmly fastened by
screws or solder blobs.
3) Can somebody explain a "flyback circuit" in terms a layman can
understand?

 

I looked at this pix and brightened it up with IrfanView,and it appears
that the transistor has a part number that could be researched IF one could
read all the marking,which I couldn't.It starts with BU.Get me the whole
PN,and maybe I can find what it is and it's specs.Knowing the manufacturer
maker on it would help greatly,too.

I could not read the number on the transistor(xstr).
It seems to be a standard BU-type semi.It might be a combo MOSFET/bipolar
with a internal protection diode,like what's used in a TV's high voltage
flyback,or just a plain bipolar PNP xstr.

Dunno.Japanese power supplies commonly use metal clips to hold a power semi
to the heatsink;quicker and cheaper.

"flyback" is when a coil is energized,a magnetic field is built up,and when
the current is quickly removed,the field rapidly collapses and induces a
REVERSE current from the original charging current.The coil's magnetic
field is an energy storage device.This is how a high voltage spike is
generated. This also holds for transformers.It's how many PC power supplies
work,too.


Ignition "dwell" time (for the older points-type ignitions) is the length
of time the points stay closed to charge up the ignition coil,thus
determining how much spark energy is generated with the flyback
pulse.Modern electronic systems can control this much better,no points
bounce,either.

 

I looked at this pix and brightened it up with IrfanView,and it appears
that the transistor has a part number that could be researched IF one could
read all the marking,which I couldn't.It starts with BU.Get me the whole
PN,and maybe I can find what it is and it's specs.Knowing the manufacturer
maker on it would help greatly,too.

I could not read the number on the transistor(xstr).
It seems to be a standard BU-type semi.It might be a combo MOSFET/bipolar
with a internal protection diode,like what's used in a TV's high voltage
flyback,or just a plain bipolar PNP xstr.

Dunno.Japanese power supplies commonly use metal clips to hold a power semi
to the heatsink;quicker and cheaper.

"flyback" is when a coil is energized,a magnetic field is built up,and when
the current is quickly removed,the field rapidly collapses and induces a
REVERSE current from the original charging current.The coil's magnetic
field is an energy storage device.This is how a high voltage spike is
generated. This also holds for transformers.It's how many PC power supplies
work,too.


Ignition "dwell" time (for the older points-type ignitions) is the length
of time the points stay closed to charge up the ignition coil,thus
determining how much spark energy is generated with the flyback
pulse.Modern electronic systems can control this much better,no points
bounce,either.

 

True, but in this application the transistor (FET or BJT) is always
either off or in saturation, so thermal runaway isn't an issue.

 

True, but in this application the transistor (FET or BJT) is always
either off or in saturation, so thermal runaway isn't an issue.

 

They usually still need a capacitor. The primary voltage shoots up to
lethal voltages before the secondary can fire the spark plug. If that
went into a protective avalanche diode, there'd be no power for a spark.

I have a gizmo that drives two old-school ignition coils out of phase.
The MOSFETs (Two NTE2385 in parallel) are rated for >500V and can
survive avalanche breakdown. I can get away without using a capacitor
only because the coils are rather lossy and the MOSFETs are rather
expensive. I once had a similar setup with better coils that would burn
out instantly without a capacitor.


http://www.pixelmemory.us/Photos/Nerd/Wire%20Corona/Violet-Corona.jpg

 

They usually still need a capacitor. The primary voltage shoots up to
lethal voltages before the secondary can fire the spark plug. If that
went into a protective avalanche diode, there'd be no power for a spark.

I have a gizmo that drives two old-school ignition coils out of phase.
The MOSFETs (Two NTE2385 in parallel) are rated for >500V and can
survive avalanche breakdown. I can get away without using a capacitor
only because the coils are rather lossy and the MOSFETs are rather
expensive. I once had a similar setup with better coils that would burn
out instantly without a capacitor.


http://www.pixelmemory.us/Photos/Nerd/Wire%20Corona/Violet-Corona.jpg