Too
bad this isn't 1960 and the Ed Sullivan show was on Sunday
nights because the presenter is a much better comedian then
engineer. His escapades would go over quite well with dancing
bears and guys who spin plates on poles.
?
However,
he'd be tossed out of, and banned, from any university
electronics laboratory for his foolishness.
?
Suggesting
using a resistor divider to reduce direct AC mains to feed a
microcontroller is downright stupid verging on criminal.
?
The
way you measure ultra high DC voltages is with a electrostatic
voltmeter.
?
?
I
bought a ESH model 600085 at a surplus sale for $5 that will
measure 5, 10, 15, or, 20kV. Other then testing it in a real
electronics lab, I've only used it once to measure the high
voltage for an night scope (starlight scope) tube power
supply.
?
However
for measuring the ignition voltage for anything other then a
model airplane engine, which uses a 1.5V glow plug, one needs
something like either the?gizmo
made from plastic with a screw adjustable gap to measure the
ignition/spark voltage, however this measures the voltage
under "no load."
?
Or
the Leslie unit I mentioned earlier which actually shows you
how strong the arc is with the engine running.
?
When
the cylinder rises during the power stroke, the 'air' pressure
increases, if you have an engine with 10:1 compression, then
your pressure when the spark occurs would be 10 X 14PSI,
140PSI.
140PSI
= ~ 7240 torr.
see
the graphic at
?
The
chart maxes out at 720 torr and shows the voltage required to
be in excess of 70,000V. [I have doubts about this graph but
don't feel like working out the math this morning.]
?
Wiki
goes into Paschen's law in quite a bit of detail.
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All
of this is interesting from a theoretical angle, but the
practical aspect is simple:
?
"Just
because your ignition system produces a spark/arc in a spark
plug outside the engine does not mean it will produce a spark
in the engine under compression."
?
I've
seen this in Honda CB350s, 1968 and 1969 stock VW bugs. The
ignition coils in the Honda twins was located where they were
heated by the engine, I never had a hard failure but I could
tell when it was time to replace one when the power dropped
way off and the engine sounded funny, both ignition coils
never failed at the same time so the power was really
imbalanced between the cylinders. I limped home from Mason
Ohio [near Kings Island] to Lexington one night sweating "Will
I make it home...."
?
VW
coils just failed for the fun of it. West German manufacture
wasn't quite as perfect as they'd have liked for you to
believe.
?
I
learned more about ignition systems then I wanted with those
vehicles. I've never had an ignition coil/system fail in
Chevy
Nova [My wife's when she was my girl friend. Car died when
someone t-boned it in a parking lot. Bummer]
Subaru
[two cars, 1980 station wagon, 1984 compact]
VW
transporter van with Porsche engine
[I
have no idea why a very similar engine never experienced a
fuel pump failure or ignition coil failure.]
Toyota
[3 cars]
Ford
[1 car we put over 200K miles on.]
?
I
did have the ignition coil fail on a Plymath Omni, about a
month before the engine decided to emulate a grenade. [Way too
exciting at 80MPH on the Mountain Parkway at 3:00AM. You've
never lived until you have parts of the engine come through
the hood right before your windshield is covered in oil and
coolant. Loads of unfun.]
?
?
[I
always carried a spare fuel filter, fuel pump and ignition
coil. <and fan/generator/ belt> for the VWs. I've
changed the fuel pump and ignition coil by feel in pitch black
dark out in the boonies more times than I care to remember.
Yea for a person who collects flashlights it was silly not to
have one, but the batteries were always dead when I needed the
light. I finally got smart and made a 12V trouble light with
20 feet of wire, a fuse and power port to the battery and
never had a fuel pump or ignition coil go bad again.]
?
A
dying ignition coil can produce what appears to be a very
strong arc in a spark plug outside the engine and not work or
sort of work in the engine.
?
Sort
of work to mean, rough idle, stalls when you give it gas.
?
Modern automotive/light truck ignition coils are extremely
reliable.
?
Briggs
and Stratton lawn mower ignition coils not so much.....
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-------------------
Real
mechanics with real garages with real test equipment designed
for cars often have specialized oscilloscopes that will
display the ignition voltage. It's worthwhile getting a
glimpse if you have a friendly mechanic.
?
I
would never consider trying to build an adaptor to allow me to
see the ignition voltage waveform on my DSO. One could
probably salvage the ultra high resistance resistors from cold
war civil defense ion chambers and add plenty of diode
protection clamps but I'll let others fry their DSO when the
Leslie ~$20 device works very well.
?
BTW
I have no business relationship with Leslie, I'm just a very
satisfied customer.
?
For
the really brave...[or foolish]
?
I
have no idea if the device will work or fry your scope.
?
Ya
pays your money and takes your chances. [not me.]
?
Oh
changing the two drive belts was amazingly easy, took two
hours, mainly because I removed the pulies and lubricated them
[one bearing will need replacing sooner then later, it's on
order] and cleaned the space under the deck, used a wire brush
to remove some rust and painted it with a high quality epoxy
paint, and I blew dead grass bits out of 'everywhere.' I also
added a kill switch to the seat, get out and the engine shuts
down. The twins are a bit careless. I do not want anyone to
lose a foot. [Yea I'm paranoid.]
?
?
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