Paul,
am I correct in remembering that your unit will fire once with a
trigger from a Hall effect sensor and maybe an LM1815?
I would be interested in trying to replace one mag on my IO 360 and
see how it works- I would have to place magnets and HE sensors on the
flywheel to make it work for testing. If it works, then I would make
a part that would bolt in the place of the existing mag.
Or, I could easily write a bit of code for one of my boards that will
let it fire at the right time for multiple sparks. I would probably
start with single spark and go from there. Nothing to be affected by
the noise from the discharge.
My Wheeler # 2 is flying, the one with the IO 360 Lycoming in it.
Could use 4, and make them individual for each plug, or waste spark
and use 2. I can even replace 1, 2 or up to 4 plugs and see how it
goes. I have a full engine monitoring system that monitors CHT and
EGT for each cylinder, so I can compare which ever cylinder(s) with
the CDI to the regular mags.
Kevin Alderman A&P, GROL, ASEL Comm/Inst
Excuse me while I think out loud. My CD coil requires a 15 usec 12V
pulse to trigger no more no less.
At 3000 RPM it takes 20 msec to make one rev. A 4 cycle piston
engine fires every other rev so that is 40 msec 40 msec divided by
360 degrees is 100 usec per degree. so every 5 degrees is 500 usec.
No problem at all. In fact you could fire it every 2 degrees or
every 200 usec.
I use a computer but if you program your own computer you can do it.
The coils alone are $200 each so you will need 4. The coils have a
5 amp fuse wired in series with the 12 volt supply. Not because they
draw 5 amps. They don't. They draw less than one amp on average. The
5 amp is to handle surges.
That is one LI CD coil per plug of course.
If you designed and machined a distributor to replace the mag and
used a 4 cylinder off the shelf distributor cap and rotor you could
get way with only one LI CD coil. But not firing each plug every 2
degrees. The system needs a 100 usec breathing room per spark.
I am now using an optical link from the computer to the coil so you
need a driver from the computer to the coil such as a $1 CD4050. I
have tested this with three CD4050 CMOS push pull gates wired in
parallel.
Each CD4050 has six gates. Each gate will put out 5 ma at 85 degrees
C at 12V. So the total for 3 is 15 ma. This activates an LED in the
coil. I did it this why to make the trigger line to the coil immune
from RF interference and spike feed back to the computer. AKA a
current loop. It worked so well it amazed me :) One could wire all
six gates in parallel if one wished. The LED current limiting
resister is in the coil.
The CD4049 is an inverter version of the CD4050.
Paul Lamar
Kevin, If all you want to do is a cheap replacement for a Mag use 4
LS1 Chev V8 coils and Turn the coils off at the timing mark. You
will get one spark.
Wait about 20 ms and turn them on again. Real simple to program with
an Arduino. Not optimum from a current consumption point of view as
all the dwell time they really need in theory is 4 ms. RX8 coils
will also work.
All the coil on plug coils may run e a bit hot with this software
scheme but here is a heat sink idea.
Paul Lamar
Not so much as a cheap solution, I don't have a problem the plane runs
well. I was thinking more along the line of another potential market for
the coils. The first step is testing. I can handle the microcontroller
programs and the hardware installation too.
A test bed first has to have a known stable platform which I have.
Was just a thought.
KA
Kevin Alderman
President Aviation and Avionics Services Inc.
Since Reluctance sensor are so wide spread on cars I am on my way
up to a surface mount shop to have some LM1815 daughter cards
made. I will be selling them relatively cheap.
BTW if anyone is curios about what we are talking about just
google it.
Paul Lamar
I have a board that I bought for my EFI that has 4 LM 1815s on it just
for this purpose. I am just not as far along on the EFI as I am the
other Lycoming powered plane. I had planned to use the board I have and
a pair of Hall effect sensors to fire the system. Once I have good
results at the fixed 25 degrees like the existing Mag, then I can
experiment with multiple sparks, varied timing etc. My plane has a
myriad of sensors, EGT and CHT on each cyl, MP, OT, OP, FT, FP. I just
had to remedy a semi clogged injector- it was easy to find. As MP went
up with the throttle, Cyl 4 EGT started to go up then fall off to almost
nothing as the skip and vibration increased. Idled great.
With good instrumentation engine monitoring and performance can be
determined much easier. My plan would be to use the CDIs on the bottom
plugs of all cyls, and the regular mag plugs on top. I could run the
engine off of each and see what the differences are. Could also swap top
and bottom plugs and compare.
KA
If you are going to Sun & Fun this year I hope to have a forum on the
ignition.
At low manifold pressure (high altitude) and a real lean mixture you
can fire the plugs
at 50 degrees BTDC with benefits to the BSFC. You might put a pot on one
of the A to D inputs to the Arduino that will adjust the advance.
For the new guys I recommend the very easy to program $50 Maximite for
this kind of work.
Built in black box and EFIS. Google it :)
Paul Lamar
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