Not really enough power to worry about. Main time the ballast resistor
comes into play is during startup when the ECU doesn't have enough info
to
accurately control the dwell (coil goes into saturation and current
sky-rockets). Under normal running conditions the current is limited by
coil inductance and does not saturate. Stock resistor does get a bit
hot at
rpms above 4500 due to marginal rating, no airflow around it and
location
(under the cowl). It might be possible to reduce dissipation by 3-4
watts
by bypassing it after startup but that's probably more trouble than its
worth.
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
Question Tracy. Is the Chev GM coil per plug a simple pulse
transformer or is the saturation current type?
Paul Lamar
Only thing different about the GM coil (used on LS-1 engine) Is that it is
magnetically biased so that it can store a large amount of energy in a
small, light weight package. It will saturate if dwell time is not
controlled and uses a transistor instead of a resistor to limit saturation
current but the wasted power is the same.
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
Too bad. I was hoping it was a pulse transformer type.
Pulse transformers are used in capacitor discharge systems and only
enough current, as required to fire the plugs, is used. Low RPM low current
high RPM, higher current. A capacitor stores the energy in the form of charge
instead of storing energy in the form of current flowing in a coil. At high RPM
the power is about the same but no power is wasted in a ballast resistor or
transistor for the CDI system. The FET switch device is extremely low resistance
when on. It appears that the MSD type is the best. Multiple Spark Discharge.
I am usually about five years ahead of my time so this design should be used
in a rotary any year now in the next six years :-)>
Paul Lamar
Here is a chart from Heinz Heisler's book Advanced engine tech.
this one shows the power consumed by various types of ignition
systems. 60 watts is about 5 amps at 12 volts. 30 watts would
be 2.5 amps. The Mazda is an inductive solid state type.
Paul Lamar
This one shows the voltage available to fire the plugs.
Paul Lamar
What this one shows is how fouled spark plugs leak off the voltage
available to fire the spark plugs. The CD system scores big time
when it comes to firing fouled spark plugs.
Paul Lamar
Now here is the downside to a simple, single spark CD system.
The spark don't last very long :-)> This is why you need a multiple
spark CD system if you are going CD and you are concerned with low
RPM operation.
If it fires twice or three times that will be twice or three
times the power consumed probably. The power consumed would
probably be about the same as an inductive system.
The story at 6000 RPM and above might be different.
An "ms" or short for milli second is 1/1000 of a second.
At 6000 RPM a two rotor fires twice per rev so that is 100 revs per second
or 100 sparks per second for each rotor. That allows a total of 100 milli
seconds for each spark. If we relate that to e-shaft degrees that is
.277 milli seconds per degree. A 20 degrees e-shaft angle change takes 5.5 milli
seconds. That is about how long a simple single spark CD system spark last anyway.
So it appears there is little advantage at high RPM for Multiple Spark Discharge
CDsystems. Check my math. I could be wrong.
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
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