Wendell Voto wrote:

I got the resistors from Mouser. They are on the internet.

Mouser.com

Part # 284-HS25-.33    (.33ohm 25 Watt)
       # 284-HS25-5        (5 ohm 25 Watt)
Wendell

That brings up a good point.
Tracy what can we do to eliminate this waste of alternator power?
Also at issue; how can we extend the range of the aircraft
on battery power alone after the alternator fails?

Paul Lamar

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
 
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