Quote:
Originally Posted by Bill Palmer
CJ, Some "Food for Thought:" If you're thinking about going with the Electroair ignition, I would recommend that you install the new Kelly Aerospace "E-Drive" starter. Bill Palmer 
Chino Hills, CA RV-8A Still In-Work! |
I see Kelly's E-Drive does not use a Bendix drive, which is a good thing, but I have a comment, it's a PM or "Permanent Magnet" starter. PM starters, like the original Skytec Flyweight. PM starters usually use way more current (drawing voltage down more) than "wire-wound" starters like Skytec's later Hi-Torque & "NL" starters, both wire-wound.
I saw the link you posted showing the E-drive draws less current than the "NL" with that
cool chart. If its that efficient, cool. I suspect because it turns 1/2 as fast its really geared down (guessing). The NL is also geared and can provide more total torque at higher RPM, albeit at higher current. Kelly claims the best crank speed for an engine is 120 and 180 rpm (not 300 rpm). They also state required torque for a 6-cyl Lyc, is only 50-60 ft-lb. So it makes sense to use a smaller electric motor, geared way the heck down?
Note: They tested the 24 volt version. Wounder how the 12 volt versions compare? Also note the voltage drop curves at top. They don't explain how to use it, but the "NL" voltage drop is "shallower" or less, at least at higher torques? Price wise between the E-drive ($456) and NL ($450) is not much different.
The kick-back issue is there; I agree, but many have used the Electroair EI, even with fast turning PM starters, with out kick-backs. Electroair is straight about the Kick-Back issue. You are right 8 volts is min, 6.2 volts for the lightspeed. The lightspeed should be more kickback resistant but not immune? At the bottom of this link they talk about it:
http://www.electroair.net/technical.html
Here is a good link from Skytec and their take on starter current draw.
LINK The graph (bottom first page) compares current draw of various starters. The old style prestolite (big & heavy) had the least current draw, just under 200 amps. The PM starter was over 300 amps.
The NL was one of the lower draw starters in this group. The E-drive was not tested or listed, nor was the torque or RPM listed.
Here is another skytec technical note about Electronic ignition and using an Aux battery: (
http://www.skytecair.com/EI.htm) They offer two suggestions, one using a battery, the other a capacitor. I would NOT recommend the capacitor, its not practical or effective. Go with the small battery if you want to assure sufficient starting voltage for the EI. A small 2-3 Ah would work at almost 2 lbs, but if you want a true back-up, 4-5 Ah battery would be a better size, but the down side is the +2.5 lbs added. If worried, add the aux battery, which also can be an in-flight back-up. A side benefit of the Aux battery is it can also drive avionics during start. My engine monitor drops off line during start. An Aux bat could do double duty for both EI and engine monitor. Blue Mountain Avionics has a gouge on this:
http://bluemountainavionics.com/pdf/battery_backup.pdf
A "wire wound" starter (just the Hi-Torque or B&C) with a good battery, proper wiring & ground and an engine that starts normally, in good health, should give you a kick-back safe set-up. #4 wire for starter? Yea that would work if the E-Drive really only draws 75 amps @ 60 ft-lbs torque (and you only need 60 ft-lb). Our battery-starter cable run is short, so not too much weight is added going with a #2, which gives less voltage drop as well. The only down side of the "BEST" starters is they do weigh more and cost a little more; it might be a good investment with EI equipped engines, especially the Electroair.
New E-Drive Starter
Linear Mode
