Cactus Charlie
Well-known member
- Joined
- Mar 1, 2025
- Posts
- 399
- Type aircraft owned
- CCX-2000 (FX-3)
- Base airport
- KDVT
- Ratings
- Commercial ASEL, ASES, AMEL, glider. CFI glider, ASE, Instrument.
As some of you know I've been considering using a TCW IBBS to replace the 2 AH emergency ignition battery on my FX-3.
The XCub uses a TCW IBBS as right emergency power source for its Lycoming EIS (electronic ignition system) so I've been looking at how CubCtrafters designed the installation in case I could improve on my design.
I have found a feature of the CubCrafters design that concerns me. The warning LED is driven by the IBBS "low voltage alarm" output. The LED will function as a low voltage indicator rather than an "emergency ignition in use" indicator as implemented on the FX-3. This means that, if the XCub emergency ignition switch is accidentally left in the Off position, and Main bus voltage drops below 11.5 V, the LED will light which is exactly the same indication as if the emergency ignition was armed and had taken over powering the right ignition.
In a bench test of this configuration I confirmed that the LED is lit when voltage drop to 11.5 V then progressively dims as voltage reduces towards zero.
I think this very misleading as the schematic labels the LED as an "In Use" indicator but it doesn't work that way. I have not checked how the XCub AFM describes the LED indicator.
I plan to go back to my design in which the LED functions as a true "in use" indicator and cannot be lit when the emergency ignition switch is Off.
I think XCub owners should be aware of what the LED means and double check that the switch is On or Armed if the LED becomes lit.
The XCub uses a TCW IBBS as right emergency power source for its Lycoming EIS (electronic ignition system) so I've been looking at how CubCtrafters designed the installation in case I could improve on my design.
I have found a feature of the CubCrafters design that concerns me. The warning LED is driven by the IBBS "low voltage alarm" output. The LED will function as a low voltage indicator rather than an "emergency ignition in use" indicator as implemented on the FX-3. This means that, if the XCub emergency ignition switch is accidentally left in the Off position, and Main bus voltage drops below 11.5 V, the LED will light which is exactly the same indication as if the emergency ignition was armed and had taken over powering the right ignition.
In a bench test of this configuration I confirmed that the LED is lit when voltage drop to 11.5 V then progressively dims as voltage reduces towards zero.
I think this very misleading as the schematic labels the LED as an "In Use" indicator but it doesn't work that way. I have not checked how the XCub AFM describes the LED indicator.
I plan to go back to my design in which the LED functions as a true "in use" indicator and cannot be lit when the emergency ignition switch is Off.
I think XCub owners should be aware of what the LED means and double check that the switch is On or Armed if the LED becomes lit.
