MOD Upgrading the ignition backup battery in a Carbon Cub E/FX-3 to a TCW IBBS 3AH battery

[Neal]

While I'm still testing the EarthX backup battery as outlined in this thread, I'll start a thread for those considering use of the TCW IBBS 3AH LiFePO4 battery. I welcome discussion on wiring required for a EX-3/FX-3 which the factory uses a 12V AGM battery, typically the PowerSonic P1221S which is a 2AH battery.

Items required:

Integrated Battery Back-up System (IBBS) - TCW Technologies

The Integrated Battery Back-up System (IBBS) provides an engineered solution to enable an endurance bus for critical loads found in aircraft. The IBBS system provides back-up power to critical electronic loads such as EFIS, GPS, Autopilots and engine monitoring systems.

www.tcwtech.com

IBBS Installation Wiring Harness w/mating DSUB Connector - TCW Technologies

Premade, color-coded wiring harness with mating D-SUB connector for Integrated Battery Back-up System (IBBS) units. Available models in: • 10' or 20' Length • Experimental or Certified units Please select your product options below.

www.tcwtech.com

The FX-3 has a two position emergency ignition switch OFF/ON.

From my high level overview and not looking at the current schematic of the ignition backup circuit, hopefully someone can post that, it seems the current incoming positive would go to PIN 5 and the ground PIN 9. However, the difference here is the OUTPUT of the IBBS battery goes out 6,7,8 so this would require some wiring change so that output goes to the Light Speed Ignition. I'm interested in how that's currently wired and what would need to be changed to effect this battery upgrade.

Open to discussion and share knowledge to help others that may be considering this option.

Light Speed diagram below, others and manual attached.

 

[Neal]

Would tying pins 5 and 6 together work as a drop in replacement for the current setup? PIN 5 would the incoming charge and sense, pin 6 would be the output from the battery to the ignition.

 

[Neal]

A consideration that needs thought is how we engage the backup battery and power the LSE ignition module by turning emergency ignition ON. We need to make sure doing so removes the charge current, triggers IBBS sense to provide power and powers the R ign module for ground testing.

 

[Neal]

My assumption is the OFF/ON toggle in the FX-3 for emergency ignition is a "charger" control? In the OFF position, charger is enabled. In the ON position, charger is removed?

Nope. Doesn't make sense. We need to enable the R ign circuit to be powered by the battery. Cancel above.

Click images if needed. Sourced from AMM REV B

 

[ve6yeq]

If you are going as far as to replace the PowerSonic AGM with a TCW IBBS, I think that it makes much more sense remove the PowerSonic completely and connect the right ignition directly to the existing TCW IBBS 3Ah. This would then have a 3.93 A load out of a max continuous current of 5 Amps. The 3Ah capacity of the IBBS will then give you >30 min IFR-required minimums. If you want more time, swap out the IBBS 3 Ah for a TCW IBBS 6Ah or an EarthX EBBS (7.8 Ah).

I am just completing a design to be able to power the majority of the avionics, including a radio and transponder, and the right ignition off a single EarthX EBBS. Hopefully, this week, I will be able to measure real-life current draws to compare them to the datasheets.