EarthX and IBBS compatibility

[Andy]

EarthX documentation states -

"The BMS disconnects the battery from the load if it is drained to less than 5% of remaining charge (an over-discharge condition). An over-discharged battery typically has a voltage less than 11.5V. If the BMS disconnects the battery, the voltage reading of the battery will be zero volts."

TCW IBBS documentation states -

"Pin 5 provides charging and bus voltage sensing for the IBBS unit and must be connected to an aircraft power bus. When the voltage on pin 5 falls below about 11 volts the system automatically transfers the load current on the output pins to the internal back-up battery source. "

That information suggests than the EarthX battery could drop off line before the IBBS has switched to backup power. This would result in a re-boot of all systems powered by IBBS. Unless the aircraft was fitted with a G5 EFIS with integrated battery all critical flight data would be lost.

What testing, if any, has been conducted to verify that IBBS will always come on line before an EarthX battery shuts down?

[ve6yeq]

Can this not be simply tested by turning off master while leaving ibbs on?

[Andy]

Can this not be simply tested by turning off master while leaving ibbs on?

That's the way I always shut down and IBBS switches fast enough to prevent a re-boot. I suppose there is no reason to think IBBS would react differently for loss of 11.5 V than for loss of 14.2 V.

GDU 465 is specified to operate down to 10 V so hopefully it would ride through the transient loss of input power. I have not found a minimum voltage for the GSU 25.

Perhaps the sudden loss of engine power should be more of a concern?

I have not fitted an EarthX yet but I have been thinking about how I would revise my procedures for loss of alternator if I did fit one.

73

[n789am]

I'm not sure what your exact procedure is or how your aircraft is wired (are you using passthroughs on the IBBS or the dual power inputs on the PFD). If your aircraft is wired to both power inputs on the GDU465 it always has power and the two sources are diode protected internally. So there shouldn't be any reboot scenario I can think of unless you have your IBBS off normally and only turn it on in a failure scenario. That would likely cause an issue if your earthx cut out before you could turn your IBBS on.

The IBBS also has two sources of power, pass through input (pins 6, 7, and 8) and the charge / voltage sense input (pin 5). If your passthroughs are wired to your main aircraft bus even with the switch off the devices on the output will receive power. Once the IBBS switch is on, if you are using the pass through and the power voltage is sensed as being low it will transparently handle swapping over to its internal battery. I just wired a panel and tested this exact scenario with no reboot.

That's the way I always shut down and IBBS switches fast enough to prevent a re-boot. I suppose there is no reason to think IBBS would react differently for loss of 11.5 V than for loss of 14.2 V.

GDU 465 is specified to operate down to 10 V so hopefully it would ride through the transient loss of input power. I have not found a minimum voltage for the GSU 25.

Perhaps the sudden loss of engine power should be more of a concern?

I have not fitted an EarthX yet but I have been thinking about how I would revise my procedures for loss of alternator if I did fit one.

73

[Andy]

I'm not sure what your exact procedure is or how your aircraft is wired (are you using passthroughs on the IBBS or the dual power inputs on the PFD). If your aircraft is wired to both power inputs on the GDU465 it always has power and the two sources are diode protected internally. So there shouldn't be any reboot scenario I can think of unless you have your IBBS off normally and only turn it on in a failure scenario. That would likely cause an issue if your earthx cut out before you could turn your IBBS on.

The FX-3 is wired so each LRU on IBBS has 2 diode isolated power input pins wired. One is wired to main bus via a circuit breaker and the other input is wired direct to IBBS backup power output. IBBS backup outputs become live only when charging input drops below threshold. Each LRU will take power from whichever power input pin has the higher voltage.

I always have IBBS enabled before engine start and it stays enabled until after engine shutdown. No IBBS powered equipment re-boots. All equipment that is not on IBBS is powered by the avionics bus except the G5 which has its own backup battery. Avionics bus is normally off until after engine start and off before engine shutdown.

As I said in an earlier post, I no longer think there will be any issue with IBBS reversion if/when the EarthX main battery cuts off. That scenario should not be any worse than the routine shutoff of Master (except for the possible inconvenience of the engine stopping).

I was thinking originally that loss of alternator should prompt close monitoring of Main bus voltage with manual activation of IBBS and emergency ignition at, perhaps, 12.0 V. I'd set a Red BATT VOLTS alert at whatever voltage I decided on.

It may still be a good idea to manually revert to IBBS power even if auto switching works as intended. IBBS will power essential equipment for over 2 hours but the ignition battery won't last much longer than 30 minutes even if in perfect condition. Shedding all the IBBS powered LRU from the main battery will give more time before reversion to emergency ignition is required.

I'd rather think about how I'd handle this sitting in front of the computer than while flying at night or in IMC.