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IBBS No Power When Charging

iamtheari

Well Known Member
I am trying to track down a weird issue I have with my alternate trim system. I wired up two switches so that I can run my pitch trim from my IBBS backup battery in the event the main electrical system or the wiring for the main trim system (buttons on control sticks and VP-X Pro) fails. I have a Norm/Alt switch that selects whether the alternate trim or VP-X outputs are connected to the trim servo. The alternate trim up/down momentary switch is wired from an output of the IBBS and a firewall ground.

The VP-X can control the trim servo just fine in Norm mode.

The IBBS can control the trim servo just fine in Alt mode, but only when the main battery contactor (and thus the VP-X) is off. There is not a voltage difference between the trim motor outputs when the master switch is on and the alternate trim switch is run up or down. There is a ~12.5V difference when the master is off and I run the alternate trim switch. (Positive voltage one direction, negative the other, as expected.)

I am not using pass-through power on the IBBS, just the charging input and the four power outputs. The IBBS is charged by one circuit output of the VP-X. The VP-X also has the aux battery voltage input correctly wired to the battery information wire on the IBBS.

I am trying to rule things out. And before I really go nuts ruling out every wire in the panel, I want to rule out these questions:

Does the IBBS turn off its outputs when the charging input is active?

Is there any other set of conditions in which the IBBS turns off its outputs?

I hope someone knows. My sanity is awaiting your replies. Thanks in advance!
 
IBBS Charging and Bus Voltage Sensing

I have recently spent time planning the installation of VPX-PRO and IBBS systems for my RV-7 build.

The installation manual for my IBBS-12V-6ah 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."

From that language, my conclusion for my installation is that the four output pins are turned off when the VPX is charging the IBBS. By definition, the bus voltage in that case is greater than 11v.

Without knowing the exact configuration of your electrical system, or which model of IBBS you are using, the above or equivalent language in the install manual may be a reference point.

I am a first time builder so would defer to those who may have more experience knowledge that might care to comment.
 
Thank you for sharing that information. I definitely read the manual but that tidbit did not come to mind later when I was troubleshooting my issue.
 
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