TCW IBBS (backup battery) - Battery Master Switch - Do you need it?

[tracstarr]

I have the TCW IBBS 6ah found here (https://www.tcwtech.com/Installation%20instructions%20model%20IBBS-12v-6ah%20rev%201.6.pdf). There is a backup power master switch. Do you really need a separate switch here? I know you can't tie it to ground permanently as then your equipment will always be powered, but could I just connect this to the same switch as my main master? Note, I'm not wiring the pass-thru mode here in which you can skip this pin all together. Page 17 shows basically what I have setup.

I don't see a reason I can't wire them together. They are both just switches that connect to AF ground. You'd always want both on or both off. I can't see a reason you'd ever want one on and not the other.

[efwd]

I don't pretend I know anything about the electrical stuff but...
When my battery should die, I throw a switch and pick up the power off the back up battery. That battery then only operates mission essential equipment long enough to get on the ground. Would my back up battery not just die simultaneously as the main dies if it were wired together? It seems to me that doing it that way would be the same as just installing a bigger battery. Maybe I am just showing how niaeve I am.

[Clark in AZ]

I've seen it wired separately so that when you get to the aircraft, you flip on the backup battery which boots up the Garmin screens while you do your walk around. When your finished you hop in and everything is ready to go, start up as normal then switch off the backup. I think having them separate is a good idea. My .02

Clark

[efwd]

That's how mine works.

[tracstarr]

Right, but if you actually look at the documentation by TCW you do not turn off your backup power until you shut down and have already turned your master back off. Plus I don't see an advantage to having both switches. The equipment is smart enough to decide which power source it draws from. So if your main battery is low it's going to pull from the backup battery. At least that's the way I see it.

Sent from my SM-G973W using Tapatalk

[Delta Whisky]

Tracstarr - having and using the switch in question gives you the chance to verify (preflight if you will) the unit by powering everything it drives before turning on the master and to be able to verify it is still working when you shut down if you leave it on after shutting down the master. IMHO, not a bad idea for a back up system.

[tracstarr]

Agreed, this is a valid use of a secondary switch.

Lets consider my specific setup with a G3X and the TCW outputs on pin 2 & 3 (batt-info and low volt warning) being pushed as inputs to the G3X. In the single (dual) switch scenario, I would be getting information on screen about the status of the backup battery and basically know that it's in good condition or not. I guess what I would be missing is if it actually worked to power units in the event the main power source dropped below 11v or whatever the garmin threshold is.