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GNC355 Dual Power

Hi all,

My project is an RV14 with two 10' G3X. I also have a GNC355.
I am installing a TCW standby battery which will feed the GDU,GSU etc. via the second power input.
However the GNC355 does not appear to have this functionality.

Any ideas how I can power the GNC from the TCW. The TCW does have feed through power, but this would power all the other units which I don't want.

Cheers.
 
I see where the GPS connector on the GNC 355 has two power input pins and the COM connector has three. If they are internally diode isolated they might be able to be separated between primary and backup power. I don't know for sure as the installation manual doesn't go into this.
 
TCW IBBS Wiring

See the following example of how to wire the TCW IBBS to devices without dual power input pins ... it shows the GTN650. It could be that the GNC355 is similarly configured ... ie with no dual power inputs.
 

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Thanks Steve,

The setup shown in the example would also provide pass though power to the G3X units as well. This is not what I want.
My question was more about if there is any direct way for dual power on the GNC335.

Cheers.
 
Did anyone ever figure this out? I’m going through the same question now. I want to power the GNC355 in event of total electrical failure but it operate on my avionics bus switch normally, the backup battery would be plugged into other things like electric trim and all the backup inputs for GAD29, 11
 
The high density pins are not rated for the amperage required hence multiple pins are used for current sharing. You will need to put together your own diode ‘OR’ circuit if you wish to use a BU battery supply on the 355.
 
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I want to power the GNC355 in event of total electrical failure but it operate on my avionics bus switch normally ...

Isn't that trying to achieve two rather different goals? Having one avionics switch is a single point failure but then you want to provide a back-up in the event of (a quite unlikely) "total electrical failure".

If your electrical system is designed with a little redundancy more than one component will have to fail to prevent power reaching the bus. The back-up battery will prevent stuff falling over during cranking. You could wire the GPS side of the 355 to the battery and the COM side straight to the bus to avoid over loading the BBU. As Walt said all the power pins are required to pass the current through the small size pins.
 
Hi all,

My project is an RV14 with two 10' G3X. I also have a GNC355.
I am installing a TCW standby battery which will feed the GDU,GSU etc. via the second power input.
However the GNC355 does not appear to have this functionality.

Any ideas how I can power the GNC from the TCW. The TCW does have feed through power, but this would power all the other units which I don't want.

Cheers.

I got exactly same problem with my airplane TCW and GNC355. Wanted to have primary avionic bus power and backup power from IBBS. What I did, i installed a full diode bridge (GBPC2506-E4/51 25 Amps) and used only one part of the bridge (3 pins). With that, I have 2 sources of power and 1 output to the GNC355. 1 source from master avionics and 1 source from TCW IBBS. In that way, i can isolate both sources in case of problem... but my GNC 355 still having power in any failure mode...

I hope this can help you.

Regards,

Louis
C-GGVX
 
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This is my plan, but scratch the 8 AA batteries and use 8 C cell batteries.
 

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This is my plan, but scratch the 8 AA batteries and use 8 C cell batteries.

Older Diamond DA-40's do this with AA Duracells, albeit with 16 AA's since the Diamond has a 24 volt bus. C or D size alkalines will do the same while giving more time on usable backup power with a weight trade off. With off-the-shelf alkalines they could be replaced every condition inspection with new and the removed batteries could be used around the shop. Most shops I know of already have a whole box of Duracell D size cells from ACK 121.5 ELT battery replacements.
 
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