VP-X Emergency buss

[rleffler]

Originally Posted by gsmini

Randy,

Can I ask what you came up with? I?m going through the same thing. Did you put one switch between the battery and fuse block?

It's a difficult question to answer. This is because almost no two aircraft have the same schematics. Without seeing the existing schematic, there isn't enough info provide accurate advice.

On my RV-10 w/ VPX Pro, I do have two Master Bus switches/solenoids that each connect a battery to the main bus. on the EBUS I do have a fuse panel that provides power to individual devices that have a backup power input.

Since the GTN650 doesn't have this feature, I have a dedicated emergency switch that switches the power in between the two buses. The only down side is if you flip the switch in flight, it will power cycle the gps.

There are pros and cons to any solution. This is why I don't share my schematic. There are very few that have the identical requirements as me. I will help discuss requirements and the decision tree around it requirement so that individuals can generate their own unique schematic.

If you haven't already done so, create a table of every electrical device in the aircraft. Add a column to identify if it's a must have for VFR flight and another column for IFR (assume solid IMC). The another pair of columns for IFR/VFR risk mitigation. in these columns how will you mitigate the risk if that device fails. The last column is to identify the best solution to solve the risk mitigation you previously defined.

A couple people that I've walked through this process with were surprised at the outcome. Many folks jump into solutioning right away. The surprise is that some folks over designed and other under designed the solution.

Paul Dye wrote an excellent article describing this approach to determining the best way to design fault tolerance into your aircraft is needed several years ago.

[Brantel]

If you don't want all the redundant switches for the critical bus items, you can use one appropriately rated switch or a switch/relay combination to power a critical bus fuse block that feeds the individual devices's backup power inputs. Yes, this is a single point of failure but only when exclusively using the critical bus..... What are the statistical odds of a failure of both the primary and backup at the same time?

For devices that do not have a built in backup power input....like the GTN series, you can basically recreate that feature external to the box by adding two back to back appropriately selected diodes to the single power input. This is essentially how many devices that have built in backup power inputs are built inside anyway.

Just be careful with the selection of the diodes. Forward voltage drop, current, and power dissipation ratings must be considered. Keep in mind that excessive forward voltage drop will increase the minimum voltage required to keep your device operating. Might be important for maximum endurance.

If you want to get fancier, there are some more advanced ways to do this with more components to minimize forward voltage drop and wasted power.

[rocketman1988]

?...the statistical odds...?

Like the change in draft of an aircraft carrier when a fly lands on it...

[Paddy]

I also have a dual batt/dual alternator setup. My system is similar to what Brantel describes. The E-buss is controlled by a single switch that can be used either to cross-tie the two (LiFePo) batteries, or activate the E-buss as a stand-alone sub system.

The objective is to power only the systems necessary to facilitate a safe landing after a major electrical failure in IMC. These are IMHO;
PFD
MFD
Primary NAV/COM
Auto Pilot

[MCA]

Hi Paddy,

Thanks for posting. Just want to clarify a few things on your diagram:
1. What is the shunt connected to the VP-X? The VP-X does not have a function to read external shunt values. Shunts are typically wired to the engine monitor box.
2. What is the purpose of the backup power to the Dynon D6? It has an internal backup battery in case of main power failure.

Thanks!

[Paddy]

Hi Marc,
Good catch - I'd expect nothing less from the creator of the VPX!
The shunt is actually part of the G3X system, that version of the diagram showed it connected to the VPX in error - I've fixed that. As for E-Buss power to the Dynon D6, I have a particular mission in mind. I'll be flying the airplane across the North Atlantic to Ireland this summer, so I want to preserve the availability of the backup instrument for as long as possible in the event of a total electrical failure. God forbid - if the E-Buss battery reserve were to be exhausted, I'd still have the D6 internal battery to give me something to look at until I'm within sight of land.

[MCA]

Wow, that'll be an interesting flight and trip!

Thanks for the additional context, and exactly why I say in the book to build a plane that meets *your* needs, as those needs are likely different than someone else's.

[RandyAB]

Originally Posted by gsmini

Randy,

Can I ask what you came up with? I?m going through the same thing. Did you put one switch between the battery and fuse block?

If you PM me your email I will send you a copy of the schematic I came up with. I had a fellow RV 10 builder who is also an electrical engineer look it over and he approved.
Randy

[patterson]

I need some advice on an EBuss I'd like to use
Have installed a VPX Sport on my plane already. Because I don't have full confidence in the thing Not going dark, I want to have 3 Essential items on a basic EBuss. My Com radio, my backup Efis (G660) and an Alternator Field. That comes to 3A + 3A + 5A = 11 Amps. Below is my crude schematic. I have one SureFly emag. I figure if the alternator charges the battery I could fly on to my destination with com and GPS.
I'd appreciate your critique.


https://photos.app.goo.gl/cKjoX8T4DJrXGrZWA

[MCA]

Ron,

IMO you are making your system less reliable by adding in extra complexity and failure points. There is guidance in the VP-X install manual about backups.

My 2c.