VPX-PRO configuration

Don't read this diagram and post as my final electrical configuration, however the diagram at this point is pretty close to my final MAIN Bus configuration. The first realization that you should have if you are looking at this is the number of pins you actually need in a modern avionics package. For the most part, every one of my connectors is fully populated. And this is just one of my busses, I still have another AUX bus in addition to this MAIN bus! Also an Essential bus on top of that!

I have a Z-14 inspired design (which is not depicted in the default VPX planner diagram). This is a two alternator and two battery design (again, not depicted here) that can be connected via a single X-Feed contactor. Both of the outputs of each bus contactor feed a Schottky E-Bus Diode to create an essential bus for my electronic ignition.

The Main alternator is a AL12-EE70/B while the backup is a FS1-14B. Only one alternator will be live at any given point in time and the switch over between the two is a manual operation via a physical panel switch that controls the VPX ALT1 and ALT2 power pins. There are actually two switched inputs into the VPX for ALT1 and ALT2 that are connected to a SPDT on the VPX, but the VPX does also manage the ALT lines to ensure only one alternator can be active at any given point in time.

The VPX is physically located above my left side rudder pedals on a custom bracket that spans the firewall to mid-panel. This turned out to be a great place for the VPX, however I will warn you, think about your connectors with the wires attached when planning where to put your VPX box. With the connectors and wires connected, there is not much room above the rudder pedals.

Trying to avoid single points of failure was the goal in my setup.  I mention my alternator setup because that is one of the first things I struggled with that I was not fully excited about (but the best of the options I came up with). Having two batteries and two alternators is obviously for redundancy however while designing you have to balance redundancy with complexity. If you look at the VPX configuration you will see both ALT1 and ALT2 switches as well as ALT1 and ALT2 Field wires. The actual schematic for a given alternator to be enabled is not straight forward. A ground line comes into the my MASTER/ALTERNATOR switch. When the Master switch is moved to the ALT position, this connects ground to the input of a SPDT Alternator selector switch. This in turn tells the VPX-Pro to enable the alternator that is chosen.

From the pilots perspective this alternator setup is not bad. If the alternator appears to not be charging, flip from ALT1 to ALT2. If the system is still not charging at that point one could look at the MFD VPX configuration page to see if the ALT1 or ALT2 power lines have any current draw, but after that, there is not much you would want to do in the air. There are just too many variables behind the panel. 

The second issue that did not excite me was my coil packs on my electronic ignitions. All three coil packs come to a single point and FlyEFII recommends keeping those three feeds together. The problem with this though is that if you loose a connector on your coil pack line your engine is no longer running. At least with the ignitions themselves there is redundancy. The coil pack is a single point of failure. I ended up really not liking the options I came up with on how to feed power to my ignitions and coil packs. Should I bring them back straight to the battery? Which Battery? Do I split the ignitions between AUX and MASTER? If I split up the ignitions on the busses, and the bus that powers the coil pack goes down, whats the point?

I ended up biting the bullet and putting an essential bus in on top of the 2 alternator 2 battery design. Each power contactor feeds a schottky diode making an essential bus. If either the AUX or the MASTER or both are on, the essential bus will have power. I ran a dedicated line from the rear or the aircraft forward for the essential bus and this ultimately goes to the only three physical breakers I have on the plane. A 15A for the Coil pack and 2 5As for the ignitions.

While again, the decision to add a third bus adds complexity, I feel better about the redundancy in the system for the critical components to keep the engine running.

Speaking of complexity... When I first setup my rear mounted avionics tray I forgot that my AUX and X-FEED contactors are reverse from each other, i.e. they are back to back. My MASTER contactor is in the stock location and feeds both the X-FEED contactor as well as the main power line running up to the starter and VPX. 

 

On the left of this image is the AUX contactor with the right being the X-FEED contactor. When installed into the plane, the top right post of this photo gets a 2GA jumper to the output of the MASTER contactor. The top left post of this photo gets a 2GA jumper to the battery. Do you see the problem?

To Shunt or not to Shunt

As I was wiring my GEA24 today I realized there was a decision to be made about where and if to install a shunt for measuring current. I already actually installed a shunt on the firewall to measure the current coming in from the alternator B-Leads to the Main Bus. (again, I will go over my bus decisions later, but this is a Z-14 inspired design where there are two alternators and two batteries). Thinking more about that though, I am not sure I want/need a shunt up there.

The decision impacts what information I will on my EFIS display. I am already pretty accustomed to monitoring Bus1 and Bus2 Amps and Volts from flying a G1000 and G500 system with dual busses. I like having that information available to me as a pilot.

The thing about my design is that the VPX-Pro already speaks to the G3X over RS-232 to relay the main bus voltage and current draw to the EFIS. So the EFIS can be configured to use that VPX information about the Main bus. The downfall of my setup is that the VPX current draw is not the full story for my entire electrical system. Some of the current is being sourced from the AUX bus which the VPX does not have visibility of.

So my original thinking was that I wanted to be able to see how hard the alternator was working. Only one of my alternators will be active at a time because they both feed the same bus. In thinking more about it though, I think it would make more sense to know how much current my AUX bus is using.

Sources of data:

• Main Bus Volts: VPX
• Main Bus Current: VPX
• AUX Bus Volts: GEA24 J244-Pin28 (attached to the aux fuse block)
• AUX Bus current: Rear mounted shunt (or maybe I am going to co-located this up front with the aux fuse block)

The thing that I find a little confusing about this is that the "Main Bus Current" is not the current that is going over the 2GA wire going to the battery box, it is what the VPX is outputting. So if I was flying and wanted to know how stressed my electrical system is in total, there has to be some math involved. That said, there was no way around that. Ideally I would talk to Garmin and they would provide a touch screen option to the EFIS page that when you tapped current you could flip flop between battery current and alternator current with both busses being depicted. I think for now though I am happy. (although I have to go remount my shunt to a new location)

Here are the relevant sections from both the G3X manual and the Vertical Power manual regarding sensing current.

G3X installation Manual

Current
The GEA 24 and GSU 73 have provisions to monitor bus current from two different sources. Current can be measured either using a shunt resistor such as the UMA 1C4 (50mV/100A type) or a Hall effect sensor such as the Amploc KEY100 series.

Shunt sensors: Shunt sensors are connected to the SHUNT 1 and SHUNT 2 inputs on the GEA 24 and GSU 73 (see Figure 30-2.2 and Figure 30-3.1). The SHUNT 1 input can be configured to display either "Bus 1 Amps" or "Main Bus Amps". The SHUNT 2 input can be configured to display either "Bus 2 Amps" or "Essential Bus Amps". 

Hall effect sensors: Hall effect current sensors are connected to the GEA 24 or GSU 73 general purpose (GP) inputs (see Figure 30-2.2 and Figure 30-3.1). Hall effect sensors can optionally be calibrated to adjust for installation differences (see Section 34.4.19.4). The supported configurations for Hall effect current sensors on GP inputs are similar to those supported for shunt current sensors:

• Bus 1 Amps (Hall)
• Bus 2 Amps (Hall)
• Main Bus Amps (Hall)
• Essential Bus Amps (Hall)

Vertical Power: When using a Vertical Power unit, configure SHUNT 1 to "Vertical Power Main Bus
Amps" or "Vertical Power Bus 1 Amps" to use primary bus current data from the Vertical Power unit.
Configure Shunt 2 to "Vertical Power Bus 2 Amps" to use secondary bus current data from the Vertical Power unit.

Vertical Power Installation Manual

3.7 Alternator Current Sensing (Shunt) When planning your aircraft electrical wiring you must consider whether to wire an ammeter (usually a shunt or hall effect sensor provided with the engine monitor) on the wire connecting the alternator(s) to the main bus. The ammeters indicate the amount of current the alternator is providing. 

A shunt is not required to tell if the alternator is working. It is very easy to tell if the alternator is working correctly by simply looking at voltage. If you see 14 (or so) volts with the engine running then it is working. If you see 12 (or so) volts it is not working or not turned on or the devices are drawing more current than the alternator can provide (note, engine must be running). If you set your low voltage alarm on the EFIS at 13 volts, then you will get a low voltage alarm if the alternator fails. 

Since the VP-X provides basically the same information as a shunt installed on the alternator b-lead, our position is that adding a shunt gives you no additional meaningful information. 

A shunt on the alternator b-lead shows the amount of current the alternator is providing to power the devices and charge the battery. The VP-X total current reading shows the total amount of current the devices attached to the VP-X are using. The delta between the two is the battery charging current, which goes to (basically) zero after re-charging any loss from starting the engine or charging a run-down battery. 

If the battery charging current is important to you, then you should install a shunt. If not, then simplify your wiring and don’t install it. Your call. And of course each builder’s needs are different so there is no absolutely right answer. 

The EFIS displays a VP-X page which shows individual device current as well as total current through the VP-X. The EFIS also has an ‘Amps’ gauge that is used to show the readings from the shunt. In some cases the EFIS ‘Amps’ gauge can be used to display total system current from the VP-X. Please check with your EFIS manufacturer for details. 

If you don’t install the shunt then the shunt wires on the engine monitor/ EFIS are not used

Panel Layout

One of the most rewarding aspects about building your own plane is configuring the electrical systems and avionics just the way you want. While I am not Instrument rated right now, I fully intend to get my IFR ticket as soon as I free up some time by not building, but flying. Ideally, I would also perform my IFR training in my own 10. We will see how that works out. 

I will get into the 2 battery 2 alternator system I have installed in later posts, but I figured I would start with my actual avionics. I selected the following: Vertical Power VPX-Pro, x2 GDU460, 3 axis autopilot with a GMC307, GTN650, x2 GSU25, GMU22, GTR20, GTX45, GMA245, GEA24, ACK ELT and all of the components to have these packages work together. I am leaving my right panel open for a RAM ball mount for an iPad and I did install 3 mechanical backup gauges front and center.

These components are installed into a Aerosport 310 Panel with a throttle quadrant in the center console.

It is a bit of a mess right now, but the heart of this system is physically installed into N50412K.

Vertical Power

I was about to place a digi-key order a couple of weeks ago in order to buy the molex crimper for the vertical power molex connectors when I came across a document on the vertical power website that stated Vertical Power has molex (professional series) crimpers available for free rental. I figured it was one of those marketing lines that when you try to actually contact them they either ignore you or tell you that they don't have anything available.

To my surprise I was completely wrong. They shipped the crimper out the day after I contacted them, and here I am 1 week later with all of my connectors done!