I’ve received some requests for my electrical system specifics. So I have exported the diagrams to a PDF file. This file includes some things that aren’t specifically “electrical” such as the graphics for the switch panels and instrument panel layout.

621CM Electrical System

If you have any questions about my electrical system, please don’t hesitate to ask.

I will offer up one opinion: The Vertical Power VPX-Pro is probably one of the smartest choices I’ve made with respect to product selection. Here is a very short list of some of the features that have me grinning like a kid at Christmas:

• Wiring is significantly easier than it would have been had I used traditional circuit breakers.
• You can see exactly how much current individual devices are drawing.
• Changes (and no matter how much you plan, there are always changes) are much easier to implement.
• Built in starter switch lock out.  When the engine is running, you started button is disabled.
• Built in landing light wig-wag which is activated by a pre-set speed.  (the downside is now I have a Xevision wig-wag module that I don’t need)
• Variable speed pitch trim.
• Support for backup EFIS battery.
• Support for dual alternators.

Any questions I submitted to Vertical Power were responded to in usually less than 4 hours.  Many times by Marc Ausman himself. But a few years ago Vertical Power was acquired by Astronics.  I was worried that the support would suffer. But that has not turned out to be the case.  Responses are just as quick and helpful as before.

But in the spirit of full disclosure, there are some downsides.  The biggest for me is the number of available circuits.  There are only about 23 user definable circuits. That sounds like a lot, but once you start adding up all your devices, you come up short real fast (I have about 32 individual devices not including the accessory power ports). So you have to take one circuit and split it off and use fuses to support more devices. For example, I have one of the VPX circuits driving the Overhead Lights, Panel lights, Map Light, and Warning Lights. Because each of these are independently dimmed, each leg had to be protected by a fuse.

Long ago when I began this project, I decided on a glass panel. At the time, there were a number of vendors offering EFIS (Electronic Flight Information System) solutions. I decided on the Grand Rapids Technology product.  At the time, they had the HX EFIS products and an Engine Analyzer.

So I was going to have a single screen on each side of the instrument panel with the “radio stack” in the middle. This stack would have the communications/navigation radios, audio panel and GPS.

Once I started building, they released the HXr EFIS displays.  These displays support “remote” devices.  Which means the radios and audio panel are controlled through the EFIS and do not have to be located on the instrument panel. There was no IFR GPS option though so I was going to go with a Garmin 400W WAAS GPS mounted on the instrument panel.

Then a couple years ago I heard that GRT had an IFR GPS in the works. I asked them about it and was told that it was “in development” but would be ready in a year. Since I was still a couple years from needing it, I decided to go that route.

When I was time to order all the avionics equipment I placed the order.  But the GPS still wasn’t ready. So I started installing the avionics and left a spot available for the GPS.  In October of last year, I finally received the GPS!  Hooked everything up and I was good to go.

Except that I realized that I had never loaded the GPS database.  When I asked for instructions about doing that I learned that the software for the EFIS wasn’t finished. I was told November or December.

But I didn’t want to run version 1.0 software while shooting an instrument approach to minimums.

So I returned the GPS and began looking for a used Garmin 400w.

One of the glitches with this particular operation is that when I was laying everything out, I didn’t allow for a 12″ deep, panel mount GPS.  That means I have to do some rearranging.

This is the avionics shelf behind the instrument panel. The multi-color rectangle is where I figure the panel mount GPS will be.

Obviously the audio panel is going to have to be moved. I think the cables from the hub (white cables to the left of the audio panel) will be able to be pushed down.  The pitot lines (red tubing) will have to be relocated as well.

My first plan was to remove the top shelf which currently holds the GPS, remove the trim controller and mount the audio panel just above With the audio panel out of the way, then I would just have to re-route the pitot tubes.

So here I’ve removed the old GPS, trim controller and power stabilizer (more on that later) and relocated the audio panel above the VPX.

But there’s a problem… The audio panel cables aren’t long enough to reach to the new location.  Since I was going to need cables for the new GPS, I got in touch with Tim Hass at Approach Stack to ask if I could get an extension cable for the audio panel.  Normally, I would just replace it with a new, longer cable but the existing cable has wires running to all the headset jacks, control stick, right switch panel, etc. and I didn’t want to have to pull and reconnect all those connections.

While I was talking to Tim, I told him that I was looking for a used 400w but not having much luck and that if he knew of one to let me know. He said that he had a brand new Garmin GTN625 that he could sell me. This is basically the new, improved replacement for the discontinued 400w.  And the price was just a little more than I was finding for the old units. So I told him “sold”!

A while later, a box showed up with the new GPS, mounting hardware, cables and my new audio panel extension cables.

Uh-Oh…

The audio panel cables are huge.  They are thick and they don’t bend very much. Add in the connectors and I was having trouble routing the cables so that they didn’t interfere with important stuff. So I set that problem aside and started working on getting the GPS mounted.

I decided to mount the GPS in the center of the panel directly between the two EFIS screens. But the compass was in the way.  Since I had to eliminate the power stabilizer, I needed to create a backup power source for the primary EFIS/AHRS/Magnetometer. That means I do not need a traditional whisky compass. But I do need to fill in the hole where the compass used to be. Once that was done, I had to determine how I would support the back to the GPS.

I decided to support it from above rather than build supports from the avionics shelf. So I located the center of the inside of the fuselage just aft of the canard opening. Then I used spring clamps to hold the GPS tray in place while a used structural adhesive and rivets to attach a pair of aluminum angle brackets using the tray as a guide.

Once that cured, I made some short aluminum supports to allow the tray to sit farther forward so that it could reach the panel.

Then I leveled the tray up and marked the panel where I would have to cut an opening for the GPS.

After I cut the opening (which took a while because I cut it small and gradually increased the size), I had to support the tray where is met the panel. I chose to bond a couple of aluminum angle brackets to the back of the panel.

And then just to look at it with the GPS inserted.

Then I removed the tray, mounted it to the rear support, put the instrument panel in and attached the tray to the panel brackets.

That’s when I discovered something; There’s enough room under the tray to fit the audio panel.  By placing it there, it would be almost in the same location as before so I wouldn’t need the extension cables (and the associated routing problems).

So I pulled the GPS tray out and built a drop-down support from the GPS tray.

Then everything goes back in.

I rotated the wiring hub so the cables weren’t pointing straight up.

The last task is rerouting the pitot-static lines. I used the heat gun to heat up the tubes and bend them.  I’ll redo this to make it prettier later.

Now it’s time to put everything back together and power it up.

Because I have an “all electric” instrument panel, there are some challenges. One of those is powering the basic instrumentation during engine start. When you hit the starter button, the battery gets loaded down and the output voltage can (and usually does) drop enough that the EFIS reboots. It takes the HXr about a minute to boot up. So for that first 60 seconds after starting the engine, all I’ve got for engine health is the “Low Oil Pressure” warning.

To resolve this, I installed the TCW Technologies Intelligent Power Stabilizer (IPS).  This small, lightweight box gets power from the battery and provided a constant 24 volts even when the input voltage drops to as low as 9 volts. It can only output 24 volts for a couple of seconds when the input power drops but that is sufficient to keep the EFIS up and running during engine start.  The HXr has three separate power inputs.  The primary power input is connected to the battery.  The secondary power input is connected to the IPS.

With the GPS swap requiring me to move things around, I had to eliminate the IPS. To keep the HXr powered up during engine start I will have to go with a backup battery.  I would have done this originally except that the optional backup battery is only available for 12v HXr’s. I looked for a 24v backup battery, but they were either too big or too expensive. This is what happens when you go with a 24v electrical system.

So I decided to think outside the box.

I call these “Barbie Batteries”.

I found a store that sells “Scooter Batteries” for things like mobility scooter, small electric cars… You know, those little cars that parents get their little kids?

I found that while the 24v batteries were big and pricey, I could get a pair of small 12v batteries that were very affordable. The batteries I got were 5ah SLA (Sealed Lead Acid). By connecting them in series, I would get 24v, 5ah.  Not only would this power the primary EFIS, AHRS and magnetometer during engine start, it would also keep the devices powered for at least an hour if the main electrical system failed.  An added bonus is that since the Magnetometer and EFIS will have an independent power source, I can eliminate the compass in the panel.

The down side is that they weigh 3.5 pounds each. Once I’ve verified this works, I may look for some new, fancy, hi-tech, low-weight batteries.

As for where to put these, I decided to put them in the nose. I noticed when flying alone that I required quite a bit of nose-down trim for level flight. Seven pounds in the nose should help that.

The first step is to make a tray for the batteries. So I wrapped the batteries with duct tape, took a piece of spare fiberglass, cut it to size and then applied some fiberglass strips to create the sides. Once it had cured, I removed the batteries and trimmed to size.

Mounting in the nose was a bit of a challenge.  First I had to find a spot that was as far forward as possible but not interfere with the nose gear or anything else. Then I had to fabricate the supports and hold it in position while in glassed everything in place… And it had to be level.

Once that was bonded in place, I had to fabricate the hold downs.

Then I just had to wire everything up.

The primary power comes on whenever the master switch is on.  I’ll have a second switch on the panel to apply the backup battery power to the secondary input of the EFIS. So I’ll throw the backup battery switch while I’m doing the pre-flight check, Then when I’m ready to start the engine, the EFIS will be up and running.