J

jpharrell

Well Known Member
I was taught in flight training to keep the avionics powered off during engine start to protect the expensive electronics from voltage spikes. I am putting together the final layout for my instrument panel and I see that Dynon specifically says ?SkyView?s robust power allows it to be powered on during engine start?. That?s good because I was also trained to watch for the oil pressure to rise at startup. But I also have a TruTrak Gemini PFD in the panel and that installation manual says to keep it off during engine start. I was planning to switch all the avionics through a single Avionics Master switch (using a Vertical Power VP-X) but now I am wondering if it makes more sense to add a separate power switch for the EFIS which I can power on before engine start then turn the rest of the avionics on after the engine is running (and off again before shutdown). Or should I simply wire the Skyview to the Master switch so it comes up automatically and put the rest of the avionics on the Avionics Master circuit for power up after engine start? What are other people doing with modern EFIS systems?
 
My EFIS is powered by a separate battery.

There is no "brown out" or other load that the EFIS sees when I start the engine.
 
Wire SkyView to the master. It will come on when you turn the master on, and will live through any spike the starter throws at it. If you need to ever turn it off in flight, just hold down button #1 and it will turn off.

The only issue here can be that it might reboot during engine start if your battery voltage gets below 6V. Having a backup SkyView battery will solve this.

If you have the backup battery, you can also power on with button #1, so you could wire SkyView to your avionics master and still power it up on the backup battery before engine start, but this is kind of unnecessary complexity. It's nice to hop in the plane, throw the master, and have everything ready for you by the time you are ready to crank. It's how my plane is wired.
 
It helps to change the way we think - specifically, I don't think of the EFIS as "avionics" - the EFIS is really part of the airframe. I keep the "avionics" (essentially radios) powered off until after engine start partly to save juice for the starter, partly to keep them from browning out, and partly to preserve tradition.... ;)
 
Paul was a faster typist than me ....

It all depends on what you lump together under "avionics".

For me, the EFIS/EMS has a backup battery so it can be "on" during engine start to give me my engine instruments.

Both main and backup battery power run thru a Schottky diode to feed my essentials for startup - so when the started drops the main voltage, the EMS is automatically feeding from the backup. When the main voltage rises back up and the alternator is active, then its voltage is higher than the backup and the Schottky is now feeding the essentials from the main source.

My Avionics - consisting of the radio, AP, Xponder, GPS, ADS-B, etc - are switched on after engine start.
 
humptybump said:
My Avionics - consisting of the radio, AP, Xponder, GPS, ADS-B, etc - are switched on after engine start.
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Just a note about all of those as well. ALL Dynon equipment is designed to handle engine start. Our radio, our servos, our ADS-B receiver, etc. If you have all of those, they draw less than 500mA total when powered but not "operating." They won't drag your battery down, and of course don't really matter if they reboot when you crank the engine since they come back on-line in under a second.

So in a plane that is all Dynon, you can seriously consider not having an "avionics" switch at all and reducing your operational complexity and weight.
 
DA - my reasoning for having an avionics switch is partly as Paul noted "tradition" but it could also be relabeled my "not absolute essentials" switch.
 
dynonsupport said:
...you can seriously consider not having an "avionics" switch at all and reducing your operational complexity and weight.
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I have my left Skyview with backup battery on my master switch and everything else on an avionics switch. With the VP-X, I can change that to any configuration I want in a few minutes with no re-wiring.
 
The answers on here are good, except that they don't take into account the Vertical Power system. I had a look at the X manual and it looks like the primary EFIS gets wired differently than other avionics (not just the data feed to the EFIS but also the power. There's also a section in the manual about it. I think you should ask Vertical Power (maybe Marc will spot this and chime in) but it looks like the EFIS should come alive with the VP unit and the rest of your avionics with the avionics switch, handled by the VP unit. So you don't have to wire to the directly to the contactor or anything. One reason I like the VP-200 is it is mode smart so you can tell it what to turn on/off in each mode. For instance, which units to have on or off during engine start. But it looks like the X will let you at least set up the switches in an intelligent fashion.
 
Good with VP-X

Patrick,

The VP-X requires that the primary EFIS be wired to pin J12-9 but it lets you assign any switch to that pin or assign "always on" if you want it to power up as soon as the Master is turned on. You can also assign "always on" to the second display so it boots up with the primary.

John
 
Thanks, John, that's what I thought. So, problem solved. Use the VP-X to decide what is switched on at start.
 
Reviving this thread in hopes experienced GRT Horizon (HS or WS) users will share their experience.

As I am finalizing a panel re-design I'm trying to get a feel for how well the GRT Horizon units handle brown-outs associated with engine starts.

Current panel design has a single main 12V bus and a switched avionics bus. The Horizon HS EFIS is powered from the main bus so it will be "live" during engine starts. Engine is Lyc O-360 with a B&C starter, battery is an Odyssey PC680 mounted forward of the firewall. In this configuration, will the EFIS likely brown-out and commence re-alignment (Red-X'd display) following engine start?

I'm planning on replacing steam ASI/ALT with a GRT Mini-X - this makes me electrically dependent, so adding a backup battery to run an Endurance Bus is in the works. My design goal is to keep things as simple, light and reliable as possible. As a result, I'm planning on having only 3 primary loads tied to the Endurance Bus, the Mini-X EFIS, the AFS2500 Engine Monitor, and an LED gooseneck light; two other devices have their own internal batteries so their power is optionally provided by the E-bus - a Garmin 396, a 12V power plug to power the handheld VHF COMM radio. In this manner the Endurance Bus will be lightly loaded and powering only the last-ditch critical equipment.

My real concern here is that if the Horizon EFIS is going to provide better performance by having a tie to the E-Bus to prevent brown-outs during starts then I need to add a switch to disconnect the Horizon EFIS from the E-bus for all but engine start events.

For those with experience using the Horizon EFIS, what are your recommendations?
 
I have a small battery back-up system on my GRT.

My normal procedure is to turn on the battery back-up as I sit down. The EFIS will boot by the time I get my belts and headset ready. I then turn on the master switch to run the boost pump and start the engine.

I have started it without the battery and it did reboot but the main battery was weak.
 
I have PC925 starting battery and PC680 powering the panel. Two GRT HX's both wired to main bus and ebus through two 2-pole power switches. Whichever power source voltage is higher takes over the load. Each HX draws 1.0 A on dim and 1.5 A on bright at 12.6 VDC(my particular test voltage).
 
The main reason for having avionics off during starting is that the start relay coils (or any relay coils for that matter) can induce a large voltage on the power line as the field collapses (power removed). In the old days, that voltage could exceed what the electronics could handle. In modern certified avionics in which all equipment are all tested to RTCA DO-160 for voltage spikes, the spikes can be handled by the electronics. Also, if you design your electrical system, be sure to place a reverse biased diode across the relay coils and most of the spike will be shorted by the diode and not propagated into the power distribution system. It is better to solve the problem at the source than depend on the avionics to handle it.
 
Thanks, Sid & Wayne, for sharing your real-life experiences. After doing some more digging around and discovering the amount of time the GRT Horizon units take to come back after they've been browned out I think I will wire the Horizon to the backup battery through a switch so I can keep it alive during engine cranking.

Dan - thanks for your comments. What I was worried about isn't the little transients that develop as flyback from solenoid coils. While your comments about DO160 are valid to a certain extent, if one spends a while with DO160 you'll see that it was written with the intent of covering considerably more than solenoid spikes. In fact, it specifies both short duration events (spikes) as well as much longer duration events, both for under- and over-voltage conditions. Think of the power transients associated with multi-engine airplanes like a DC3 where you connect the aircraft to an external power source, then crank the engines, then bring the generators on line and transition from external to internal power. These activities create large, long-duration transients. It's these latter conditions which are of the greatest concern to me, particularly the relatively long-duration low bus voltage condition resulting from cranking a reciprocating engine with the starter.

In DO160 you'll find the specified duration of the under-voltage condition is considerably shorter than the cranking duration in most of our airplanes, so whether we have certified avionics or not, most of our airplanes don't meet the DO160 power requirements. That's when we get into considering a backup battery to keep EFIS systems and engine monitors alive through the engine start cycle.
 
CJ,

I guess I was mostly responding to the OP which mentioned "voltage spikes" and the need for an avionics switch to switch everything off for protection. I do agree with you on the low voltage testing duration may not be adequate to ensure adequate protection from brown out, but in any DO-160 testing that I have performed, I've never seen damage from undervoltage either.
 
Canadian_JOY said:
Reviving this thread in hopes experienced GRT Horizon (HS or WS) users will share their experience.

As I am finalizing a panel re-design I'm trying to get a feel for how well the GRT Horizon units handle brown-outs associated with engine starts.

Current panel design has a single main 12V bus and a switched avionics bus. The Horizon HS EFIS is powered from the main bus so it will be "live" during engine starts. Engine is Lyc O-360 with a B&C starter, battery is an Odyssey PC680 mounted forward of the firewall. In this configuration, will the EFIS likely brown-out and commence re-alignment (Red-X'd display) following engine start?

I'm planning on replacing steam ASI/ALT with a GRT Mini-X - this makes me electrically dependent, so adding a backup battery to run an Endurance Bus is in the works. My design goal is to keep things as simple, light and reliable as possible. As a result, I'm planning on having only 3 primary loads tied to the Endurance Bus, the Mini-X EFIS, the AFS2500 Engine Monitor, and an LED gooseneck light; two other devices have their own internal batteries so their power is optionally provided by the E-bus - a Garmin 396, a 12V power plug to power the handheld VHF COMM radio. In this manner the Endurance Bus will be lightly loaded and powering only the last-ditch critical equipment.

My real concern here is that if the Horizon EFIS is going to provide better performance by having a tie to the E-Bus to prevent brown-outs during starts then I need to add a switch to disconnect the Horizon EFIS from the E-bus for all but engine start events.

For those with experience using the Horizon EFIS, what are your recommendations?
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I have very similar equipment as yours and my setup is different than most who have responded here. I have setup only my EIS4000 to the main bus that gets powered with the master and thus I will know about the oil pressure or lack of, right away. A master avionics switch will power all my avionics minus Auto pilot which has its own dedicated switch. Of course all the lights, fuel pump, etc. they have their own dedicated switch as well. The minimum advantage of this setup is that my battery will have only the EIS and the starter to power during the startup and in case of an alternator issue/emergency, I can power everything down yet have my EIS (engine status) available
 
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A master avionics switch will power all my avionics minus Auto pilot which has its own dedicated switch. Of course all the lights, fuel pump, etc. they have their own dedicated switch as well. The minimum advantage of this setup is that my battery will have only the EIS and the starter to power during the startup and in case of an alternator issue/emergency, I can power everything down yet have my EIS (engine status) available
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Don't all the avionics have power buttons/knobs/switches?

I've had a couple of alternator failures years ago flying Cessnas and Pipers, and it was pretty easy to shed loads by turning off the devices using the knobs on the boxes.

I have no avionics master, and just leave everything on. Yes, the radios and comm panel drop off-line during start, but that's not really any different than cutting power to them by flipping an avionics master to "off". If for some reason I ever get convinced that's a bad approach, then I'll just power each of them off at shutdown, and on again after startup. Problem solved, and no single-point failure at the avionics master switch. (Plus, they're all DO160 certified, so theoretically should handle any transients the system might generate during engine start).
 
Most EFIS and engine monitors don't have power switches - they come on as soon as power is applied, hence the conversation about whether or not they should have a stand-alone switch installed.

At this point I've pretty much decided the secondary EFIS and engine monitor (AFS2500) will be powered from the Endurance buss directly. The primary EFIS and its AHARS will likewise be powered directly from the primary buss. A secondary power feed to them will be routed through a switch from the Endurance buss. In this manner I'll be able to provide uninterrupted power to the primary EFIS during engine start, then flip the switch so the primary EFIS takes its power solely from the primary buss during normal operations. This should get us past any need to delay moving the aircraft after the engine is started; by that time the AHARS should be fully aligned and ready to go.
 
Just an FYI, but while Dynon EFIS and EMS units come on with power, they can be turned off by pressing and holding button #1 for two seconds. So you can shed load if needed.

They are also fully designed to DO-160 specs for voltage spikes, so we have no issues with them being on during engine start. We attempt to stay on as low as we can in voltage as well (about 6V) but there are a lot of planes that sag below this during starts, especially on cold days or with permanent magnet starters.
 
Canadian_JOY said:
Most EFIS and engine monitors don't have power switches - they come on as soon as power is applied, hence the conversation about whether or not they should have a stand-alone switch installed.
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Yep...not much of an engine monitor if it isn't on during engine start (and as Dynon has said, if voltage get waaaay too low, then their backup battery suffices to keep the thing running until the engine starts).

I'm not sure what problem people are trying to solve here...it sounds to me as if it's a conflation of fear of voltage spikes or sags or something during start, and the totally separate failure mode of an alternator failure or some other situation requiring a load shed.

Not to beat an old dead horse, but Knuckolls made this argument years ago for not having an avionics master.
 
I've wired up two different RVs with the D100 + D120 systems and both planes' owners wanted the EFIS and EMS units to simply power up with the master switch. Both aircraft do have pullable breakers for each D100 and D120 "just in case" but are fed from the main bus, not the "avionics bus". Both aircraft have now accumulated about 400 hours each with no problems whatsoever regarding the EFIS/EMS powering up with the master switch and staying on while the starter is cranking.
 
Just to clarify... the GRT EFIS, as I've been learning here, is not like the Dynon in that it will not stay alive at 6V. It browns out, reboots, then has to go through an alignment. While basic alignment of the AHARS is fairly quick, not moving the airplane for a couple of minutes is the manufacturer's recommendation.

If one is starting the airplane, then, one wants the EFIS NOT to brown out and reset. That's the problem I'm trying to overcome. The EFIS is not attached to the Avionics bus but rather to the primary bus, so the avionics master switch is not called into question. I was really trying to figure out whether GRT EFIS users found it beneficial to wire the EFIS to an alternate (non-cranking) battery to keep it alive during engine starts.

BTW, in my "flying" aircraft I have a D100 with internal battery, wired to the main bus, so it comes on when the master is switched on. It's never even blinked during engine starts. Love the Dynon, but our "project" aircraft came with a GRT product pre-installed, so that's what I have to live with.
 
Canadian_JOY said:
Just to clarify... the GRT EFIS, as I've been learning here, is not like the Dynon in that it will not stay alive at 6V. It browns out, reboots, then has to go through an alignment.
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The Dynon won't stay alive at 6V, either...thus, the backup battery. Too bad the GRT doesn't support that, but I now understand the problem you're trying to solve.
 
Canadian_JOY, the GRT EFIS has three separate diode isolated power inputs, so there is no reason why you couldn't have it wired to both the main and endurance buses at the same time so it can pull power from either. Presuming your starter is only pulling power from the main battery, this should prevent it from browning out during engine crank.

The AFS might also have this, not sure, but if it doesn't it is easy to also wire it to both buses using a couple of diodes.

No need to install a separate switch for them.

fyi

-Dj
 
Dj - the multiple GRT power inputs are indeed a great thing. I'll be using the 2nd GRT power input to supply power to the primary EFIS from the E-bus. I will be running this power lead through a switch, simply because I want to be able to take the primary GRT EFIS off the E-bus should the primary bus fail. The "endurance" of the Endurance Bus will be based on that E-bus carrying a minimum load - the backup EFIS, the backup Garmin 396 GPS (if its internal battery isn't functional), an LED cockpit light, and a DC power plug in the event my backup handheld COM battery dies.
 
RV7A Flyer said:
The Dynon won't stay alive at 6V, either...thus, the backup battery.
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Just to be clear, Dynon's SkyView WILL stay on at 6V. The point of the backup battery is for in-flight power failures, not engine crank.

tx0d.jpg
 
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Canadian_JOY said:
Just to clarify... the GRT EFIS, as I've been learning here, is not like the Dynon in that it will not stay alive at 6V. It browns out, reboots, then has to go through an alignment. While basic alignment of the AHARS is fairly quick, not moving the airplane for a couple of minutes is the manufacturer's recommendation ... I was really trying to figure out whether GRT EFIS users found it beneficial to wire the EFIS to an alternate (non-cranking) battery to keep it alive during engine starts.
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Zackly. The wiring diagram that came with my GRT system showed on/off switches on both displays, to my surprise. I installed a pair of micro-toggles that have proved handy at times. There are times when one wants the master on w/o the EFISs powered up. OTOH, my EIS4000 is wired directly and comes on with the master as intended (and stated) by GRT.
 
Canadian_JOY said:
Dj - the multiple GRT power inputs are indeed a great thing. I'll be using the 2nd GRT power input to supply power to the primary EFIS from the E-bus. I will be running this power lead through a switch, simply because I want to be able to take the primary GRT EFIS off the E-bus should the primary bus fail. The "endurance" of the Endurance Bus will be based on that E-bus carrying a minimum load - the backup EFIS, the backup Garmin 396 GPS (if its internal battery isn't functional), an LED cockpit light, and a DC power plug in the event my backup handheld COM battery dies.
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So the GRT can't be powered down without an external switch?
 
dynonsupport said:
Just to be clear, Dynon's SkyView WILL stay on at 6V. The point of the backup battery is for in-flight power failures, not engine crank.

tx0d.jpg
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That's interesting...I guess because it powers down (or goes on backup battery) when voltage gets below 10 or so that it wouldn't power up (or stay up) at that low a voltage. Nice robust system if it will.
 
Admittedly the logic is complex, but we do think it makes for a very robust solution:

1) We will switch to backup battery (if it exists) when the voltage gets below 10V. This is to take the load off your aircraft system if the voltage droops. Why put an extra load on the battery when starting if the SkyView can shed the load itself?

2) If there is not a backup battery, we will stay on down to 6V, but only for 10 seconds. We require the voltage to be above 10V to stay on permanently. This allows you to crank and start the engine without the system tuning off, but if you accidentally leave SkyView on and drain your aircraft battery, at least SkyView won't pull the battery all the way down to 6V. 6V will generally permanently damage a battery, while 10V is just very drained.

3) We won't power on until voltage gets above 10, for the same reasons in #2 of further wearing out a very low battery.

4) We don't charge the internal backup battery unless the input voltage is 12.25V or above, which indicates the alternator is on-line, again, to not drain your aircraft battery more than needed.

As a point of technical pride, SkyView can actually stay on much below 6V, but the issue is that the current required goes way up (It's almost 10A at 3V), so our software shuts us down to keep that current limit reasonable at the 5A we specify.

--Ian Jordan
Dynon Avionics
 
RV7A Flyer said:
So the GRT can't be powered down without an external switch?
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Correct. Neither could the main General Purpose Computers in the Space Shuttle. ;)

Same thing is true with G3X - no internal power switch.

This is why I wire my EFIS's through circuit breakers - I can power them off by pulling the breaker if required. But....the only time I do that is for power cycling when setting up, troubleshooting, or loading software. I'd (almost) never power off an EFIS in flight becasue the power draw is so tiny it is not going to make a difference in a load-shed situation. Well...maybe one screen.... :)
 
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