Dual Buss, EMS volts and Lightspeed questions

[n97kd]

I apologize if this subject has been discussed previously, I looked back through the forum but didn't see this covered.

Finally, the fun begins, my SkyViews are out of the boxes where they have sat for six months.

I'm installing a dual SkyView with one EMS220 for a Lyc 540, and a dual [u]independent electrical system (two alternators, and dual LightSpeed Plasma III ignition. The busses are not tied together.

My questions are:
1) I want to read voltage on both busses so I connected buss 1 to pin 1 on the EMS and moved an unused wire to pin 2 to read buss 2. I assume this will work?

2) I would like to read the load on each alternator. I connected my shunt wires from buss 1 to pins 24/25 per the manual. Is it possible to configure one or the GP inputs to measure the amps from the shunt for buss 2? If not, would a Hall effect donut work?

3) With the dual Lightspeeds, can I connect the pulse signal from their pin 6 to the left/right low volt rpm pins 32/33 respectively? How will that be displayed on either of the two SkyView displays. My hope is I can display rpm from one LightSpeed on one SkyView and the other LightSpeed on the other SkyView. 

4) last question> I'm using two Honeywell pressure sensors (mlh02kpsb06a) for reading up and down hydraulic pressure. The spec sheet from Honeywell says they use a 5V excitation so am I correct to use the supply off pin 18 and connect the output to a GP input compatibility C? this sensor is a 0-3000psi so any information on how to configure the files would be appreciated.

That's it for now. I'm sure more to come.

Thanks in advance.

 

[mmarien]

[olist][*]Pin 1 and 2 are made to read two different voltages. I had mine read the main bus and the avionics bus. It's recommended to add a 1A fuse on the wire.
[*]I believe you can use a hall sensor for current: http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1321910185
[*]The two pins are to maintain the RPM reading if one magneto is turned off during a mag check. For electronic ignition the signal is usually there through the mag checks so you only need one connection. The two displays are reading from one EMS so it's probably not possible to have separate readings on each display.
[*]If the sensor output is in the range of 0-5V Skyview can probably read it on an enhanced GP pin. I designed a O2 sensor that way.
[/olist]

 

[dynonsupport]

1) Yes

2) You can only read one shunt, but we do support multiple hall effect "donuts".

3) You can't display one tach on one SkyView and another on a second SkyView. SkyView is an integrated system, and both will share the same configuration, so they will show the same RPM. Remember, they are getting the same information from the same EMS module, so the screens don't know about a "left EMS" and a "right EMS"

The EMS module has two inputs for RPM. Most users hook both mags (electronic or standard) up to the EMS, and the EMS will show you the RPM of whichever is highest (this is how it shows you RPM during a mag check with traditional mags).

If you really want to see both RPMs at the same time, it is possible to show two RPM displays on SkyView at the same time. Let us know if you really want to do this. Both RPMs will show up on both SkyViews. I'd also be interested to know why this is helpful.

4) Yes, you can use the 5V from pin 18 for these sensors. They will need to go into an Enhanced GP input pin. They are 0 PSI at 0.5V and 3000PSI at 4.5V, and should have no pull up resistor. Please read up on how to make your own sensors, and ask us if you have any questions:

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1268164287

 

[n97kd]

I didn't understand how the rpm inputs worked initially. I really don't want to display two separate rpm displays. I was thinking left/right as in left and right engines in a twin. The lightbulb in my head went on when I realized its for the two mags.
So. .. if I connect one electronic ignition to the left rpm input and the other to the right input, SkyView will display the highest of the two or if one fails or is turned off the functioning ignition rpm will be displayed. True?
That leads to a new question. With dual SV displays on separate busses and one EMS, if one buss fails will the remaing powered display continue to power the EMS? In other words, will the EMS continue to function with only of either display powered?

 

[jakej]

Simply, yes & yes. If one Skyview or bus fails then the other does the job without blinking

Jake J

 

[dynonsupport]

Everything about the SkyView network is designed to be redundant. As long as one screen is operating. everything on the network will be working, even if that screen is only running on a battery. The fail-over will be automatic.

The SkyView network even has redundant power and data, so that if any wire in the cable breaks or shorts the network will still work.

 

[lgabriel]

I have been struggling with the dual bus decision as well--your plan is to power each screen independently?

How well does Dynon's internal power distribution handle this scenario?  Say for instance one bus (and one screen) is 14V and the other is at 12V--are there diodes to protect from crossover?

My plan was to have Dynon backup batteries on each screen, and a switch to select what bus the entire SkyView system got its power from.  That way, I'm protected from any single point of failure (like the switch itself) and can continue on as normal with a bus failure.

I would like to get rid of the switch, though...and I'm intrigued by powering each screen from its own side.

 

[n97kd]

Thanks all for your valued input.

To Louis, I decided on a dual buss system with no cross over tie. Two alternators and two batteries. I have one tie contact for starting the engine only. Think of it like two aircraft in very close formation. I didn't want the busses tied in the event of a major short which could disable both systems. The two SkyView displays receive power from each buss separately, they are connected through the network cables so data from sources like EMS,GPS etc will function on either if on fails or loses power. I have a backup battery on each system. This may sound like overkill, but I don't want to worry when flying in the soup.

Hope this helps with your decision.

Don

 

[lgabriel]

Hi Don -

Similar bus setup here, due to electronic fuel injection.

My concern (should be yours too) is that the SkyView network isn't just data, it's also power.  If there is no crossover protection internally, you may find your buses bridged through SkyView...which will probably result in magic smoke.  Even if there is diode isolation, are those diodes beefy enough to stop a 14.4V differential?

Also, with two completely independent buses, there will almost always be a voltage mismatch.  Even if SkyView's power distribution is diode isolated, can it operate well with a differential across the system?  Will that throw off any sensor readings, or cause weird charging of the SV backup batteries?

All of this is why my current plan is to have an EFIS power source select switch, so I can pick which bus powers the entire SkyView system.  I don't particularly like this idea, but at present it's the lesser of two evils.

 

[dynonsupport]

There are no issues running two SkyViews off of two different busses. Just to be clear, SkyView itself only has one power input, so if you want to run one screen off two busses, you will need to deal with that power distribution externally.

SkyView does not distribute ship's power to the modules, EMS, etc. SkyView takes ship's power (which is noisy, nasty, spikes to 60V at times, etc) and makes it a clean, controlled voltage. It protects this voltage, isolates it, battery backs it up, and makes it redundant. This way the modules have a safe, clean, redundant, and backed up power source

You can have one SkyView on 12V, one on 28V. You can have one on battery backup and the other on 12V. You can have one failed, shorted, and smoking, and the other working. All your modules will keep working, and will not pass any power "backwards." In the 12V/28V case, you'd actually still be drawing 1/2 the system power from the 12V side, since the systems share the load when there are multiples online.

So, feel free to power one off one bus and the other off a second bus. There are zero issues with this and it will not bridge any power between the busses.

Now, all this being said, as an electrical engineer, I am having a hard time seeing what kind of failure in a plane could cause a whole bus to go to a voltage of zero. A "major short" that causes power loss will also cause a fire as the battery drops hundreds of amps into that short, so that's something to be avoided no matter what, and you have much more serious issues if it happens. Any short after your circuit breakers will just pop that breaker. Airplanes have been flying for a very long time with one bus. Dual busses seems complex (operationally and physically), heavy, and overkill when devices like SkyView will run for 45 minutes on backup batteries.

All up to you though, which is the joy of experimental planes. SkyView will support however you want to wire it.

 

[lgabriel]

Answering support forum posts on a Saturday morning between holidays--you guys are incredible!

That's excellent news about the power distribution of SV.  Pretty slick system.

Airplanes have also been flying for a very long time with multiple independent buses.  Only airplanes that can continue flying without electricity get away with one.

Personally, my engine requires electricity to operate, and 45 minutes doesn't always keep me within range of a landable surface.  My only real weight addition is a second alternator and some extra wire, which is pretty much offset by removing two magnetos and a vacuum system.

Generally, I'm surprised there isn't a bigger push within GA toward redundant electrical systems, given the trend away from magnetos and mechanical flight instruments. 

SkyView obviously incorporates an intelligent and redundant power system; applying that process to other flight-critical areas of the airplane makes sense.

 

[n97kd]

Thanks Dynon Employee for confirming that we can operate SkyView displays on separate busses. You folks have done a great job developing big jet avionics for the little guy.

As far as multiple busses go, I have been flying business jets for a long time that incorporate multiple busses so I kind of like it.
Like Louis, my Glasair III will rely on electricity to power two LightSpeed ignition systems. I want total independence just like magnetos, hence the dual buss system.
I havent ventured into the electronic fuel injection yet. I want to get this bird flying first using the old mechanical fuel injection system I know works. I would be interested to know how your system works out. I will most likely experiment with it in the future.

Thanks again to all for your advise and opinion.

Safe building and flying to all!