Power dual Skyviews with dual power busses

[JoshT]

I'm planning a dual Skyview system, dual ADAHRS.  My engine is also electrically-dependant so there will be two independent electrical systems.  Each with their own alternator, battery, contactor, voltage regulator, etc.  I will not be using the Skyview backup batteries.

I want to power the displays separately.  There doesn't seem to be any problem with that until you look at the way network devices are powered.  The ADAHRS, AP Panel, Engine Monitor and a few others are powered off the network.

From page 2-4 of the installation guide:

These devices are connected to SkyView Network, which is powered by the SkyView display(s). 
If you have two or three displays, the current requirements of these devices are shared equally between the displays. 
If you have one display, add 100% of a SkyView Network device’s current to the display’s current requirement. 
If you have two displays, add 50% of SkyView Network device’s current to each display’s current requirement.

This means that if I power display1 with Bus1 and display2 with Bus2, this method of "blending" the power from each would be the only point in the aircraft that the two circuits "touch". 

Since they have independent regulators, they will each have slightly different voltages.  Won't these common connections tend to allow bleeding of some power from the higher voltage bus to the lower one?

During a power failure, will the display on the dead bus try to operate thru the network power wires? 

How about a overvoltage event?  Say a regulator fails and puts 100V on the power bus.  Is this going to fry both displays and network-powered components?

What about the power lines on the skyview network where they connect to the displays?  If Bus/Display1 have a higher voltage, will Display2 try to draw some of its power off the skyview network since those lines will be higher voltage than its supplied power?

Appreciate any help here.  I love the Skyview system, but right now this seems to be a weak link in the design unless I'm not understanding it correctly.

 

[lgabriel]

I asked a similar question during the design phase for my airplane (I also have independent electrical systems).  The answer from Dynon is that you'll have no problem with each screen powered separately:

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1387741089/8#8

I'm a little curious about the answer to the overvolt scenario, but otherwise it sounds like we're in the clear.  I only have one display installed at the moment--otherwise, I'd happily provide more data.

Edit: You might also want to reconsider your backup battery plan. I originally didn't want backup batteries because I would have such a robust electrical system, but I'm glad I installed one. It's nice to be able to power up the screen independently for things like data downloads and updates. Also, you don't have to worry about voltage sag during startup.

 

[dynonsupport]

The power on the network wires is not aircraft power. It's power after all the voltage regulation in each screen. It's at a completely different voltage than the plane's main power, and it's protected from all the noise and spikes on the main aircraft power.

Clearly the system is designed to work with one screen off. The power from the on screen does not make it out of the screen that is off. It doesn't even really make it into the screen that is off given there is a diode at each power pin that prevents backflow.

So overall, it's a very robust system.

Dynon doesn't test for 100V overvoltage events. We test to DO-160, which requires 60V overvoltage on 28V planes, and 30V on 12V planes. Same requirements that any certified stuff is made to. With a lead acid battery present, it's not really feasible to get to 100V.

It is possible to theorize some voltage high enough that it breaks down so many protections that both screens fail. It is however hard to theorize how an aircraft system could generate such voltages given our tolerance without any damage to 60V.

 

[JoshT]

It's nice to be able to power up the screen independently for things like data downloads and updates.  Also, you don't have to worry about voltage sag during startup.

Thanks for the link, that didn't come up in my searches. My EBUS will have a small battery and won't be connected to the starter. So I'll power that up before engine start and have all skyview/radio/IFD440 stuff up and running with no hiccups when the starter cranks over.

I think with the newer Lithium batteries having the second bus help starting is overkill. This saves the expense and weight of the individual batteries. For less weight I can have backup power on all my important stuff (radio,IFD440,lights etc), not just the displays.

Dynon thanks for the response. Makes me feel a lot better about your system. Diodes at the input pins, that helps me understand how this all works.

One question - you mention lead acid batteries absorbing voltage spikes. Do you have any knowledge of how the new generation lithium batteries perform under the same circumstance?