VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 05-20-2020, 09:29 PM
N546RV's Avatar
N546RV N546RV is offline
 
Join Date: Aug 2010
Location: Houston, TX
Posts: 905
Default The E-bus alt feed: a different idea

So I've been thinking about the Nuckolls E-bus setup, specifically the handling of having an alternate feed off an always-hot battery bus in case of a failure affecting the main bus. Bob's setup takes the same basic form everywhere I've seen it: the main bus feeds the E-bus through a diode, and the alternate feed is provided through a switch and/or relay (depending on expected E-bus loads).

The reasoning behind the diode between the main and E-bus is to prevent the E-bus from feeding the main bus and possibly popping a fuse/breaker. Bob's assertion seems to be based on an alternative scenario where two switches would be provided, and it would be incumbent on the pilot to ensure the main->E-bus feed switch was opened before closing the E-bus alt-feed switch, to prevent the aforementioned backfeeding.

However, it seems this issue can be fairly easily solved with careful switch choices, such that it's not possible to have both feed paths closed simultaneously. For example, if a five-pin relay is used for feed switching, the main bus could feed through the normally-closed contact, and the batt bus through the normally-open one. The choice of how to feed the bus is still controlled by a single switch throw, the only difference being that that switch position definitively disconnects one feed while connecting another one.

Example diagram:



This seems elegantly simple enough that I'm immediately suspicious that I'm missing some downsides. Some thoughts that come to mind in this vein:
  • There's the possibility of the relay somehow failing such that both contacts close, thus possibly blowing the batt bus fuse and killing the E-bus in an emergency. Not sure what the likelihood of this is.
  • If the relay somehow fails with both contacts open, the E-bus is now dead. This question seems to come down to the relative chance of failure between the diode and the relay.
  • Switching feed paths means momentarily cutting power to the E-bus. This seems inconsequential since, when switching to the E-bus, presumably power has been lost already.

Any other detractions I'm missing? Any thoughts on the concerns above?
__________________
Philip
-8 fuselage in progress (remember when I thought the wing kit had a lot of parts? HAHAHAHAHA)
http://rv.squawk1200.net
https://www.meetup.com/Houston-Area-RV-Enthusiasts/
Reply With Quote
  #2  
Old 05-20-2020, 10:09 PM
jcarne's Avatar
jcarne jcarne is offline
 
Join Date: Jul 2016
Location: Worland, Wyoming
Posts: 1,145
Default

Hmmm how interesting, I'm still looking for problems that may arise. Looking forward to seeing what more electron wizards say on this one.

Also, queue the E-Bus haters now...
__________________
Jereme Carne
PPL
RV-7A Emp. done
Wings done
Fuselage done
Finish kit almost done
Exempt but gladly paying!
Reply With Quote
  #3  
Old 05-20-2020, 10:20 PM
Bicyclops Bicyclops is offline
 
Join Date: Oct 2012
Location: LA, California
Posts: 281
Default

Switching to an alternate feed for e-bus isn't usually because power to the e-bus has been lost. It's because the alternator has been lost and there is plenty of time to get it done. Switching off the main bus cuts off all the high amp exterior lighting and such to preserve battery power for the stuff you really need. Closing the alt feed switch first and then opening the main would prevent an interruption to radios and such, though most of the newer EFIS wouldn't shut down and reboot as long as you get the e-bus powered up within 30 seconds of shutting down the main. In my old 6A, I just closed both the e-bus alt feed and the main buss switches as a matter of course. I would close the e-bus before start and listen to ATIS, so the alt feed was tested before flight. When I did actually lose my alternator, which did happen, all I had to do was open the main switch. No muss, no fuss.

My new 6 carries 2 batteries and I have 3 position switches for both - OFF-EBUS-ON. I have fusible link protected wires from the batteries to the center E-BUS terminals. I can power the e-bus or the main with either or both batteries. Normal position is both ON with both charging. If I lose the alternator, I'll shut off one battery entirely and hold it in reserve. The other battery goes to E-BUS and when it's used up, I'll turn on the other battery and start looking for someplace to land. I did it this way because I have 2 electronic ignitions.

An alternative would be to have a back-up alternator and you wouldn't even need an e-bus or a second battery.

Ed Holyoke
Reply With Quote
  #4  
Old 05-20-2020, 10:49 PM
N546RV's Avatar
N546RV N546RV is offline
 
Join Date: Aug 2010
Location: Houston, TX
Posts: 905
Default

Quote:
Originally Posted by jcarne View Post
Also, queue the E-Bus haters now...
I'll certainly confess that I've wondered if the E-bus is unnecessary complexity in my case. I'm already planning a dual alternator setup, with the #2 alternator set up as a standby to come online automagically should the primary fail. I'll also have a dedicated backup battery for each EFIS screen, along with a backup battery system for the dual SDS CPI2 ignition.

So there's a lot of redundancy there (naively speaking), but then again we're talking about an electrically dependent airplane as well. And that, in a nutshell, defines my wondering on this topic.

As Ed alludes, one might wonder whether the E-bus is still necessary with a second alternator. My general thought is that it adds protection against a wiring or contactor fault that causes the main bus feed to go dark. That wouldn't be a code-brown moment in my airplane - dedicated backup battery systems would ensure that the ignition kept firing and the EFIS displays stayed on and kept an attitude reference - but it'd be a bare-bones affair finishing the flight. Adding the E-bus alt feed idea allows me to retain stuff like pitot heat, IFR navigator, etc. Worth the system complexity? My current opinion is yes, but I'm certainly willing to entertain contrary viewpoints.
__________________
Philip
-8 fuselage in progress (remember when I thought the wing kit had a lot of parts? HAHAHAHAHA)
http://rv.squawk1200.net
https://www.meetup.com/Houston-Area-RV-Enthusiasts/

Last edited by N546RV : 05-20-2020 at 10:53 PM.
Reply With Quote
  #5  
Old 05-20-2020, 11:24 PM
jcarne's Avatar
jcarne jcarne is offline
 
Join Date: Jul 2016
Location: Worland, Wyoming
Posts: 1,145
Default

Quote:
Originally Posted by N546RV View Post
I'll certainly confess that I've wondered if the E-bus is unnecessary complexity in my case. I'm already planning a dual alternator setup, with the #2 alternator set up as a standby to come online automagically should the primary fail. I'll also have a dedicated backup battery for each EFIS screen, along with a backup battery system for the dual SDS CPI2 ignition.

So there's a lot of redundancy there (naively speaking), but then again we're talking about an electrically dependent airplane as well. And that, in a nutshell, defines my wondering on this topic.

As Ed alludes, one might wonder whether the E-bus is still necessary with a second alternator. My general thought is that it adds protection against a wiring or contactor fault that causes the main bus feed to go dark. That wouldn't be a code-brown moment in my airplane - dedicated backup battery systems would ensure that the ignition kept firing and the EFIS displays stayed on and kept an attitude reference - but it'd be a bare-bones affair finishing the flight. Adding the E-bus alt feed idea allows me to retain stuff like pitot heat, IFR navigator, etc. Worth the system complexity? My current opinion is yes, but I'm certainly willing to entertain contrary viewpoints.
Ya with a 2nd alternator (assuming it is large enough to power all your goodies an E-bus is kind of redundant it would seem). However, you mention a valid point, if the main bus is taken out for some reason you still have the devices on your E-bus. Someone is probably going to chime in and say "even under IFR you can fly without those things..." yadayada but that doesn't mean it's as safe or certainly as comfortable to you. Flying in less than an optimal aircraft in IFR is not joke, especially if you don't do it for a living.

I also like the E-bus for what it was intended for. Bob wanted a quick one switch method to continue a flight should the alternator fail. I really like the idea of flipping a switch and flying to my destination instead of worrying about battery life or tracking down another alternator etc. (once again mitigated by your second alternator)

Finally, the biggest thing that I can never understand is how many people mention how complex it is. Uhhh... The only thing extra is a diode and a relay. granted there are a few extra connections but it's nothing like the internals of a Falcon 9. Even if I didn't have an E-bus I don't think I could have fit all my circuits on one single bus. (unless there are some large ones I didn't know about)

Long story short, I like the E-bus for the reasons mentioned but mainly due to a teeny bit extra redundancy should the main bus take a dump.
__________________
Jereme Carne
PPL
RV-7A Emp. done
Wings done
Fuselage done
Finish kit almost done
Exempt but gladly paying!
Reply With Quote
  #6  
Old 05-20-2020, 11:52 PM
rapid_ascent rapid_ascent is offline
 
Join Date: Mar 2008
Location: Dublin, CA
Posts: 1,202
Default

I think you might be missing how I at least thought this would be used. First I would normally have both the ebus and the main bus switched on. Then in the case where loads need to be shed then the main bus is switched off. There is no power interruption to the ebus since the power is provided by the ebus switch/relay. The diode prevents the main bus from back feeding from the ebus.

Also, I would suspect that it is more likely for relays to fail in a shorted position. The contact usually stick versus the actuator not moving to close the switch.
__________________
Ray Tonks
2020 Donation Paid
Titan IOX-370, Dual PMAGs, 9.6:1 Pistons, FM-150
RV-7 Fuselage in progress
* Cabin Interior - In progress
RV-7 SB Wings
* Both Wings fully skinned
* Fuel Tanks Complete - No leaks finally
* Ailerons Complete
* Flaps Complete
RV-7 Empennage - Complete (a little fiberglass work left)
Vans Training Kit # 2 - Complete
RV-7 Preview Plans
Vans Training Kit #1 - Complete
EAA Sheet Metal Class - Complete
Reply With Quote
  #7  
Old 05-21-2020, 08:57 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,868
Default

changing poles on that switch/relay will create a momentary open to your e bus feed. That will cause a reset/brown out for any circuitry, requiring a reboot/restart for advanced equipment.

creative wiring of a triple throw switch could avoid that, but it would combine the two busses for a brief moment.

Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Reply With Quote
  #8  
Old 05-21-2020, 09:32 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is online now
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,402
Default

Quote:
Originally Posted by jcarne View Post
. SNIP
I also like the E-bus for what it was intended for. Bob wanted a quick one switch method to continue a flight should the alternator fail. I really like the idea of flipping a switch and flying to my destination instead of worrying about battery life or tracking down another alternator etc. (once again mitigated by your second alternator) SNIP
Very good design point - not only for shedding loads to conserve battery capacity, but for rapid isolation of big loads in the event of an electrical fault.

This can also be achieved by having “critical for IFR flight” loads on the battery side of the master solenoid(s). All the big loads (engine starter, pitot heat, landing lights, boost pump, etc.) on the output of the master solenoid.

With two “avionic master” switches, each getting power from the battery(s) to run half the panel, you add redundancy to mitigate a fault on one of the avionic busses taking down both EFIS screens, both radios, etc.
Carl
Reply With Quote
  #9  
Old 05-21-2020, 09:40 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,990
Default

Quote:
Any other detractions I'm missing? Any thoughts on the concerns above?
Bob N's diagrams have two current paths supplying power to the E-Bus, one
through a diode and one through a relay (or switch). Eliminating one of those
paths greatly reduces the reliability of the E-Bus. Relays are much more likely
to fail than a diode.
__________________
Joe Gores
RV-12 Flying
Reply With Quote
  #10  
Old 05-21-2020, 04:16 PM
jcarne's Avatar
jcarne jcarne is offline
 
Join Date: Jul 2016
Location: Worland, Wyoming
Posts: 1,145
Default

Quote:
Originally Posted by Carl Froehlich View Post
Very good design point - not only for shedding loads to conserve battery capacity, but for rapid isolation of big loads in the event of an electrical fault.

This can also be achieved by having “critical for IFR flight” loads on the battery side of the master solenoid(s). All the big loads (engine starter, pitot heat, landing lights, boost pump, etc.) on the output of the master solenoid.

With two “avionic master” switches, each getting power from the battery(s) to run half the panel, you add redundancy to mitigate a fault on one of the avionic busses taking down both EFIS screens, both radios, etc.
Carl
All good points as well Carl. I like your double avionics master idea. Another way to skin the cat. I like how you pointed out conserving battery capacity as a nice feature of the quick load shedding method should the backup alternator not work/ not come online for some rare reason.
__________________
Jereme Carne
PPL
RV-7A Emp. done
Wings done
Fuselage done
Finish kit almost done
Exempt but gladly paying!
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 06:26 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.