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  #1  
Old 05-14-2016, 11:36 AM
YvesCH YvesCH is offline
 
Join Date: Feb 2015
Location: Basel, Switzerland
Posts: 255
Default Electrical System Planning - Inputs are welcome

Dear all

I am currently planning my Electric Power distribution and wanted to know what you think about it.

Basic infos: I am building a RV-8 for VFR and Night VFR flying.
Equipment: G3X 10" Touch, GNC-255, GTX23ES, GMA245, Garmin A/P and Electric Trim. As I will install a light Catto Prop, the Battery
(PC680) will be mounted on the Firewall. On the engine I have planned a B&C starter and a Plane power alternator "with OV".

As the Panel is glass I really want to have a Ground Power Jack.

My current Problem is that I do not know if I need a Avionics Bus to save the
Avionics during engine start (Com, Audio Panel etc). During startup the G3X, GSU73 and the GEA24 will be kept alive with the GAD27.

Here is what I have so far. Am I missing something?



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RV-8 #83458 HB-YUA
Donation 2020 done

Last edited by YvesCH : 05-14-2016 at 11:58 AM.
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  #2  
Old 05-14-2016, 12:02 PM
skylor's Avatar
skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 1,022
Default Electrical

Quote:
Originally Posted by YvesCH View Post
Dear all

I am currently planning my Electric Power distribution and wanted to know what you think about it.

Basic infos: I am building a RV-8 for VFR and Night VFR flying.
Equipment: G3X 10" Touch, GNC-255, GTX23ES, GMA245, Garmin A/P and Electric Trim. As I will install a Catto Prop the Battery (PC680) is mounted on the Firewall. On the engine I have planned a B&C starter and a Plane power alternator "with OV".

As the Panel is glass I really want to have a Ground Power Jack.

My current Problem is that I do not know if I need a Avionics Bus to save the
avionics during engine start (Com, Audio Panel etc). During startup the G3X, GSU73 and the GEA24 will be kept alive with the GAD27.

Here is what I have so far. Am I missing something?
Hi Yves,

I don't think I had a chance to discuss my electrical system when you visited last November, but here are some of my opinions on the subject:

1. When I designed my panel and electrical system, I chose to go without an avionics master because I feel a single avionics switch is potentially a single point of failure.

2. Every item in my radio stack has built in power switches, which I use to power them up with after engine start.

3. My dual EFIS displays do not have internal switches so I installed a pair of miniature toggles next to the ignition switch to switch the displays. The AHRS/Air Data unit is also powered from these two switches so that turning on either display will provide it with power.

4. I chose to keep my lighting switches off of the panel and put them in the right side console. This leaves the panel a little less cluttered with only "flight essential" switches.

Skylor

Last edited by skylor : 05-14-2016 at 12:05 PM.
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  #3  
Old 05-14-2016, 12:31 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,252
Default

Some thoughts:
- Fr a 60 amp alternator use a 70 amp output fuse/breaker.
- If you want to run your panel on ground power, you need not install the clunky ground jump connection. As you should never run your panel on a battery charger, you can make a connection on the output side of your master to plug in a quality, 20amp or so regulated power supply. The point here is you leave the master off such that your battery is not connected.
- I agree about not doing engine start with all the panel up. You can solve this by putting a switch in line with the diode from the main power buss to the essential buss. As you have an essential switch anyway you have a second path to power the essential buss if this switch fails.
- Put both pMags on the main buss. Power is only needed for engine start.
- You have too much load on the essential buss for the single #14 wire feeding it.

Carl
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  #4  
Old 05-14-2016, 04:02 PM
YvesCH YvesCH is offline
 
Join Date: Feb 2015
Location: Basel, Switzerland
Posts: 255
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Thank you Skylor and Carl! I added my comments

Quote:
Originally Posted by skylor View Post
Hi Yves,

I don't think I had a chance to discuss my electrical system when you visited last November, but here are some of my opinions on the subject:

1. When I designed my panel and electrical system, I chose to go without an avionics master because I feel a single avionics switch is potentially a single point of failure.

Yes that`s what I had in mind as well but in my current configuration some of the avionics are not switchable (e.g. GMC307)

2. Every item in my radio stack has built in power switches, which I use to power them up with after engine start.


Unfortunately not mine (see above)


3. My dual EFIS displays do not have internal switches so I installed a pair of miniature toggles next to the ignition switch to switch the displays. The AHRS/Air Data unit is also powered from these two switches so that turning on either display will provide it with power.

this could be a solution!

4. I chose to keep my lighting switches off of the panel and put them in the right side console. This leaves the panel a little less cluttered with only "flight essential" switches.

yes this I wanted to do as well, and the CBs like Pauls Dye below

Skylor
Quote:
Originally Posted by Carl Froehlich View Post
Some thoughts:
- Fr a 60 amp alternator use a 70 amp output fuse/breaker.

will do!

- If you want to run your panel on ground power, you need not install the clunky ground jump connection. As you should never run your panel on a battery charger, you can make a connection on the output side of your master to plug in a quality, 20amp or so regulated power supply. The point here is you leave the master off such that your battery is not connected.

Yes but as I live in Switzerland I want the ability boost my battery in cold conditions, therefore I decided to use this connector. As it is "aviation standard" I can find a suitable booster in nearly every FBO

- I agree about not doing engine start with all the panel up. You can solve this by putting a switch in line with the diode from the main power buss to the essential buss. As you have an essential switch anyway you have a second path to power the essential buss if this switch fails.

Hmm good Idea but I need the G3X and the GEA24 running to see if I get fuel flow and after starting if I get Oil pressure

- Put both pMags on the main buss. Power is only needed for engine start.

Ok will do!

- You have too much load on the essential buss for the single #14 wire feeding it.

I have a max of 13.33A therefore a #14 wire should do the job, no?

Carl
Any other thoughts about this topic?
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RV-8 #83458 HB-YUA
Donation 2020 done

Last edited by YvesCH : 05-14-2016 at 05:09 PM.
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  #5  
Old 05-14-2016, 06:45 PM
Walt's Avatar
Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 6,340
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Personally I'm not a fan of the essential bus with it's diode feed, if your alt fails just load shed and land (or turn on the back up alt and keep going). Replace the diode with a high quality switch and make that your avionics bus.
Install a high quality master solenoid. I also like stand alone back up batteries, if the whole system fails it will continue to support critical instruments.
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Last edited by Walt : 05-14-2016 at 06:50 PM.
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  #6  
Old 05-15-2016, 03:04 PM
YvesCH YvesCH is offline
 
Join Date: Feb 2015
Location: Basel, Switzerland
Posts: 255
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Thank you for your input. After starring at it for a while I came to the idea that a Avionic Bus and a Essential-Bus could work out. Now I can switch on the Engine with the Avionic-Bus OFF but the critical devices (G3X, GEA24 and GSU73) are kept alive with the keepalive power from the GAD 27 on the Main -Bus. If my Alternator goes banana I can always switch ON my E-Bus feed and I have all I need to land safely.

Any different Ideas or mistakes?

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RV-8 #83458 HB-YUA
Donation 2020 done
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  #7  
Old 05-15-2016, 04:19 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,252
Default

#6 wire and a 60 amp fuse for you main buss is way too much. Use the #6 on the alternator output.

You now have a diode preventing essential buss power from getting to the avionics buss. Considering you are a single alternator, single battery system, I'm afraid you added complexity without gaining reliability.

There are a lot of ways to go. For example, if you divide your Essential buss and Avionics buss into "Avionics #1" and "Avionics #2" such that the left EFIS on #1, right EFIS on #2, Nav/Comm #1 on #1 and Nav/Comm #2 on #2, and so forth. Power these using a 30 amp relay connected directly to the battery. This allows you to independently control the avionics without having the master solenoid on. This comes in handy if you are using a traditional master solenoid as it draw ~3amps just to stay shut. So for a loss of alternator the first step would be to open the master and dump all the loads not on the avionics buss. You can always add them back (like fuel pump) when it comes time to land. By doing this you greatly extend the battery reserve for a loss of alternator casualty.

Now add a simple toggle switch to cross connect between Avionics #1 and Avionics #2 to use if one of these 30 amp relays fails.

To simplify, divide all your loads into three groups:
Avionics #1 (I call this "Left Vital")
Avionics #2 (I call this "Right Vital")
Main Buss (I call this "Non-Vital"). The Non-Vital buss gets the pMags, electric fuel pump, nav lights, strobes, landing lights, pitot heat, and any misc. stuff like seat heaters and USB connections.

The Vital Busses will include things like trim, flaps, autopilot and panel lights.

If you want to get the biggest leap in capably and redundancy you will need to go to a two battery, single alternator set up. If you do this you can dump the clunky external power stuff as two PC-680 (or PC-625 like I'm using) will crank your engine under the most severe conditions. Two batteries will also provide ~3 hours of full IFR flight with no alternator.

Carl
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  #8  
Old 05-15-2016, 06:12 PM
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vlittle vlittle is offline
 
Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,370
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I submit that the concept of an essential bus is flawed. Predetermining what is essential means that you can foresee every possible failure scenario. Other than keeping the engine running, what is essential in VFR flight? What about IFR flight... A second engine?
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  #9  
Old 05-16-2016, 02:49 PM
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sportflyer sportflyer is offline
 
Join Date: Jul 2011
Location: New Zealand
Posts: 10
Default Backup alternator

I decided not to have an essential bus and installed a backup 20A alternator from B and C http://www.bandc.aero/standby-regulators.aspx
All of my circuit breakers are pop-able, except the 20a backup one.
The idea is that should the primary alternator fail, once the battery voltage droops the backup alternator starts providing power. You then pull circuits till you get your current consumption below 20A.
Very simple, effective and does not complicate the bus with diodes and extra relays.
The B and C site has a good installation and operation guide.
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  #10  
Old 05-17-2016, 04:07 AM
ariel_arielly ariel_arielly is offline
 
Join Date: Apr 2009
Location: Hod Hasharon, Israel
Posts: 42
Default RV8 Electric Dwg.

Dear Yves,
Looking at your schmatic, I found some issues I would recommend you to notice:
1. There are no wires from tha SHUNT to the Garmin ammeter.
2. The diode between the main bus to the essnttial bus should be a low voltage drope schotkey diode.
3. I would add an additional fuseof 60A as close as practical to tha alternator "B" lead (this will protect the wire between the alternator and the SHUNT in case when the engine is running and a short circuit between the SHUNT and the A/C ground occures).
4. You better choose C.B's to protect electrical wires in accordance with AC43-13 (don't forget that fuses or circuit breakers protect electrical wires not equipment).
Ariel Arielly, Israel
RV8a S/N 80295 200 hours
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