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Essential Buss

jpowell13

Well Known Member
I wired my 6A using Van's harness and design of about 10 years ago. There is no separate avionics buss just a main buss. My plan now is to upgrade the wiring so that, if I have an alternator failure, I can bypass the battery contactor and shed other unnecessary power draws per Bob Nuckolls' Figure 17-4.

Not wanting to add an "essential buss" which would be difficult I plan to revise Nuckolls'design per the photo. If I have it right, I'd be able to bypass the battery contactor and shed individual electrical items. Am I correct?

Sorry for the poor image and thanks in advance for the help. John

20220124_084757.jpg
 
My suggestion would be to add an ESS Contactor in place of the switch in your diagram and use a switch to enable to ESS Contactor. If you go with a SPDT switch can be used to select which source you would like to devices should be powered On (Main Contactor or ESS Contactor).
 
SPDT switch

Not sure why your idea wouldn't work, and it would be simpler in operation, but Mr Nuckolls recommends using a steering diode and the single throw switch. I think the diode protects the electronics from overvoltage while preventing them from being turned off during switching to the battery buss. As I understand it, you can tern on the battery buss feed and then turn off the main power switch without harming anything.

The advantage is that you bypass the battery contactor which requires 2 amps to stay "on".

John
 
Another Option

John,

Another option is to replace the battery contactor. I went with a Gigavac MX11SA that has two coils with a 0.082A holding current so there isn't much drain on the battery if the alternator dies.

Downside the cost. Upside it's hardened against vibration and water so it will outlast humanity.

Bob
 
My plan now is to upgrade the wiring so that, if I have an alternator failure, I can bypass the battery contactor and shed other unnecessary power draws per Bob Nuckolls' Figure 17-4.

John, VFR or IFR? And what is considered truly essential?
 
IFR

IFR Dan. Essential for me is my EFIS. A com radio, my GPS400W and my iFly portable GPS. I have G5 PFD/HSI with it's own backup battery, an ADSB receiver with battery and a smartphone with iFly software which I also carry.

I'm planning to update my TCW backup battery, and to get one of those 8 amp vacuum pad mounted backup alternators from B&C after making the wiring upgrades.

John, I've reached out to Bob Nuckell's by email. I'll pass on his advice when I hear back from him. John
 
...

John, I've reached out to Bob Nuckell's by email. I'll pass on his advice when I hear back from him. John

Probably best to post to the list - there are several very good people there that can give you advice.

http://forums.matronics.com

Bob also has a book that's free, and gives a lot of good information with a lot of background to help understand the why, not just the what and the how.
 
SNIP

I'm planning to update my TCW backup battery, and to get one of those 8 amp vacuum pad mounted backup alternators from B&C after making the wiring upgrades.

I recommend the very nice 20 amp B&C vacuum pad standby alternator over the little 8 amp option. For the same money you get an alternator that can take you home if needed.

Carl
 
IMO an ‘EBUS’ is a waste of time and adds unnecessary failure points. Just load shed if you lose the alternator. I installed the gigavac contactor years ago, much better than stock and draws almost nothing. KISS always good.
 
Failure Mod?

IMO an ‘EBUS’ is a waste of time and adds unnecessary failure points. Just load shed if you lose the alternator. I installed the gigavac contactor years ago, much better than stock and draws almost nothing. KISS always good.

If you follow the simple layout of the Aeroelectric Z-11, it’s hard for me to understand what “unnecessary failure points” could possibly be added by the Endurance Bus. It’s about as simple as it gets while using well proven components.

The idea behind the EBUS is to allow a quick and easy changeover to essential equipment by flipping just two switches without any thought or decision making by the pilot in middle of an electrical emergency, thus allowing him to continue doing the most important part of flying - aviating. The second function of the EBUS is to prevent the master contactor circuit and the main bus feed from becoming a single point of failure for essential avionics and instruments.

One mistake that I’ve seen many make is to put more than just truly essential equipment on the EBUS. This not only defeats the purpose of having it, but it also potentially overloads the isolation rectifier, which can then become a failure point.

Skylor
 
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I see there have been no responses that answer your question directly. Here’s my take.

You plan to have one buss (called Main/E Bus) that powers everything and a separate Batt bus. You have a main alternator and a SD8 backup alternator.

From your sketch, ignoring the diode for now, normal operation has the main alternator feeding the Main/E Bus and the battery and the Bat Bus.
In case the alternator fails, the battery contactor is switched off and you switch on the E Bus Alt Feed switch. You state you wish to remove the Essential Bus (I’m imagining your sketch as if it is a piece of wire – see attachment). So the E Bus Alt Feed would connect to the Main/E-Bus and you would shed loads individually as needed.

The diode is not needed. Its purpose in Fig 17-4 is to isolate the Essential Bus. When power is applied to the Essential Bus, the diode ensures just the Essential Bus is powered by preventing current flow to the Main/E-Bus.

Hope this helps.

Jim Butcher
 

Attachments

  • IMG_20220131_0001_NEW.pdf
    1.1 MB · Views: 285
Diode

Good to know the diode is unnecessary Jim, and it makes sense. In case of an alternator failure, the process would be to turn on power from the battery buss, then turn off the main or battery contactor switch. (The power to the avionics stays at 12v even when both switches are on.) Then, turn off unnecessary lights and avionics and land.

Something I do look forward to having in the system are positive and negative battery busses.... not just for bypassing the battery contactor, but for an easy way to connect a battery charger or jump starter without having to remove the battery cover. I also like having my cigarette lighter power plugs on when rhe main switch is off (with in-lines fuses) so I can be booting up my ifly gps and picking up ATIS on the handheld before startup. The busses will make that easier.
 
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Re post #1:
  • If the alternator is externally-regulated as shown, main alternator output voltage will rise by the diode voltage drop.
  • Bob Nuckolls would limit the endurance bus feed diode to 7-1/2 A unless a relay is used. Ref FAR 23.1361 Master Switch Arrangement. Bob allows a 7-1/2 A fuse vs a 5A breaker because fuses are faster I2T.
Re post #3:
  • The diode has no function re overvoltage.
  • Your master contactor probably has a 15 Ohm coil, 0.96A at 14.4V.
  • If a relay were used in the aux feed to the endurance bus, A 20A automotive relay has a 144 Ohm coil and a 40A one has a 90 Ohm coil.
Re post #13: If you leave the diode out the endurance bus fuse will blow under the scenario master off/endurance bus on/starter engaged. Of course you don't plan on doing it but it's a baited trap.

Z templates are at http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/:
  • Figure 17-4 of the Aeroelectric Connection is shown in greater detail in the Z13 template.
  • Z13-8T shows the endurance bus fed with a 15A fuses and relay. The fuses could be larger if desired.
  • Z13-8 E-Bus Feeders shows endurance bus fed with 7-1/2A fuse and switch.
  • Z101 is Bob Nuckolls' latest. No fuses are shown to the bus now called clearance delivery/brownout/aux and the asterisks indicate the relay, bus, and diode are close to the battery such that a short to ground is considered impossible. Z101 incorporates a high-capacity aux alternator such as B&C 410 or 462.
As mentioned in post #10, you could choose an aux alternator larger than the SD-8, link below is a summary of aux alternator outputs on a Lycoming engine.

https://vansairforce.net/community/showpost.php?p=1581613&postcount=21
 
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That's great information John. This is what I needed. Many thanks.

Regarding the 8a alternator, I once lost my alternator on a VFR flight due to a loose battery wire connector. I was surprised how well my 32 amp AGM battery kept the avionics going (over one hour). This convinced me that the smaller/lighter 8a backup alternator would be adequate in an alternator out situation, if I were to shed unnecessary power draws.
 
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What I did.

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20220218_134349.jpg

Sorry for the orientation of the photos. I'm a little old for working under the panel, but managed to install positive and negative busses behind the rudder pedal support tubes. Used a 30amp in-line fuse and a 10 gauge wire to stsp switch in the panel. Works fine on the ground.

Already used the busses to connect a jump starter and get my engine started on a cold morning in TN. (My Pmags are great, but not as good at igniting the fire on a cold day as the old Bendix.)

My next step will be to update my old TWC backup battery with the Li Fi Phosphate version. John
 
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