Essential Buss

[jpowell13]

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

[Strikhedonia]

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).

[jpowell13]

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

[rlmccarter]

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

[jpowell13]

Didn't know about that option Bob. Thanks

[johnbright]

I would ask on the Aeroelectric List, Bob Nuckolls hangs out there.

[DanH]

Originally Posted by jpowell13

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?

[jpowell13]

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

[rv8ch]

Originally Posted by jpowell13

...

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.

[Carl Froehlich]

Originally Posted by jpowell13

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