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Permalink Reply by Stan Cooper on March 29, 2018 at 7:53pm

Ron, if you don't have a copy of Bob Nuckolls' book The AeroElectric Connection, you should pick up a copy. $23.50 and well worth it. Or, you can download the pdf free.

The AeroElectric Connection 12th Edition

For eliminating a bus tie switch and provide automatic isolation of the power distribution bus from the essential bus during failed alternator operation, Bob recommends a silicon diode array having a forward current rating of 20 amperes or more. For current of more than 3-4 amperes, you'll need a heat sink for the diode array.

B&C sells this essential bus diode which should work:

B&C D-25 Diode Array

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Permalink Reply by Stan Cooper on March 29, 2018 at 8:21pm

B&C also offers the diode array mounted to a heat sink capable of handling a full 25 amperes.

B&C Essential Bus Diode w/ 15 Watt Heatsink

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Permalink Reply by Gary Welch on March 30, 2018 at 1:14am

This is what I used.

I found it hard to take any other advice than Bob Nuckoll's when it comes to wiring. He has spent a lifetime designing aircraft electrical systems and has learned what works - and what is practical. He uses these exact diodes in most of his wiring diagrams. His book explains why. 

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Permalink Reply by Charles Miller on March 30, 2018 at 12:03pm

Great book! Simple electrical designs and well explained. Thank you for the link.

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Permalink Reply by Charles Miller on March 29, 2018 at 11:01pm

I would suggest taking a look at several other options, Look into a MOSFET or transistor switch with a current limit. Or possibly a solid state relay setup if you're not so comfortable with building circuits.  Lots of ways to do this simple power supply isolation.  One reason to look at other options is the Diodes' forward voltage drop (.6-.7).  At 15a that could produce 10w of heat at the diode. The low Rds of the MOSFET makes it a good choice for high current switching.  A relay could also be used to do the same job low cost easy install. Just a few thoughts.

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Permalink Reply by Stan Cooper on March 30, 2018 at 6:23pm

Charles, reviewing Bob Nuckolls' 12th edition, it appears he now recommends a Schottky diode for isolation, which he says is more efficient and with less voltage drop than the diode array he suggested in the 10th edition which I've been using.

It's part number AEC9001-1 and doesn't need a big heatsink.

AEC9001-1 Schottky Diode

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Permalink Reply by Charles Miller on March 30, 2018 at 9:21pm

I like the simplicity of the diode, however i felt it should be known this does waste quite a chunk of power.  (unless its cold out in which case its just an electric heater)  There are a lot of modern boards that handle this sort of thing very well.  An example of an assembled Mosfet source selector switch would be http://www.linear.com/docs/35205  or just a simple IC http://www.linear.com/docs/17899  Just a couple of examples search digikey or mouser for "Source Selector" there should be a few hundred options out there.

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Permalink Reply by Ronald J Stamschror on March 31, 2018 at 2:14pm

Good info, Thanks

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