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Full Wave Bridge Rectifier

Im running through the systems of a new to me RV10. This plane was completed in 2009 so the avionics and bus structure are a little dated. I have identified what I believe to be a Bridge Rectifier in the Bus structure as seen in the picture link I posted below.

My understanding of a bridge rectifier is to transform AC to DC power. How it’s used in the application is confusing me.

My best guess, and hopefully someone can validate this, is as follows.

The airplane has two batteries, 1 primary, and 1 standby. During normal operation with the Alternator running and voltage above 13V, both batteries are connected to the system for charging. If the voltage drops below 13V, a low voltage warning system automatically sheds the standby battery leaving only the primary battery providing electricity. The inflight procedure at this point, assuming I cannot regain the alternator, is to engage the endurance bus switch and turn off the primary battery. In preparation for landing, I would then turn on the primary and standby battery to land the airplane.

So, back to the rectifier. When I am operating with only the endurance bus energized, is the rectifiers job to choose which battery (primary or standby) to power the endurance bus? It does this by only letting the supply with the highest voltage pass through to the bus? And as that battery’s voltage starts to drop, it would switch to the other battery, back and forth Etc?

I’m obviously not an Electrical Enigener so pardon my description and I’m sure my nomenclature is way off, but hopefully you get the gist of what I am describing.

Thanks

https://share.icloud.com/photos/03cfO-bnJX3r_IC8K6zEccS1g
 
rectifier

That rectifier is likely used to provide two sources to one load. Example: DC #1 bus and DC #2 bus power the Essential bus at the same time. That way, if either DC #1 or DC #2 fails, the essential bus remains powered...
 
With just those 3 wires connected to the bridge the circuit functions like the picture. Which is just two high current diodes to isolate the two inputs. I think…
 

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Yes ... that is a bridge rectifier. However, in this application it is not being used as such. You will notice one terminal is not connected to anything ... so the device is not being used as a traditional bridge rectifier.

Inside the square rectifier package are four diodes .... so these packages are a convenient way to obtain diodes that can handle a fair amount of current. If you trace the wiring, you will see that the diodes are wired for isolation for your essentials bus as Bob mentioned in the previous post.
 
It surprises me that it seems like everyone has to re-invent the wheel when it comes to essential bus design for redundancy.

By now I would have thought there would
Be a “standard design.”

And there is! Great news below pointing us to Aerolectric!

If the material for beginners was more easily indexed into a regularly updated and perhaps vetted format, people like me might ask fewer uninformed questions.
I’d like to see migration of institutional level knowledge here toward wikidom.
Things like this. Google isn’t enough. And posterity needs the answers, not our saved conversations and musing. So I edited mine mostly away.

Thanks to all.
 
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It surprises me that it seems like everyone has to re-invent the wheel when it comes to essential bus design for redundancy.
SNIP

Or for me, an “Essential” buss is not the best approach. Power distribution should have a graceful degeneration following any practical fault - without pilot immediate actions to maintain IFR flight.

Carl
 
It surprises me that it seems like everyone has to re-invent the wheel when it comes to essential bus design for redundancy.

By now I would have thought there would
Be a “standard design.”

An example: off the top of my head, I’d think about a 3-position switch on the console for Main battery/alternator vs Backup battery/alternator vs Bridge (main + backup through diode bridge). With lights to show nominal voltage. But not everyone does it that way.
And an argument can be made that a diode bridge is foolish: 0.6V drop,
Hardware that can fail independently,l annd wreck both sources, and out of the pilot’s control when a simple 2 way switch with indicators is more solid.
And I’d never power the starter through that, only direct from main battery.

But this is basic power electricity design that must have industrial standards.
Let’s copy the industry experts. Where do we look for that standard?

I'm not sure you are understanding the bridge principle; you are continuously powering ONE bus using TWO independent sources. The only way the one bus becomes unpowered is for BOTH sources to fail...of course, the bridge could also fail but then again, so could your switch. Also, there is no pilot action required with the bridge. The single bus remains powered with the failure of either source.

As far as the 0.6v difference, with modern avionics, that difference is insignificant.
 
But this is basic power electricity design that must have industrial standards.
Let’s copy the industry experts. Where do we look for that standard?

For light GA aircraft, there is one guy that has contributed ion both the experimental AND the certified world for decades - Bob Nuckolls. He has been involved in the design of electrical systems for most of the central Kansas airplane companies - so he is as close to an expert on “industry standards” as they come.

Fortunately, he doesn’t keep all of this knowledge to himself - he has a great book called the Aeroelectric Connection and a website where he shares pretty much everything. Well worth the time and investment (heck, at one time, the book was free…maybe it still is!)

Paul
 
By any chance does this aircraft have electronic ignition? Looks like the two wires into the diode pack are labeled Main something and the output is labeled emergency. How many batteries are installed? That's right out of Bob's Z diagram for an electrically dependent aircraft.

Might be able to do some more sleuthing and determine what the rest of the system architecture looks like ... but my guess is that it's a Z- ...
 
For light GA aircraft, there is one guy that has contributed on both the experimental AND the certified world for decades - Bob Nuckolls. He has been involved in the design of electrical systems for most of the central Kansas airplane companies - so he is as close to an expert on “industry standards” as they come.

Fortunately, he doesn’t keep all of this knowledge to himself - he has a great book called the Aeroelectric Connection and a website where he shares pretty much everything. Well worth the time and investment (heck, at one time, the book was free…maybe it still is!)

Paul

Yes, Aeroelectric Connection is free as a PDF, ref first bullet of my notes here.

And you will find Bob Nuckolls on the Aeroelectric List forum.
.
 
If the plane has only one alternator but two batteries, the alternator would need to be connected to the batteries via two diodes (or half of a rectifier). This way both can be charged at the same time but current can't flow from a good to a dead battery that has a short.
So that is one way to use diodes.

The other way was already described: if you have an essential bus you can feed it from two batteries via diodes and as long as one has juice, you are good to go. You can still have a bypass switch to cover the case that diodes burn out.

Diodes / rectifies are old electronics and get hot because they have a voltage drop. The modern flavor is called a zero volt drop battery isolator and consist of MOSFET transistors. They are commonly used for camping RVs and for boats which have more than one power source and more than one battery bank and manage all that with isolators.
 
I replaced my older school bridge rectifier's heat and larger voltage drop with a 60A 30V Schottky diode that used to be marketed. (By Perihelion Design)

http://www.mykitlog.com/users/displ...one&project=401&category=0&log=112221&row=379

Perihelion Design later switched to DSS2X61-0045A, the case of which is isolated from ground. No diodes currently on their website. DSS2X61-0045A is now obsolete, some research would find an alternate, still listed on eBay though, two diodes in package. I mount it on Wakefield 401K or 403K heatsink depending on power requirements although I could believe aluminum or SS bulkhead is adequate in some cases.
.
 
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Perihelion Design later switched to DSS2X61-0045A, the case of which is isolated from ground. No diodes currently on their website. DSS2X61-0045A is now obsolete, some research would find an alternate, still listed on eBay though, two diodes in package. I mount it on Wakefield 401K or 403K heatsink depending on power requirements although I could believe aluminum or SS bulkhead is adequate in some cases.
.
Many alternatives, also in better packages like this one where the diodes are isolated from the case. No need for a fiberglass isolation shim.
https://www.digikey.com/en/products/detail/stmicroelectronics/STPS24045TV/1039641
 
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