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Electrical distribution basics

joew

Well Known Member
Forgive me if this a redundant question. Just send me to a good picture. I have a dual screen G3X set up. One Battery, a PP 60 amp alternator and a SD-20 on the vacuum pad. Dual bus; a main bus and an avionics bus. Dual e-mags

Trying to figure out the firewall forward wiring and am stumped a bit.

My batt is on firewall. The batt and start contactors are below that. My 60amp ANL is to the left of the contactors and my ammeter shunt is next to the ANL.

I need a diagram of the connections showing the AWG size and where they terminate. I have the initial batt connections as well as the inter connection between the master and starter contactor.

I don’t have an understanding on where the B lead, Field wire go not how it all hooks up to the ANL as well as the shunt.

Do I need a second ANL and shunt for the Stby alternator?

What’s a good source? I have the aero electric connection, but can’t get an exact match. So some real plane pics would go a long way.

Thanks for talking me off the cliff

Joe
 
Marc,

I have your book. Helpful, but some pictures of where some things are placed would be helpful. It’s hard to visualize. Page 68 shows TAA IFR setup that I have. I do not see any Inline fuses around the ANL’s or shunt that others have used. Are they needed?

The back up alternator I have has an external regulator. It’s 20 amps. Would I need a separate 20 amp ANL? Any ideas where to mount it? Does it need a shunt?

Wire gauge from the batt contactor to my main bus? Was considering 6awg, could I get away with 10 (smaller wire going through the firewall).

My panel is wired already, but noticed my PFD, MFD, G5 and Autopilot are on the main bus. Would it be hard to move the MFD to the avionics bus?

Lots of questions, Lol

Thanks for getting back to me
 
Joe,

Take a look at some of the aeroelectric schematics. Z-13/20 has a dual bus with a 20 amp backup alternator. You might consider buying the book since it has a lot of background which would probably help you. That should get you started.

The Emagair manual for the PMAGs has the suggested wire sizing for the PMAGS. There are a few ways people wire them so do a search. The first option is using a keyswitch (which I did) versus using toggle switches and push to start. There are a few variations that different folks have used.
 
What is an ANL? Why not carry a spare alternator instead of having a backup installed, a Denso is about the size of a softball 6 pounds, $128 brand new and jeez simple to pop in and out, thats what I would do anyway, or buy an AGM battery from autozone if the alternater quit on a trip and press on with battry power and load shed. I use an internal regulated Denso, if you have one of those wiring us cake.. simply use a toggle for the field protect with 5 amp breaker, thats with a 40amp Denso Alt.. not sure the field cb might be different with 60amp alt.

Heres a link to a Super Cub forum discussing the Denso in the schematic below https://www.supercub.org/forum/showthread.php?54722-Replacement-over-voltage-relay-recommendation
.
Heres the Denso alt schematic that many pilots have in there certified craft
FcE94Op.jpg
 
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In the schematic above, the start solenoid is displayed up side down and there is no over voltage protection.
 
In the schematic above, the start solenoid is displayed up side down and there is no over voltage protection.



How do you know there is no overvoltage protection? From what Ive read it is protected from overvolt internally and will shut down

A conversation discussing that here https://www.supercub.org/forum/showthread.php?54722-Replacement-over-voltage-relay-recommendation

and another one here https://vansairforce.net/community/showthread.php?t=4089

Heres the alternator, I have used it for 7 years and its never overvolted or given me a problem, only worked perfect for 400 hours.

I will try contacting Denso tomorrow at get an answer
.
http://www.ase-supply.com/product_p/nd-021080-0760.htm
ND-021080-0760-2.jpg
 
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Aeroelectric Connection

… Take a look at some of the aeroelectric schematics. Z-13/20 has a dual bus with a 20 amp backup alternator. You might consider buying the book since it has a lot of background which would probably help you…

FYI:
  • Bob Nuckolls retracted Z13/20 some years ago calling it a cluge or something along those lines and pointing folks to Z12. Now he would point you to Z101.
  • The Aeroelectric Connection book does not contain the latest Z schematics. I made some notes and links.
  • Z101 is Bob Nuckolls' latest and is recommended in almost every case where a vacuum pad is available for a 2nd alternator although that alternator is optional.
  • The B&C “20A” alternator makes 32A at 2,700 Lycoming RPM. The Monkworkz PM generator (I think of it as an alternator) has the advantages it makes 32A at 1,800 Lycoming RPM and up and it starts with no battery present; admittedly IMO it’s for early adopters at present.
 
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Automotive alternators

Be aware automotive IR alternators generally (virtually always?/always?) have an enable wire folks mistake for a field wire. There have been incidents where upon an OV event the lead-acid/AGM battery held the voltage down and the pilot turned the master off mistakenly thinking this would kill the alternator; with no battery present the voltage goes into the hundreds and all connected electronics are destroyed. BTW an LiFePO4 battery with internal battery manager will disconnect itself during an OV event so OV protection is mandatory.
 
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My comment was not directed primarily at you. It was for builders in the future that might use that schematic and damage thousands of dollars of panel candy without knowing that it needed O.V. protection under extreme situations.

Can you get by without O.V. protection..... Yep!... until you have an O.V. situation.....:eek:

And then there's "the rest of the story" http://www.aeroelectric.com/articles/The_Truth_about_Crowbar_OV_Protection.pdf
 
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Hey Gasman, I was not directing that at you either..<BIG SNIP>

Same goes for this overvoltage protection.. is this actually true info or is this aeroelectric spreading bogus info? I have read that Denso is protected from overvoltage, I posted the links a couple posts back that says they are.. only one is correct and we need to find out which. I will donate my Denso to someone that can make the thing have an internal overvolt and see if it shuts down. I cannot find anything from Denso saying it is or is not, and am not going to believe someone on the internet just because someone says it IS THAT WAY. Lets try to overvolt a known stock off the shelf Denso and see if it shuts down before damaging equipment

35 years ago I was an avionics tech and studied gates and the other things gmcjetpilot talks about below, sounds like this is true info and he explains how the overvolt protection works in the Denso internal regulator, here is the link to the thread of the quotes below
https://vansairforce.net/community/showthread.php?t=174487&page=14
.

I recently converted my perfectly functional ND alternator to external regulation after following every alternator thread I could find. I originally believed that the integrated ND regulator to be bulletproof and after gutting one to convert to the external regulation I'm even more convinced. As I ripped the guts out of this well potted, tiny board brimming with SMDs and replaced it all with some blobs of solder and lengths of copper wire I couldn't help thinking I just took a huge step backwards in reliability.

That said, I took that step backwards to protect against the one failure mode that the IR can't protect against - over voltage. I'm now electrically dependant and an overvoltage event will turn me into a glider in a split second. Yes, its unlikely that the IR will fail in the first place, but if it does go rouge, I can't expect that same misbehaving device to shut off power to the field. An externally regulated alternator has a physical hard wire to the field windings that if disconnected will absolutely shut down the alternator.

I looked at some brute force options like a transorb diode on the alternator output, but that would require a relay and a big CB. By the time you trip the chain of components and get the crowbar action, enough stray voltage my have made it to the ECU.

If anyone knows of a super fast acting device with enough capacity to cut off the snake's head before it strikes, I'm all ears. I'd go back to the IR Denso unit in a second.


Great post but I would put a finer point on with one thing. I-VR alternators DO have OV protection but it's different from a "crow bar". It has proven to be very reliable, not withstanding the quality of clone parts, Taiwan, Malaysia, China vs. original ND Japan produced.

Take a look at this IC chip. Page one shows a typical application. The field is driven by a MOSFET. Page 2 shows the inner workings of the IC, more sophisticated than a B&C voltage regulator. It does soft start, monitors shorts, under and over voltage, while controlling the alternators field (which controls Alt output). The IC has internal redundancy and fault monitoring.

https://www.mouser.com/datasheet/2/302/mc33099-1188084.pdf

The IC drives an external MOSFET power transistor. Pretty bullet proof transistor. The IC controls the flow through that transistor to the field. The IC is very well protected and has redundancy. Any under, over, short will dump the control power (GATE) to the field power transistor. What if the MOSFET fails? IC removes power to the transistor gate which shuts the power down to field and alternator shuts down..... MOSFET transistor is likely to fail OPEN, so problem is no power from the alternator. However they could fail shorted. If that happened it would get very hot and melt then open. This is a very rare occurrence. Still keeping it as cool as possible is goodness, even though they are rated to 120 C.

What does the B&C do. It is a simple VR and can fail due to diode, resistor, transistor failures. However on top of the VR is a "crow bar". It is typically a thyristor or SCR (silicon controlled rectifier) There are many trade names. It is a switch, will pull down, close a circuit with a small input voltage. This will DEAD SHORT the power to VR/field to ground. It shorts and pops a CB (or blows a fuse). It's brute force, shorting power to ground to blow circuit protection. It does work unless it does not. SCR can fail as well. Also unlikely.

OV is pretty rare. Loss of electrical power is more common than OV. Again a lot of this fear comes from the mechanical external voltage regulator days. Aircraft alternators in GA have always been AUTOMOTIVE based. Some of the old certified stuff is pretty scary by today's standards. Most alternators die and fail to produce power.... However to each his own. I have seen photos and description of doing I-VR to E-VR surgery as being a little crude, but it works.
 
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Ruready, I'm sure one of the moderators will be along shortly to edit your posts. Please don't be grumpy about it. I'm sure your views are shared by many, but politics are prohibited here, with the overwhelming support of users.
 
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