Please Critique My Electrical Plan

[mfleming]

A PDF of my electrical plan can be found here. (Hit refresh until it loads if it say's forbidden)

This is my first pass at the basic electrical architecture for my -7.
The mission is Day VFR, IFR, very little IMC, maybe pass through a marine layer.

This electrical schematic is a variation of one being developed on the Aeroelectric list.

This is a single battery, dual alternator system with a clearance delivery feature.

My version uses a B&C BC410-H 20A back up alternator with their back up regulator. The back up alternator also comes in on the battery side of the master contractor.

[FinnFlyer]

Does the main alternator stop outputting when "field" voltage to is is cut?

Finn

[mfleming]

Originally Posted by FinnFlyer

Does the main alternator stop outputting when "field" voltage to is is cut?

Finn

Yes, that?s my understanding from B&C.

[Carl Froehlich]

What is the reason for running the alternator output to the battery side of the master instead of the load side?

I offer that a fault on the alternator output cable (that nice big fat one) is not isolable in your diagram. For smoke in the cabin it would be a good idea to have such things isolated by opening the master(s).

Side note - if you fly IFR I suggest you add the standard manufacture EFIS backup batteries. You will loose your radio and transponder but at least your will keep the wings level.

If you want to fly IFR with more confidence send me a note with your email address and I?ll provide some ideas.

Carl

[FinnFlyer]

Originally Posted by Carl Froehlich

What is the reason for running the alternator output to the battery side of the master instead of the load side?

I offer that a fault on the alternator output cable (that nice big fat one) is not isolable in your diagram. For smoke in the cabin it would be a good idea to have such things isolated by opening the master(s).

Carl

He does have a fusible link in the wire to the alternator.
In case of main contactor failure, battery will still be charged and can power essential bus.

However, in case of rectifier diodes in alternator partially shorts, the alternator will discharge the battery. A high-amp diode in series with the alternator B+ wire would prevent that. But then he'll need a electrolytic capacitor or small battery on the alternator side to smooth out noise to provide good regulation (if not already provided by regulator).

Finn

[DanH]

Originally Posted by Carl Froehlich

What is the reason for running the alternator output to the battery side of the master instead of the load side?

The key reason would be keeping the battery bus and navcom bus alive after opening the master contactor, without depleting the battery. It also keeps the standby alternator ballasted with the battery, which although not essential, is generally a good thing.

EDIT...I see Finn already got there.

I offer that a fault on the alternator output cable (that nice big fat one) is not isolable in your diagram. For smoke in the cabin it would be a good idea to have such things isolated by opening the master(s).

This seems to be a -7, so the standby alternator, contactor, and battery are all forward of the firewall...they can't make smoke in the cabin. A ground fault in the standby's B-lead would open the circuit protection anyway. The CP is drawn in right above the master contactor.

It does need additional circuit protection of some sort in the wire to the battery bus, as that wire does pass through the firewall and into the panel area. I'd suggest an ANL or similar with post terminals, as the terminals would provide secure junctions where the plan is currently marked "fat wire tie point".

If possible, the battery bus and its feed, as well as the feed to the navcom bus, should be physically located away from other wiring and buses. Like with coronavirus, physical separation increases the odds of survival.

I know B&C shows a backup alternator field switch in their drawings, but I don't know why. The special regulator for backup has a 13V setpoint; it doesn't turn on until the primary alternator goes offline, and then it turns on automatically. The switch doesn't hurt, but on the other hand, parts not on the airplane never give trouble.

Pretty sure you want to move the backup alternator's field supply to the battery bus, so it can regulate with the master contactor open.

[gmcjetpilot]

Main Alternator B+ is going where?

Assume you don't plan on paralleling both MAIN and AUX alternator and have a way to kill the main alternator, like pull CB.

Do you need a clearance delivery, just turn the master on. However I assume this has secondary advantage of a way to isolate an "essential bus" or clearance delivery bus with BAT master off in flight.

Hot battery bus has a lot on it, lights, clocks. There is a chance of draining the battery. I like the idea the MASTER turns everything off.

There are so many ways to wire a plane. Keep it as simple and "standard" and intuitive to operate as you can, not more complex.

[mfleming]

Originally Posted by Carl Froehlich

What is the reason for running the alternator output to the battery side of the master instead of the load side?

I offer that a fault on the alternator output cable (that nice big fat one) is not isolable in your diagram. For smoke in the cabin it would be a good idea to have such things isolated by opening the master(s).

Side note - if you fly IFR I suggest you add the standard manufacture EFIS backup batteries. You will loose your radio and transponder but at least your will keep the wings level.

If you want to fly IFR with more confidence send me a note with your email address and I’ll provide some ideas.

Carl

Contactor on the engine side of the firewall, so no smoke.

+1 on the back-up battery.

Originally Posted by DanH

The key reason would be keeping the battery bus and navcom bus alive after opening the master contactor, without depleting the battery. It also keeps the standby alternator ballasted with the battery, which although not essential, is generally a good thing.

EDIT...I see Finn already got there.



This seems to be a -7, so the standby alternator, contactor, and battery are all forward of the firewall...they can't make smoke in the cabin. A ground fault in the standby's B-lead would open the circuit protection anyway. The CP is drawn in right above the master contactor.

It does need additional circuit protection of some sort in the wire to the battery bus, as that wire does pass through the firewall and into the panel area. I'd suggest an ANL or similar with post terminals, as the terminals would provide secure junctions where the plan is currently marked "fat wire tie point".

If possible, the battery bus and its feed, as well as the feed to the navcom bus, should be physically located away from other wiring and buses. Like with coronavirus, physical separation increases the odds of survival.

I know B&C shows a backup alternator field switch in their drawings, but I don't know why. The special regulator for backup has a 13V setpoint; it doesn't turn on until the primary alternator goes offline, and then it turns on automatically. The switch doesn't hurt, but on the other hand, parts not on the airplane never give trouble.

Pretty sure you want to move the backup alternator's field supply to the battery bus, so it can regulate with the master contactor open.

• Yes, a -7
  
• What is an ANL?
  
• Aux Alt field switch does come off battery bus. I guess B&C shows a field switch in their drawings to isolate the aux alt in the unlikely event one had a double alt problem.

Originally Posted by gmcjetpilot

Main Alternator B+ is going where?

Assume you don't plan on paralleling both MAIN and AUX alternator and have a way to kill the main alternator, like pull CB.

Do you need a clearance delivery, just turn the master on. However I assume this has secondary advantage of a way to isolate an "essential bus" or clearance delivery bus with BAT master off in flight.

Hot battery bus has a lot on it, lights, clocks. There is a chance of draining the battery. I like the idea the MASTER turns everything off.

There are so many ways to wire a plane. Keep it as simple and "standard" and intuitive to operate as you can, not more complex.

• Aux alt parallels the main alt but the aux alt regulator keeps it offline until the voltage drops below a selected value then gets excited and comes online...no input from the pilot. There are indicator lights on the panel to alert the pilot of the switch.
  
• The battery bus is a artifact of copy and paste...no Hobbs, clock or dome light.

[DanH]

Originally Posted by mfleming

What is an ANL?

A big fuse.

https://bandc.com/product/anl-curren...base-standard/

https://bandc.com/product/anl-curren...-through-130a/

Aux Alt field switch does come off battery bus.

Ahh yes, brain fart. Main bus tap is a low volt sense, regulator terminals 3 and 5. Probably should move that tap to the battery bus, as page 4 of the installation manual says "If terminal 3 is not connected to power, the SB1B will not work". An open battery contactor could mean no power on the main bus.

I guess B&C shows a field switch in their drawings to isolate the aux alt in the unlikely event one had a double alt problem.

Perhaps it has some small power draw when parked, or won't shut down with power present. I dunno. I just like to know why things should be installed.

[supik]

Originally Posted by DanH

...

I know B&C shows a backup alternator field switch in their drawings, but I don't know why. The special regulator for backup has a 13V setpoint; it doesn't turn on until the primary alternator goes offline, and then it turns on automatically. The switch doesn't hurt, but on the other hand, parts not on the airplane never give trouble.

...

Maybe it would make more sense to have the MAIN alt operated by a switch and the AUX on a CB only. This way one could turn the MAIN alt off during preflight and check the AUX alt operates OK..