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Critiques Please!

rockitdoc

Well Known Member
Sponsor
I would greatly appreciate critiques of my preliminary architecture for the power distribution piece of my project. Don't be shy. :eek:

Mission is:
Day VFR, rare night VFR
Cross country, mostly

Failure scenarios:

1. Main alternator fails - Aux alt covers most everything so I can get to tools and fix it in case I am over nowhereland when failure occurs.
2. Main contactor fails - Pmags keep ship aloft, Dynon HDX1100's have backup batteries and power flight essentials (air speed, horizon, vertical speed, engine health, navigation) but not ADS-B, XPNDR, ELT, Lights, pitot heat, starter (so, landing somewhere with parts and tools would be nice.)

Even if both alternators and main contactor go south, the hot bus and self-powered Pmags keep the ship aloft. Fuel is the only limit, I think.

View attachment Wiring Diagram v2.0.pdf
 
I would greatly appreciate critiques of my preliminary architecture for the power distribution piece of my project. Don't be shy. :eek:

Mission is:
Day VFR, rare night VFR
Cross country, mostly

Failure scenarios:

1. Main alternator fails - Aux alt covers most everything so I can get to tools and fix it in case I am over nowhereland when failure occurs.
2. Main contactor fails - Pmags keep ship aloft, Dynon HDX1100's have backup batteries and power flight essentials (air speed, horizon, vertical speed, engine health, navigation) but not ADS-B, XPNDR, ELT, Lights, pitot heat, starter (so, landing somewhere with parts and tools would be nice.)

Even if both alternators and main contactor go south, the hot bus and self-powered Pmags keep the ship aloft. Fuel is the only limit, I think.

View attachment 34074

Most people use 2AWG for the starter wire. Also, your ground return to the battery will carry the starter load and should be the same guage as the starter guage (2 AWG). The primary alternator outputs 60 amps max, so 8 AWG is normally suitable unless you have an exceptionally long run to make. The start switch shouldn’t need more than 1 amp, so the 20 AWG may be a little overkill. Other than the 6awg to the negative battery terminal you would likely be ok. The 4 AWG May get a little hot during that 150 amp power rush on start though. At least you have a diagram. Many don’t even do that.
 
Most people use 2AWG for the starter wire. Also, your ground return to the battery will carry the starter load and should be the same guage as the starter guage (2 AWG). The primary alternator outputs 60 amps max, so 8 AWG is normally suitable unless you have an exceptionally long run to make. The start switch shouldn’t need more than 1 amp, so the 20 AWG may be a little overkill. Other than the 6awg to the negative battery terminal you would likely be ok. The 4 AWG May get a little hot during that 150 amp power rush on start though. At least you have a diagram. Many don’t even do that.

Much obliged, Jon.
 
2 ground straps

You might consider two ground straps to the engine, just in case. It's what Bob Nuckolls recommends, since the consequences of losing one can be so expensive.
 
You might consider two ground straps to the engine, just in case. It's what Bob Nuckolls recommends, since the consequences of losing one can be so expensive.

Maybe direct to neg terminal instead of to engine mount.
 
As drawn, the starter return current (Ground) passes through the braided strap to the engine mount, through the engine mount, through the firewall (serving as a ground path), and then through the braided strap that leads from the firewall to the battery negative post. I suggest that the two braided straps be attached to the same post that carries the ground path through the firewall to what's labeled FOT. I don't see a reason to include the engine mount in the starter ground path.

Thanks for including just the main power distribution in your plan rather than the entire electrical system. This made the analysis much easier. Nice diagram.

You may want to consider adding a switch for the hot bus. The items on that bus would draw battery power unless switched off individually. That would increase the chances of a dead battery. It would require a switch that could handle 30 amps or so or a relay in the circuit. If you had an electrical smoke or fire incident, you would want a way to depower the hot bus. I know, that makes it something other than a hot bus. You could call it an essential bus.
 
As drawn, the starter return current (Ground) passes through the braided strap to the engine mount, through the engine mount, through the firewall (serving as a ground path), and then through the braided strap that leads from the firewall to the battery negative post. I suggest that the two braided straps be attached to the same post that carries the ground path through the firewall to what's labeled FOT. I don't see a reason to include the engine mount in the starter ground path.

This is per plans for the -14A, but I agree with you. I will run a strap from engine direct to -12v batt.
 
Quote:
Originally Posted by koupster View Post
As drawn, the starter return current (Ground) passes through the braided strap to the engine mount, through the engine mount, through the firewall (serving as a ground path), and then through the braided strap that leads from the firewall to the battery negative post. I suggest that the two braided straps be attached to the same post that carries the ground path through the firewall to what's labeled FOT. I don't see a reason to include the engine mount in the starter ground path.


This is per plans for the -14A, but I agree with you. I will run a strap from engine direct to -12v batt.


This method eliminates one high current connection and also reduces the possibility of the starter current flowing back thru the engine control cables should the ground connection develop resistance.
 
The engine mount should not be used to conduct electrical current.
The starter contactor needs a diode across its coil with the banded end connected to positive.
The pilot should have the ability to shut off all electrical power as close to the source as possible.
This is very important in case of smoke in the cockpit or an imminent forced landing.
After a crash, that arcing and sparking 10AWG wire will ignite gasoline.
Move most of the loads from the always hot bus to the main power bus with the exception of the
cockpit lights and possibly the stall warning. Move the always hot bus next to the battery and rename it to battery bus.
Actually you don't even need a battery bus. Just connect inline fuses to the
battery side of the battery contactor for the one or two remaining loads.
 
The Latest Iteration.....

Thanks for all the comments. I used most of them. If I didn't it was probably because I'm just not smart enough to understand......yet. Moved the starter contactor diode to the position that is called out in the plans.

View attachment Wiring Diagram v2.5.pdf
 
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hall effect devices?

Are the hall effect devices on the alternator outputs used in lieu of shunt resisters to measure current?
 
Trim & Flaps

Jusy curious.
Are the trim and flaps controlled by the EFIS or wired direct to switches?
If the EFIS were to fail how do the motors get signal?
Just curious.
 
Jusy curious.
Are the trim and flaps controlled by the EFIS or wired direct to switches?
If the EFIS were to fail how do the motors get signal?
Just curious.

No. Trim and flaps are independent and have their own switches. Trim on the pilot yoke, flaps on the panel above throttle.
 
NO unprotected wires off the battery, ie: hot buss wire should be fused, personally don’t see any need for an always hot buss.
NO 22ga wires FWF unless they are signal wires (master sw).
 
NO unprotected wires off the battery, ie: hot buss wire should be fused, personally don’t see any need for an always hot buss.
NO 22ga wires FWF unless they are signal wires (master sw).

That 10AWG wire from the master contactor to the hot bus is on the firewall and immediately penetrates to the sub panel. The chances for it getting compromised will be very slim if carefully installed. However, I get your point and wondered how best to include a fuse or breaker and where best to put it. Of course, for that matter, the 6AWG after the master contactor is not fused/CB'd either. Why do published wiring diagrams not fuse this one?

Why no 22AWG FWF unless signals?

The hot bus idea is to provide power to items that would be nice to have in the event of a master contactor failure.
 
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SNIP
The hot bus idea is to provide power to items that would be nice to have in the event of a master contactor failure.

Many ways to have this capability, but a length of #10 wire going directly to the battery is not one of them as has been pointed out. For that matter a #10 wire is oversized for the loads you list.

For your basic VFR install I agree that this always hot buss is not needed, and presents more down side than up.

Side note - years ago helping an RV-14 builder I contacted Van’s on the per plan Rube Goldberg instructions to ground the engine via the engine mount. They were not receptive to my critique. On this subject however make sure you ground the pMags to the engine case, not back to the firewall.

Carl
 
Many ways to have this capability, but a length of #10 wire going directly to the battery is not one of them as has been pointed out. For that matter a #10 wire is oversized for the loads you list.

I'm obviously a noob at this, but running a few 'nice to have' items off the battery was the only obvious way to retain these in case of a master contactor failure. Is there a source I can study to get me at least to the apprentice stage? I've been using Knuckolls's writings and they have helped ALOT.


On this subject however make sure you ground the pMags to the engine case, not back to the firewall.
Carl

Yes. PMags are grounded to case. And, I wonder why Van's didn't take the critique well. Grounding the engine direct to the batt is simpler and probably lighter.
 
The engine is more likely to quit than the battery contactor is to fail.
After a forced landing, that always hot #10 wire could make sparks which will ignite leaking gasoline.
Having fuses in series is not a good idea. A shorted load could blow both the load
fuse and the main fuse. Do not fuse the 6AWG main bus feeder.
If the battery contactor fails while flying, you probably won't even know it
because the alternator is supplying electrical power, not the battery.
If you are still concerned about the main contactor failing, see the attached circuit.
 

Attachments

  • Contactor Bypass.pdf
    18.6 KB · Views: 112
The engine is more likely to quit than the battery contactor is to fail.

I am leaning away from the 'hot bus' idea because of this. And, because it is unlikely both alternators and the master contactor would fail, even if the contactor did fail, electric molecules still come via either alternator.


Having fuses in series is not a good idea. A shorted load could blow both the load fuse and the main fuse. Do not fuse the 6AWG main bus feeder.

I am not sure where there are fuses in series in the plan. And, the 6AWG main bus feeder is not fused. However, that means that during flight a rather largish wire is penetrating the cabin without protection. Should it be? Or, is it protected by my stellar construction skills? :D
 
Is a backup alternator needed?

I am appreciative of the discussion here as I will have to "design" or borrow a similar diagram soon for my 14. I am currently not planning on the engine with the backup alternator pad although I may change that choice, however for mostly day VFR flying you have backup instruments already so why bother with the weight and complexity of a second alternator for this scenario? Obviously there is no right or wrong here, just curious about your thinking as it may influence mine.
 
I am appreciative of the discussion here as I will have to "design" or borrow a similar diagram soon for my 14. I am currently not planning on the engine with the backup alternator pad although I may change that choice, however for mostly day VFR flying you have backup instruments already so why bother with the weight and complexity of a second alternator for this scenario? Obviously there is no right or wrong here, just curious about your thinking as it may influence mine.

I originally wasn’t using the aux alternator. But, much of my flying will be long trips so getting to a decent repair field was my reasoning. If I just flew local VFR, I d skip it. Resaleis also a consideration.
 
Also, for a VFR airplane, do you feel strongly that a backup alternator is worth it? You should have a battery backup for your EFIS anyway. Just a thought to lower complexity and cost.
 
Also, for a VFR airplane, do you feel strongly that a backup alternator is worth it? You should have a battery backup for your EFIS anyway. Just a thought to lower complexity and cost.

If I were day VFR and just local, I wouldn't bother. But, my mission will be longish trips to both coasts from northern CO sometimes over bleak (read, no services) terrain. So, getting back to tools and parts after an alternator takes a hike is part of the plan. Also, resale to potential IFR folks would be a plus.
 
In v2.5 the flyback diode on the starter contactor is backwards.

Is the starter permanent magnet?

Have you seen Z101? Maybe use its Clearance Delivery Bus vs your Hot Bus.
.
 
If I were day VFR and just local, I wouldn't bother. But, my mission will be longish trips to both coasts from northern CO sometimes over bleak (read, no services) terrain. So, getting back to tools and parts after an alternator takes a hike is part of the plan. Also, resale to potential IFR folks would be a plus.

Assuming you design enough reserve battery capacity to mitigate an inflight power failure, then the backup alternator’s main function in life becomes a way to get home during a cross country when the primary alternator goes south.

I’m of a different camp as my main mission is long cross-country IFR, so redundancy is a key element. But here again the backup alternator’s primary function remains a way to get home if the primary one fails.

If you are relying on EFIS back batteries and such a strongly recommend testing to see just how long they will last, and repeating this test often. For VFR 30 minutes of backup might be ok, but not IFR. Don’t assume the only electrical failure you will have is a broken alternator…..

Carl
 
In v2.5 the flyback diode on the starter contactor is backwards.

Is the starter permanent magnet?

Have you seen Z101? Maybe use its Clearance Delivery Bus vs your Hot Bus.
.

Thanks John.

Diode rotated on Figure 2.6.
Yes. SkyTec XLT
I have. But, I have decided to simplify my setup with the following changes:

1. One Main bus (I will have to link two fuse blocks together as I have only found blocks with a max of 20 fuses) and it looks like I have 25.

2. One Hall Effect Sensor (only one alternator is powered at a time)

3. Aux Alternator 'B' Lead wired to Battery side of Main Contactor (in case of main contactor failure, aux alt still works)

4. Fusible Links for Alternator 'B' Leads (latest Z101B diagram shows this in lieu of ANLs. Presumably because of easy/fewer issues with connections, space and size advantages and reaction time, but I don't really know)
I would prefer this method, if justifiable, cuz I haven't drilled the holes in my FW, yet, required by the ANL mounts.

Any comments related to the fusible links vs ANLs appreciated. I looked but could not find the references I think I read about this issue in the past few weeks of doing this excerize.
 
Assuming you design enough reserve battery capacity to mitigate an inflight power failure, then the backup alternator’s main function in life becomes a way to get home during a cross country when the primary alternator goes south.

Yes. Hopefully, I will never need it.


If you are relying on EFIS back batteries and such a strongly recommend testing to see just how long they will last, and repeating this test often. For VFR 30 minutes of backup might be ok, but not IFR. Don’t assume the only electrical failure you will have is a broken alternator…..
Carl

Yes, I am. But, the aux alternator should power the EFIS's, right? The only reason the EFIS batteries would be needed is if both alternators took a holiday. Or, do I need more study?

In this most recent iteration (v2.7), some failure scenarios are:

1. Alternator fails: aux alternator takes over - fly home shedding whatever to satisfy 40A of charging ability
2. Main contactor fails open: No battery for starting, but flying still possible
3. Main alternator fails and main contactor fails: Fly home with Aux alternator

What other failure modes have I missed?

View attachment Wiring Diagram v2.7.pdf
 
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Unswitched

I was debating a very small hot bus for cabin lights only. Very low amps and fused. Still debating it :D

my only power in the cabin that is not on the master is the baggage area lights. I used a fusible link off the battery and ran it to the panel switch and then back to the baggage area. It is very low power, so very small wire and a even smaller fusible link. If it shorts, it is so small of wire I would probably not notice it. But I have been camping where it was so dark, it was impossible to do much. this baggage lite I can reach in and turn on before climbing in, and allows me to get stuff out of the plane without turning on the master; even my kids can do it without me having to worry they left the master on.
 
my only power in the cabin that is not on the master is the baggage area lights. I used a fusible link off the battery and ran it to the panel switch and then back to the baggage area. It is very low power, so very small wire and a even smaller fusible link. If it shorts, it is so small of wire I would probably not notice it. But I have been camping where it was so dark, it was impossible to do much. this baggage lite I can reach in and turn on before climbing in, and allows me to get stuff out of the plane without turning on the master; even my kids can do it without me having to worry they left the master on.

That was my thinking, too. Originally, I only had the baggage light and stall horn on this bus for lighting up in a dark hangar and so during preflight the master was not on while I walked around the plane to check if the horn worked.

Then I started adding more and more and more....and as usual, things got out of hand. I may go back to the 'hot' bus through a fusible link, like you did, though. Makes sense.
 
Yes. Hopefully, I will never need it.




Yes, I am. But, the aux alternator should power the EFIS's, right? The only reason the EFIS batteries would be needed is if both alternators took a holiday. Or, do I need more study?

In this most recent iteration (v2.7), some failure scenarios are:

1. Alternator fails: aux alternator takes over - fly home shedding whatever to satisfy 40A of charging ability
2. Main contactor fails open: No battery for starting, but flying still possible
3. Main alternator fails and main contactor fails: Fly home with Aux alternator

What other failure modes have I missed?

View attachment 34155
For a VFR ship, the other failure risks are perhaps below the level of concern. Keep in mind we tend to forget the little things, like a bad terminal, high resistance contact or a loose ground. These are are low probability but have caused dark panels. In most cases however the plane should be talking to you along the way providing hints that all is not right.

I do suggest however that you fully test your ship with the master solenoid open, first on the ground then in the air. Three tests:
- Primary and aux alternator on line
- Primary alternator on line, aux alternator off
- Primary alternator off line, aux alternator on
Keep a sharp eye on buss voltage and have your headset and radio on to listen for new noises.

Don’t rely on this as a backup mode before you verify it will maintain system stability.

The battery provides your first line of protection for an over voltage event (assuming you are not using an EarthX battery). The battery will absorb the over voltage until it fails - but that should be much longer than you need to see the issue and trip the alternator if your crowbar does not do it first.

Carl
 
The battery provides your first line of protection for an over voltage event (assuming you are not using an EarthX battery).

No Li battery. PC680

The battery will absorb the over voltage until it fails - but that should be much longer than you need to see the issue and trip the alternator if your crowbar does not do it first.
Carl

I think my Plane Power internally regulated alt has a 'crowbar' but I will have to ask them. I will also do so for the B&C
 
'Last' Iteration of Power Distribution Design?

I think I'm closing in on this with all of your help.

This last iteration removed the 'hot' bus and just put the baggage compartment light and stall warning horn on the hot side of the master contactor protected by 24ga fusible links. Not sure these are correct for 20ga wire or the draws, but that's something to research.

View attachment Wiring Diagram v2.8.pdf
 
Assuming you are using LED lights and such, I suspect your constant load to be closer to 20amps, not 35. Turn off the NAV/Strobes and Landing Lights and you will be in the 10-15amp range.

Carl
 
Assuming you are using LED lights and such, I suspect your constant load to be closer to 20amps, not 35. Turn off the NAV/Strobes and Landing Lights and you will be in the 10-15amp range.

Carl

Yes. AeroLEDs everywhere. I just added up the fuse values, shown in red on the wiring diagram. I forgot that the draw is prolly less than half. But, I will be running strobes and navs. Of course they draw minimal amounts.
 
Critique not me!

I tend to find we all set ourselves up to fail? In my 9A I wired everything my self just focusing on Vans standard drawings, I,m a sparky so all crimps done with my Cresent pliers and good saddle a seem technique, No soldered connections and good cable layout and tied up together, never had a single flicker in 5 years💪. Good work 👍
 
I tend to find we all set ourselves up to fail? In my 9A I wired everything my self just focusing on Vans standard drawings, I,m a sparky so all crimps done with my Cresent pliers and good saddle a seem technique, No soldered connections and good cable layout and tied up together, never had a single flicker in 5 years��. Good work ��

That helps ALOT! Thanks. I was gonna throw in the towel. Im no sparky if you couldnt tell.
Ian, are you anywhere near Cairns?
 
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Power Distribution v 2.11

This iteration has:

1. No CBs for Pmags, fuses and switches, instead
2. No idiot light when Alt#2 is engaged since Alt#1 light will be lit upon failure of Alt#1.
3. No Alt#1 or #2 switches, CBs instead

View attachment Wiring Diagram v2.11.pdf

Panel layout based on this iteration:

Panel v3.0.jpg

I am not sure about the location of the ELT or pitot heat switches. I might relocate to co-pilot side since I am day VFR, only and neither of these will be used much, if at all.
 
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I like things to be in a line.

I'd move all your breakers over to the right side, under the MFD.

I'd move all the switches to under the PFD. Master, PMAGs, Strobes, NAV, Lights, pitot.

Then, I'd put a small EFIS (or leave space for it) to the left of the PFD.

I had to decide where to move my ELT test panel, and have pretty much decided it will be on the far right.
 
I like things to be in a line.

I'd move all your breakers over to the right side, under the MFD.

I tend to agree. Keep things out of line of sight unless needed.

I'd move all the switches to under the PFD. Master, PMAGs, Strobes, NAV, Lights, pitot.

Then, I'd put a small EFIS (or leave space for it) to the left of the PFD.

Also, tend to agree in order to make room for a small EFIS.

I had to decide where to move my ELT test panel, and have pretty much decided it will be on the far right.

Great minds.....

I already made that decision, too.
 
Lines

I personally don't like things in a line. Groupings make more sense. When I turn off the runway, I can reach up (big iron but that is what I'm flying now) to the light switches without looking and turn them off. A row of switches in a line may look pretty but require you look at them to verify your hand is on the right switch.
 
To Each His/Her Own

I personally don't like things in a line. Groupings make more sense. When I turn off the runway, I can reach up (big iron but that is what I'm flying now) to the light switches without looking and turn them off. A row of switches in a line may look pretty but require you look at them to verify your hand is on the right switch.

Actually, no need to look. Lights on the right, nav/strobes on the left. Whatever you get used to is best I think.
 
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