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Basic Elec. Diagram -critique pls

supik

Well Known Member
This is my preliminary diagram for my RV-10

Single battery, dual alternator setup. (60amp B&C + 30amp B&C)
Backup & Master switches ON during normal ops.

Both alternators will be ON during normal ops.
ALT-1 (60amp) regulator preset at 14.4V
ALT-2 (30amp) regulator preset at 13.8V

Both regulators are LR3C-14
LV lights from regulators NOT utilized. Respective BUS voltages monitored by G3X Touch.
-MAIN BUS threshold monitoring at or below 13.8V triggers (MASTER CAUT) MAIN BUS LV
-ESS BUS threshold monitoring at or below 13.0V triggers (MASTER WARN) ESS BUS LV
I hope this is possible to setup with the G3X Touch, expert opinion is welcomed.

Shall the ESS-BUS relay fail, ESS-BUS alternate feed is provided by a diode.

EDIT: Diagram replaced with v.006 (wire size labels removed, battery capacity corrected)
EDIT: v.007 (E BUS relay replaced)
EDIT: v.008 (E BUS updated wire size & protection) peak max draw incl. intermittent draw is 33,7 Amps on the EBUS)
EDIT: v.009 (E BUS AWG updated)

EDIT: Diagram v.010 Relay substituted with cont. duty contactor

2v1kis9.jpg
 
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Igor,

Some thoughts:
- I?m assuming the 17amp-hr battery is something like a PC-680. If so, it is less than marginal for the RV-10. Also remember the RV-10 needs the battery weight aft so no need to scrimp and use an undersized battery. I use two PC-625 batteries with a modified stock battery mount. This has worked very well for me and I recommend a similar approach.
- The #4 run from the battery to the starter is undersized. This is a big boy engine, it needs a lot of juice to crank. The long run from the battery with the #4 will have too much voltage drop. Recommend using #2 welding cable for the battery positive and negative connections.
- The #14 wire from the standby alternator back to the battery is way undersized. Follow the B&C install manual for this standby alternator - it calls for #10 wire on the output.
- The amp shunt for the standby alternator is a waste of time. If your primary alternator fails you will know it by both the primary amp reading and the buss voltage dropping from the normal 14.2vdc or so. Also the nice little yellow light that comes with the B&C regulator will light up on the panel. At that point you don?t care what the standby alternaor is putting out, just that buss voltage is maintained. Dump this shunt and reduce your connections - always a good idea.
- Figure out how you will keep the battery connected to the standby alternator if you have a failure, such you opening the master as an immediate action to smoke in the cabin, a component or connection failure.

As I have posted on several occasions, I strongly recommend a two battery, single alternator scheme as a superior starting point for IFR RVs. A second alternator can be added if desired, but it is more important to have two batteries in a thoughtful design so that you mitigate most common single point failure risks.

Carl
 
Igor,

Some thoughts:
- I?m assuming the 17amp-hr battery is something like a PC-680. If so, it is less than marginal for the RV-10. Also remember the RV-10 needs the battery weight aft so no need to scrimp and use an undersized battery. I use two PC-625 batteries with a modified stock battery mount. This has worked very well for me and I recommend a similar approach.
- The #4 run from the battery to the starter is undersized. This is a big boy engine, it needs a lot of juice to crank. The long run from the battery with the #4 will have too much voltage drop. Recommend using #2 welding cable for the battery positive and negative connections.
- The #14 wire from the standby alternator back to the battery is way undersized. Follow the B&C install manual for this standby alternator - it calls for #10 wire on the output.
- The amp shunt for the standby alternator is a waste of time. If your primary alternator fails you will know it by both the primary amp reading and the buss voltage dropping from the normal 14.2vdc or so. Also the nice little yellow light that comes with the B&C regulator will light up on the panel. At that point you don?t care what the standby alternaor is putting out, just that buss voltage is maintained. Dump this shunt and reduce your connections - always a good idea.
- Figure out how you will keep the battery connected to the standby alternator if you have a failure, such you opening the master as an immediate action to smoke in the cabin, a component or connection failure.

As I have posted on several occasions, I strongly recommend a two battery, single alternator scheme as a superior starting point for IFR RVs. A second alternator can be added if desired, but it is more important to have two batteries in a thoughtful design so that you mitigate most common single point failure risks.

Carl

Carl,

good catch! I have basically taken Bob Nuckoll's Z12 and modified it (Thanks Bob for sharing his drawings and knowledge!). I haven't spend enough time to check all the details. The battery will be a Concorde 24AH (This batt. is available in Europe, the Odyssey is not very common here -I'll have to go with the standard option).

For the moment I have removed all wire size descriptions.

My load analysis tells me the main alternator (ALT-1) would be above 80% at standard IFR ops with pitot heat ON. This is a little bit misleading as our rules require to calculate with the equipment's max draw and 1radio in TX mode -stupid but this is the local regulation. To comply I have the standby alt (ALT-2) always ON. 1 alternator is not an option for me.

B&C will not light up, I am not going to use the lights with the current layout (mentioned in my OP).

I agree on the split bus system eg Z14, but this in my opinion is safer only if you go with 2batteries and 2 alternators. If you go with 2 batteries and 1 alternator, you will always be limited by the remaining batteries capacity if the alternator fails.
 
SNIP
B&C will not light up, I am not going to use the lights with the current layout (mentioned in my OP).

I agree on the split bus system eg Z14, but this in my opinion is safer only if you go with 2batteries and 2 alternators. If you go with 2 batteries and 1 alternator, you will always be limited by the remaining batteries capacity if the alternator fails.

Adding the tiny yellow light is strongly recommended. It will be your first indication of an electrical fault. I can think of no reason not to add it and it comes included with the B&C regulator.

Yep - a second alternator will mitigate the loss of the primary alternator - but nothing else. So the single battery, dual alternator schemes can fail and leave you with two perfect alternators and no power to the panel (as has happened in twin airplanes). I also offer you can do better than the Z14 drawing for a two battery IFR bird, and be less complicated than what you have posted.

But as with all such things it is your bird, build it as you want.

Carl
 
Adding the tiny yellow light is strongly recommended. It will be your first indication of an electrical fault. I can think of no reason not to add it and it comes included with the B&C regulator....
Carl

The reason is: If I can preset the warning in the G3X Touch as described in my 1st post, the LV warning lights from the B&C regulators would be redundant.
 
I am planning to have two batteries as Carl mentioned.

If someone has a tried and true battery isolator solution, I would appreicate hearing about it. (My apologies if this a bit too off topic, I hope not).

Charlie
 
I am planning to have two batteries as Carl mentioned.

If someone has a tried and true battery isolator solution, I would appreicate hearing about it. (My apologies if this a bit too off topic, I hope not).

Charlie

Charlie, have a look at the Z14 diagram from Bob N.
 
Igor,

The switch layouts strike me as confusing. Perhaps I can suggest an alternate way to lay out the switches. My recommendation is 3 switches:
1. Master (not the Cessna split master)
2. ALT1/OFF/ALT2
3. Ess bus

A couple of comments:
Not sure I fully understand the reason for having both alternators on at the same time. They are not additive. The loads will use the output with the highest voltage, and the other one will be basically invisible. I recommend running on the primary alternator, then when you get a low voltage alarm on the EFIS you know it has failed. You can switch over to the backup alternator. As long as the bus voltage stays stable (not declining) you know it is supplying enough current for the loads. When running with both on, and less than 30A load, you will not know that one of them has failed.

As far as a second battery for IFR operations, most EFIS now have a backup battery capability, either built-in like the G5 or Dynon D10, or an external battery backup like the TCW product. A backup radio could be a handheld with headset and antenna adapters. In other words, IMO you don't need a whole bus backup, just key instruments to stay safe.

Just my 2 cents. Enjoy the -10!
 
SNIP...

Not sure I fully understand the reason for having both alternators on at the same time. They are not additive. The loads will use the output with the highest voltage, and the other one will be basically invisible. I recommend running on the primary alternator, then when you get a low voltage alarm on the EFIS you know it has failed. You can switch over to the backup alternator. As long as the bus voltage stays stable (not declining) you know it is supplying enough current for the loads. When running with both on, and less than 30A load, you will not know that one of them has failed.

...SNIP

A standby alternator, like the B&C vacuum pad unit, is on all the time and only has a current output when buss voltage drops below a set level, as would be the case if the primary alternator failed. No pilot action required or desired.

You know the standby alternaor is carrying the load by buss voltage stabizing at the lower set point (typically about 13.5vdc) and if you have the B&C unit there is a yellow indicator light that you can mount on the panel.

Carl
 
ESSENTIAL BUS:
Peak draw: 42.5 Amps
Typical draw: 21 Amps


I would go with an 50 Amp Klixon 5TC50-50 (85% capacity at peak draw) breaker between MAIN BUS and ESSENTIAL. This breaker is much more compact compared to the 60 Amp breaker.

The Diode between MAIN BUS and ESSENTIAL is there just in case the ESS BUS Contactor fails.

Should the MAIN BUS Contactor fail open, ALT1 could still supply everything through the Deuce Schottky Diode incl. battery charge.

This should not happen normally;
-let's assume I have a flat battery (24Ah),
-the MAIN BUS Contactor has failed open
-ALT2 is OFF
-ALT1 (60Amp) would try to feed everything on MAIN BUS and ESSENTIAL + Battery charge

-what loads shall I expect to see across the the CB from MAIN BUS to ESSENTIAL? My concern is the 50Amp circuit breaker


-opinions?
 
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Loadmeter

Hi Igor,
very interested in the hall effect sensors,
what load meter are you using?
Does it go to the EFIS as well?
 
The Diode between MAIN BUS and ESSENTIAL is there just in case the ESS BUS Contactor fails.

Should the MAIN BUS Contactor fail open, ALT1 could still supply everything through the Deuce Schottky Diode incl. battery charge.

This should not happen normally;
-let's assume I have a flat battery (24Ah),
-the MAIN BUS Contactor has failed open
-ALT2 is OFF
-ALT1 (60Amp) would try to feed everything on MAIN BUS and ESSENTIAL + Battery charge

-what loads shall I expect to see across the the CB from MAIN BUS to ESSENTIAL? My concern is the 50Amp circuit breaker.
-opinions?
Some thoughts:
- If your battery is flat, this is a hard ?ground the airplane? issue. Use a real charger to bring it back, or better yet replace it as most AGM batteries suffer permanent capacity loss if you abuse it (e.g. leave the master on).
- I suggest you eliminate the ground power jump connection. This is a left over from vacuum driven gyros and mags. In other words, never jump start your airplane. You will be launching into the ether with no clue of battery capacity, if any. On top of that, these are massively clumkly plugs with big fat wires - both are on the list of things to minimize in our airplane.
- On loads for each alternator, you will need to carefully adjust each voltage regulator to make sure you have current flowing as you think you do (for each of your primary and back up modes). Adding diodes complicates this as voltage drop across the diode needs to be measured to achieve the load balance you want.
- Running everything off the one 60 amp alternator is not an issue. Even if you have low charge lithium batteries they will not take more current than associated with the buss voltage, and buss voltage will drop under heavy current load. So unless you are doing something weird the alternator will carry the load and buss voltage will increase with time. Note however that 60 amp alternators will put out more than 60 amps, so upsize your current limiter to 70 amps. But again if you are trying to use the alternator to breath life into a dead battery, you are violating a prime rule as discussed above.
- On my planes I do add a ?shore power? breaker to the main buss. I use this to connect my 30 amp regulated power supply using a short #14 jumper cable to run the plane on the ground. 30 amps is more than enough to run the whole panel and to keep the batteries topped off (just like the alternator does). In practice with both (charged) batteries on line and all avionics up - current draw is about 10 amps.

Carl
 
Some thoughts:
- If your battery is flat, this is a hard “ground the airplane” issue. Use a real charger to bring it back, or better yet replace it as most AGM batteries suffer permanent capacity loss if you abuse it (e.g. leave the master on).

You are right, bad wording from my side. I meant the situation when for some reason the battery was discharged in flight (wrong procedures etc).

- I suggest you eliminate the ground power jump connection. This is a left over from vacuum driven gyros and mags. In other words, never jump start your airplane. You will be launching into the ether with no clue of battery capacity, if any. On top of that, these are massively clumkly plugs with big fat wires - both are on the list of things to minimize in our airplane.

Already installed very close to the battery for the purpose of ground maintenance, avionics setup and battery recharge.

- On loads for each alternator, you will need to carefully adjust each voltage regulator to make sure you have current flowing as you think you do (for each of your primary and back up modes). Adding diodes complicates this as voltage drop across the diode needs to be measured to achieve the load balance you want.

Normal ops is: both ESS(ESS Contactor) + ALT2 and MASTER (BATTERY Contactor) + ALT1 ON.
Normal current flow is expected to pass through the contactors and 'avoid' the Schottky Diode with voltage drop. Only in case the BATTERY Contactor fails open, current starts flowing through the diode from MAIN BUS to ESS BUS. Correct me if wrong.

- On loads for each alternator, you will need to carefully adjust each voltage regulator to make sure you have current flowing as you think you do (for each of your primary and back up modes). Adding diodes complicates this as voltage drop across the diode needs to be measured to achieve the load balance you want.

ALT 1 reg. is set to 14.4V
ALT 2 at 13.8V
-With both ALTs ON, ALT2 should take over as soon as Voltage drops to 13.8V sensed at the ESS BUS
-Regulators sense their respective bus they are feeding. In case ALT 2 failed, ALT 1 output won't be effected by the voltage drop across the diode to ESS BUS.
Should ALT 1 fail, ALT 2 can still feed both the ESS and MAIN BUS as long as both contactors are closed and load shedding performed by pilot.

Note however that 60 amp alternators will put out more than 60 amps, so upsize your current limiter to 70 amps. But again if you are trying to use the alternator to breath life into a dead battery, you are violating a prime rule as discussed above.
- On my planes I do add a “shore power” breaker to the main buss. I use this to connect my 30 amp regulated power supply using a short #14 jumper cable to run the plane on the ground. 30 amps is more than enough to run the whole panel and to keep the batteries topped off (just like the alternator does). In practice with both (charged) batteries on line and all avionics up - current draw is about 10 amps.

Carl

B&C 60Amp Alternator install manual says to use a 70amp CB or 60amp ANL, I'm going with the ANL.

I'll have a look at the shore power breakers.

Thank you for your comments.
 
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Why build such a simple aircraft with such a complicated electrical system?

5 busses, multiple relays, high current diodes etc., is it really necessary or is it just fun to work on the designs?
 
Why build such a simple aircraft with such a complicated electrical system?

5 busses, multiple relays, high current diodes etc., is it really necessary or is it just fun to work on the designs?

I could eliminate the avionics buses but it allows me to perform load shedding if I need to (ALT 1 failure / ground ops/flight preparation with engine out / engine start without additional draw from avionics on cold days)

The diode between MAIN BUS and ESS BUS is there for redundancy. I'm planing IFR+night ops.
 
I have to agree with Walt on this one. In the quest for redundancy, you'll likely get lower reliability and tricky troubleshooting in the future.

The great think about Exp aircraft is we can build what we want! :)
 
Replace the 40 amp ANL alternator fuse with a 35 amp and move it close to
the E-Bus. The alternator does not need protection, the E-Bus does.
 
Hi Egor,

Have you seen Bob Nuckolls' document called "Magneto Switch Options"? Some important differences from what you show.

http://www.aeroelectric.com/articles/MagnetoSwitchOptions.pdf

I see the v32 jpg but not the pdf.
.
.
.

John,

I think I have the same setup as suggested by Bob N. unless I missed something? -except the Right Mag is not grounded (Left Mag (SureFly) is not impulse coupled). And I have omitted the BO pole by mistake but this one is not connected to anything either.

New PDF link: OM ELA Basic Electr Scheme v.32

Here is another guide from B&C which corresponds to Bob's setup + MOV across the S pole. https://bandc.com/wp-content/uploads/2019/03/s811-1_contactor_501-3_fig4.pdf
 
Replace the 40 amp ANL alternator fuse with a 35 amp and move it close to
the E-Bus. The alternator does not need protection, the E-Bus does.

Joe,

I'm a little bit puzzled with this. B&C recommends the 40amp ANL for the backup alternator. I understand it's not going to put out more than 32amps untill I go above 2700rpm on the engine. So, yes 35 seems to be sufficient but will it make any difference?

You are right about protecting the ESS BUS:

-if ANL placed on the engine side of firewall:
  1. (condition: short is developed in the alternator), the ANL will protect rest of the wire leading through the firewall to the ESS BUS. Firewall feed through remains hot from ESS BUS.
  2. (condition: alternator has no fault but wire makes contact with firewall) - no protection to ESS BUS until ESS BUS is isolated. (ESS Switch to OFF)

-if ANL placed on the cockpit side of firewall:

  1. (condition: short is developed in the alternator), the ANL will protect the wire leading from the ANL to the ESS BUS.
  2. (condition: alternator has no fault but wire makes contact with firewall), ESS BUS is protected but short will be present until ALT 2 is turned OFF (ESS Switch to ESS BUS only)

Both variants IF specific faults develop require pilot action, but cockpit side protection will allow for ESS BUS to remain available.

So yes, I'm now leaning towards placing the ANL on the cockpit side of FW - thoughts?
 
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The aux alternator "B" lead definitely needs to be protected between the E-Bus and
the firewall. If that wire shorts to the firewall, battery current will cause smoke or fire.
Take a look at an ANL data sheet. A 35 AMP ANL will carry 80 amps indefinitely without
blowing. How many amps will the E-Bus normally draw? I think that a 35 AMP is adequate.
Isn't the E-Bus switch normally shut off and E-Bus current flows through the diode?
What happens if the "B" lead shorts out? Does the 50 amp circuit breaker trip
before the ANL blows? Or does the diode smoke? Do any of Bob N's diagrams
have the aux alternator connected directly to the E-Bus?
There are 3 unnecessary points of possible failure between the E-Bus and the avionics bus:
a 20 amp breaker, a switch, and a relay. Why not eliminate the avionics bus
and power the avionics from the E-Bus?
Why have a 50 amp breaker? The E-Bus is not going to short out if properly installed.
Since the E-Bus is essential, eliminate unnecessary points of failure.
 
Isn't the E-Bus switch normally shut off and E-Bus current flows through the diode?

-no, normally the ESS BUS is powered from it's own relay and diode feed is there only in case the ESS BUS relay fails open

If that wire shorts to the firewall, battery current will cause smoke or fire.
Take a look at an ANL data sheet. A 35 AMP ANL will carry 80 amps indefinitely without
blowing. How many amps will the E-Bus normally draw? I think that a 35 AMP is adequate.

-rating makes sense, the idea of protecting the bus is priority -valid point. but this does not eliminate the case when the B lead shorts to the firewall and ALT 1 keeps running. You still have fumes or fire until you kill the ALT, at least you don't loose the ESS BUS, I take that.

What happens if the "B" lead shorts out? Does the 50 amp circuit breaker trip
before the ANL blows? Or does the diode smoke? Do any of Bob N's diagrams
have the aux alternator connected directly to the E-Bus?

-main ESS feed is through the ESS Relay; the 50amp CB shouldn't trip before the ANL does. If it does, it can be reset (1time), by that time ANL should have melted already as ESS BUS still fed from relay. Diode is rated up to 100A.

The split backbone allows for big fault isolation, thus should either part -MAIN or ESS develop a fault/short, I could possibly isolate the wrong side and land asap without loosing all systems.

Why have a 50 amp breaker? The E-Bus is not going to short out if properly installed.

ESS BUS max load is 30A + possible batt recharge, so that 50A breaker is there to protect the diode, rating is to prevent nuisance trips & isolate the MAIN BUS should the ESS BUS develop a total failure.

AVIONICS BUS is a requirement by local authority (I live in Europe) and my preference as well. The risk of total avionics loss is split between two AVIONICS BUSES (MAIN and ESS).
 
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John,

I think I have the same setup as suggested by Bob N. unless I missed something? -except the Right Mag is not grounded (Left Mag (SureFly) is not impulse coupled). And I have omitted the BO pole by mistake but this one is not connected to anything either.

New PDF link: OM ELA Basic Electr Scheme v.32

Here is another guide from B&C which corresponds to Bob's setup + MOV across the S pole. https://bandc.com/wp-content/uploads/2019/03/s811-1_contactor_501-3_fig4.pdf

Hi Egor,

My observations are:
  • Surefly will be your engine start magneto, conventionally on the left as you show. Surefly retards timing for start and provides high energy spark, no need for right mag to be impulse coupled.
  • If right magneto is not impulse coupled, it should be locked out during start by adding jumper to Gerdes switch between R terminal and its adjacent GND terminal.
  • The central GND terminal of the Gerdes switch should be connected to the mag wire shields only, not to ground of the airframe.

I was able to view the pdf this time but I can't download it so I use the jpg. Oftentimes jpg is not detailed enough but this one is.
.
.
.
 
Hi Igor,
Which Diode did you use for the Deuce diode?
standard schotkky?
or very low dropout FET driven equivalent such as:
https://media.digikey.com/pdf/Data Sheets/ST Microelectronics PDFS/SPV1002.pdf


John,

I think I have the same setup as suggested by Bob N. unless I missed something? -except the Right Mag is not grounded (Left Mag (SureFly) is not impulse coupled). And I have omitted the BO pole by mistake but this one is not connected to anything either.

New PDF link: OM ELA Basic Electr Scheme v.32

Here is another guide from B&C which corresponds to Bob's setup + MOV across the S pole. https://bandc.com/wp-content/uploads/2019/03/s811-1_contactor_501-3_fig4.pdf
 
Hi John,

thank you, good catch! I will use a jumper between R and and the adjacent GND.

I am using an ACS key switch and according to their schematics the center GND terminal(5) should be connected to nearest structural member.

under Notes:
C. Use SHIELDED wire on all connections and ground shielding to nearest structural member.

http://acsproducts.co/wp-content/uploads/2013/10/Wiring-Diagram.jpg


Hi Egor,

My observations are:
  • Surefly will be your engine start magneto, conventionally on the left as you show. Surefly retards timing for start and provides high energy spark, no need for right mag to be impulse coupled.
  • If right magneto is not impulse coupled, it should be locked out during start by adding jumper to Gerdes switch between R terminal and its adjacent GND terminal.
  • The central GND terminal of the Gerdes switch should be connected to the mag wire shields only, not to ground of the airframe.

I was able to view the pdf this time but I can't download it so I use the jpg. Oftentimes jpg is not detailed enough but this one is.
.
.
.
 
I would ask Bob on Aeroelectric List about keyed start switch ground connections

... I am using an ACS key switch and according to their schematics the center GND terminal(5) should be connected to nearest structural member.

under Notes:
C. Use SHIELDED wire on all connections and ground shielding to nearest structural member.

http://acsproducts.co/wp-content/uploads/2013/10/Wiring-Diagram.jpg

Hi Egor,

I believe the ACS switch and the Gerdes switch Bob Nuckolls speaks to in "MagnetoSwitchOptions.pdf" are the same or functionally the same. You could ask Bob on Aeroelectric List about the ground connections.
 
Hi Egor,

I believe the ACS switch and the Gerdes switch Bob Nuckolls speaks to in "MagnetoSwitchOptions.pdf" are the same or functionally the same. You could ask Bob on Aeroelectric List about the ground connections.



John,

You were right! Thx!

Here is Bob?s answer to my question:

There is no BENEFIT for connecting to ground locally . . .
but there is RISK for damaging p-lead shields due to
starter currents flowing in a ground-loop situation.
Wire per examples in the z-figures where shields are
terminated at the mags and NO grounds are added at
the switch(es) whether a o-l-r-b-s keyswitch or
toggles.
 
I really like the general concept with a high integrity essential bus that can be fed from the main bus, the battery and its own alternator. But, at a detailed level...

1. Have you considered placing the ANL 35 fuse between the battery contactor and the essential bus contactor. If you did that, you could use a smaller wire than 6 AWG for the feed to the ess bus and you could replace the ess bus contactor with a 40 amp relay - both worthwhile weight savings and also a useful reduction in the current consumption.

2. The ess bus backup feed has a 50 amp breaker on it, so the diode would need be capable of taking whatever the breaker lets through, so 50 amps continuously and probably rather more. If we assume a forward voltage of 0.5 volts, 50 amps will generate 25 watts of heat, which is a big heat sink (around 5" x 5" x 1" at a guess). Are you sure you need all those amps?

Raiz
 
I really like the general concept with a high integrity essential bus that can be fed from the main bus, the battery and its own alternator. But, at a detailed level...

1. Have you considered placing the ANL 35 fuse between the battery contactor and the essential bus contactor. If you did that, you could use a smaller wire than 6 AWG for the feed to the ess bus and you could replace the ess bus contactor with a 40 amp relay - both worthwhile weight savings and also a useful reduction in the current consumption.

2. The ess bus backup feed has a 50 amp breaker on it, so the diode would need be capable of taking whatever the breaker lets through, so 50 amps continuously and probably rather more. If we assume a forward voltage of 0.5 volts, 50 amps will generate 25 watts of heat, which is a big heat sink (around 5" x 5" x 1" at a guess). Are you sure you need all those amps?

Raiz

Raiz,

thank you for your comments!

1. Assume the ALT-2 develops a hard fault
If I placed the ANL 35 fuse between battery and the ess contactor -the 50Amp CB protecting the diode gets popped and the blown ANL35 would isolate the entire ESS bus. -the ESS bus is lost completely. -or maybe I overlooked something?

2. yes the heat sink is big, I expect (load analysis) the ESS BUS will take max 30amps at peak, 16 at normal. The 50 amps sized CB is there to avoid nuisance trips at spikes. Should the ESS BUS develop a hard fault, the CB would help with isolating the MAIN BUS from the ESS BUS.
The contactors (3x GX11-SA) I use need very little Amps to hold closed and they are all the same. I agree: there is added weight but they can be interchanged 'in the field' if needed. Thus, I could replace the main or ess contactors with the ext power contactor if needed (serves as spare part on board).
 
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+ I plan to move the autopilot controller and servos from the AVIONX ESS bus to the ESS BUS to avoid inductive loads on the avionics bus..
 
Supik, I missed the fact you plan to run with alt 2 on and the ess bus contactor closed, in normal flight. In those circumstances, I agree with your placement of the fuse, but I now I also agree with the earlier comments about the complexity.

Raiz
 
Here is my calculation to avoid a situation when the AVIONICS ESS CB trips before the equipment on this bus does. Taking care about the AVIONX ESS BUS CB in series:

The total PEAK DRAW on the AVIONX BUS is 9.04 Amps.

The biggest Delta PEAK DRAW vs CB protection is on the GTN COM connector: 5.98 Amp

When I sum up the Total BUS Peak Draw (9.04A) + Top Delta Peak of the GTN COM connection (assume this connection is shorted): TOTAL PEAK with fault on the GTN COM side equals 15.02 Amp

Adding 20% reserve - I would need 18.8 Amp minimum CB rating for the AVIONX ESS bus. Thus a 20Amp CB is enough.

The AVIONX MAIN bus would require a 25Amp CB..

Is my approach correct?

avionx_ess_bus_cb_742.jpg
 
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