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E-Bus alternate feed: switch or relay?

KayS

Well Known Member
Hi All,

didn't find an answer to my question in past threads... I want to install an E-Bus (name it essential, endurance, emergency or whatever) in my electrical system. The devices i intend to put on the E-Bus will draw well below 20 amps.

Bob's book (Aeroelectric Connection) shows to ways to connect the E-Bus to the main battery: On Z-12 via a simple Switch and on Z-13/8 with a switch and a relay.

I understand that one can transmit more amps through an relay than through an toggle switch. But are there any other reasons for the switch/relay combination?

My toggles are good for 20A so i should be fine...? I just don't want to install an relay.

Cheers
Kay
 
Kay,

The relay is really only a requirement if a higher current is needed than your switch is rated for. A switch can have the advantage that you can put the 2 sides in parallel for some level of redundancy. I really don't like relays. They are old technology but required in some instances. Do make sure you look at the specs of your switch carefully and get a good switch like a Honeywell TL series.
 
Relays are simply electrically controlled switches that are designed to handle more current than a traditional switch which make/break the connections without damage due to arcing etc. In other words, they perform the job better than a simple switch when the current is higher.

Bevan
 
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Hi All,


Bob's book (Aeroelectric Connection) shows to ways to connect the E-Bus to the main battery: On Z-12 via a simple Switch and on Z-13/8 with a switch and a relay.

I understand that one can transmit more amps through an relay than through an toggle switch. But are there any other reasons for the switch/relay combination?

Cheers
Kay

Hi Kay. I scratched my head over this one but eventually managed to figure it out. There is more to it than just the current capability of the switch. On Z 13/8 there is an asterisk next to the feeder from the battery bus to the E-Bus relay, denoting that this wire should be kept to 6 inches or less. This is because this wire is always "hot" even when the whole electrical system is shut down.

I can't find it right now, but somewhere Bob has a note saying that any "hot" wiring fused at more than I believe 10 amps should ideally be 6 inches but maximum 12 inches to reduce fire risk in a crash.

If you take a look at Z 10/8 there is a dashed box around the batteries and relays with the note that items inside the box are to be located "Aft with Battery".

So the problem with following these Z diagrams exactly is that they are generic and not really specific to a particular airplane. It is necessary for us to fine tune wiring sizes and lengths to suit our own airplane's configuration. I guess if the battery were really close to the panel it might be ok to use a switch but with my firewall mounted battery I opted to place a battery bus immediately behind the firewall with the shortest possible wiring run to the battery, and then the E-bus relay is mounted right next to the battery bus.
 
Essential bus

Here's a diagram from the aeroelectric connection book that I have:

AeroElectric-Essential-Bus-17-3.png


Shows a basic switch and a fusible link protecting the essential bus. Don't forget the diode. The book is great, and it does take some investment to understand all the details. I have really enjoyed this part of the build - I'm happy that my RV-8 didn't come with a completed harness.
 
Relays are simply electrically controlled switches that are designed to handle more current than a traditional switch which make/break the connections without damage due to arcing etc. In other words, they perform the job better than a simple switch when the current is higher.

Bevan

Errr, well, relay contacts still get arcing (unless you install a clamping diode), theyre just made more robust so they can take more arc pitting. But if you can use a switch, use a switch. Go with simple. Its just a human operated relay!
 
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Given the choice between a relay and a switch -

If the current rating is OK in both, the switch will have less physical connections once the relay drive circuit is included. Reliability is based both on components and physical connections.

I'd go (and did) for a switch....:)
 
With todays modern glass panels that generally have dual power inputs for most critical items, and back-up batteries to support them, what advantage does a ESS buss have?

The way I see it the ESS buss adds both parts count and failure points, especially the diode which if it fails likely kills most of your avionics (perhaps at a critical time when power failure could cause high workload like IFR). Don't think diodes fail... think again.

I think the orginal premise for the ESS buss was easy load shed for a VFR aircraft, not so sure it's a great feature in today's typical glass panel design.
 
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I agree with Walt. Ess busses were designed for large aircraft with lots of systems that need load shedding for failure modes. Most small airplanes do not need them. The biggest issue in a small plane is alternator failure. Almost every current draw in the plane has an on off switch. Problem solved. Keep it simple and light.

Bob burns
Rv-4 n82rb
 
Hi All,

didn't find an answer to my question in past threads... I want to install an E-Bus (name it essential, endurance, emergency or whatever) in my electrical system. The devices i intend to put on the E-Bus will draw well below 20 amps.

...

Cheers
Kay

I just checked some pictures i have taken of my SkyView in flight and it shows i was drawing only 6 amps.

With backup batteries on pretty much everything, do you really need an E-bus?

Just asking.
 
I don?t know your typical mission, but for most of us Sunday flyers I also agree with reassessing the need for an E bus. I intalled one and have never used it once or known of anyone else ever using one. I also had an AUX bus for brown out. After flying several hundred hours I now think all that redundancy, for me, was silly and I always regretted adding the complexity and weight.
Keeping it simple and light is very good advice for most of us.


Tim Andres
 
...and

Something that no-one has mentioned is that using a relay will allow you to keep the big wire runs short and use a small wire for control.

For example:

If you are switching 20 amps, you will be using a 10 or 12 AWG wire, using a switch, those relatively large wires must run all the way to the switch.

Using the relay, you can place the relay near the load, and run a much smaller wire, like 22 AWG to the switch as a control wire.

Obviously, there are multiple ways to accomplish the switching task; the switch and relay are both tools...use the best tool for the job at hand.
 
With todays modern glass panels that generally have dual power inputs for most critical items, and back-up batteries to support them, what advantage does a ESS buss have?

The way I see it the ESS buss adds both parts count and failure points, especially the diode which if it fails likely kills most of your avionics (perhaps at a critical time when power failure could cause high workload like IFR). Don't think diodes fail... think again.

I think the orginal premise for the ESS buss was easy load shed for a VFR aircraft, not so sure it's a great feature in today's typical glass panel design.

Walt,

Don't these modern systems just put the diodes inside the box, with theoretically the same risk?. I am not an electrical expert, but I thought there needs to be diodes whenever you have two battery sources to prevent cross-draining.

I am discussing an ESS buss fed from a second battery. I tend to agree that a second buss, just to have two, doesn't make that much sense.

Larry
 
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Something that no-one has mentioned is that using a relay will allow you to keep the big wire runs short and use a small wire for control.

For example:

If you are switching 20 amps, you will be using a 10 or 12 AWG wire, using a switch, those relatively large wires must run all the way to the switch.

Using the relay, you can place the relay near the load, and run a much smaller wire, like 22 AWG to the switch as a control wire.

Obviously, there are multiple ways to accomplish the switching task; the switch and relay are both tools...use the best tool for the job at hand.

I am going through this right now. I prefer a switch, but in the case of the 10, that means running an unfused line, with no means for disconnection, the length of the fuselage and a relay back at the battery prevents that. I suppose I could add a fuse at the battery tap, but prefer a breaker on the panel in case it needs to be reset in flight.

Larry
 
I don?t know your typical mission, but for most of us Sunday flyers I also agree with reassessing the need for an E bus. I intalled one and have never used it once or known of anyone else ever using one. I also had an AUX bus for brown out. After flying several hundred hours I now think all that redundancy, for me, was silly and I always regretted adding the complexity and weight.
Keeping it simple and light is very good advice for most of us.


Tim Andres
When I was designing my electrical system, I took that into account and understood where I was coming from. I had been flying antiques without any electrical system so I knew airplanes fly just fine without radios.

I also realized that with a battery backup in my EFIS (D100 at that time) and the handheld GPS that was always being charged, I knew I could keep the plane upright and navigate.

Now, three panels later, the 496 is still in there and will eventually be replaced by another handheld GPS, regardless of what other GPS nav system I might have on board. The SkyView has its own battery only now, in addition to that, I have a Dynon PocketPanel to help keep me upright.

My fear with all the complexity we are installing in our planes is that when things go bad, we will either take an incorrect action or forget about it.

Simple is always best.

So is practicing! I know of one RV builder/pilot who landed 15 miles short of his uncontrolled home airport because of an electrical problem that took out his radio. It was day VFR conditions and he told me how nervous he was making that landing and what a bad job he did of getting it on the ground.

While being on the ground is good, don't rush things to the point of making bad choices. In his case, he landed at an unfamiliar airport, one he had never landed at before, let his stress level rise, etc.

What I'm getting at is, if you install emergency systems, practice with them. Practice with them enough that they don't feel like emergency systems. (The same goes for crosswind, short, soft field, and engine out landings.)
 
Ed,
That 6" spec was for *un*-fused (unprotected) feeders.

The 'essential bus' came about precisely to deal with alternator failure, and not for 'large' a/c; not very many homebuilts could be considered large.

There are variations on the meaning of 'simple'. One big bus and lots of switches is 'simple'. Two buses and flipping one or two switches when dealing with an alternator failure in a plane with both electrically dependent instruments and engine while in IMC...that might meet the definition of 'simple', too. If you're day VFR with magnetos, then multiple buses are pointless. Just turn off the master & fly home. But if you have an electrically dependent engine, or you're IFR, the math changes. Will your battery(s) carry you to the end of your IFR flight plan, including the alternate, without breaking a sweat? No? If simply flipping a switch or two could make that happen, would you consider it worth the trouble while wiring the electrical system?

On switches vs relays: Looks like Bob covered the best reason for a relay before I could hit 'send'.
 
Walt,

Don't these modern systems just put the diodes inside the box, with theoretically the same risk?. I am not an electrical expert, but I thought there needs to be diodes whenever you have two battery sources to prevent cross-draining.

I am discussing an ESS buss fed from a second battery. I tend to agree that a second buss, just to have two, doesn't make that much sense.

Larry

Yes the boxes with dual power inputs do so with diode isolation.

An ESS buss with a second battery as the source is basically a back-up battery system, not an ESS buss as typically thoght of.
 
So, who's defining 'essential bus' (or 'endurance bus')?

From the Aeroelectric Connection book:

A Short Discussion on the ?Endurance? Bus
For a number of years the ENDURANCE bus was called the
ESSENTIAL bus . . . bad choice. Words like ?emergency?,
?critical?, and ?essential? conjure up tense images of things
going badly in the airplane. I?ve had a lot of queries from
builders asking about running flaps, fuel pumps, and lighting
systems from the e-bus. The purpose of an e-bus with two
feeds was to provide reliable power for the minimum
equipment necessary for comfortable continuation for the en
route phase of flight using only the battery for power.
Unless you?re planning TWO alternators (Z-12, Z-13 or Z-
14) then the purpose of the e-bus is to provide a minimum
power consumption mode of operation in a battery-only
condition such that comfortable arrival is assured after you
have a clearance to land. Then, you can re-close the battery
master and run any accessories you like on whatever
remains of the battery?s energy. If the battery goes flat then,
it doesn?t matter.
What endurance do you want from the battery? If your
design goal is to permit only fuel aboard to dictate
endurance, then your battery capacity needs to be matched
to your e-bus loads such that a fully charged battery will
carry the e-bus for time equal to or exceeding fuel duration.
If your personal endurance value is less, then you can
increase the e-bus loads accordingly. Know further that a
battery?s useful capacity goes DOWN as load increases. An
18 AH battery may well have received that rating based on
a 20 hour discharge rate . . . or about 0.9 amps! If your
proposed e-bus loads are, say 3 amps, it is not reasonable to
expect 6 hours of performance from the 18 AH battery . . .
it WILL be less, probably more like 12-15 AH
Consider further that you?ll want to periodically test the
battery so as to KNOW its capacity or simply replace it
every year. The choice is yours. The goal is to KNOW how
long your battery will carry an e-bus load so that you can
depend upon it. Most single engine airplanes flying right
now have ?failed? batteries aboard . . . they cranked the
engine but do not carry enough energy for really useful
battery-only endurance. Worse yet, the pilots of those
airplanes don?t have a clue as to what the battery?s
capabilities are.
As you craft your dream project, keep in mind that the e-bus
and your battery maintenance philosophy can provide
system reliability that few single engine airplane drivers
enjoy. But you MUST understand how it works, what it?s
for and how to maintain it.
 
Simpler Endurance bus feed

When I built my -10 I used a two bus system. The second bus was an endurance, not emergency in the AeroElectric terminology. It had the things critical to flying, Lightspeed ignition, Radio, Com (to keep passengers calm), transponder and trim. (flying a -10 without trim is a issue and a very small load.) The Dynon screens have their own 45 minute backup battery. Its only function is to be able to operate with a failed master or to be able to quickly reduced power demand by turning off the master and the alt feed on.


The E bus was initially fed from the main bus thru a 30 amp fuse to a blocking diode. (I use fuses rather than circuit breakers) The E-bus switch went directly to the battery with a 40 amp fuse. The Dynon voltage pickup was from the E-bus, what you want to see in an emergency.


In the 40 hour period I did not like that there was a .3 to .4 V drop across the blocking diode. I checked at the normal bus and voltage was the expected 14.2. I did not like to look at voltage and see lower than 14 V, it required a double look to assure it was still good.

As a result, I rewired it and got rid of the blocking diode. I used a single pole double throw switch (SPDT ON-ON) The two feeds were same as before, one from the normal bus with a fuse and the second from the battery with fuse. The center went to the E-bus. Down was "normal" feed so the switch is down, the normal position for most switches while not in use.


Now the E-bus voltage was the same as the alternator output . From a failure analysis standpoint I had removed the diode, a very low failure item. Switches are a extremely low probability for failure.


AS an added note, I don't use an avionics bus. I have a four pole single throw switch (from Digikey). To isolate a radio, I can pull its fuse. Saves a bunch of wires.
 
I just checked some pictures i have taken of my SkyView in flight and it shows i was drawing only 6 amps.

With backup batteries on pretty much everything, do you really need an E-bus?

Just asking.

I don't have a backup battery, also not on my skyview. I voted for an backup alternator instead. An backup main battery, in my very personel opinion, doesn't make much sense.

btw... thank you all for the helpful responses here.
 
I don't have a backup battery, also not on my skyview. I voted for an backup alternator instead. An backup main battery, in my very personel opinion, doesn't make much sense.

btw... thank you all for the helpful responses here.

Keep in mind a backup alternator mitigates one risk only, the loss of the primary alternator. Twins (two engines, two alternators) have gone dark panel as a result of a common failure connection.

If the option is two alternators and single battery, or two batteries and single alternator, the later provides far more robust design opportunities.

Carl
 
Hi All,

didn't find an answer to my question in past threads... I want to install an E-Bus (name it essential, endurance, emergency or whatever) in my electrical system. The devices i intend to put on the E-Bus will draw well below 20 amps.

Bob's book (Aeroelectric Connection) shows to ways to connect the E-Bus to the main battery: On Z-12 via a simple Switch and on Z-13/8 with a switch and a relay.

I understand that one can transmit more amps through an relay than through an toggle switch. But are there any other reasons for the switch/relay combination?

My toggles are good for 20A so i should be fine...? I just don't want to install an relay.

Cheers
Kay
Kay,

Going back to your original question..... :)

First, you really should ask that kind of question over on the Matronics Aeroelectric List, instead of here. The reason should be obvious from this thread, where instead of answering your question, you're told that your whole idea is wrong (obviously, it's not, for your purposes).

I went back & looked at Z-12 & Z-13-8, and the reason for the switch vs relay feeding the E-bus is as you suggest, purely based on current. Z-12's E-bus is there as a '3rd layer', that would come into play only if both main and backup (20A) alternators go south. IIRC, Z-12 assumes that with magnetos powering a conventional engine, even the backup 20A alternator could handle all in-flight electrical loads. Note that both alternators feed the same point, on the load side of the master contactor. The idea is that if both alts are dead, you'd shed as much load as possible; therefore the 7A supply fuse to the E-bus and normal switch to feed it.

Z-13-8 assumes an 8 amp backup alternator, but it feeds the *battery side* of the master contactor, so it's available even with the master *off*. I *think* (but don't remember for certain) that Bob's idea with 13-8 is that you'd be using the 8A alternator as a 'range extender' rather than an unlimited endurance source, like the 20A backup would be in Z-12. Hence the relay for 15A load (greater than alternator capacity) on the E-bus instead of <7A load on the E-bus in Z-12. 15A would be right at the edge of the switches Bob specs for the drawings, so... we get a relay there. If you have a switch that can easily handle the full load of the E-bus, and wiring runs don't dictate a relay for shorter heavy gauge wires, then I'd use a switch. I did use a switch for similar purposes in the plane I'm building.

To repeat myself, sign up for the Aeroelectric List, and ask electrical questions there. The advice you get will be a lot more reliable than what you get here.

Charlie
 
Kay,

Going back to your original question..... :)

First, you really should ask that kind of question over on the Matronics Aeroelectric List, instead of here. The reason should be obvious from this thread, where instead of answering your question, you're told that your whole idea is wrong (obviously, it's not, for your purposes).

Charlie

Could not agree more!

http://forums.matronics.com/viewtopic.php?t=16768151&highlight=hot

Take a look at Bob Nuckoll's detailed reply to a similar question.
 
Short answer, Bob said that if the e-bus load exceeded 5A in Endurance Mode, then install a relay. Bob said that Legacy type aircraft design conventions of Max 5 A was to limit a battery's ability to start fires in the event of an aircraft accident. A 7A fuse on a 5A expected load is in place to limit the damage.
 
An e bus certainly doesn't solve every problem

For once, I have a relevant data point to add in an electrical discussion! Although I wish I could have skipped the whole thing...

Apologies in advance for my ignorance, since I'm not the builder and know very little about electrical systems. Although I'm learning more.

Last week, on a night flight on an IFR plan, fortunately in gorgeous VMC, I smelled a brief plastic-y burning smell and then everything on my avionics bus went dark. Except for my battery powered G5, for which I developed an even greater appreciation at that moment.

I later determined that I had blown the 15 amp fuse upstream of my diode.

When this happened, I flipped the ebus switch. Everything came back up, which made me happy, and then... everything on the avionics bus promptly died again.

Because I had now blown the 15 amp fuse upstream of the ebus switch.

I've rooted around under the panel since then, and everything is now working with the fuses replaced. I'm planning my next moves to keep this from happening again. But already I have some key lessons:

1. If installing a G5, pay the extra $ for the battery backup.

2. ATC is good at diagnosing electrical failures. Apparently losing comms and transponder simultaneously is a clear sign.....

3. Check the battery on your handheld before flying. Note that even if you do so, and even if the battery indicator is at "half," that handheld, which you have carried FOR YEARS for JUST SUCH AN EMERGENCY, might still go dead when you push the transmit button. :)

4. The principal problem with losing all comms at night is that it's hard to turn on the lights at airports. This never occurred to me during instrument training regarding lost comms.

5. Airports are extremely dark at night without runway lights. The green/white beacon can be readily identified but doesn't give you enough light to see. :)

6. ATC can turn on the lights for you, even at a non-towered field with pilot-controlled lighting! I somehow never realized this. Or at least they could at W96, maybe it has to be close to a big transmitter (which W96 presumably is). Can't tell you how grateful I was for that assistance.

7. ATC, for its part, is very grateful when you call PROMPTLY after ending a no-radio IFR flight. Proud to say that I managed to check that box.

8. An RV-9 can of course be readily landed with no flaps, even when it's still trimmed for 150 knots....

9. If instrument rated, always file an instrument flight plan for night flight, even in VMC. That way, if you lose comms, somebody will know that you need the lights turned on.

10. Flying and navigating in an RV at night with just a G5, and an iPad with Foreflight, is no major problem. Did I mention that the battery backup option for the G5 is a good value?
 
For once, I have a relevant data point to add in an electrical discussion! Although I wish I could have skipped the whole thing...

Apologies in advance for my ignorance, since I'm not the builder and know very little about electrical systems. Although I'm learning more.

Last week, on a night flight on an IFR plan, fortunately in gorgeous VMC, I smelled a brief plastic-y burning smell and then everything on my avionics bus went dark. Except for my battery powered G5, for which I developed an even greater appreciation at that moment.

I later determined that I had blown the 15 amp fuse upstream of my diode.

When this happened, I flipped the ebus switch. Everything came back up, which made me happy, and then... everything on the avionics bus promptly died again.

Because I had now blown the 15 amp fuse upstream of the ebus switch.

I've rooted around under the panel since then, and everything is now working with the fuses replaced. I'm planning my next moves to keep this from happening again. But already I have some key lessons:

1. If installing a G5, pay the extra $ for the battery backup.

2. ATC is good at diagnosing electrical failures. Apparently losing comms and transponder simultaneously is a clear sign.....

3. Check the battery on your handheld before flying. Note that even if you do so, and even if the battery indicator is at "half," that handheld, which you have carried FOR YEARS for JUST SUCH AN EMERGENCY, might still go dead when you push the transmit button. :)

4. The principal problem with losing all comms at night is that it's hard to turn on the lights at airports. This never occurred to me during instrument training regarding lost comms.

5. Airports are extremely dark at night without runway lights. The green/white beacon can be readily identified but doesn't give you enough light to see. :)

6. ATC can turn on the lights for you, even at a non-towered field with pilot-controlled lighting! I somehow never realized this. Or at least they could at W96, maybe it has to be close to a big transmitter (which W96 presumably is). Can't tell you how grateful I was for that assistance.

7. ATC, for its part, is very grateful when you call PROMPTLY after ending a no-radio IFR flight. Proud to say that I managed to check that box.

8. An RV-9 can of course be readily landed with no flaps, even when it's still trimmed for 150 knots....

9. If instrument rated, always file an instrument flight plan for night flight, even in VMC. That way, if you lose comms, somebody will know that you need the lights turned on.

10. Flying and navigating in an RV at night with just a G5, and an iPad with Foreflight, is no major problem. Did I mention that the battery backup option for the G5 is a good value?

So what was the root cause? How did you blow the fuse to your E-buss, in addition to the main buss?
 
Doug,

Please start a new thread on your experinece. Perhaps the discussion will shine a light on E buss design limitations.

Carl
 
Doug,

Please start a new thread on your experinece. Perhaps the discussion will shine a light on E buss design limitations.

Carl

Like, don't load the ebus with more than the feeder is fused for, and make sure that the downstream fuses aren't anywhere close to the value of the feeder fuse, and reasonable care that you can't have foreign objects shorting your ebus to ground, and...
 
I think I've already explained this badly

Apologies for being unclear.

The main bus was okay the whole time. I lost the avionics bus, when the fuse upstream of the diode blew. I then turned on the ebus switch, which sent power to the same avionics bus--briefly--before blowing the 15 amp ("feeder"?) fuse for that as well.

Basically my avionics bus decided to go into the 15-amp fuse-blowing business. Not sure what put it over the top, but I'm working on that now.


So what was the root cause? How did you blow the fuse to your E-buss, in addition to the main buss?
 
Apologies for drifting the thread, but have a directly related question to this incident.

I will have two batteries with a cross tie. I plan to run off of one and the second will feed a backup buss that feeds only key devices. This E buss needs to be switchable. I planned a 20 amp relay back at the battery, but also like the idea of a 20 amp toggle breaker. However, that leaves me a long un-fused run from the battery in the back. I could put an additional fuse back there, but not sure I like two fusable points on the same line.

Any thoughts from the experts?

Larry
 
Apologies for drifting the thread, but have a directly related question to this incident.

I will have two batteries with a cross tie. I plan to run off of one and the second will feed a backup buss that feeds only key devices. This E buss needs to be switchable. I planned a 20 amp relay back at the battery, but also like the idea of a 20 amp toggle breaker. However, that leaves me a long un-fused run from the battery in the back. I could put an additional fuse back there, but not sure I like two fusable points on the same line.

Any thoughts from the experts?

Larry
A few:
- Delete the cross tie and use two Master solenoids.
- Run both batteries in parallel (normal operation) unless there is an electrical problem. At that point open both masters to split the systems. For single alternator setups this immediate action dumps the non-vital loads as well as the power hungry master solenoids, and goes a long way toward isolating most potential failures. These loads are available at any time by shutting a Master - like just before landing.
- Each battery to have two, 30 amp avionics relays, a primary and alternate (when on they typically draw 100ma).
- Split your panel into Avionics #1 and Avionics #2. Avionics #1 will run on battery #1 via the primary relay, or battery #2 via the secondary relay if needed. Avionics #2 will do the same with battery #2. These loads will include all avionics, autopilot servos, Trim, Flaps and such.
- Run all larger loads and non-panel stuff off the common starter/alternator connection (it has power if either master solenoid is shut). Stuff here includes pitot heat, landing lights, nav/strobe, seat heaters, the mulitude of USB charging ports, etc.

Think of this as two E busses that can get power from either battery.

The objective here is to maintain IFR flight after a component/wire/junction failure with no pilot action. Minor pilot action (moving a switch from normal to alternate) will restore the rest of the panel.

With two PC-625 batteries a typical dual EFIS IFR install with two radios should have at least 2.5hrs of reserve electrical power capacity. Belts and suppenders would be to add a standby alternator - but most will not need this. I put one on the RV-10 but will not on the new RV-8 as I sharpened my pencil on load analysis.

Carl
 
Q.

- Run both batteries in parallel (normal operation) unless there is an electrical problem. At that point open both masters to split the systems.


Q. How would an electrical system problem show itself with two batteries run in parallel?

I could see a charging system problem showing up, but the two batteries would only provide additional capacity...
 
- Run both batteries in parallel (normal operation) unless there is an electrical problem. At that point open both masters to split the systems.


Q. How would an electrical system problem show itself with two batteries run in parallel?

I could see a charging system problem showing up, but the two batteries would only provide additional capacity...

An electrical fault will show up exactly the same way as if running one battery. Again, the immediate action for any electrical fault is to open both master solenoids. This places the system in the most stable condition. Once established the pilot has option to investigate or just land.

No charging system problems, period. The alternator does not care if one or two batteries, and the batteries mostly don't care if in parallel (however same chemistry and identical batteries makes life simpler).

Two batteries in not about adding capacity (but are sized to achieve a capacity design target). Two batteries are for in depth redundancy - and to allow for graceful degradation after a fault as compared to a dark panel. Faults will happen - design to either accept the fault or a way to mitigate it. Look beyond the simple alternator failure risk. The more severe risks have nothing to do with the alternator.

Carl
 
Schematic

Carl; Can you please send me a copy of your RV10 elec schematic. I think this is the best, simplest, safest system I have seen proposed. 2 alternators, feeding 2 batts feeding 2 avionics busses. Easily separated or tied together. I think you are right about the gear drive 30 amp alt. Its biggest advantage would be allowing you to loose the belt, proceed on to dest, turn around and go home, IFR. Then put on on a new belt in the comfort of home.

Thanks,

[email protected]
 
A few:
- Delete the cross tie and use two Master solenoids.
- Run both batteries in parallel (normal operation) unless there is an electrical problem. At that point open both masters to split the systems. For single alternator setups this immediate action dumps the non-vital loads as well as the power hungry master solenoids, and goes a long way toward isolating most potential failures. These loads are available at any time by shutting a Master - like just before landing.
- Each battery to have two, 30 amp avionics relays, a primary and alternate (when on they typically draw 100ma).
- Split your panel into Avionics #1 and Avionics #2. Avionics #1 will run on battery #1 via the primary relay, or battery #2 via the secondary relay if needed. Avionics #2 will do the same with battery #2. These loads will include all avionics, autopilot servos, Trim, Flaps and such.
- Run all larger loads and non-panel stuff off the common starter/alternator connection (it has power if either master solenoid is shut). Stuff here includes pitot heat, landing lights, nav/strobe, seat heaters, the mulitude of USB charging ports, etc.

Think of this as two E busses that can get power from either battery.

The objective here is to maintain IFR flight after a component/wire/junction failure with no pilot action. Minor pilot action (moving a switch from normal to alternate) will restore the rest of the panel.

With two PC-625 batteries a typical dual EFIS IFR install with two radios should have at least 2.5hrs of reserve electrical power capacity. Belts and suppenders would be to add a standby alternator - but most will not need this. I put one on the RV-10 but will not on the new RV-8 as I sharpened my pencil on load analysis.

Carl


Cross tie may have been the wrong term. I have two batteries with two masters, both connecting to main buss. Batt 2 master would only be on for starting, troubleshooting, etc. Normally it's off and master buss is fed by Batt 1. Batt 2 also has a relay/switch to feed a backup buss (SOP = on). This buss has a variety of small relays/switches for powering semi-essential items, such as GPS, AP servos, trim, etc. (SOP = all on) Only the G3X and EI are directly tied into the buss. All other items can be taken on or off the buss based upon condition. I will probably drop these switches for for every item that has an on/off switch.

All Emerg buss feeders enter the circuit at the appropriate CBs, along with the master buss feed. Appropriately sized diodes installed on each CB feed from the main buss. Charging feed from Master 1 to Batt 2 with 20 amp schotky diode (requires me to remember to have master 2 on if battery is drained to avoid blowing the diode - non emergency situations).

With an alternator failure, I can shut off the b/u buss and run on batt 1 to depletion, giving me an idea of remaining capacity or leave both on, depending upon the situation. With the b/u buss on (SOP), I should be able to survive an alternator failure or other electrical issue requiring me kill the Master (batt 1 contactor) without a hiccup.

Back to my question. With the the 20 amp toggle CB, I am not too worried about this tripping before any of the downstream CB's (10 or less) as they are are similar in their design, so the smaller ones should trip first. However, this leaves me 10' of unfused wire from the battery to the CB. I am concerned about putting a fuse back there, as most are fast blow and I am afraid it could blow before the smaller and slower individual circuit CB's trip, killing the whole buss with no way to reset it. Maybe I shouldn't be too worried about the unfused run, as I already have a much larger, un-fused master feed in the same place.

I could also put a relay back at the battery, then run that feed to a 20 amp CB on the panel. This is a bit safer, as I can kill the relay if there is a problem. However, the reality is that I probably wouldn't figure out that problem in time to make that worthwhile.

Is the relay with panel CB or the toggle/breaker the better approach.

Larry
 
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Larry,

There are off-the-shelf devices available that will do what you want. Commonly used term is 'current limiter' (horrible term, but there you go). They have much longer time constants than typical fuses; more like 'slow blow' fuses we used to see in smaller values. They are very well documented, with load curves showing overload vs time so you can see what they do.
edit: Search for 'ANL fuse' or 'MIDI fuse'. They are different devices, but either should achieve what you want.

You can also roll your own 'fusible link' that's 4 wire sizes below the primary wire. Since all you're worried about on that run is a truly catastrophic fault, I'd be tempted to go that route. I've done it in a couple of places in my build. You can buy fusible link wire in various gauges, and it has heavier, higher temp insulation to contain the 'fire' if the link actually blows. My choice is to solder the link wire to the feeder, and heat shrink over the joint. You can also use a regular PDIG butt crimp for the join, if you're not comfortable with solder. I like this solution since with a soldered joint, it's effectively an extension of the wire. With any of the fusing solutions, you have about 8 more joints between the feeder and the battery. Obviously, the link goes on the battery end, just like a fuse.

All this stuff has been discussed to death on the Aeroelectric list.....

Charlie
 
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SNIP

Back to my question. With the the 20 amp toggle CB, I am not too worried about this tripping before any of the downstream CB's (10 or less) as they are are similar in their design, so the smaller ones should trip first. However, this leaves me 10' of unfused wire from the battery to the CB. I am concerned about putting a fuse back there, as most are fast blow and I am afraid it could blow before the smaller and slower individual circuit CB's trip, killing the whole buss with no way to reset it. Maybe I shouldn't be too worried about the unfused run, as I already have a much larger, un-fused master feed in the same place.

I could also put a relay back at the battery, then run that feed to a 20 amp CB on the panel. This is a bit safer, as I can kill the relay if there is a problem. However, the reality is that I probably wouldn't figure out that problem in time to make that worthwhile.

Is the relay with panel CB or the toggle/breaker the better approach.

Larry

If you use a 20 amp relay at the battery, feed the attached buss with a #10 wire. The buss will then have all the smaller breakers. No 20 amp breaker on the panel.

Protection:
As you say, we have big #2 wires connected to batteries via a master solenoid (thus the common practice of opening the master(s) on an electrical fault). So options include:
- Consider the 20amp relay a ?fuseable link?. These are cheap, test one. Hook it up to a power supply and see at what current it fails. This should be well within the capacity of the #10 wire.
- Put a 25 amp breaker on the input or output of the relay at the battery.
- Establish POH emergency proceedures to address your specific install.

Carl
 
Larry,

You can also roll your own 'fusible link' that's 4 wire sizes below the primary wire. Since all you're worried about on that run is a truly catastrophic fault, I'd be tempted to go that route. I've done it in a couple of places in my build. You can buy fusible link wire in various gauges, and it has heavier, higher temp insulation to contain the 'fire' if the link actually blows. My choice is to solder the link wire to the feeder, and heat shrink over the joint. You can also use a regular PDIG butt crimp for the join, if you're not comfortable with solder. I like this solution since with a soldered joint, it's effectively an extension of the wire. With any of the fusing solutions, you have about 8 more joints between the feeder and the battery. Obviously, the link goes on the battery end, just like a fuse.

Charlie

That's a good idea/approach. Thanks for the tip. If I go this route, do you think that a failure downstream of the 20A CB, but before the smaller CB's, would allow the 20A CB to trip before the fusible link blows?

Larry
 
Two batteries

An electrical fault will show up exactly the same way as if running one battery. Again, the immediate action for any electrical fault is to open both master solenoids. This places the system in the most stable condition. Once established the pilot has option to investigate or just land.

No charging system problems, period. The alternator does not care if one or two batteries, and the batteries mostly don't care if in parallel (however same chemistry and identical batteries makes life simpler).

Two batteries in not about adding capacity (but are sized to achieve a capacity design target). Two batteries are for in depth redundancy - and to allow for graceful degradation after a fault as compared to a dark panel. Faults will happen - design to either accept the fault or a way to mitigate it. Look beyond the simple alternator failure risk. The more severe risks have nothing to do with the alternator.

Carl


I'm still a bit confused...

Is an in-flight failure of a battery an occurrence that has happened to anyone?

And if so, would that failure have been masked by a parallel connected battery?

Also, could that battery failure cause the parallel battery to simultaneously fail too?

How would the battery fault manifest itself in a parallel condition?

I would expect a drastic battery failure - as opposed to a slow capacity loss - to be either an open circuit, and masked by the parallel battery, or a short which could take out the parallel battery.

Are two batteries that are usually paralleled in flight achieving anything?
 
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I'm still a bit confused...

Is an in-flight failure of a battery an occurrence that has happened to anyone?

And if so, would that failure have been masked by a parallel connected battery?

Also, could that battery failure cause the parallel battery to simultaneously fail too?

How would the battery fault manifest itself in a parallel condition?

I would expect a drastic battery failure - as opposed to a slow capacity loss - to be either an open circuit, and masked by the parallel battery, or a short which could take out the parallel battery.

Are two batteries that are usually paralleled in flight achieving anything?

Gil,

Sorry, but you are looking at a battery as an isolated component. Remember there are things connected to it.

So to answer you questions:
1. I know of a Lance Air that flew after clear indications of something wrong as they had just one battery. The last landing the plane burned to the ground. The battery provided the energy but a melted connection caused the fire.
2. Masking a problem - think about that. If a battery was dead and the plane was able to start anyway on the other battery, the pilot failed to follow common sense. If a battery ground wire fell off (or more typically had a high resistance contact) that will show up on start. Open one master and the batteries are split out and you know have buss voltage readout from each battery.
3. Both batteries in parallel for normal operation translates to each at full charge if a fault happens. Exactly what you want. As there are no downsides to this it is the logical way to operate.

A battery is the most reliable element you can put in an airplane (assuming you didn?t abuse it). The stuff you connect it to are not as reliable. Here having multiple power feeds to a single essential or avionics buss that has a fault is not about having two batteries, it is about understanding what happens when any element fails (so the reason why I press for two avionic busses). Plan accordingly. POH proceedures are needed to help some not do stupid things, like jump start and airplane then fly off into the clouds with no clue if they have any electrical reserve or not.

Carl
 
I just checked some pictures i have taken of my SkyView in flight and it shows i was drawing only 6 amps.

Sorry for a slight thread drift, but how can I use Skyview to tell what I'm drawing in flight? I thought what I was looking at with Skyview's "Battery Amps" widget was charge rate not total load. Mine normally shows about 1a after a short while in flight.
 
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That's a good idea/approach. Thanks for the tip. If I go this route, do you think that a failure downstream of the 20A CB, but before the smaller CB's, would allow the 20A CB to trip before the fusible link blows?

Larry

Fusible links have a *VERY* long time constant unless there's a catastrophic fault, meaning a dead short to ground between the link and (in your case) the CB. Be aware that current ratings for wire are based on risk of melting the insulation and on voltage drop (related to length of run). Copper wire will carry a lot more current without failing open than the ratings you see in wiring guides. For example, a 22ga wire is typically fused at 5A, but it's perfectly safe to fuse at 7.5A, and it will carry around twice *that*, if it's in free air and you can tolerate the heat & voltage drop.

If your wire is 12ga for 20A, you would insert a 16ga fusible link. 'Fusing current' is the term for actually melting the wire. Try this page for some info:
https://en.wikipedia.org/wiki/American_wire_gauge
Caution: if you 'roll your own' (can be done; I've done it), remember that the insulation of regular wire (as in not fusible link wire) will disappear long before the wire melts, and since the only thing that will 'blow' it will be a catastrophic short to ground, it's likely to go with a bang. You need to protect it with some kind of silicone impregnated fiberglass, or at least, heavy silicone tubing to contain the damage. Not trying to scare you; it's not that difficult to do.

Get 'the book'. And read it. Then ask questions on the Aeroelectric list. ;-)
 
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