E-Bus alternate feed: switch or relay?

[Carl Froehlich]

The simplist E buss day in the sun has passed. There are better approaches.

Carl

[KayS]

Originally Posted by N941WR

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.

[Carl Froehlich]

Originally Posted by KayS

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

[rv7charlie]

Originally Posted by KayS

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

[Z-EDD]

Originally Posted by rv7charlie

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/viewtopi...&highlight=hot

Take a look at Bob Nuckoll's detailed reply to a similar question.

[Bcone1381]

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.

[rocketman1988]

Originally Posted by Z-EDD

Could not agree more!

http://forums.matronics.com/viewtopi...&highlight=hot

Take a look at Bob Nuckoll's detailed reply to a similar question.

Definitely

[Dugaru]

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?

[RV7A Flyer]

Originally Posted by Dugaru

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?

[Carl Froehlich]

Doug,

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

Carl