Ess Buss

Brambo · #1 08-13-2007, 11:29 AM

I'm still wrestling with what should/shouldn't be on the Ess Buss. Should the AFP Boost pump (IO-360) be on the Ess Buss? At 5 amp it's kind of a heavy user.

Bill Rambo
RV-7A

dan · #2 08-13-2007, 12:11 PM

Let's consider the scenario where your master contactor fails. You're now running off your e-bus and ONLY your e-bus...and you don't have a choice about that. You don't have the option to "flip on the master on final" to use your boost pump.

The boost pump may consume considerable current, but it's OFF 95% of the time.

In my book, I opt for LOW WORKLOAD and simplicity...which on my airplane translated into putting several items on the e-bus that are normally OFF. They are items for the use of which I do not want to (a) depend on a master contactor, and (b) have to flip the master back on. Examples would be the boost pump & flap motor. Both on the e-bus.

Just my 2 cents.

mike newall · #3 08-14-2007, 11:09 AM

I thought the electric pump needed a 7 - 10 amp supply ?

ccarter · #4 08-28-2007, 01:17 PM

My boost pump and flap motor are on the EBuss as well. My focus is to complete the mission or execute a quick landing in the event of contactor/Alt failure or other. I can focus more on flying with just the essentials this way and make a safe landing.

Mark Burns · #5 08-28-2007, 01:53 PM

Quote:

Originally Posted by dan

Let's consider the scenario where your master contactor fails. You're now running off your e-bus and ONLY your e-bus...and you don't have a choice about that. You don't have the option to "flip on the master on final" to use your boost pump.

The boost pump may consume considerable current, but it's OFF 95% of the time.

In my book, I opt for LOW WORKLOAD and simplicity...which on my airplane translated into putting several items on the e-bus that are normally OFF. They are items for the use of which I do not want to (a) depend on a master contactor, and (b) have to flip the master back on. Examples would be the boost pump & flap motor. Both on the e-bus.

Just my 2 cents.

Dan,

Just to play the devil's advocate here. (where have I heard that before?)

What are the chances of a safe landing without running the boost pump?
I'm not trying to be smart, I'd really like to know.
I think (hope) they would be pretty good.

I'm not flying yet so take what I'm saying with a grain of salt but I hope that flaps won't be high on the important list either.
Most of my flying lately has been in a Decathlon and flaps are not an option.

I'm just getting started on the wiring now but I don't plan to have either the flaps or my little boost pump (Carb) on the e-buss.
Am I making a big mistake?

Mark

kentb · #6 08-28-2007, 02:00 PM

Last weekend I flew to the Home Coming (15 minute flight from 7S9).
After take off the engine monitor started complain about "over-voltage" a quick check and sure enough I was at 18.6 volts. Not good on a 12 volt plane. I turned on my E-bus and my standby alt. (8 amp from B&C), then turned off the 60 amp alt and the main bus.

Yikes. I was down to one EFIS, plus my backup round gauges. My GNS430, the 496 (I had to press a button to make it continue to work), audio panel and engine monitor. I was making over 8 amps and continues on.

When I got to Independence and entered the pattern, I slow to 85kts and hit the flap switch. Nothing happened.

I turned the main bus back on (not the alternator though) and lowered the flaps.

So should I move the flaps to the E-bus? I am not so sure. I can land at most airports just fine without the flap and turning on the main bus is not that big of a deal.

If the switch and relay failure is why you are using the E-bus then I think that I would want my fuel pump to be on that curcuit. Not for landing, but more for some inflight problem that you would want to increase fuel pressure for (say engine fuel pump failure).

By the way the alt. failure was fixed by replacing the build in voltage regulator ($48.00).

Kent

ccarter · #7 08-28-2007, 03:07 PM

For me it's about reducing "mental" workload in a situation that was not really expected but planned for. I've read a number of accounts about alternators. I know this is a possiblity as the equipment ages so I put it in my emergency planning. I can flip two switches with less mental work and lower the power requirments of the aircraft, therefore I've trained myself to think this way. My Dynon 180 has the internal battery as does the 496. They will run longer on internal batt. than I have fuel capacity when full. The essentials can then run on the firewall batt. (including fuel boost and flaps) both of which will only be needed momentarily upon landing or perhaps in a more severe case if the engine pump goes kaputz. I also have the round gauges. If I get an over voltage (or under for that matter) the "crowbar" circuit defeats the alternator and pops the field breaker automatically. It's a relatively smooth transition and allows me to think about flying the plane and finding a safe landing spot.

If this were to happen at night or in IMC the benefits are obvious.

dan · #8 08-28-2007, 03:09 PM

Quote:

Originally Posted by Mark Burns

What are the chances of a safe landing without running the boost pump?
I'm not trying to be smart, I'd really like to know.
I think (hope) they would be pretty good.

I'm not flying yet so take what I'm saying with a grain of salt but I hope that flaps won't be high on the important list either.
Most of my flying lately has been in a Decathlon and flaps are not an option.

I'm just getting started on the wiring now but I don't plan to have either the flaps or my little boost pump (Carb) on the e-buss.
Am I making a big mistake?

Mark,

I don't disagree with your implications. I have landed without the boost pump on. I have switched fuel tanks without using the boost pump. I didn't fall out of the sky. However...WHAT IF Murphy just happens to be in town, and your engine-driven fuel pump gives up the ghost on the same flight your master contactor gives it up? You'll be wishing you put your boost pump on that e-bus! I mean, I realize this is very, very unlikely...but possible!

Flaps, sure. Leave 'em off the e-bus if you don't want 'em.

You're not making a big mistake...but consider the rationale behind the e-bus. It's intended to provide a safe & "comfortable" completion of the flight. To me, comfort is having everything I want at my disposal with minimal workload. For you, comfort may mean different things...and that's ok!

johnp · #9 08-28-2007, 03:29 PM

Quote:

However...WHAT IF Murphy just happens to be in town, and your engine-driven fuel pump gives up the ghost on the same flight your master contactor gives it up? You'll be wishing you put your boost pump on that e-bus!

i don't have a problem with putting the fuel pump on the "e-bus", but philosophically, i only plan redundancy for single-point failures. once you start down the road of "what if this fails AND that fails", there is no end, because the "what if" can be extended to include whatever measure you just put in to ameliorate the last postulated failure.

as an aside, i have opted against an "e" bus. instead, i have (planned) a dual-battery system. i struggled with dual alternator/dual battery for a long time, and have arrived at the dual battery solution. i will have two batteries and two master contactors. there will be no diode isolation or trickle charger for the off-line battery. my plan is to alternate batteries on every other flight. in the event of alternator, battery, or master contactor failure, i will just flip on the other master for 30-40 minutes of flight time. (oh, but what if _both_ master contactors fail? -- well, too bad for me. hope i'm not in imc if that happens.)

Mark Burns · #10 08-28-2007, 05:51 PM

Quote:

Originally Posted by dan

Mark,

You're not making a big mistake...but consider the rationale behind the e-bus. It's intended to provide a safe & "comfortable" completion of the flight. To me, comfort is having everything I want at my disposal with minimal workload. For you, comfort may mean different things...and that's ok!

Dan,
Thanks for your insight. Your web site is what pushed me over the "edge", making me realize that I really could build an airplane and have fun doing it!

I'll have to give this e-buss thing a little more thought. I've thought about so much already a little more won't hurt.

One thing to consider is how big your fuse is on the e-bus. If you get close to landing and start turning on things like the fuel pump and flaps you might blow the fuse. This could make the landing "uncomfortable" with you loosing it all at once and trying to figure out what's going on.

Things like this should be tested in phase 1 I suppose.

Mark