Essential Bus and how often do battery contactor's fail?

[Mich48041]

Keep in mind that the battery is not powering the electrical system, the alternator is. And many alternators will continue to function if the battery is disconnected. Mine did. My PC680 failed internally due to a broken weld. The affect was identical to a battery contactor failure. Everything electrical kept working, but the voltage fluctuated causing alarms to go off on the Dynon D-180. Closing the throttle for landing caused very low voltage, not desirable if IFR or at night.

[svyolo]

Originally Posted by Mich48041

Keep in mind that the battery is not powering the electrical system, the alternator is. And many alternators will continue to function if the battery is disconnected. Mine did. My PC680 failed internally due to a broken weld. The affect was identical to a battery contactor failure. Everything electrical kept working, but the voltage fluctuated causing alarms to go off on the Dynon D-180. Closing the throttle for landing caused very low voltage, not desirable if IFR or at night.

Yeah, I have heard that as well. I just don't know how well. My system will be drawing about 20 amps, most of that for the EFI. Maybe that is enough of a load I don't need the second battery. I will try it both ways on the ground.

[Bicyclops]

Originally Posted by airguy

And there is a valuable point for discussion and/or dissension. I have glass screens that monitor voltage and amperage draw from the battery with alerts for off-nominal condition, and with dual alternators of which only one is on at any time. The idea is that I would get an alert from my EFIS if/when my primary alternator goes TU, and then I manually activate my backup alternator. I don't WANT it to be automatic without pilot action, because I want to absolutely ensure the pilot is in the loop and KNOWS the primary alternator is on vacation, and take positive action to bring the backup online. Then, should the backup fail as well, the EFIS will again do its job to alert the meat servo that he's on battery power only and the clock is ticking to find a place to put down.

Some things should be automatic backup without pilot action, with an alert after the fact - but I want my airplane to require positive pilot intervention to make certain the pilot is aware of the problem. YMMV.

Yup. Gotta immediately and for sure know when battery is all you have left. And you gotta know for sure how much battery. Capacity check at annual is the only way you can be sure of your battery's condition. Need to do an alternator out load calculation so you can run your cap check at a similar load and get a real life time to all gone number in minutes. Set a stopwatch when the battery only ops begins and land with some reserve.

Ed Holyoke

Ed Holyoke

[Hartstoc]

Originally Posted by rocketman1988

“...If you can design redundant systems that cannot be defeated...”

Unfortunately, you cannot. If it is a mechanical system, it can be defeated.

The best you can do is minimize the risk involved in a failure... and there are many, many opinions on how best to accomplish this...

Depends upon what you mean. Obviously, you can always be really stupid and shut your airplane off in flight. What I mean by cannot be defeated is that there is no combintion of pilot inputs like switch positions that can render the redundant feature unavailable. That would describe my electrical system. It is also pretty much impossible to inadvertantly discharge both batteries after an alternator failure.- Otis

[Hartstoc]

Originally Posted by Bicyclops

The B&C voltage regulator has an output to flash a light when the buss voltage drops below 13. That gets your attention as soon as the alternator goes offline so you can start conserving electrons by turning stuff off. One could also set up a low voltage alarm on an EFIS.

Ed Holyoke

That is true, but pilots have on occasion shown an incredible talent for missing glaring warning devices- ususlly under conditions of elevated stress.- Otis

[DanH]

Originally Posted by airguy

...The idea is that I would get an alert from my EFIS if/when my primary alternator goes TU, and then I manually activate my backup alternator....Some things should be automatic backup without pilot action, with an alert after the fact - but I want my airplane to require positive pilot intervention to make certain the pilot is aware of the problem. YMMV.

That's entirely sensible. However, note there's nothing very urgent about an alternator failure. The battery supplies electrons without pilot intervention. The pilot action merely re-configures for extended duration.

The urgent things should always be automatic, or if not fully automatic, the necessary action should be a trained response common to the pilot community. Urgent things are mostly in the category of "Keep the fan turning". The test is the classic departure scenario; engine goes silent 300 feet above the trees.

[rocketman1988]

?Protect Essential!?

...and no, it wasn?t automatic...

[Captdf]

?Protect Essential? ... haven?t heard that one in a few years.

Fastest way there was to bust an FE checkride. Fun times!

[Hartstoc]

Originally Posted by Hartstoc

The whole idea of an essential loads bus(ELB) is that no failure modes should separate it from available battery power, so it is crucal that there be no switching or contactors of any kind between it and the battery. The simplest ELB is the battery post itself, but all should be located as close as possible to the battery as they are always ?hot?. Truely essential loads like electronic ignition and electric primary fuel pumps sould always connect directly to ELB?s and never to the main bus. Each essential device must be breaker-protected, switch-connected to the ELB, but unaffected by master switch position. Yes, you have to manually turn off each essential load at shutdown.

My RV has twin elecronic ignitions AND twin primary electric fuel pumps. I run a single B&C alternator so have identical-twin 16AH EarthX batteries. Each battery has a contactor to the main bus and its own ELB. It is completely symmetrical, so the master switch is an on-off-on switch allowing either but not both batteries to act as primary(*-see note). Each essential load is also powered through an on-of-on switch protected by two breakers that can route power from either but not both ELB?s. The batteries, the ELB?s, the essential load switches and breakers, and the contactors are all located in very close proximity in a console separating the pilot and passenger? feet, with the switches in a vertical stack above the fuel selector valve. There is a fifth on-off-on switch there energizing a sub-bus of breakers feeding alternate power inputs on several Garmin devices with dual power inputs, allowing selected access to avionics and communications with the main bus shut down. This system is simple, symmetrical, and fool-proof. There is no ?emergency mode?, just alternate, normal, everyday operation of essential loads. I can fly an entire tank of gas with one fully charged battery.- Otis

(*)- There is one exception- A guard-protected, spring-loaded to ?OFF?, DPST switch will activate both main bus contactors when held ?ON?. This allows switching between the two batterys in flight without interrupting main bus power, and it allows the option of starting the engine with both batterys working. Both batteries, the added busses, breakers, wiring and contactors all together weigh less than one PC680, but have four times the cold cranking Amps.

I?m quoting myself here for a couple of reasons. First is to stress that this setup, using twin and symmetrical main batteries, each capable of full aircraft operation, is a departure from convention that is made possible by powerful, lightweight lithium batteries. It guarantees an ample, uninterrupted supply of power for electron-dependent aircraft with little or no pilot intervention. I?ll be covering this in due course with a dedicated thread including photos and a wiring diagram.

Second is to describe a sublety not previously mentioned for simplicity sake. The On-Off-On master switch is actually a DPDT, whose function makes it impossible to discharge both batteries inadvertantly in the event of an alternator failure, but also also to guarantee that the battery acting as ?backup? at any given moment remains fully charged even if some of the essential loads are using it in normal flight.

One pole of the master switch energizes the contactor for either but not both batteries to the main bus. It absolutely does not matter which battery is serving as ?primary? for a given flight. The second pole energizes one but not both of two lightweight solenoid switches that feed main bus voltage through a 25Amp Schottkey diode, protected by a 20Amp breaker, to the OPPOSITE battery serving as backup.

This will allow the ?backup? battery to be recharged if it was used in tandem with the other during engine start, and to support any essential load that happens to be using the ?backup? battery during flight. SOP will be to have one of the two electronic ignitions connected to it, but that is a mere 1.5Amp draw in my case.

[springer]

Originally Posted by cajunwings

While contactor failure itself is rare there is a little more to think about. Any issue with the master switch, related wires, terminals, crimped connections ect can cause the master contactor to open and un-power everything downstream. The primary alternator will probably loose field power and go off line as well. Back when I was a shop rat I saw most of these problems first hand. For my plane a E Buss with its own switch and alternate wire path will allow access to whatever stored amps are in the main battery. I’m planning 2 screen ifr panel, 1 B&C primary alternator, a back up battery and a G5 with its integral back up battery.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

My only electrical failure in my 40+ years of flying was my $4.79 battery master switch on my -8.