Ovation Emergency Bus

[Jerry 5TJ]

My 2000 Ovation has the standby alternator installed, and I'm glad to have it in my all-electric plane.

If the main 100 ampere alternator fails the backup 20 amp alternator can be switched on.  

If necesary the pilot may pull the battery circuit breaker and then the 20A alternator feeds only items on the "Emergency Buss" which include, in my plane:

• ESI2000 standby AI with airspeed and altitude
• Nav/com #1. GTX750
• audio panel
• transponder & encoder
• TKS and pitot heat
• engine instrument cluster & glareshield lights

but that's all.     Originally the KCS-55 was also part of this emergency buss, says the POH supplement.  

The G500, GTX650, autopilot, shadin all go dark.  (Even the XM music goes away, a real hardship)

The idea is to save your battery charge (both of them) until approach when you can then run gear, flaps, landing lights & etc.  That makes sense.  

Q:  As the G500 only uses about 3 amps could it and it's related AHRS, magnetic sensor be connected to the emergency bus?

 

[Godfather]

Personally I would keep one of the batteries connected/active to keep the voltage stable when starting motors like the tks pump.  

Pre-DX (2004) ovations do not have a true dual bus setup so the emergency bus is really just a way to quickly reduce the load without going unit by unit.  

Probably the old emergency bus had the backup vacuum pump so you probably have amps to spare. 

More important questions for an all electric panel IMO:

Do you check the batteries every year for reserve capacity?  

Have you tested the backup alternator for proper operation under load and has it been rebuilt / inspected lately?  Its spinning every time the motor is on...

 

To me the backup systems on the ovation buys me time.  Personally the only time I would hit the emergency switch is if I was really in the thick of it.  Otherwise I would shed the load until the backup alternator was able power what was remaining (very easy to observe on the amp meter).  This means the AP, GPS, etc.

[carusoam]

I am in agreement with the GF.  I may have said it slightly differently.  So here it goes...

Sounds like an updated plan review is in order each time instruments or systems get added or changed to the plane.  

Fortunately, electronics add a small amount of load for the value they represent.  Electric motors and heaters use the most.  Old style lights are also in the heater category.  Flaps, trim, landing gear, AP use a fair amount of electricity in short bursts. The servo motors will be on and off a lot.  At least the back up electric vacuum pump isn't going to be needed any longer.  Not sure if the fuel pump is critical for a perfect landing.  Ice on the wing, high speed approach, a full power go-around it may be in the late plan...

Between two batteries and two alternators, I would find a way to separately power an AI and a GPS navigator/VOR/ILS on each battery/alternator system.  Buys time to figure out what has departed from Plan A on the way to the first airport.

If you defined your worst case electrical failure can you fly to safety using 20 amps?  Icing, dark, and IMC...  I want to be on the ground, NOW!  What would I use? Pitot heat, prop heat or TKS on prop, TKS, LED landing nav and taxi lights, AI GPS/ILS, windshield defroster (also a motor).

If you define the best case like day VFR what would you want running on your 20 Amps...

My old O has a pair of batteries, no second alternator.  Plan B: is shed everything but the minimum.  Talking with ATC and about ready to declare the E word... The CBs are organized in groups.  Essential and less essential...

Check your current procedure for turning off both batteries....(?) That may be less than ideal.  The battery has the ability to smooth out some voltage spikes and fill in some drops.  Running with just one alternator and no battery may not be possible. That's what made the generators of yore such nice devices....

sounds like professional guidance specific for your ship may be the way to go on this question.  There is not a lot of shared experience at this level...

The problem with alternators on an IO550 not working, they don't tell you what just went wrong with them...shedding their drive system, or clutch or is it just a broken wire?  Landing soon to verify system health becomes the primary plan.

These are thoughts of a PP, not a mechanic or electrician. I lost the generator in my C once, day VFR.  The battery being worn down was my hint of the failure.  You guys ask tough questions.

i may not want to dump the Bluetooth tunes too fast.  My cell phone and my last effort may include a cell phone call....

If you are fully prepared, you'll never need to use it....  (Comforting thought)

Best regards,

-a-

[Jerry 5TJ]

On 4/25/2016 at 8:09 PM, Godfather said:

Personally I would keep one of the batteries connected/active....  

Probably the old emergency bus had the backup vacuum pump so you probably have amps to spare. 

More important questions for an all electric panel IMO:

Do you check the batteries every year for reserve capacity?  

Have you tested the backup alternator for proper operation under load and has it been rebuilt / inspected lately?  Its spinning every time the motor is on...

 

To me the backup systems on the ovation buys me time.  Personally the only time I would hit the emergency switch is if I was really in the thick of it.  Otherwise I would shed the load until the backup alternator was able power what was remaining (very easy to observe on the amp meter).  This means the AP, GPS, etc.

Thanks for your detailed replies, guys.  

The plane as delivered in 2000 had a vacuum AI.  The Emergency Buss kept the Turn Coordinator powered as a second gyro.  Now Emergency Buss only runs the ESI2000 and there's no vacuum powered anything.  As it is now there's only one AI "gyro" running on Emergency Buss.

Yes, the 2 batteries are load checked with a constant current electronic load at annual.  Doesn't everyone do that?

Yes, I have tested the backup alternator under full load at 2500 rpm.  The pre-flight check at 1900-2000 rpm only tells you it comes on line.  I know will run and regulate at ~27 volts with no battery, at least if you start it first and then pull battery CB.  

The stand-by alternator per its manufacturer is to be overhauled at 1700 TT.  Mine has 1100 hours so far.  The main alternator and its drive / clutch have 40TT. 

Agree that leaving battery CB in and shedding load until reaching ~ 0 amps on load meter is preferable under almost all conditions.  I think I'll work out a list next long cross country of what it takes to get to 20A.  

I think if not the G500 then at least the FS210 should be on Emergency Buss so the iPad and 796 still provide secondary AI.  Maybe power for the 796 as well could come from Emergency Buss.  

Worst case electrical fault scenario:  If I lose all aircraft electrical power.  ESI2000 has its own battery (calibrated annually), as do the iPad and Garmin 796.  

Then if all those batteries go dead before I can exit IMC and land....well, that's a pretty bad day.  

 

[carusoam]

Jerry,

do you have a digital amp meter in your magic panel?   A JPI 900 or something?

It would be interesting to be able to test your hypothesis with accuracy prior to an emergency.

Have your flight engineer take notes while you bring things on line.  Let me know if you need a flight engineer...

 

OK, I'm not a flight engineer.  Just a flying engineer.

Best regards,

-a-

[Jerry 5TJ]

Yes, there's a digital amp meter in the original Ovation cluster that shows battery discharge as - numbers.  Resolution is 1 amp.  

I have got some trips coming up this week and I'll try pulling loads to see if I can keep "basic functionality" of, say the

• G500
• GTX750
• transponder & encoder
• GDL69 for XM weather plus 60's on 6
• TKS & pitot heat

all under 20 Amps.  

Will report.

If that doesn't work I'll take a flight engineer along, thanks.

 

[Godfather]

I forgot to mention before that I appreciate the fact that you started this thread.  Got me thinking about my own checklist and how temperature or weather conditions might change my thought process.  Sounds like you are keeping your backup systems in tip top shape.

...60's on 6

Keep in mind the windshield bar runs the second pump - I have not needed this feature yet.

Also the pitot heat will draw twice the amps on startup (I would not have a problem using RMS loads because of the battery reserves)

[Marauder]

I just get amped up when you engineers start talking about your loads.

Sent from my iPad using Tapatalk

[Jerry 5TJ]

For the Ovation with "20 amp" standby alternator, the available output varies with engine RPM. 

If you do need to use the standby alternator you should select the maximum available engine RPM.  Those of you with the 2700 RPM STC gain a few amps compared to us 2500 RPM fellows. 

Alternator output versus Engine RPM for the IO-550:

Note that the alternator mounted to the IO-550 accessory pad spins at 1.5 X the engine RPM. 

The diamond shaped data points are from the manufacturer.   The dashed line is a best-fit polynomial. 

Reference: http://www.bandc.aero/pdfs/quickfacts_bc410-h.pdf

 

[Jerry 5TJ]

I do have one data point from yesterday's flight:

At 2400 rpm with all external lights off, TKS off, pitot heat off but everything else running the standby alternator held the bus at about 26.5 volts and around 0 to -1 amp.  No need to go to emergency buss.  With both alternators off the current was around -16 at 24.5 volts from one battery alone.

UPDATE:  14 July.  As above, 2400 rpm, everything on including strobes and LED taxi lights, except TKS and pitot heat off.  Main alternator buss reading 28.4 volts.  Standby alternator stabilized at the same current (+2) but at 27.5 volts. 

 

 

 

[hais]

@carusoam do you check standby alternator function as a pre-flight item? If so, what is your method?

I just discovered that I don't know how to verify that the thing works before a flight. 

[carusoam]

2 hours ago, hais said:

@carusoam do you check standby alternator function as a pre-flight item? If so, what is your method?

I just discovered that I don't know how to verify that the thing works before a flight. 

Bummer…

I don’t have the second alternator… yet.  

 

Something to consider…

Once the engine is started, each alternator can be switched off, independently…

Charging voltage for the 24v system is probably above 26V…

So… if you see charging voltage above 26V, the alternator is working…

 

This is probably something that needs the rpm available during the run-up… alternators are not as sensitive to rpm as generators are… but, at idle rpm the out put of the Alternators is pretty low.  Low enough, I get a light on the annunciator panel…

 

Standby for somebody with a two alternator system to reply… (this is an interesting topic, you might want to start a new thread for it! )  let’s invite @Jerry 5TJ for his insight…

+1 for testing both system prior to departure…  or have an indicator light connected to the voltage regulator from each alternator…

PP thoughts only, not a mechanic…

Best regards,

-a-

[GeeBee]

From the Mooney POH:

Standby Alternator Preflight Check
(Will not show a charge until approximately 2000 rpm)

Alt Field Switch .............................................................. OFF ............................................... Verify Red ALT VOLTS light illuminates

StdbyAlt/Emerg Bus switch..................................................... ON ............................................. Verify Amber Emerg Bus light illuminates

Verify positive charge on battery ammeter ............................................. Verify Red ALT VOLTS light extinguishes

StdbyAlt/Emerg Bus switch.................................................... OFF ............................................... Verify Red ALT VOLTS light illuminates

Alt Field Switch ............................................................... ON ............................................. Verify Red ALT VOLTS light extinguishes

[BravoWhiskey]

I am currently replacing a faulty alternator and flew the plane in EM mode.  I Had enough to power system and charge batteries, but did not use O2,AC, or TKS... or lights.  Having gone through 2 alt failures in flight I will now be doing a preflight test each time to make sure that backup is there if i need it again.  

[carusoam]

Great shared knowledge and experience gents!

Go MS!

-a-

[hais]

Good that I asked, turned out, mine isn’t working - voltage warning light stays on and ammeter discharging. Left it with a mechanic to fix. 

[GeeBee]

Most common point of failure is a diode that is soldered inline with the field wire, or the field connector itself. You cannot see the diode because it is usually covered with a wrap around the wire.