Backup Alternator & Air Conditioning

[Jeff_S]

Had an interesting experience yesterday. Was out cruising around, getting some fuel for an upcoming trip. During runup before heading home I decided to test the backup alternator, which I don't always do (but should, I know) but since I have a trip coming wanted to check everything out. In testing the alternator, could never get the flashing Master light to go off, meaning not enough amps into the system. "Hmmm," I said, "good thing I checked this before the trip. Have to call Clowdus to check it out."

But on the short cruise home I happened to glance at the amps readout and see that my volts were solid at 28.1 but the amps were pulling +15. And then it dawned on me...I have the A/C on. (And yes, the Ovation 3 is certified to have the A/C on during takeoff.) So figured that was the reason during runup I couldn't get enough amps out of the backup alternator.

Since I'm not a big fan of doing a lot of testing in the air, once I landed I went back to the runup, turned off the A/C, and the backup alternator was fine. Note to self, turn the A/C off if I ever really need to use the backup alternator in flight. I'm guessing this is listed somewhere in the POH and I've read it a thousand times, but some lessons you just don't learn the easy way!

[Bob_Belville]

Backup alternators and air conditioning! Rub it in. 

[Marauder]

Backup alternators and air conditioning! Rub it in. 

If you want to feel better, I believe they need to have the engine running to have A/C (no GPU). For me, the hottest part is getting in the plane and running the pre-start checklist. They are sweating like us till the big fan is spinning.

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[Jerry 5TJ]

2 hours ago, Jeff_S said:

...... In testing the alternator, could never get the flashing Master light to go off, meaning not enough amps into the system.....

To be technically picky: It is a low voltage warning that is a trigger for the Master Warn light in our Ovations. 

In my 2000 M20R the current meter shows battery charge as + and discharge as - amps. In cruise after the alternator has recharged the battery the amp meter typically reads 1 to 2 amps + or towards battery.  

If I turn off alternator in flight the meter reads about -17 amps (from battery) which I believe is mainly power drawn by avionics.

 

 

 

[Hank]

1 hour ago, Hyett6420 said:

No amount of a/c will cool us down as we pull her off the "grass" (read gravel) at LFMU tomorrow.  It is forecast to be sunny, 30c and a 100 yard manual pull!  

I feel your pain. We are in the mid-30s here. But for that distance, I would pull full Up elevator and feed in enough throttle to keep moving, ending up with as short a push as possible. Towbar don't work well in grass, especially if alone!

[carusoam]

Back to alternator testing...

Jeff, were you testing this on the ground?

My only alternator can't keep up unless it is at 2,000rpm or so.  During taxi at low rpm, I may get a red light as the output just isn't there.   

Bumping up the throttle leads to high taxi speeds.  Doing during run-up just takes too many stones thrown to make it interesting.

Unlike mags and gov's, Aren't alternators considered reliable enough to test in the air?  If it fails you have another one. If they both croak you have a pair of batteries....

Somebody posted some nice graphs of alternator output vs engine rpm  for the back-up alternator.  Turns out alternators are pretty sensitive to engine rpm.... Sensitive E enough that the manufacturers prin graphs detailing the issue.

Best regards,

-a-

[Jeff_S]

To Jerry: yes, I do get amps and volts mixed up on the panel. I know that volts are a measure of how big the pipe is, and amps are a measure of how much current is flowing through the pipe. What I can't always figure out is what the dang meter is showing. I just know that when the lights go blinky-blinky something isn't right!

Anthony, I do test on the ground and yes, the RPM has to get to 2000 for the backup alternator to provide enough current to the system. And you're right, I could probably test this in the air, but some little voice in the back of my head says why introduce the potential for an emergency if I don't have to!

To everyone else complaining about the heat...SORRY! Karma is a bitch and I certainly wasn't trying to rub it in. I have thrown an A/C belt once already so I'm now knocking on wood.

[flyboy0681]

On 6/5/2016 at 7:52 AM, Bob_Belville said:

Backup alternators and air conditioning! Rub it in. 

I know what you mean, even I'm getting moist.

[PMcClure]

Ah - A/C and back up alternators just take up too much useful load. And all that gas you can fit in your 89.5 gallon tanks just means you can't take any passengers. And don't get me started on WAAS and the STEC G1000 planes. Who would want an Ovations or Acclaim, all those new gadgets just make the plane useless? Better stick with the F model or earlier. Electric gears can fail too, better consider an earlier model with the Johnson bar! 

[Hank]

Yes, I enjoy my "earlier model," but my shoulder is very happy I don't have a Johnson bar. Had I bought one, I'd have been stuck and probably sold it . . .

[Bob_Belville]

37 minutes ago, PMcClure said:

Ah - A/C and back up alternators just take up too much useful load. And all that gas you can fit in your 89.5 gallon tanks just means you can't take any passengers. And don't get me started on WAAS and the STEC G1000 planes. Who would want an Ovations or Acclaim, all those new gadgets just make the plane useless? Better stick with the F model or earlier. Electric gears can fail too, better consider an earlier model with the Johnson bar! 

Another "R" driver thinks is clever to mock the huddling masses. The humanity!

[PMcClure]

On June 5, 2016 at 5:15 PM, Hyett6420 said:

Fortunately I have a very keen fit 26 yr old in the right seat tomorrow. So I will use my 52 years of wisdom to just steering. . 

I have a 19 year old who is a work horse. I am amazed at how much work we can get done with my "wisdom" and his back. All it takes is  a little boat gas money and food to get him to take a challenge.

 

[Jerry 5TJ]

On 6/6/2016 at 0:51 PM, Bob_Belville said:

Another "R" driver thinks is clever to mock the huddling masses. The humanity!

If they have no bread (to purchase Avionics) we "R" drivers say 'let them eat cake.' 

[Bob_Belville]

On 6/6/2016 at 0:18 PM, Hank said:

Yes, I enjoy my "earlier model," but my shoulder is very happy I don't have a Johnson bar. Had I bought one, I'd have been stuck and probably sold it . . .

Hank, I think it's about technique and feel, not strength. Moving my JBar up and down is not much more work that reaching up to throw your electric selector. Mooneygirl lowered the gear in my plane from the right seat when we landed at KGGG a couple of weeks ago and reported it was easy.  

[Bob_Belville]

Just now, Jerry 5TJ said:

If they have no bread (to purchase Avionics) we "R" drivers say 'let them eat cake.' 

Off with your heads!

[PMcClure]

43 minutes ago, Bob_Belville said:

Hank, I think it's about technique and feel, not strength. Moving my JBar up and down is not much more work that reaching up to throw your electric selector. Mooneygirl lowered the gear in my plane from the right seat when we landed at KGGG a couple of weeks ago and reported it was easy.  

Hahahahah - this made me laugh. So many openings here for zingers. Alas, I think you have suffered enough. I'll just let it lie. 

[Bob_Belville]

2 hours ago, PMcClure said:

Hahahahah - this made me laugh. So many openings here for zingers. Alas, I think you have suffered enough. I'll just let it lie. 

No double entente intended. Get your mind out of the gutter or I'll sic my friend Marauder, and his girls, on you! 

[Jeff_S]

Oh God, I feel "Spacers' Law" coming on strong...

[Marauder]

2 hours ago, PMcClure said: Hahahahah - this made me laugh. So many openings here for zingers. Alas, I think you have suffered enough. I'll just let it lie. 

No double entente intended. Get your mind out of the gutter or I'll sic my friend Marauder, and his girls, on you! 

Do I hear a thundering heRd?

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[kj2016]

Hi! Jeff, just curious . You turned off the alternator switch and turned on the emergency bus switch on ovation 3 to test the back up alternator. I have not tested my  back up alternator yet. Is this the correct procedure to test you backup alternator on Ovation 3. Thanks

[Hank]

5 hours ago, Marauder said:

Do I hear a thundering heRd?

 

We are . . . Marshall!!

[Jeff_S]

18 hours ago, Kuljit hundal said:

Hi! Jeff, just curious . You turned off the alternator switch and turned on the emergency bus switch on ovation 3 to test the back up alternator. I have not tested my  back up alternator yet. Is this the correct procedure to test you backup alternator on Ovation 3. Thanks

Yes, the procedure is simple. During run-up:

1) Throttle to 2000 RPM (you do this anyway to test the mags and prop, so test backup alternator right after that)

2) Turn off ALT switch, and note the annunciator panel and Master Warning lights activating

3) Turn on Emergency Alternator switch, and the lights will extinguish if it is working correctly (and you're not running too much load...see above!) You can also check the output on your voltmeter on the MFD.

4) If you're still getting the blinky-blinky lights, try increasing RPM a bit more. You shouldn't have to go too much higher than 2000 RPM though. If you've got to 2200 RPM and still no joy, then you may have something wrong with your backup alternator system. (Again, check your load before worrying!)

5) When finished with the test, turn off Emergency Alternator and turn back on the ALT switch.

Hope that helps. It's all in the POH (AFM) so you can look for it in the preflight section.