Failure of Battery in Mooney Ovation

[kortopates]

50 minutes ago, Dale said:

This is a standard part of the electrical system check that is routinely done.  He switches the batteries in the air and checks their voltage.  Corby did so today in testing two G1000 Mooneys at Premier that had just come out of annual.  Premier mechanics concur that as long as the batteries are good, there is no problem switching from one battery to the other in the air with the alternator on and the electrical system operational.  No relays will fry.  

I don't think anyone has said relays will fry as soon as you switch battery's while the system is powered. I don't think its fair to say its routine to change them either. But Don Maxwell has repeatedly posted about these system meeting an early demise from doing this frequently and its a costly repair. I don't specifically recall what fails first, but he has been very vocal over many years to avoid unnecessarily switching batteries in flight or once on to avoid premature failure. I'd suggest giving him a call for further details. It wasn't long ago I saw him post another example of this on Facebook with pictures.

[carusoam]

The fun part of a two battery system…. In your Mooney…

They are wired with two relays, one for each battery…

…and a switch, to operate the relays….

When switching from one battery to the next….

It is designed to momentarily connect both before dropping the first one off line…

 

If you experiment with the switch…

…And move it really slowly….

You can find a dead spot where both batteries are not connected…

Things go dark momentarily… before the second battery relay makes the connection…

 

What an ordinary PP finds out….
Holy cow…  it’s an ordinary mechanical device using magnetic fields, driven by a human being…

Move the switch with intention…

 

Findings….

You can flip that switch any time you would like…. Chance of wearing out a relay is pretty slim…

Relays do suffer from internal sparks knocking off bits of material internally… the bits collect and finally cause challenges for the relay’s ability to operate… after decades….

 

Having a battery get drained….

Causes all kinds of challenges… get it charged before trying to use it…

 

Trying to use the alternator to charge a dead battery has a tendency to overload the system… Causing challenges to be fixed later…  the system wasn’t designed to charge a battery from a dead state…  (neither are my car’s alternators…) 

PP thoughts only, not a mechanic…

Best regards,

-a-

[LANCECASPER]

4 hours ago, Dale said:

a.  Provided both batteries are good and fully charged, you can switch from battery 1 to battery 2 in the air with the master switch on and the main alternator on and operational without any injury to the electrical system, the batteries or the alternator.  Corby told me that he does this when he flies the Acclaims and the Ovations and has done this many times and there are no problems.  He also does this on test flights for Premier on the Acclaims and the Ovations as part of a general electrical system check.  This is a standard part of the electrical system check that is routinely done.  He switches the batteries in the air and checks their voltage.  Corby did so today in testing two G1000 Mooneys at Premier that had just come out of annual.  Premier mechanics concur that as long as the batteries are good, there is no problem switching from one battery to the other in the air with the alternator on and the electrical system operational.  No relays will fry.  

A couple thoughts come to mind, first how do you know for sure that the batteries are good and fully charged before  they are switched in the air? There's no gauge showing the condition of the other battery.

Second, the guy that you quote that does this regularly is not an owner. It may not have ever have happened to him, but not being an owner and having to foot the bill or worry about the long tern consequences might make one a little more willing to change batteries in the air when there have been reported instances of expensive things happening when that's done. @mike_elliott has talked about this before.

[Dale]

Good points that I am going to bring up with the Mooney CFI.  I don't know if there is a ground check you can do with the batteries that would differ from switching them in the air.  Maybe on the ground check, with the alternator off, low rpm's and then switching the batteries will demonstrate the voltage output to determine if the battery is good and not cause any problems.  It is a good point and one that I want to discuss with the CFI, among others, when I get my plane back and we go over the electrical system issues.  I don't want to have a repeat of this in the future.  Thanks for your input, it really helps when I make a list of questions for the CFI.  Thanks again.

[carusoam]

Dale,

Check your pre-start checklist…

The O1 checklist has a step to check voltage of both batteries, and use the higher voltage battery for start…

That pretty much gives a good indication of battery status prior to the alternators adding voltage to the mix…

The O1s have a crummy voltage gauge… a push button on an analog gauge with crummy resolution…. But, it works…

-a-

 

[FloridaMan]

If they’re not replacing the alternator, chances are you’re going to end up replacing the regulator twice and the alternator once. Regulators sacrifice themselves to protect your avionics from a bad alternator. 

[Dale]

This is an update on my Mooney Ovation 3.  I just got my plane back this week.  It took almost 5 weeks because they couldn't get the voltage regulator replaced because they had to get a letter from Mooney and then go to the OEM and have them rebuild/replace my old one.  Also, both of my Concord batteries failed the cap test and I had to replace both of them.  They were almost 4 years old but had been operating fine and passed the cap test at my last annual.  The alternator was fine and all the electronics were fine.  Final analysis - Being stupid and not turning on the alternator before taking off and running the battery so low it was pulling so much amperage from the alternator that it burned out the voltage regulator before it burned out the alternator and my instrument panel.  Also, not catching any indication on the panel that the voltage regulator was not on.  I had the panel lights checked, so it should have been caught at that point.  In any event, the voltage regulator did what it was supposed to, the pilot did not do what he was supposed to.  I got an expensive lesson on electrical systems from this experience.  Basically, I learned the following: 

1.  turn the damn alternator on before takeoff (duh); 

2.  You can switch batteries in the air with the alternator on provided one of the batteries is not totally drained or really, really low; 

3.  You can't turn on the alternator onto a dead or almost fully drained battery or you will get an electrical rush into the lines that can damage your electrical system; 

4.  The back up alternator has its own voltage regulator (so burning out the main one has no effect on the back up whatsoever) but is not strong enough to run any nonessential items like flaps, trims and landing gear; 

5.  Training to lower the gear manually on my biannual flight reviews is NOT a waste of time; 

6.  Upon the voltage regulator burning out on the main alternator, I could have switched to the number 2 battery which was fully charged, popped the circuit breaker back in (provided the system had cooled down sufficiently and I was on the #2 battery, I had tried it a couple of times and it wouldn't go back in but was told I needed to give it more time, how much I don't know and don't want to find out in the future) and then turned on the back up alternator.  Everything would have worked as designed including the flaps, trim and landing gear, but land as soon as possible; 

7.  Both batteries operate off the same circuit breaker;

8.  The loss of the voltage regulator does not affect the batteries as it protects the alternator but is not on the same line as the batteries; 

9.  Make sure I do the run up and check that both alternators are operational - the back-up won't kick in until about 2000 rpm or more on my Ovation; 

10.  Spend more time with my instructor on electrical system issues and failures;  

11.  I was lucky this all happened on a perfectly clear day in VFR conditions.  Had I been on an approach or in rough IMC, it could have been different;

12.  You have to pull the battery breaker if you go to the emergency buss back up alternator, otherwise it could pull to much amperage if the other good battery is low.  However, if the circuit breaker will go back in, you can turn on that battery long enough to configure the planes trims, flaps and landing gear for the landing.  Then, it may need to be turned off since my understanding is that you can't chance that the backup alternator would send current to charge that battery and overload that system.

13.  Never rush doing a checklist because you have to get off the runway because other planes are waiting to land.  There is no taxiway at River Ranch so I had to do the runup on the runway while planes were waiting.  No excuse just poor timing and planning.  I should have taken my time.  I didn't go through the full checklist and therein lies the problem.  Don't rush, don't get out of your routine and always pull the full checklist from the checklist sheet and not from memory.

14.  I did the correct procedure for a dead battery and an electrical system failure, if the battery circuit breaker would not reset on battery 2, shut down the main alternator button, turn on the emergency bus, fly the plane, contact the nearest tower with a sufficient length runway, lower the landing gear manually (lower gear knob, pull gear breaker, pull handle until the gear indicator panels shows gear is down and handle pull gets a little tight), land as soon as possible, land a little hotter with no flaps on a longer runway.  At least I did one thing right.  If the battery circuit breaker did reset, then I could have configured the plane for landing and after it was configured, pulled the battery circuit breaker to make sure there was not to much load on the backup alternator causing a failure there.

All in all, it was an expensive, but important, lesson on the Mooney Ovation's electrical system.  I don't hope to repeat it again.  I would like to thank everyone for their comments.  They were very, very helpful.  Thank you, everyone.

[Mufflerbearing]

On 1/25/2022 at 5:03 PM, kortopates said:

I don't think anyone has said relays will fry as soon as you switch battery's while the system is powered. I don't think its fair to say its routine to change them either. But Don Maxwell has repeatedly posted about these system meeting an early demise from doing this frequently and its a costly repair. I don't specifically recall what fails first, but he has been very vocal over many years to avoid unnecessarily switching batteries in flight or once on to avoid premature failure. I'd suggest giving him a call for further details. It wasn't long ago I saw him post another example of this on Facebook with pictures.

I believe Don's cautions is not necessarily because of the electrical system, but the on board electronics.  I remember him saying these spikes in the electrical power when switching batteries can damage the electronics.

[LANCECASPER]

6 minutes ago, Mufflerbearing said:

I believe Don's cautions is not necessarily because of the electrical system, but the on board electronics.  I remember him saying these spikes in the electrical power when switching batteries can damage the electronics.

that may be true but there's also a very expensive battery relay that can be damaged when you switch batteries under power.

[carusoam]

Great details shared Dale!

 

Go MS!

Best regards,

-a-

[Yetti]

Interesting to note that the Eagle POH says to turn master on and the Alt Field on before starting the engine.   Published in 1999.

[PaulM]

On 2/22/2022 at 9:07 PM, LANCECASPER said:

that may be true but there's also a very expensive battery relay that can be damaged when you switch batteries under power.

You can also blow out the 5A trickle charge fuse if you start on #1... and it hasn't recovered yet, and you switch to #2.   The depleted battery will take more than 5A.. and kill that fuse. 

I don't start on the best battery, I just switch #1 to #2 every full start (but not a just got fuel restart) 

Given the discussion about 2000+rpm for the alternate alternator this is the  G1000/AC powered system with the backup alternator on the vacuum pump pad.