Simultaneous Dual Alternator Failure

Fearless Tower

Fearless Tower

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Fearless Tower
Any twin drivers ever experienced one?

Had both alternators in the Baron this morning fail at the same time. It was on the ramp a few minutes after startling while waiting for the oil temp to come up. Both alternator warning lights came on near simultaneously and the volt meters confirmed no charging. JPI also came up with battery warning.

Tried turning off the alternators, then back on, but no luck.

Frustrating as all hell. Had the morning off of work and was finally going to get to fly my plane after sitting on the ground for 3 months!
 
Fearless Tower said:
Any twin drivers ever experienced one?

Had both alternators in the Baron this morning fail at the same time. It was on the ramp a few minutes after startling while waiting for the oil temp to come up. Both alternator warning lights came on near simultaneously and the volt meters confirmed no charging. JPI also came up with battery warning.

Tried turning off the alternators, then back on, but no luck.

Frustrating as all hell. Had the morning off of work and was finally going to get to fly my plane after sitting on the ground for 3 months!
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Does your airplane use a single regulator for both alternators or does it have a regulator for each alternator?
 
RotorAndWing said:
Does your airplane use a single regulator for both alternators or does it have a regulator for each alternator?
Click to expand...

Per POH, each alternator has its own voltage regulator, but according to the description, only one regulator is in use at any given time. The other is in standby. So if I understand it correctly, it may be that one regulator had previously failed and the second one failed this morning.

After startup, I always check that each alternator is working by securing one and then the other to ensure that each will carry the load independently. I would think that if one regulator had previously failed, it would show when running them independently.
 
Fearless Tower said:
Per POH, each alternator has its own voltage regulator, but according to the description, only one regulator is in use at any given time. The other is in standby. So if I understand it correctly, it may be that one regulator had previously failed and the second one failed this morning.

After startup, I always check that each alternator is working by securing one and then the other to ensure that each will carry the load independently. I would think that if one regulator had previously failed, it would show when running them independently.
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Yea, it's been a few years since I dealt with a Baron, but I suspect you are correct. Is there a switch to change from one regulator to the other?

The Cessna 310 has a similar arrangement. It's late and I'm in Incheon doing a redeye so my minds a bit blurry on it.

Look at any point that the two share in common, such as a switch or terminal.
 
RotorAndWing said:
Yea, it's been a few years since I dealt with a Baron, but I suspect you are correct. Is there a switch to change from one regulator to the other?

The Cessna 310 has a similar arrangement. It's late and I'm in Incheon doing a redeye so my minds a bit blurry on it.

Look at any point that the two share in common, such as a switch or terminal.
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Well, this is interesting. Your post just reminded me that there IS indeed a voltage regulator switch underneath the circuit breaker panels. I totally forgot about it and what is interesting, is that while the switch is shown in the instrument panel diagram, the elect system description and chart makes no mention of it.

So, it sounds like I lost the voltage regulator that was selected.
 
Fearless Tower said:
Well, this is interesting. Your post just reminded me that there IS indeed a voltage regulator switch underneath the circuit breaker panels. I totally forgot about it and what is interesting, is that while the switch is shown in the instrument panel diagram, the elect system description and chart makes no mention of it.

So, it sounds like I lost the voltage regulator that was selected.
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Great, hope it's a quick fix. If you have to replace a regulator look at the Zeftronics.
 
Just curious here as an experimental dual alternator, dual batt, dual bus operator; Does the Baron have dual buses corresponding to each alternator? (I suspect not since they share a regulator). But if so, are they routinely linked together or left to run separately?

OT: I've had to learn to keep my 2 buses running independently (except for starts) so that faults can most easily be detected. I have 2 regulators.

Glad it happened on the ground for you.
 
Sorry I missed you earlier.

There are two common setups on twins for dual alternators. The earlier style had two regulators with only one in use at a time. The 1/2 (or Main/Stby) switch determines which regulator is in use at a time. Because of this, a single regulator failure will take out both alternators at one. Also if the 1/2 switch fails, that will cause the same issue. You can also have bad wiring that will be a single point failure and switching the regulator won't help.

If you flip the 1/2 switch and the alternators come back online, you probably have a failed voltage regulator. I have a few spares, so if you let me know your P/N I'll see if the ones I have are the same. If that doesn't do it, you have one of the more complex failures.

The theory behind the old setup was that you could lose a regulator but still keep both alternators working. The practice was you had pilots not properly detect the failure and run out of power when the battery went dead, or else have one of the odd single point failures.

Later twins went to a setup where each regulator is dedicated to an alternator. This works better and provides improved redundancy. A voltage regulator or alternator failure results in that circuit not working. It is possible to convert an old style to a new style. We just did this on the 310 (combined with new PlanePower VRs and 150A alternators) and I'm very happy with the setup.
 
Bill Watson said:
Just curious here as an experimental dual alternator, dual batt, dual bus operator; Does the Baron have dual buses corresponding to each alternator? (I suspect not since they share a regulator). But if so, are they routinely linked together or left to run separately?

OT: I've had to learn to keep my 2 buses running independently (except for starts) so that faults can most easily be detected. I have 2 regulators.

Glad it happened on the ground for you.
Click to expand...

I've not seen any piston twins that separate busses per alternator. Usually you only have a main bus and an avionics bus, which is really just a take off of the main bus and allows you to shut off your avionics before the main. The real advantage is not having voltage spikes while you start your engines.
 
Ted DuPuis said:
Sorry I missed you earlier.

There are two common setups on twins for dual alternators. The earlier style had two regulators with only one in use at a time. The 1/2 (or Main/Stby) switch determines which regulator is in use at a time. Because of this, a single regulator failure will take out both alternators at one. Also if the 1/2 switch fails, that will cause the same issue. You can also have bad wiring that will be a single point failure and switching the regulator won't help.

If you flip the 1/2 switch and the alternators come back online, you probably have a failed voltage regulator. I have a few spares, so if you let me know your P/N I'll see if the ones I have are the same. If that doesn't do it, you have one of the more complex failures.

The theory behind the old setup was that you could lose a regulator but still keep both alternators working. The practice was you had pilots not properly detect the failure and run out of power when the battery went dead, or else have one of the odd single point failures.

Later twins went to a setup where each regulator is dedicated to an alternator. This works better and provides improved redundancy. A voltage regulator or alternator failure results in that circuit not working. It is possible to convert an old style to a new style. We just did this on the 310 (combined with new PlanePower VRs and 150A alternators) and I'm very happy with the setup.
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Thanks Ted. I'll let you know what I find. In-laws in town this weekend, so I probably won't get back to the airport to next week.

Mostly frustrated that I forgot about the voltage reg switch when I was in the plane this morning. That's what I get for not flying for 3 months!
 
Well, this is frustrating. I am starting to think it night be a wiring problem. Fired it up today and everything was good. Both alternators on line. Both regulators work. Couldn't recreate the problem.
 
Fearless Tower said:
Well, this is frustrating. I am starting to think it night be a wiring problem. Fired it up today and everything was good. Both alternators on line. Both regulators work. Couldn't recreate the problem.
Click to expand...

Did you cycle the switches? Could have been a little bit of corrosion on the contacts. Has the plane been sitting?
 
RotorAndWing said:
Did you cycle the switches? Could have been a little bit of corrosion on the contacts. Has the plane been sitting?
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During the original issue on Friday, I did cycle the alternator switches but forgot to cycle the voltage regulator switch. Yes, the airplane had been sitting in the T-hangar for the last 3 months. I just moved it to a corporate hangar because the T-hangars here are pretty crappy (lots of moisture inside).
 
Fearless Tower said:
During the original issue on Friday, I did cycle the alternator switches but forgot to cycle the voltage regulator switch. Yes, the airplane had been sitting in the T-hangar for the last 3 months. I just moved it to a corporate hangar because the T-hangars here are pretty crappy (lots of moisture inside).
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I would say that was your problem. Cycle a few times and go fly.
 
I found an interesting and related issue in my new 8. I went flying this am and the alternator was not working. As I was turning for home I decided to cycle the 5 amp "Alt Field" breaker by pulling it. As soon as I touched it the alt came back on line. It must have been dirty or tired of sitting in that position. :dunno:
 
Fearless Tower said:
Well, this is frustrating. I am starting to think it night be a wiring problem. Fired it up today and everything was good. Both alternators on line. Both regulators work. Couldn't recreate the problem.
Click to expand...

As R&W suggested, it was probably just the switch. The switch on my Aztec could be finnicky and sometimes when I would switch it back and forth (which I did regularly to make sure both regulators were still working) sometimes it would seemingly get "stuck" and neither would work. I'd have to flip it a few times and it always went back to working.
 
The corroded/dirty contacts thing is especially likely if you still have traditional mechanical point regulators, as they are especially prone to corrosion and resistance in the contact points.

I really like the solid-state Zeftronics units.
 
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