If you ever have an alternator fail in flight...

cowman

cowman

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I've now had the honor of experiencing in-flight alternator failures in both PA-28 and PA-32R Pipers. I'm not too familiar with other types so maybe this doesn't apply to all aircraft but it's definitely applied to the ones I've owned.

Both of these aircraft had the three square orange annunciators.... VAC ALT OIL. In both cases the ALT light was so dim in daylight that it was barely visible. Even cupping my hands over it to provide shade it was barely possible to tell it was on. This will NOT get your attention in the event of a failure. In the PA-28 my first warning was my GPS screen going blank as voltage dropped too low for it to stay on.

In the PA-32R I had an EDM-800 engine analyzer that started flashing the voltage at me. I dropped the gear right away and flew about 30min in VFR conditions back home, didn't lose nav or comms the entire time. I had about 11.5-11.8V all the way to landing.

Anyway what I really wanted to get across is that annunciator light is basically useless. Unless you're watching your ammeter like a hawk you probably won't notice it moving from just above 0 to 0. That engine analyzer made a HUGE difference in detecting the problem quickly. If getting one of those isn't in the cards and you have a cigarette lighter there are digital voltmeters that will plug into them and have USB charging ports on them for very reasonable prices on amazon. Better than nothing, I'd suggest something especially if you fly in IMC or are flying a retract.
 
Good point and the very reason my digital voltmeter for the cigar lighter arrives this week. I’ve been watching the load meter (ammeter) like a hawk lately.
 
Alt failure? Dozens of times in my 180. I chased that issue for years. Finally stripped and re-wired the plane and changed to a B&C alternator. Never a hiccup since.
 
Funny, my one alternator failure (and subsequent low batt issue) was in a PA28 as well. Good point on the volt meter
 
I enjoyed the one I had in a 182 on a long xc at night over desolate terrain, pre-handheld days. That was a good test of navigating without..anything.
 
I was skimming the tops over Albany at 10K in the PA-28R when the autopilot pitched up and to the left. Hit the autopilot disconnect and glanced at the autopilot annunciator panel - all the lights were flashing. I recalled the autopilot manual stated that all the annunciator lights will flash if voltage drops below 11V. That is when I noticed the ALT annunciator light was on. Good news - Bad news. Good news as I was over KALB and within seconds and a clearance to 5K and a heading to set up for the ILS. Reduced electrical load and dropped the gear to help descend and while I still had battery power. Broke out at 1000 feet at two miles and made an uneventful landing in light rain. As I taxied into parking the master relay dropped and all electrical power was gone. I was on the ground for less than 10 minutes, not much room for IMC with no electrical power.
The Bad News.. If it had failed two hours earlier I would have been near home base a would have saved a couple hundred on the alternator repair.
Always better to be down on the ground wishing you were up there instead of up there wishing you were on the ground.
 
I've lost the alt twice, but there are so many redundant ways to be warned in our plane.

  1. HIGH/LOW VOLT light on the annunciator panel.
  2. Ammeter
  3. Volt meter
  4. Separate LOW VOLT red light on panel
  5. JPI flashes on low volt
If I can't figure it out at that point, I'm an idiot.
 
I had the avionics shop add a test button for the annunciator panel in a previous plane. I found my oil light and my alternator lights went bad before flight using that tester.
Standard in the Cirrus that I fly now.

Tim

Sent from my HD1907 using Tapatalk
 
tspear said:
I had the avionics shop add a test button for the annunciator panel in a previous plane.
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Yup, the Mooney has a test button for the annunciator, great thing to have. I also test the marker lights (although I haven't run across an active marker in a while) and the AP test button tests all of the AP annunciator lights as well. Part of the runup portion of the checklist.
 
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My MVP50 throws a big yellow light when the alternator drops off line. It's hard to miss now.
 
Plane Power alternators have a nice bright ALT INOP light.
 
Gill and Concorde each have a continued airworthiness requirements for their battery, very few people comply with it and put it in the log book. Just how long should your battery 25 amp hour or 35 amp hour last, if you fly IFR and the ALT. light comes on it would be nice to know if it will only last a few minutes or over a hour or more.
 
TrueCourse said:
Good point and the very reason my digital voltmeter for the cigar lighter arrives this week. I’ve been watching the load meter (ammeter) like a hawk lately.
Click to expand...

I went with one of these in my 172 after the first alternator failure, so I was able to catch the second alternator failure pretty quick. In my 10 I put a bright yellow 'Low power' light that blinks
 
brien23 said:
Gill and Concorde each have a continued airworthiness requirements for their battery, very few people comply with it and put it in the log book. Just how long should your battery 25 amp hour or 35 amp hour last, if you fly IFR and the ALT. light comes on it would be nice to know if it will only last a few minutes or over a hour or more.
Click to expand...

The second ALT failure was at night, luckily VFR, but the lights went out before I got to the runway. That's why I immediately pull the power, and while the plane is slowing to Vlo, I turn off unnecessary equipment and pull breakers to shed load. Once below Vlo, get the gear down. Yes, I know we have the lawnmower cord to lower the gear, but I'd rather not rely on that. In my case I landed flaps up as by the time I was close to the airport the zots were gone.
 
agree on those annunciation lights.. i had a vac failure once and the last thing i noticed are those warning lights when i started looking for it.
 
The Archer has the three annunciation lights on the panel [ VAC ALT OIL ] and they’re pretty visible when illuminated in test during the run-up.
 
Ryanb said:
The Archer has the three annunciation lights on the panel [ VAC ALT OIL ] and they’re pretty visible when illuminated in test during the run-up.
Click to expand...
yes but hardly visible in flight depending on which way sun is shinning, unless you are looking for those lights. when i had my vacuum failure - i noticed the AP was going bonkers, then i noticed the AI rolling over , then checked the Vac gauge and found it was dying (not yet dead), then i looked for the damn light and saw it barely on. when you hit the test button, its lot more illuminated.

i haven't had the honor of alt failure mid flight yet, there, i just jinxed it
 
get one of these chiefaircraft.com/ei-va-1a.html
it has a discharge red light that is sunlight readable and it is also a primary replacement for the ammeter. it shows the current draw, has a switch to see battery voltage too. of course if you have a JPI, that will flash in your face too
 
Ryanb said:
The Archer has the three annunciation lights on the panel [ VAC ALT OIL ] and they’re pretty visible when illuminated in test during the run-up.
Click to expand...

Yes, when you push the test button they are. When the alternator actually fails though, the light is nearly invisible. That's the thing I don't think most people would expect until you actually see it happen.
 
cowman said:
Yes, when you push the test button they are. When the alternator actually fails though, the light is nearly invisible. That's the thing I don't think most people would expect until you actually see it happen.
Click to expand...
Good to know!
 
Among the other visual alerts mentioned above, a voice annunciator that audibly warns for voltage, oil press, vac, eng monitor (fuel, shock cool, etc). Gets your attention.
 
cowman said:
Yes, when you push the test button they are. When the alternator actually fails though, the light is nearly invisible. That's the thing I don't think most people would expect until you actually see it happen.
Click to expand...

I did not have this issue when I lost alternators.
Could the battery be weak?

Tim
 
cowman said:
I've now had the honor of experiencing in-flight alternator failures in both PA-28 and PA-32R Pipers. I'm not too familiar with other types so maybe this doesn't apply to all aircraft but it's definitely applied to the ones I've owned.

Both of these aircraft had the three square orange annunciators.... VAC ALT OIL. In both cases the ALT light was so dim in daylight that it was barely visible. Even cupping my hands over it to provide shade it was barely possible to tell it was on. This will NOT get your attention in the event of a failure. In the PA-28 my first warning was my GPS screen going blank as voltage dropped too low for it to stay on.

In the PA-32R I had an EDM-800 engine analyzer that started flashing the voltage at me. I dropped the gear right away and flew about 30min in VFR conditions back home, didn't lose nav or comms the entire time. I had about 11.5-11.8V all the way to landing.

Anyway what I really wanted to get across is that annunciator light is basically useless. Unless you're watching your ammeter like a hawk you probably won't notice it moving from just above 0 to 0. That engine analyzer made a HUGE difference in detecting the problem quickly. If getting one of those isn't in the cards and you have a cigarette lighter there are digital voltmeters that will plug into them and have USB charging ports on them for very reasonable prices on amazon. Better than nothing, I'd suggest something especially if you fly in IMC or are flying a retract.
Click to expand...
Thanks for sharing this Jaime. We have one of those cigarette lighter voltimeter/USB port/aural voltage alert things in all of our club planes and it's nice to know that I'll get some warning if the charging system craps out. They're under $15
 
brien23 said:
Gill and Concorde each have a continued airworthiness requirements for their battery, very few people comply with it and put it in the log book. Just how long should your battery 25 amp hour or 35 amp hour last, if you fly IFR and the ALT. light comes on it would be nice to know if it will only last a few minutes or over a hour or more.
Click to expand...

Fully charged battery lasts about two hours in a PA 28 with all radios and nav lights on
 
All these alternator failure stories sound like what I was told in training years ago, and that it'd take another 30-45 minutes prior to total loss of power.

Here's a different version that students should be aware of:

Was on a night flight in my previous Tiger. My alternator separated and cantored 20* on a locked pulley with the belt still spinning on it. My "annunciator" was a cockpit full of smoke from that belt and total loss of ALL electrical power instantly. The battery also exploded in the event, but am unsure of the sequence. Plane flew fine in the dark the last 2 miles home (great timing). Plane was 1 week out of annual.

My field was FT runway lights, so didn't need to pull out the handheld to activate them.
 
danhagan said:
Was on a night flight in my previous Tiger. My alternator separated and cantored 20* on a locked pulley with the belt still spinning on it. My "annunciator" was a cockpit full of smoke from that belt and total loss of ALL electrical power instantly. The battery also exploded in the event, but am unsure of the sequence.....Plane was 1 week out of annual.
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My guess is that the alternator had been out and reinstalled but the hardware wasn't doen up properly. Or the bracket broke. The alternator output wire shorted on something, causing a massive battery load that blew it up and also loaded the alternator to the point that it wouldn't turn with the now-loose belt.
 
I've said it too many times already: aircraft alternators need regular brush inspections. Aircraft alternators are adapted from cars, but they spin much faster in the airplane than they do in the car. They're geared so that at engine redline the alternator is near its redline, too, so that at idle it's spinning fast enough to power everything. Except that in the car they almost never reach redline, but in the airplane they're near it all the time except on the ground. Those brushes wear out faster, so the airframe manufacturers include it in their inspection sheets. Almost all alternator failures are due to worn-out brushes.

Failures of new or exchange alternators are often due to too much grease in the rear bearing, which gets out and ends up on the slip rings and brushes and forms a high-resistance sludge that limits the field current. Kelly/Hartzell is famous for that; I've seen it for 20 years or more and they still can't get it right. Some small shops also make that mistake.

Alternator failures are occasionally due to broken wiring at the alternator or regulator, and that's just another shortcoming in inspections.

I'd like to know what the findings were on all the alternator failures in this thread. When I looked after the flight school fleet we always did the 500-hour alternator inspections and never had an alternator fail unless it was a new or exchange one that had been overgreased. Had one fail because someone left the master on after a flight, which sends full field current into the rotor windings and they get hot and can cook themselves in an hour or so with no cooling airflow. Had a couple of other system failures when the "new-and-improved" electronic regulators were burning out after very few hours.

Regularly inspecting and replacing the brushes prevented at least 95% of failures.
 
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brien23 said:
Gill and Concorde each have a continued airworthiness requirements for their battery, very few people comply with it and put it in the log book. Just how long should your battery 25 amp hour or 35 amp hour last, if you fly IFR and the ALT. light comes on it would be nice to know if it will only last a few minutes or over a hour or more.
Click to expand...

Not sure what you mean by how long the battery will last. If you mean how many years before needing preemptive replacement, then I guess they can give you an idea when to replace it event though it still works.

if you mean how long it will have enough energy to operate the plane accessories, that’s near impossible. The only way you can know that is to know the amp hours of charge left in the battery at that time and know th current load at the time. Too many variables involved to know without some petty serious instrumentation involved.
 
Dan Thomas said:
I'd like to know what the findings were on all the alternator failures in this thread.
Click to expand...

Most recent one was straightforward enough, brushes were OK mechanic found an excessively high resistance on the rotor windings. Hopefully the new alternator will fix it and that will be the end.

The previous one on my Archer was a much longer and more confusing saga.... I'll give the cliff's notes version:
Far far from home on a cross country I had an intermittent alternator that would come back briefly with a reset of the ALT master switch. Alternator checked out good, replaced the regulator, flew home with no further problems... seemingly.

Within about 10-15hours of that repair I had yet another failure. Wiring was fine, A&P replaced brushes and it checked out good on the ground. I went for a test flight, tested good on the runup, failed right at rotation. This went back and forth a few times ending in us ordering a reman alternator.

Ground check was again good, I went up and all seemed well. I decided to do some steep turns, immediately on entering the turn my ALT light came on, the field breaker popped, and I smelled burnt electrical odor. Apon landing it was discovered that the regulator had burnt up. Wiring was checked, voltages were checked, resistances were checked... all fine. We all shrugged and figured I got a bad regulator. Hahaha... the replacement didn't work either but fortunately had a protection circuit. Many hours of hair pulling, wire checking, etc later and we were stumped. A&P finally noticed abnormal amounts of wear on the brushes for a "new" alternator. Apon disassembly the problem was found- the rear bearing had one needle that had fallen flat against the back of the shaft, allowing the shaft to wobble slightly and creating an intermittent short. :|
 
I have a generator and lost electrical at 2:00 AM between Vegas and Phoenix but the generator was fine. It was a very intermittent CB that was cutting in and out for several months but would never stay failed long enough to trace as the cause. Give me fuse any day. They are either 100% good or 100% blown. No intermittent. The dimming interior lights and ammeter told me everything. Went into KPHX no transponder as they had me on primary radar.
 
Dan Thomas said:
Regularly inspecting and replacing the brushes prevented at least 95% of failures.
Click to expand...

Direct drive alternators have a torque slip clutch to prevent an alternator lock up taking out the accessory drive train. If it fails in a "slip" mode the alternator will only turn if there is no load on it. That is what my failure turned out to be.
 
MBDiagMan said:
Not sure what you mean by how long the battery will last. If you mean how many years before needing preemptive replacement, then I guess they can give you an idea when to replace it event though it still works.

if you mean how long it will have enough energy to operate the plane accessories, that’s near impossible. The only way you can know that is to know the amp hours of charge left in the battery at that time and know th current load at the time. Too many variables involved to know without some petty serious instrumentation involved.
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In the shop we used this machine we used to test battery capacity:

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The battery is first fully charged and then let sit until cool, maybe an hour or two. Then the machine is connected, the battery's rating punched in, and you hit Start. It loads the battery and runs it down to a calibrated voltage and figures the capacity from the time it took to do that. Gill (Teledyne) says that anything above 80% is OK. I've seen over 100% a few times on fairly fresh batteries. The machine gives a really good idea as to how long you might have left with it.

A properly operating alternator and regulator will bring the battery to a fully-charged condition. The capacity at that point is dependent on the condition of the plates and electrolyte. Plates tend to accumulate a permanent layer of lead sulfate over time that reduces their performance. Running a battery dead and then leaving it like that for some time sulfates it badly and really reduces its life. The electrolyte can be diluted by people filling the cells with water up to the split ring when the battery isn't under charge at the time, and that results in some electrolyte loss when the alternator starts charging it and the electrolyte expands due to temperature and gassing. That not only makes a mess in the battery box (and sometimes the aircraft belly) but adding water and boiling off electrolyte and adding more water is diluting the electrolyte. You should only top it up if it's charging and actively bubbling a bit, as per Gill's or Concorde's instructions. If not on charge I topped it to halfway between the plates and the split ring and never lost a drop. The plates only need to be covered.
 
Dan Thomas said:
My guess is that the alternator had been out and reinstalled but the hardware wasn't doen up properly. Or the bracket broke. The alternator output wire shorted on something, causing a massive battery load that blew it up and also loaded the alternator to the point that it wouldn't turn with the now-loose belt.
Click to expand...

Neither ... the screws that hold the front and rear assembly sheared, front was no longer attached. No work on alternator during annual other than belt tension (which might have been a contributing factor).
 
An alternator light on a gear driven alt/gen like on a Continental 520 could be reeeeeaaaaaaalllllly bad. There have been very recent posts on beechtalk with grenaded engine that were still running but the case was trashed.

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Smelled burning rubber on takeoff as gear was raising. Looked at voltmeter and realized belt burned up.
 
I have a fadec system and an alternator failure can become an exciting event.
 
Yes had comms fail on ride in a 182. Batt was low when we fired it up. Probably shouldn't have left the ground.

Sent from my SM-G975U using Tapatalk
 
How many of y'all wait until the engine is running before turning on the ALT side of the Master Switch?
 
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