First failure

[azure]

Well it had to happen eventually. No, I didn't fail my checkride, this is Maintenance Bay, remember? Anyway since I bought my airplane everything has been running fairly smoothly except for minor glitches. Then yesterday I had 8JT over at PHN to recalibrate the Sandel heading indicator and also to swing my wet compass, which was way off on some headings. On the way back I decided to ask for the LOC BC 27L @ PTK to see if I remembered how to activate Back Course mode on the 480 (I didn't -- have to look that up again). Just as I went missed and started to raise the gear, I noticed that my EDM 700 was stuck on the BAT screen displaying a voltage of about 11.6V. Okay, I had just pulled the power to near idle and had noticed that sometimes the battery didn't charge at low rpms. My mechanic said that was normal. Waited for the gear to raise, full power for a while, but it was still showing 11.6. Then the Sandel started displaying the "Inverter frequency too low" error message Bill McKelvey had just told me about. Scary. Then the Sandel started powering itself off and then on again. As I turned towards VLL I tried to troubleshoot this. No breakers were tripped. Low voltage, Sandel acting weird. So I just shut it off and waited. Voltage went down to 11.2. So it wasn't the Sandel. Probably the alternator. By then I was close to VLL but I still waited, a little longer than I should have, before lowering the gear and adding flaps. It was a long 12 seconds but the gear did come down and locked. Voltage down to 10.4. Added flaps and landed. Back on the ramp I turned off all the avionics and the voltage came up to 12.4. Shut down and called my mechanic and announced "I think I've had an alternator failure." He agreed.

Then today I had second thoughts. What if there was something on the avionics bus that had failed in such a way as to draw so much current that even a healthy alternator couldn't keep up? My mechanic thought that wasn't likely but we did start the engine today and tried various loads. The battery was charging, up to normal charging voltage (13.4V) as long as only the beacon, panel lights, and TC were powered. Add anything else and it dropped below 13, add the avionics and it dropped below 12. So he's convinced it's the alternator and has already found a replacement. He'll pop it out and take it to an auto parts store to test, but he says "when" (not if) it tests bad, he'll put in the new one.

Oh, the old one had only 140 hours on it. It's a Kelly Aerospace rebuilt.

 

[wabower]

Ding-ding-ding! We have a winner! No further entries will be accepted.

Oh, the old one had only 140 hours on it. It's a Kelly Aerospace rebuilt.

 

[bbchien]

I just installe my SPARE kelly aerospace altenator on the right engine, to send the OEM Factory Reman Kelly Aerospace Alternator back for warranty repair. Nothing else is wrong with your airplane.

 

[Clark1961]

I just installe my SPARE kelly aerospace altenator on the right engine, to send the OEM Factory Reman Kelly Aerospace Alternator back for warranty repair. Nothing else is wrong with your airplane.

All I can say is have your local automotive alternator rebuild shop do the repair as an A&P supervised rebuild. I've got the same engine as you do Doc and I'm convinced that any auto alternator shop that knows Dodge rebuilds will be able to do a good job. It's just bearings and and diodes. It'll work out better in the end...

Now the alternator drives are a completely different story (unfortunately).

 

[Steve]

13.4 V seems low to me...

 

[N801BH]

Don't ya just love those YELLOW TAGGED FAA approved parts ???

Ben.

 

[Henning]

13.4 V seems low to me...

13.4 is at the low end of the "everything is fine" scale. Your battery is 13.2V static at full charge. Anything above that and you are charging, the higher you go above that the harder you are cooking your battery and the shorter its lifespan.

 

[azure]

13.4 is at the low end of the "everything is fine" scale. Your battery is 13.2V static at full charge. Anything above that and you are charging, the higher you go above that the harder you are cooking your battery and the shorter its lifespan.

Okay, here is something I've been wondering about for a while. I do usually see 13.6-13.8 when the engine is first started, if I idle for a while with the radios off. I'm not 100% sure but I think it comes down to 13.4 with the avionics running. In flight it would vary between 13.2 and 13.4 but never higher than 13.5. Was that a sign that the alternator was weak all along? I always assumed that 13.2 meant the battery was at full charge for the moment and didn't need any higher, but after I'd seen the occasional 11.4-8 on the ground at low rpms I was always nervous when it dropped to 13.2 in flight and watched it carefully when I noticed that. But it never went any lower in flight -- until Tuesday.

 

[bbchien]

How old is the battery? At 13.2 it's not easily cooked....

 

[Henning]

Okay, here is something I've been wondering about for a while. I do usually see 13.6-13.8 when the engine is first started, if I idle for a while with the radios off. I'm not 100% sure but I think it comes down to 13.4 with the avionics running. In flight it would vary between 13.2 and 13.4 but never higher than 13.5. Was that a sign that the alternator was weak all along? I always assumed that 13.2 meant the battery was at full charge for the moment and didn't need any higher, but after I'd seen the occasional 11.4-8 on the ground at low rpms I was always nervous when it dropped to 13.2 in flight and watched it carefully when I noticed that. But it never went any lower in flight -- until Tuesday.

Are you sure your battery is good? It could be eating your alternator. With an alternator you should never see that low of a voltage, there may be regulator issues as well.

 

[jesse]

13.4 V seems low to me...

Agree, something isn't right. Would be looking into battery / regulator / alternator.

 

[Steve]

13.4 is at the low end of the "everything is fine" scale. Your battery is 13.2V static at full charge. Anything above that and you are charging, the higher you go above that the harder you are cooking your battery and the shorter its lifespan.

well,

http://ronkilber.tripod.com/alternat/alternat.htm

When used in a 12-volt charging system, for example, the alternator output is rectified (converted) to direct current (DC) using diodes, then clamped at approximately 14.2 volts with the aid of a voltage regulator.

14.2 volts (+/- .4 volts) is the industry standard for charging systems using 12-volt batteries.

on my car if i see <13.8vDC across the battery with the engine running i started suspecting the alternator (which on my vehicle has an internal voltage regulator). if i read correctly the OP was seeing 13.4vDC with the engine running. maybe i misunderstood the problem description

 

[somorris]

there may be regulator issues as well.

A bad regulator will cook a battery pretty quick. Not sure about the low voltage readings, though.

 

[azure]

Are you sure your battery is good? It could be eating your alternator. With an alternator you should never see that low of a voltage, there may be regulator issues as well.

Yes, we've talked about possible regulator issues. But my mechanic says it's normal for the alternator to not produce enough output to charge the battery at low engine RPMs. Is he wrong? Before Tuesday, that is the only time I ever saw voltages like that. Even running up to 1500 or so was enough to bring it quickly back to 13.4.

The battery is 1 year old and has ~100 hours on it.

 

[azure]

on my car if i see <13.8vDC across the battery with the engine running i started suspecting the alternator (which on my vehicle has an internal voltage regulator). if i read correctly the OP was seeing 13.4vDC with the engine running. maybe i misunderstood the problem description

No, you understood correctly. I've always ("normally") seen 13.4 vDC with the engine and all the avionics running, a little higher with the avionics off.

 

[gismo]

Okay, here is something I've been wondering about for a while. I do usually see 13.6-13.8 when the engine is first started, if I idle for a while with the radios off. I'm not 100% sure but I think it comes down to 13.4 with the avionics running. In flight it would vary between 13.2 and 13.4 but never higher than 13.5. Was that a sign that the alternator was weak all along? I always assumed that 13.2 meant the battery was at full charge for the moment and didn't need any higher, but after I'd seen the occasional 11.4-8 on the ground at low rpms I was always nervous when it dropped to 13.2 in flight and watched it carefully when I noticed that. But it never went any lower in flight -- until Tuesday.

First thing to do is check the voltage at the battery with a calibrated digital voltmeter and compare the reading to the JPI. Try to do that with the engine running (at 1500 RPM or higher) and all the normal stuff turned on including pitot heat. If the voltage at the battery is below 13.8 under those conditions there is definitely something wrong with the charging system but there's no way to say what specifically is wrong without going through a proper diagnosis. Also check to see what RPM is necessary to sustain at least 13 volts at the battery. If the voltage goes below that at idle you still have a charging problem.

OTOH, if the battery voltage is good while the JPI reads lower, something's wrong with the wiring or the JPI is in error.

A few other points of interest:

IME, less than 10% of the good A&Ps understand electrical systems well enough to properly troubleshoot them. If yours is in the other 90% find some knowledgeable assistance.

If your battery voltage has been running below 13.8 for any significant length of time the battery is very likely sulfated which reduces it's capacity horrendously. The fact that you saw such a rapid decline in voltage as soon as the JPI detected a problem is another indication of a weak battery. If that's the case you might be able to "restore" the battery with a "desulphator" aka battery "conditioner". The least expensive is a 12v unit made by "Battery Minder" and available online for something like$50.

I strongly recommend that you have the battery fully charged (best done out of the plane) with a 5-10A charger and then perform a capacity test. If your mechanic doesn't have access to such a tester, you can get a pretty good idea using an inexpensive automotive headlamp and a multimeter. Measure the current the lamp draws at the start of the test (should be around 20A, if it's less than 15A use two lamps in parallel) and then measure the time it takes for the voltage to drop below 12 while powering the lamp. The time should be roughly equal to the battery's rated AH divided by the current times 60 minutes. If it's significantly less either go the desulphator route or get a new battery. The battery is your source of emergency power for the next time the alternator dies and if the capacity has been compromised you may come to regret that, especially if you're in IMC and or in the dark when it happens again.

The warning threshold on your JPI us user settable. It should be set to about halfway between the normal voltage (alternator working and all systems on except landing lights) and the voltage you see with the engine stopped and everything possible turned off except the JPI and in no case should the threshold be lower than 12.5 volts. Typically the correct setting will be around 13 volts. If you use a lower setting you won't get a warning until the battery's charge is already depleted. With the proper setting the JPI will flash the voltage (and turn on an external alarm indicator if you have one) shortly after the alternator quits.

 

[jesse]

Yes, we've talked about possible regulator issues. But my mechanic says it's normal for the alternator to not produce enough output to charge the battery at low engine RPMs. Is he wrong? Before Tuesday, that is the only time I ever saw voltages like that. Even running up to 1500 or so was enough to bring it quickly back to 13.4.

The battery is 1 year old and has ~100 hours on it.

The Cherokee I fly indicates about 14.1 volts with the engine idling and the same at full power. This is where alternators shine over generators. An abnormal change in voltage is a really good indicator that there is a problem. A much better indicator then the barely-sensitive-enough ammeters some aircraft have.

 

[azure]

Lance, thanks for the detailed troubleshooting instructions. So to sum up,

1. The battery voltage should not drop below 13V even at idle.

2. I've apparently had a charging system problem for a while.

3. If the JPI is accurate (needs to be checked against a calibrated meter), then my battery has been operating undercharged for at least the last 90 hours (since I bought the airplane) and may be sulfated.

Do I have that right?

My mechanic's reasoning as far as replacing the alternator is that the fact that the charging system cannot keep up with a load -- any load, including just the strobes, beacon, and nav and landing lights -- but comes up to at least 13.6 with everything turned off points to a bad alternator. I'd like to be sure it tests bad before replacing it but his logic sounds strongly suggestive to me -- but I'm not a mechanic.

I'll talk to him about doing a capacity check on the battery as that sounds like the next step after replacing the alternator.

 

[DutchessFlier]

Just another reason to install those LED taxi and landing lights Liz!

 

[azure]

Just another reason to install those LED taxi and landing lights Liz!

The LED landing light is going in now. The taxi light is in transit -- I got an email yesterday saying it had shipped. I'm afraid my mechanic will be on to the next plane by the time I have it in hand.

Unless he finds something else that needs fixin' -- but I'm obviously not hoping for that. I can live with an incandescent taxi light for a while longer.

 

[gismo]

Lance, thanks for the detailed troubleshooting instructions. So to sum up,

1. The battery voltage should not drop below 13V even at idle.

Heavy loads (incandescent landing/taxi lights, flap motor, or virtually everything else on at the same time) can exceed the capacity of the alternator at idle but otherwise, the answer is yes.

2. I've apparently had a charging system problem for a while.

assuming the JPI is reading accurately, yes.

3. If the JPI is accurate (needs to be checked against a calibrated meter), then my battery has been operating undercharged for at least the last 90 hours (since I bought the airplane) and may be sulfated.

correct

My mechanic's reasoning as far as replacing the alternator is that the fact that the charging system cannot keep up with a load -- any load, including just the strobes, beacon, and nav and landing lights -- but comes up to at least 13.6 with everything turned off points to a bad alternator. I'd like to be sure it tests bad before replacing it but his logic sounds strongly suggestive to me -- but I'm not a mechanic.

This could be due to a bad alternator but it's also possible that the regulator is malfunctioning or even misadjusted. You could also have a wiring problem (bad crimp, loose connection, broken wire), something as simple as a slipping belt, and it's even possible you have more than one problem. All too many mechanics resort to swapping things till the problem goes away without taking a little time to properly diagnose. A rebuilt alternator is probably a few to several hundred bucks plus R&R, and that's a lot of money to throw away if the problem is elsewhere. OTOH, alternator failures are fairly common so that's likely the odds on favorite.

There are several decent charging system troubleshooting guides online. I'd urge your mechanic to find and follow one. Most problems can be resolved to a single cause in a half hour or less with a multimeter and the correct approach.

This link contains basic aircraft charging system info and (at the end) a decent troubleshooting guide:

http://tinyurl.com/charging-system

I'll talk to him about doing a capacity check on the battery as that sounds like the next step after replacing the alternator.

You don't need to wait for the charging system to get fixed other than the need for a battery while troublshooting. Get the battery out of the airplane and charged up ASAP, the longer it sits in a discharged state (it sounds like it's really down now) the faster it deteriorates. Also the worst thing you could do is replace a bad alternator and then run the engine to charge a really dead battery. This will dump way more current into the battery than it's designed to take and further damage to the battery is likely. You want to charge the battery gradually, using a current between 5 and 10 amps for a 25-35 AH aircraft battery. The best chargers feed a constant current to the battery until the voltage reaches about 14 volts at which point they switch to a lower constant voltage (around 13.5V) for another 5-10 hours of "topping off".

 

[flyingcheesehead]

A much better indicator then the barely-sensitive-enough ammeters some aircraft have.

You ain't kiddin' about them being barely sensitive enough.

We had an intermittent alternator failure on the 182 about a month ago. I noticed it because the JPI started flashing a battery warning (I believe our warning threshold is set at 12.5).

I did all the usual stuff - alternator off and back on, etc. - with no improvement. It was day VFR, so no lights. But, I did notice that the ammeter seemed to still be reading 0, as expected. There is no way I would have known that the alternator had failed without the JPI until equipment started failing (radio, transponder would be the most likely candidates in this case).

So, I'm very happy that we got the JPI installed.

I also have to agree with Lance's sentiment that even 90% of the *good* A&P's don't know what they're doing when it comes to electrical problems. I had theorized that maybe the field wire or one of the others on the alternator was corroded (/loose/whatever), but they told us that the alternator belt was loose. Then the next person to fly had the identical problem, and when it went BACK into the shop, they noticed that ALL the terminals at the alternator were bad. Um, shouldn't you have checked that the first time?

 

[gismo]

You ain't kiddin' about them being barely sensitive enough.

We had an intermittent alternator failure on the 182 about a month ago. I noticed it because the JPI started flashing a battery warning (I believe our warning threshold is set at 12.5).

I did all the usual stuff - alternator off and back on, etc. - with no improvement. It was day VFR, so no lights. But, I did notice that the ammeter seemed to still be reading 0, as expected. There is no way I would have known that the alternator had failed without the JPI until equipment started failing (radio, transponder would be the most likely candidates in this case).

So, I'm very happy that we got the JPI installed.

An attention getting visual warning that activates when the bus voltage goes below 12.5-13 (or above 15) volts provides such a safety benefit WRT electrical system that I'm surprised the FAA didn't require them for IFR certification several years ago when they became practical. And while I hate name calling I consider anyone who flies at night, or especially in IMC without one to be a fool.

I also have to agree with Lance's sentiment that even 90% of the *good* A&P's don't know what they're doing when it comes to electrical problems. I had theorized that maybe the field wire or one of the others on the alternator was corroded (/loose/whatever), but they told us that the alternator belt was loose. Then the next person to fly had the identical problem, and when it went BACK into the shop, they noticed that ALL the terminals at the alternator were bad. Um, shouldn't you have checked that the first time?

It also seems that most A&Ps prefer "mechanical" solutions to problems i.e. fixes that require a wrench. There also appears to be a strong tendency to '"fix" problems without diagnosing first whether the issue is mechanical or electrical.

 

[weirdjim]

I'd like to be sure it tests bad before replacing it but his logic sounds strongly suggestive to me -- but I'm not a mechanic.

I'll talk to him about doing a capacity check on the battery as that sounds like the next step after replacing the alternator.

That's why somebody suggested you take it to an AUTOMOBILE ELECTRICAL SHOP where they will spin it up (if they have the gearing driver) and check it under load. As that same somebody said, the usual only things going wrong (unless it has an internal voltage regulator) are diodes and bearings which are pretty much the same for that run of alternator.

Jim

 

[Skip Miller]

But my mechanic says it's normal for the alternator to not produce enough output to charge the battery at low engine RPMs. Is he wrong?

Yes, he is wrong. Depending on the load on the battery at the time, of course. Alternators produce way more amperage at low RPMs than the old generators.

I'm betting one of the three main diodes in the alternator is blown.

-Skip

 

[azure]

Well, it turned out the rotor was bad in the alternator. My mechanic took it to an auto parts shop (not quite the same thing as an auto electrical shop, I realise that, but the best he could manage) and that was their diagnosis.

So the new alternator is going in, he will put a trickle charger on the battery and run a capacity test once it's fully charged -- it sounds like he has the equipment to do that.

Then if I'm still seeing 13.4V on the JPI, we'll start serious troubleshooting and it sounds like the first thing to do is check the JPI.

Thanks for all the suggestions.

 

[bbchien]

Yes, he is wrong. Depending on the load on the battery at the time, of course. Alternators produce way more amperage at low RPMs than the old generators.

I'm betting one of the three main diodes in the alternator is blown.

-Skip

There are FOUR in a wheatstone bridge, Skip :wink2:. Liz A is a physics professor and understands this stuff.....

 

[Capt. Geoffrey Thorpe]

Yes, we've talked about possible regulator issues. But my mechanic says it's normal for the alternator to not produce enough output to charge the battery at low engine RPMs. Is he wrong? Before Tuesday, that is the only time I ever saw voltages like that. Even running up to 1500 or so was enough to bring it quickly back to 13.4.

If you have a lot of electrical junk running, it is possible to overwhelm an alternator at idle. It depends. I believe that you said he was going to get it tested at an auto parts store - that will uncover any bad diodes that would result in the alternator putting out less current than it should.

 

[azure]

There are FOUR in a wheatstone bridge, Skip :wink2:. Liz A is a physics professor and understands this stuff.....

Not a professor, but physics yes not engineering. I know enough to not pretend to know more about the innards of these units than I do. Anyway there are other kinds of bridge rectifiers that use more or perhaps fewer than four diodes and I have no idea what kind is inside a DOFF10300J.

Too many more weeks like this one and I won't even pretend to have the time or energy left over to try to troubleshoot my own airplane... much less fly it.

 

[AdamB]

Gee Liz, sounds like you're going through what I'm going through at the same time...

Coming back from Maine on my last flight, I had my Alternator Idiot light come on and noticed the analog voltage gauge down in the yellow/Red area. Digital voltage gauge was also locked in Low Voltage error mode.
Trouble shot and found shutting the NAV lights off caused the voltage to shoot right back up.

Mechanic looked at it and found a short in the tail light wiring.
Fixed it up and went to go for another flight later in the week.
After my runup, I noticed the Alternator light back on again and low voltage.
This time it wasn't anyone thing, just more load = less voltage and vice versa.
Decided to not fly that night, as dark, mountains, and possibility of a total blackout was too high.

Kelly Aerospace rebuilt showed up today..
Should be back in business soon!

 

[gismo]

There are FOUR in a wheatstone bridge, Skip :wink2:. Liz A is a physics professor and understands this stuff.....

Doc Bruce, you'd better stick to medicine. A Wheatstone bridge has nothing to do with rectification or diodes and automotive/aircraft alternators are 3 phase which requires six diodes. Then again you were correct that the count is higher than three.

 

[gismo]

Coming back from Maine on my last flight, I had my Alternator Idiot light come on and noticed the analog voltage gauge down in the yellow/Red area. Digital voltage gauge was also locked in Low Voltage error mode.
Trouble shot and found shutting the NAV lights off caused the voltage to shoot right back up.

Mechanic looked at it and found a short in the tail light wiring.

Something else is going on here. A "short in the tail light wiring" that drew enough current to exceed the alternator's output for any length of time (i.e. more than a fraction of a second) should have opened the overcurrent protection on the nav light circuit.

 

[AdamB]

Something else is going on here. A "short in the tail light wiring" that drew enough current to exceed the alternator's output for any length of time (i.e. more than a fraction of a second) should have opened the overcurrent protection on the nav light circuit.

True. Not sure one lead to the other, just the sequence of events as they happened.
The Trinidad has circuit-breaker like switches to turn on lights etc...
When it was acting up that day, the switch would pop back out on it's own.
No regular circuit breakers ever tripped.

As to why the alternator died? Not really sure. There have been a couple of times lately that we've had trouble starting the plane (i.e. low battery). Could have been something in the making for awhile...

 

[RMCN172RG]

There are FOUR in a wheatstone bridge, Skip :wink2:. Liz A is a physics professor and understands this stuff.....

That's Electronics not Physics.

 

[gismo]

True. Not sure one lead to the other, just the sequence of events as they happened.
The Trinidad has circuit-breaker like switches to turn on lights etc...
When it was acting up that day, the switch would pop back out on it's own.
No regular circuit breakers ever tripped.

Ah, in that case the switch and CB are combined into one unit so you were "popping the breaker" and that's a good thing if there's a short.

As to why the alternator died? Not really sure. There have been a couple of times lately that we've had trouble starting the plane (i.e. low battery). Could have been something in the making for awhile...

OK, the alternator issue wasn't related to the tail lamp wiring problem. If a diode in the alternator was bad it would put out it's output capacity would be significantly reduced (especially at low RPM) and that could lead to a weak battery. Just another of many charging system failures that tend to go unnoticed without a voltage sensor.

 

[azure]

So the battery is charged and tested up to spec, the new alternator is installed, and it keeps the voltage above 13 even with all the lights and avionics running. But it drops to 12.6 when the pitot heat is added, so we need to look further. Regulator problem? Wiring? At this point my mechanic doesn't have a clue and is waiting for guidance from the alternator rebuilder (T&W). He also needs to finish the oil change before anyone can do any further troubleshooting that requires the engine to be running... so most likely I won't know anything more until Monday at least.

I can't help but wonder what would cause the alternator rotor to fail. From what I've read that isn't a common failure point.

On the brighter side, my LED taxi light should arrive now by the time he's ready to button the cowl... I just hope this isn't a multi-week downtime.

 

[COFlyBoy]

That's Electronics not Physics.

Its all physics, deep down.

 

[AdamB]

Ah, in that case the switch and CB are combined into one unit so you were "popping the breaker" and that's a good thing if there's a short.


OK, the alternator issue wasn't related to the tail lamp wiring problem. If a diode in the alternator was bad it would put out it's output capacity would be significantly reduced (especially at low RPM) and that could lead to a weak battery. Just another of many charging system failures that tend to go unnoticed without a voltage sensor.

That's basically what seemed to happen. At 1500 RPM, everything seemed fine. At 1000 it was very marginal, lower RPMs were of course worse.

 

[gismo]

So the battery is charged and tested up to spec, the new alternator is installed, and it keeps the voltage above 13 even with all the lights and avionics running. But it drops to 12.6 when the pitot heat is added, so we need to look further. Regulator problem? Wiring? At this point my mechanic doesn't have a clue and is waiting for guidance from the alternator rebuilder (T&W). He also needs to finish the oil change before anyone can do any further troubleshooting that requires the engine to be running... so most likely I won't know anything more until Monday at least.

An oil change on a single takes multiple days????

The key to diagnosing this problem is to monitor the voltage on the field when the bus voltage drops. If the field voltage is significantly less than the bus voltage you have a problem in the regulator or it's wiring (don't forget the alternator and/or master switch plus the associated circuit breaker, all of which supplies power to the regulator). If the field voltage is good (when the bus is low) the regulator and it's supply are likely OK and definitely not causing the low bus voltage. Remaining culprits are the new alternator (unlikely but possible), it's output wire including any terminals, and the output CB (probably the highest amp CB on your panel).

BTW, as mentioned before, 13 volts is still way to low, you want to see at 14.0-14.2 volts with all "continuous" (i.e. everything except flap and gear motors or landing lights) loads operating.

I can't help but wonder what would cause the alternator rotor to fail. From what I've read that isn't a common failure point.

I'm not certain what the shop meant by a "rotor failure" which could be a short or open in the field winding (which would have resulted in no output), or a mechanical issue (e.g. bearings or a broken shaft). And I'm suspicious about whether or not your old alternator actually had any problem, given that you still have the same bus voltage issue.

On the brighter side, my LED taxi light should arrive now by the time he's ready to button the cowl... I just hope this isn't a multi-week downtime.

An oil change plus a taxi light installation shouldn't take more than a few hours total so it really shouldn't be a mono-week downtime.

 

[azure]

An oil change on a single takes multiple days????

He had a family function to go to in the afternoon. I'm not sure if he plans to just drop it until Monday or continue tomorrow. Hopefully the latter.

The key to diagnosing this problem is to monitor the voltage on the field when the bus voltage drops. If the field voltage is significantly less than the bus voltage you have a problem in the regulator or it's wiring (don't forget the alternator and/or master switch plus the associated circuit breaker, all of which supplies power to the regulator). If the field voltage is good (when the bus is low) the regulator and it's supply are likely OK and definitely not causing the low bus voltage. Remaining culprits are the new alternator (unlikely but possible), it's output wire including any terminals, and the output CB (probably the highest amp CB on your panel).

Thanks. According to my mechanic's earlier logic, since the deficit is still load dependent it would have to be the new alternator, but obviously that isn't necessarily the case here. I think he might be suspecting the alternator, since he's consulting with T&W for troubleshooting help, but I'm not sure.

BTW, as mentioned before, 13 volts is still way to low, you want to see at 14.0-14.2 volts with all "continuous" (i.e. everything except flap and gear motors or landing lights) loads operating.

That part he doesn't agree with. He says that 13.4 is plenty to charge the battery and so is just fine. Anything more, I gather, he believes would cook the battery.

I'm not certain what the shop meant by a "rotor failure" which could be a short or open in the field winding (which would have resulted in no output), or a mechanical issue (e.g. bearings or a broken shaft). And I'm suspicious about whether or not your old alternator actually had any problem, given that you still have the same bus voltage issue.

Yeah, I had the same thought, though I have no reason to suspect him of dishonesty and he did say that the rotor tested bad. That's all he said, I was planning to ask him if they had given further details the next time I talk to him.

An oil change plus a taxi light installation shouldn't take more than a few hours total so it really shouldn't be a mono-week downtime.

It was that, plus change the tires and brake pads, and now the electrical problem. All of that is done, except he has yet to add the oil. The electrical problem is the stickler since he clearly does not know how to troubleshoot it on his own. That's the part that worries me.

I will describe your strategy to him and see what he says.