Help! Alternator issues Cessna 150-B

What do you think is the Issue?

  • Bad Master (I did notice pulsing lights yesterday)

    Votes: 0 0.0%
  • Too much load on battery it’s a 12v System

    Votes: 0 0.0%
  • Bad battery

    Votes: 0 0.0%

  • Total voters
    9

Blake Blake Blake

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Jan 9, 2020
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Gydez12345
Hello I own a 1962 Cessna 150-B. The airplane has been a blessing till recent... the aircraft was purchased by me in 2017, I’ve used it to get my PPL and to build time. When I purchased the airplane the newly overhauled Om-200 only had 16 hours on it. As I am writing this post the TT on the engine is ~270. So nearly three years I’ve owned this two annuals and three alternators later... yes you are reading that correct! THREE alternators I’ve put in this thing. It eats them like a child eats candy. I recalled a whine with the first Ford Alternator that was in the aircraft... but was off on a work trip when my brother called me and informed me that the alternator had failed on him and was bringing the plane to the shop. We had our local mechanic who I’ve know since I was a teen, look at the airplane and replace our fried Ford Alternator. This event happened around 100 hours on the engine. So we assumed it was just poor/old parts that the old owner put in the aircraft. Over the past 12 months we’ve changed and upgraded some thing on the airplane... ADSB out and LED Landing light. We changed out our old school GE Filament bulbs that kept blowing out on average every 5-10 hours of flight time and with very very light usage. We assumed the bulbs were just crap and kept eating the 20$ bulb cost considering we were quoted over 500$ for a LED one. So now we have a fancy LED bulb that lights up the sky it’s amazing and awesome ADSB-out... well 8 weeks back I was on a night flight after work... did my normal flying routine nothing raised any red flags... call tower and after I receive my taxi instructions I turn on my LED landing light to guide the way and head to my run up area... only the bulb stays lit for a few hundred yards. It’s night time so I am taxing with my Rotating beacon, nav lights and landing light... other things on in the aircraft are my red panel lights, ADSB, radios and DC Turn coordinator. As soon as I turned my strobes on to cross a different runway... someone threw me in the dark. Everything in the airplane was on but my LED landing light. I finished crossing the runway messed around with a few switches and was able to get the landing light to come back on after some time... but during the flight the landing light would randomly go out. I usually do not fly with my landing light on but because of what happened on the ground I thought that maybe I have a loose wire that I don’t want to risk not having a light while I approach the ground to land. So I decided to fly with it on. After this flight it was a normal occurrence for the landing light to have a mind of its own. Waiting for my mechanic to get back in town from vacation I continued flying here and there. Till last week on take off my heart sank when the smell of electrical burning entered the cockpit... I immediately turned around landed the plane and brought it to another shop on the field. Now the airplane has had a whining issue since I can remember. I’ve done all of my training in the airplane and don’t know anything else other than my plane. I’ve looked online and alternator whine is just something that Cessna 150s do... is the common response I found on others threads across the internet. So when I brought the airplane in I explained what I experienced.
-alternator whine ongoing for months
-landing light bad switch
-burning smell on T/O
-Voltage meter changing with higher or lower RPMs

he assured me they would look into everything and get back to me.

I got the news one week later that. Yes I did have a failed landing switch. And they were able to get the light to work when they jumped it from the taxi light. Ok easy fix! Then he continued to tell me the the alternator seems to be functioning properly as far as load and charging the battery. I told him more concerns that I had with the whine of the alternator and that I was also transmitting the whine to Tower who had told me many times that they could hear a whine in the background. They then decided to remove the alternator and run a few more tests on it. It came back that the alternator had a failed diode or diodes... and that burning smell well multiple connections had fried in the alternator along with the insulation plate had completely melted. Grateful that they had found the issue and offered a solution my wallet was not. I’ve now had the airplane back for two days... brand new alternator no overhauled parts for me anymore I’ve already had a second one go out on me. I flew for 1.6 hours yesterday zero issues the alternator was silent in my headset all I could hear was what sound like a light wind blowing in my ear. Landing light was working great off and on at the flick of a switch! To today... start up no issues I warmed the airplane up and started through my normal routine. Started taxing with my instructions.. all avionics on in the airplane, lights (Landing light, nav lights and rotating beacon) and as I was crossing the runway I turn on my strobes... landing light goes out again... I look at my load on my battery and there is no change... I start unloading and loading things on and the needle moved only slightly when I turn on the taxi light. The landing light comes on momentarily then Back out again I turn off the strobes and turn the landing light back on nothing at the first flick of off then on then a beam of light returns to only turn off again. So I take off with my taxi light. And inflight get my landing light to work again and didn’t have any issues with it for 3 of my 4 landings. The last landing I couldn’t get the light to come on. Shortly after I landed and taxied to my hangar I could hear the infamous whine again. Only 3 hours of flight time it stayed away. I didn’t want to believe my ears so I went on live ATC to listen to the transmission and sure enough on my departure no whine was transmitted and my last landing you can her the pitch increase with more throttle.

I apologize for the length of my novel here. Any advice would be greatly appreciated the more minds on this the better. I am returning to my mechanic tomorrow to sort things out and I would like to have some things to pick his brain with. Thank you!

Blake
 
Hang on guys. I’m the usual wall of text guy but getting this back into something readable will take an expert like me. LOL.

Good god man. Paragraphs and line breaks! LOL.

Not kidding. I’m trying to read it. I’ll shoot out a TL;DR version of it if I can.... wish me luck. :)
 
Hang on guys. I’m the usual wall of text guy but getting this back into something readable will take an expert like me. LOL.

Good god man. Paragraphs and line breaks! LOL.

Not kidding. I’m trying to read it. I’ll shoot out a TL;DR version of it if I can.... wish me luck. :)
Lol my apologies paragraph structure never was my strong suit!
 
Okay wasn’t as hard as I thought:

Alternator failing regularly with smoke smell.
Changed multiple loads in electrical system.

Assumed :

No load testing of anything done.
No mention of battery replacement in three years.
No mention of condition of four decade old wiring.
Non mention of voltage regulator testing or voltage when not running vs running.

Predictions:

Going to need someone who can operate a multimeter and read a wiring diagram, and compare it to what’s actually been done to the aircraft.

You’re going to get a total shotgun troubleshooting approach to electrical systems like all PoA threads.

Sooner or later one of the long time electrical trouble shooters will lose it and yell at everyone to do the simple tests and cheap tests first.

I’m going with simple voltage measurements first. The multimeter is $5 at Harbor Freight.

Did I do good @weirdjim ?

I know I jumped past the simple making sure the stupid belt pulley is straight and the belt isn’t burning... I know... :)
 
Have your checked the voltage regulator? This sounds like you may have an overvoltage situation.

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Have your checked the voltage regulator? This sounds like you may have an overvoltage situation.

+1 - but I am NOT an aircraft electrical system expert.

The short bulb life on the conventional bulbs sounds like possible overvoltage - maybe quite short spikes?

LED "bulbs" are complex beasts internally. I wonder if the LED landing light might shut itself down if there was an overvoltage? Not necessarily by design.

https://www.amazon.com/Lascar-Elect...003DS0BS2/ref=pd_sbs_60_2/137-5740220-6135005


Well this one of not very fast. Maybe get one that can do a higher sample rate.
 
Sooner or later one of the long time electrical trouble shooters will lose it and yell at everyone to do the simple tests and cheap tests first.
That there. He's dealing with an ancient 150 that dates from 1961 or '62. Nearly 60 years old. Wiring and connectors oxidized. Fuses and fuseholder contacts oxidized. Switch contacts oxidized. Who knows how many places are contributing to the problem? Oxidized/corroded crimp terminals make a huge amount of trouble, and even the "A" wire from the alternator to the regulator might be intermittently resisting so that the regulator thinks the voltage is falling so it juices the alternator field and overvolts everything. The alternator output wire wight be chafing/shorting on something and frying the alternator internals. The little noise filter on the firewall that the alternator output goes through might be shorting internally. Lots of places. And getting it to fail long enough to track it down can be fun, too.

Alternator whine can come from a perfectly good alternator as well. All you need are the headset jacks to be grounded to the panel in an old airplane with all sorts of ground loop problems from oxidized airframe joints and you'll get whine. Can get strobe noise, too. Headset jacks shouldn't be grounded; there are insulators for that.

His alternator is gear-driven. No belts. O-200.
 
My first reaction is what does the wiring look like as Dan posted. I'm really sick of junk wiring FWF on some of these ships. Wire isn't expensive but the labor is.

I'm guessing it has a vibrating type regulator?
 
It’s gear driven alternator... the airframe is the only thing from the 60’s everything else is new the build was done in 2016... so from what I understand everything was new.
-instruments
-wiring
-switches
-engine

All new... I’m just curious if something did go wrong with a switch or the gentleman that built it didn’t ground something properly.
 
That there. He's dealing with an ancient 150 that dates from 1961 or '62. Nearly 60 years old. Wiring and connectors oxidized. Fuses and fuseholder contacts oxidized. Switch contacts oxidized. Who knows how many places are contributing to the problem? Oxidized/corroded crimp terminals make a huge amount of trouble, and even the "A" wire from the alternator to the regulator might be intermittently resisting so that the regulator thinks the voltage is falling so it juices the alternator field and overvolts everything. The alternator output wire wight be chafing/shorting on something and frying the alternator internals. The little noise filter on the firewall that the alternator output goes through might be shorting internally. Lots of places. And getting it to fail long enough to track it down can be fun, too.

Alternator whine can come from a perfectly good alternator as well. All you need are the headset jacks to be grounded to the panel in an old airplane with all sorts of ground loop problems from oxidized airframe joints and you'll get whine. Can get strobe noise, too. Headset jacks shouldn't be grounded; there are insulators for that.

His alternator is gear-driven. No belts. O-200.
I do also get strobe noise in my headset.
 
it was hard for me to follow the story skimming it, but did I notice a pattern with turning the strobes on results in the landing light going out?
 
It’s gear driven alternator... the airframe is the only thing from the 60’s everything else is new the build was done in 2016... so from what I understand everything was new.
-instruments
-wiring
-switches
-engine
The O-200 in a stock 150 of that era has a generator, not an alternator. I assume a Ford alternator was installed as part of the rebuild in 2016, but assuming an STC was properly executed, it should be in the logs. Have you contacted the STC holder for help?

Otherwise, most of my issues relative to alternators have been ground-related. The ground strap from the engine to the airframe, the local grounds where devices are connected, etc.

Ron Wanttaja
 
Not an expert here but I've found that most electrical problems are caused by bad connections and grounds. I do agree this sounds like an over voltage situation though. Probably because of the bad connections and grounds.
 
Okay wasn’t as hard as I thought:

Did I do good @weirdjim ?

I know I jumped past the simple making sure the stupid belt pulley is straight and the belt isn’t burning... I know... :)

You done good, den.

As I recall, the o-200 is a gear driven gen/alt, not belt driven. I may be wrong.

Jim
 
...the build was done in 2016... so from what I understand everything was new.
-instruments
-wiring
-switches
-engine

All new... I’m just curious if something did go wrong with a switch or the gentleman that built it didn’t ground something properly.

Something is definitely not according to schematics, then. It will take a sharp person with good understanding of electrical systems to survey the whole thing and spot the miswiring. And people like that are rare. Electrical troubleshooting seems to be the weakest area among mechanics. I've seen the evidence of it in too many airplanes.
 
I had similar issues with our C-150 years ago, until I went back and shot every wire in the system from the alternator to the voltage regulator. Ultimately, I replaced the VR with a solid-state one and repaired the wiring at the same time.
 
Starting with alternator whine:
Excessive load
A failed diode, there are 3 windings producing smooth output, unless one is not working.
2 failed diodes, a sharper whine, all the load is on one winding. The last one will fail very soon, as it is overloaded, turning off as many devices as possible may keep you with power until you land.

Some of your symptoms suggest the voltage regulator may be spiking the voltage, which can destroy diodes.
A modern solid state one is the most reliable.
The high failure rate of incandescent bulbs almost guarantees regulator problems. Bad ground at the regulator, or high resistance connections in the wires to the regulator will cause intermittent high voltage.

Returning to the excessive load, the lack of abnormal readings on the ammeter suggests that the high current path is on the front of the firewall, but may be between the firewall and the ammeter.

The landing light going off and on suggests that he wire from the switch to the bulb may be the cause of this intermittent failure.


Concentrate on every wire forward of the firewall, and connecting to the regulator or alternator. With your symptoms, 90% probability the trouble will be found here.
 
Alright Update after months of absence. We have reached our 100 hour alternator burn out... the Engine has a gear driven alternator and this will be the 4 alternator on the aircraft in 300 hours of flight on the engine... I will take a photo of the wiring, every mechanic says that our airplane is beautiful. The wiring is clean and neat. The bulb issue with the LED landing light was a shorting issue a wire was chafing on a screw. Solved that gremlin! But the alternator issues persist. Airplane is in the shop right now but any ideas that I could send over to the mechanic would be greatly appreciated!

-last alternator had a failed diode and melted insulator plate.

-current alternator has worsening whine and I am suspecting that from experience it will fail soon. So trying to get new alternator under warranty for replacement. Want to end this battle and build my time and move on with life haha!
Thanks guys and gals!

blake
 
You have issues. Burned up alternator plate is a bad sign, something is probably shorting or your electrical load exceeds the capacity of the alternator. Start simple, have the battery tested, then confirm the regulator is working, make sure the starter always disengages. Add up the electrical loads by looking up each component that draws electricity and add all the loads up. Then delve into the wiring. Start with the obvious stuff you can see. Lots of work. Hopefully you find it.
 
You have issues. Burned up alternator plate is a bad sign, something is probably shorting or your electrical load exceeds the capacity of the alternator. Start simple, have the battery tested, then confirm the regulator is working, make sure the starter always disengages. Add up the electrical loads by looking up each component that draws electricity and add all the loads up. Then delve into the wiring. Start with the obvious stuff you can see. Lots of work. Hopefully you find it.
Thank you Paul!
 
You have issues. Burned up alternator plate is a bad sign, something is probably shorting or your electrical load exceeds the capacity of the alternator. Start simple, have the battery tested, then confirm the regulator is working, make sure the starter always disengages. Add up the electrical loads by looking up each component that draws electricity and add all the loads up. Then delve into the wiring. Start with the obvious stuff you can see. Lots of work. Hopefully you find it.
Battery is Brand new. Will look into loads on the system. Never looked into the starter issue. Regulator has been looked at by 3 mechanics and they all say it is functioning properly. Gremlins I tell ya!
 
Maybe get a cheap voltmeter to plug into the cig lighter adapter and compare against the panel voltmeter in flight.
 
Check all of your fuses and make sure they are of the correct rating.
 
Cheap digital meters on Alibaba and Banggood. However, my advice is to find somebody with a digital meter that reads PEAK voltage and holds it. Unless you are looking directly at the meter when the spike goes off, you will never catch it with a regular voltmeter.

I tried looking for a RECORDING voltmeter that you could play back after the flight to see what your battery bus was doing but I can't find an inexpensive one. I could probably design one in less time than it would take to track one down, but right now I'm up to my hiney in hippos.

I'm inclined to bet alternator regulator even though three mechanics said it was OK. What three mechanics said was that WHEN THEY WERE LOOKING AT IT, it was OK. You ought to be able to scab in a Ford regulator compatible with your alternator just for a few test flights to see if it did any good.

Jim
 
I'd avoid Banggood unless you're very patient and don't like being lied to by insolent customer service droids.
 
Still smells like regulator. Assuming it is a mechanical regulator, there are a bunch (two or even three I think) of wirewound resistors under the base. Make sure none of these are open or intermittent.

Make sure there is a ground wire for ALL current returns. Do not allow any currents to have to be returned to the battery via the airframe. Wires are used to carry currents. The airframe is used to carry forces.

Assume you have wing mounted landing lite. If you have cowl mounted lights, they see a lot of stick-slip engine vibration that can be minimized by silicon spray on the baffling between the engine and the cowl. That and adding an instrument shock mounts to our 172 eliminated those 4509 light failures. (Hold a good 4509 lite to your ear and rap the lite hard with your finger tip. They ring like a high frequency bell - ii.e. there is no filament damping in the bulb housing. OK, understand you replaced same with the LED unit$$$.)

Might you have a stuttering master relay? Anything that can momentarily disconnect the battery from the alternator or starter (or other big load) while the rest of the electronics etc are connected can be guilty of wiping stuff out, although it shouldn't take out a mechanical regulator

For really nasty troubleshooting it's hard to beat a DC coupled oscilloscope. I have an HP 130C that can be a godsend.

That all's been learned by this ME in 65 years of fooling with electricityo_O! It'll be a real challenge to find. Good luck!
 
The O-200 in a stock 150 of that era has a generator, not an alternator. I assume a Ford alternator was installed as part of the rebuild in 2016, but assuming an STC was properly executed, it should be in the logs. Have you contacted the STC holder for help?

Otherwise, most of my issues relative to alternators have been ground-related. The ground strap from the engine to the airframe, the local grounds where devices are connected, etc.

Ron Wanttaja

This is important. The aircraft has been monkeyed with. Has it been monkeyed with properly? Who knows. The owner needs to figure out what stc was installed and then trace the wires to ensure they are correct to start with. That will also help with finding parts. No stc used? Good luck!
 
Burned up alternator plate is a bad sign, something is probably shorting or your electrical load exceeds the capacity of the alternator.
Something wrong with that thinking. Unlike generators, alternators can't be overloaded... they're inherently self-limiting.

That there's repeated heat damage to these alternators suggests the alternator modification is not providing adequate cooling, or there's a heat source too near by... shorting the output wire to ground shouldn't damage an alternator.
 
Do 150s have the little blast tube for the alternator? Maybe make sure it's not filled with bird nests.
 
... shorting the output wire to ground shouldn't damage an alternator.
Oh, it could. Reducing the load resistance to zero raises the amperage to infinity, in theory. Diodes and windings don't like that at all. There are no limiting doodads in the alternator. They usually don't self-destruct because their capacity is normally greater than all the constant loads added together, maybe even with the intermittent loads added in. (Generators never had that capacity. A generator regulator has a current limiter, and all the output runs through it.) And there's a breaker or fuse, sized to the alternator's capacity, in the panel to prevent shorting overloads from the bus onward. If the alternator output cable or the noise filter have shorting issues the alternator will burn.

I once had a battery get sulfated in a flight-school Champ. The sulfate fell off the plates and shorted them at the bottoms of some of the cells, and the battery's internal resistance went essentially to zero. The ammeter pegged, way past capacity, and stayed there immediately at startup. Shut the thing down to save the alternator and avoid a battery explosion.
 
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My guess is the Alternator conversion was I/a/w later model configurations.
A damaged Blast Tube will get noticed but if it was never installed it could be running hot.

If the Ground cable is left off you will likely have other paths providing a ground.
Primer Line ,Thottle Cable and shielding will try to handle the chore.

It IS possible to have the ground cable or straps installed wrong. A rubber shock mount is not a good conductor.
 
My guess is the Alternator conversion was I/a/w later model configurations.
A damaged Blast Tube will get noticed but if it was never installed it could be running hot.

If the Ground cable is left off you will likely have other paths providing a ground.
Primer Line ,Thottle Cable and shielding will try to handle the chore.

It IS possible to have the ground cable or straps installed wrong. A rubber shock mount is not a good conductor.
Never saw a blast tube for the alternator or the mags on any 150. Those alternators have effective little fans in them.
 
They are there. It is not like the small blast tube on generators that attached to
the cover. These are 2 inch CAT or SCAT that just blows air in the area.

There is a clamp that has one of the Alternator thru-bolts going through it.
Posting pix is above my pay grade or I’d take a pic today.
 
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