Getting real tired of seeing this light on, guys.

cowman

cowman

Final Approach
PoA Supporter
Joined
Aug 12, 2012
Messages
5,405
Location
Danger Zone
Display Name
Display name:
Cowman
Really tired indeed8860E89F-B7A5-4864-BDD2-C126C6F5947F.jpeg

2 new regulators, a reman alternator, a new field wire, what’s even left? Seemed like it was fixed when I started out, did a couple touch and goes. Then as soon as I entered a left steel turn there it goes again.

I guess now they want to try swapping out the field breaker and possibly temporarily bypassing the alt switch to eliminate those as the problem. *sigh*. *rage*.
 
How much does the mechanic actually know about electrical systems? Seems like there is a lot of parts swapping going on and minimal diagnosing.

If you can, post a copy of the wiring diagram from your plane.
 
Check the amp draw first and then turn on one switch at a time to see if something drawing more than it should. Recently went thru similar stuff, got a reman alternator, ammeter still showed over 70 amp draw. Turns out the ammeter was gone too, OR it was the ammeter all along
 
PaulS said:
Has anyone chased it down with a volt meter?
Click to expand...

Digital and analogue. Checked all over. They spent a day going through all the wiring. I put a cigarette lighter voltmeter in. Reads 14v when the thing is working, about 11.9 when it’s not.

mondtster said:
How much does the mechanic actually know about electrical systems? Seems like there is a lot of parts swapping going on and minimal diagnosing.

If you can, post a copy of the wiring diagram from your plane.
Click to expand...

I think he knows what he’s doing, whatever it is has been intermittent which has made diagnosis hard. Every time they think they found it I take it out, everything looks good, then it goes again.

This has been an ongoing problem for months. The first voltage regulator was installed halfway across the country and (apparently) fixed the problem. Then about 15-ish hours of flight time it came back. My mechanic put in new brushes and said they were worn. Run up on ground was good, but it died shortly after takeoff on the first flight. So then they spent a day or two going through all the wiring. No faults found. So best guess was an internal alternator problem like a break in the windings. They put in a reman. Tested good. I took it out did some maneuvers and my voltage regulator cooked and tripped a breaker. It was definitely smoked, smelled burnt. So we put in a new regulator. Alternator bench tested shown good. This time it wouldn’t put out on the ground. Mechanic said he found something wrong with the brush bar in the alternator and fixed. Ran up good in the ground....

I took it for a test flight today and it was fine for about 20 minutes. Then I entered a left steep turn and the light is back on. Cycling the alternator switch will sometimes make it come back on.

Whatever the root problem is, it’s been intermittent and hasn’t wanted to show it’s self on the ground most of the time. Last stuff in this circuit we haven’t replaced would be everything between the alternator output side and the regulator input side.

Airplane is a 78 Archer II PA-28-181. Mechanic has a wiring diagram, I’ll have to google for it.
 
I had an intermittent alternator for years. The best electron chasers in AK couldn't figure it out. I stripped all the wiring in the plane and replaced it along with adding a new B&C alternator and regulator. No problem since. Wires don't last forever.
 
Ok, still scatter-shooting.

Need to have a meter lead to direct- test field wire at alternator, and at regulator.

If field is energized and alternator doesn't put out, alternator's bad.

You might see that the filed terminal at regulator is energized, and not at alternator - a concealed break in wire (very common in aircraft).
 
WannFly said:
Check the amp draw first and then turn on one switch at a time to see if something drawing more than it should. Recently went thru similar stuff, got a reman alternator, ammeter still showed over 70 amp draw. Turns out the ammeter was gone too, OR it was the ammeter all along
Click to expand...

Amp draw on the ammeter was one of the first things I looked at when it first happened. It looks completely normal, turn on a high-draw thing like a landing light and it comes up, turn it off it goes down. Sits where it always does on startup around 35 amps, then drops back between the 0 and 35 amp marks a minute or two after startup. When the light comes on it reads 0 of course.

However, one of my mechanic's theories is that there was an AD done on this plane long ago that added a shunt around the ammeter. It's on the list of potentials left to look at.


SCCutler said:
Ok, still scatter-shooting.

Need to have a meter lead to direct- test field wire at alternator, and at regulator.

If field is energized and alternator doesn't put out, alternator's bad.

You might see that the filed terminal at regulator is energized, and not at alternator - a concealed break in wire (very common in aircraft).
Click to expand...

Yeah... we've been through all that. I even had them run a new wire thinking even though it tested good maybe it was a concealed break that only showed it's self under the vibrations found in flight. No luck.



I've had many long conversations in the maintenance shop with us spit-balling what-ifs. I kind of suspect when I had the last voltage regulator go it may have screwed up the brush bar like he said and that might have thrown us off track as far as diagnosing the initial cause of all this. It's now at least back to it's original intermittent symptoms- generally working on the ground but failing in flight in short order.

I have a digital voltmeter and some jumpers wires with gator clips/spare wire. I'm considering a flight test with those hooked up to different things... really it would be more useful if I could have someone riding along watching the meters because I can't continually look at them and fly the airplane at the same time but one must sometimes make due with what one has on hand.
 
It’s a 40 year old airplane with an intermittent electrical problem that only manifests itself in flight so I don’t want to hear all you armchair hotshot troubleshooters trash talking a mechanic you don’t even know.

This is going to be difficult but in order to isolate it you really need to fly with everything off and energize one circuit or system at a time as best you can and see if you can narrow it down. The plane will fly perfectly fine without any electricity.
 
cowman said:
I've had many long conversations in the maintenance shop with us spit-balling what-ifs. I kind of suspect when I had the last voltage regulator go it may have screwed up the brush bar like he said and that might have thrown us off track as far as diagnosing the initial cause of all this. It's now at least back to it's original intermittent symptoms- generally working on the ground but failing in flight in short order.

I have a digital voltmeter and some jumpers wires with gator clips/spare wire. I'm considering a flight test with those hooked up to different things... really it would be more useful if I could have someone riding along watching the meters because I can't continually look at them and fly the airplane at the same time but one must sometimes make due with what one has on hand.
Click to expand...

I still want to see a wiring diagram but one thing in the field circuit you've made zero mention of is the over voltage relay. You might consider temporarily bypassing that (or replacing both the regulator and relay with a Plane Power regulator) and see what happens.
 
mondtster said:
I still want to see a wiring diagram but one thing in the field circuit you've made zero mention of is the over voltage relay. You might consider temporarily bypassing that (or replacing both the regulator and relay with a Plane Power regulator) and see what happens.
Click to expand...

By my model year the overvoltage relay was integrated into the regulator... and the current regulator is a plane power one with that built in so no way to bypass it. Been looking in that direction though, it makes sense but we've never actually seen a voltage spike.

Found a wiring diagram in here
http://www.centennialaviationacadem...er_archer_ii_pa-28-181_maintenance_manual.pdf
page 823 or 4B14
 
cowman said:
By my model year the overvoltage relay was integrated into the regulator... and the current regulator is a plane power one with that built in so no way to bypass it. Been looking in that direction though, it makes sense but we've never actually seen a voltage spike.

Found a wiring diagram in here
http://www.centennialaviationacadem...er_archer_ii_pa-28-181_maintenance_manual.pdf
page 823 or 4B14
Click to expand...

If you have a plane power regulator make sure it actually got wired right. I've been less than impressed with the manual, and the descriptions on how to substitute their product for something previously installed.

Are you sure that the regulator is well grounded?
 
Had a similar issue, was a bad ground, airframe to battery. Simple fix that was continuously overlooked, until a buddy said just replace the ground and see what happens, problem free for last 500 hours.


Sent from my iPhone using Tapatalk
 
Duster said:
Had a similar issue, was a bad ground, airframe to battery. Simple fix that was continuously overlooked, until a buddy said just replace the ground and see what happens, problem free for last 500 hours.


Sent from my iPhone using Tapatalk
Click to expand...

While checking that, check the overall health of the battery, too.

I’ve seen some really strange crap with solid state voltage regulators when the battery is in that “almost dead” state where it’ll still just crank over the engine, but is highly resistive internally and is self discharging on the ground more than it should, and causing the alternator to provide too many amps to keep up with the rest of the airplane’s loads AND the weak battery charging in flight.

Anyway, if the battery is more than a few years old, test it per the manufacturer’s instructions.
 
Duster said:
Had a similar issue, was a bad ground, airframe to battery. Simple fix that was continuously overlooked, until a buddy said just replace the ground and see what happens, problem free for last 500 hours.


Sent from my iPhone using Tapatalk
Click to expand...
I had the same issue (bad ground, although mine was panel ground) on a Cessna I once owned...caused all kinds of weird things to happen, that you wouldn't expect.
 
No idea anout your issue specifically, but I’m on my fourth alternator in three years. The issue with the first three was what Hartzell termed a “flying short”. The rotating field coil, at certain temperatures and rotational speeds, was expanding and rubbing against the case, effectively shorting the field to ground. In my plane the voltage regulator regulates the low side field terminal, so when the field shorted to ground, the alternator would max output and trip the over voltage relay. This would be intermitent at first and would happen more frequently as time went on.

Maybe something similar is happening in your case?


Sent from my iPad using Tapatalk
 
cowman said:
By my model year the overvoltage relay was integrated into the regulator... and the current regulator is a plane power one with that built in so no way to bypass it. Been looking in that direction though, it makes sense but we've never actually seen a voltage spike.

Found a wiring diagram in here
http://www.centennialaviationacadem...er_archer_ii_pa-28-181_maintenance_manual.pdf
page 823 or 4B14
Click to expand...

Does the alternator and regulator continue working normally when the light comes on?

Saw someone on the Mooney FB group today said that the fail sensor on those plane power regulators fails (ha) all the time. Maybe you got two bad ones...
 
Had a similar issue in our 182. Ours didn't have an ALT light and it was instead labeled overvoltage but I think it's the same thing.

It did turn out to be a wiring problem. Before that, it would fix itself if we cycled the master usually.
 
I'm not an A&P but have chased a lot of intermittent electrical problems over the years and my vote is for a bad ground. I've seen more odd electrical problems fixed with a new ground or battery than I care to admit. Remember, "path of least resistance".
 
Is your battery a wet cell? Steep bank doing something funky with the acid uncovering the plates? (Shouldn’t if the ball if centered?)
 
If the airplane has the usual OEM-type regulator and not a Plane Power or other ACU, that light will be connected directly to the voltage regulator's "I" terminal and all it indicates is that the regulator has been shut off for some reason. The regulator is turned on by its "S" terminal, which is fed by the alternator field breaker and ALT switch and through the overvolt sensor. A loose or corroded connection anywhere along that system is the first thing to look for. A loose ground for the overvolt sensor is a prime suspect; it loses its voltage reference and shuts off. These airplanes are old enough that wires and terminals corrode, and vibration frays and breaks them.

The regulator is NOT wired the same as in a car, and the light will not indicate a failed alternator or any battery deficiency or low RPM/low charge problem. It only indicates a shut-off regulator.

If it's an electronic regulator, turn the radios on with the ALT switch on and light out, then key the PTT and see if the light comes on. If so, there are bad coax shield ground connections somewhere allowing RF to escape and enter the system, creating tiny voltage spikes that fool the supersensitive voltage-sensing circuitry in the regulator or ACU, and it trips off.
 
Last edited:
Grounds have been checked, I'm doubtful of the RF thing unless it's a transponder because I know it's gone out several times while I was definitely not transmitting but worth a try. The trouble with any theory is it's intermittent so it needs to be checked when it goes.

One big clue seems to be it often takes it a few minutes to fail but once it does it has to be turned off for some time... a minute or two to come back. That kind of suggests something getting hot then cooling off. We really wondered about the voltage spiking and the overvolt protection kicking in but never have seen a voltmeter go above 14.2.

455 Bravo Uniform said:
Is your battery a wet cell? Steep bank doing something funky with the acid uncovering the plates? (Shouldn’t if the ball if centered?)
Click to expand...

We were discussing that one too... trying to figure out a good way to test it since batteries don't necessarily grow on trees. More thinking in the direction of a plate shorting against another but who knows.

Trying to find a day I'm free and the shop has at least two people working and they're not super busy so one of them can go up and play flight engineer and watch everything while I'm busy flying.
 
How far are you from KLAF? I may have a spare Concorde AGM that you can test with. It was old but still good when I pulled it (long story).
 
455 Bravo Uniform said:
How far are you from KLAF? I may have a spare Concorde AGM that you can test with. It was old but still good when I pulled it (long story).
Click to expand...

About 200nm, plane is at KUIN. I'd normally be down to hop in the plane and head over there... but not without a working charging system. The main guy isn't back in until Mon, sometimes he's good about finding stuff like this so we'll see how that goes.
 
Fooling with the battery is wasting time. A shorted cell could cause excess charging amperage, and the alternator breaker would pop. That's what it's for. A battery that isn't charging properly gives a low flow, and the charging system doesn't care at all. The light, as I said in post #25, indicates that the regulator is being shut off somehow, which means that it's losing the voltage at the "S" terminal. Chase that instead. Much better return on time investment. And MUCH cheaper to repair.

Unless it's an ACU, which I doubt. Troibleshooting would be much easier is we had a picture or part number of the regulator.
 
Dan Thomas said:
Fooling with the battery is wasting time. A shorted cell could cause excess charging amperage, and the alternator breaker would pop. That's what it's for. A battery that isn't charging properly gives a low flow, and the charging system doesn't care at all. The light, as I said in post #25, indicates that the regulator is being shut off somehow, which means that it's losing the voltage at the "S" terminal. Chase that instead. Much better return on time investment. And MUCH cheaper to repair.

Unless it's an ACU, which I doubt. Troibleshooting would be much easier is we had a picture or part number of the regulator.
Click to expand...
Or the alternator isn't charging during these episodes due to something in the alternator, interesting problem, will turn out to be something stupid going wrong, just need to find it. It would be nice to be able to monitor the voltages at these different points while flying rather than guessing and replacing parts. Maybe a few jumper wires back to the cockpit with a Volt meter to try and find what's failing.
 
PaulS said:
Or the alternator isn't charging during these episodes due to something in the alternator, interesting problem, will turn out to be something stupid going wrong, just need to find it. It would be nice to be able to monitor the voltages at these different points while flying rather than guessing and replacing parts. Maybe a few jumper wires back to the cockpit with a Volt meter to try and find what's failing.
Click to expand...
Like I said, it's lit because the regulator is shut off, and of course the alternator would not be charging then. BUT: The alternator belt can break, or the brushes wear all the way out, or the output or field wires break, or the alternator fall right out of the airplane, and the light will not come on. Like I said, they're not wired like a car and won't behave as a car's idiot light will. The car has the regulator's "S" terminal connected to the stator terminal on the alternator, and when the engine starts the residual magnetism in the rotor produces a small current that closes the regulator relay and energizes the alternator field. It's automatic. But in the airplane, that "S" terminal is controlled by the pilot through the ALT switch, not the alternator's stator, so that the alternator can be shut off in an emergency like an electrical fire or if the regulator sticks and starts massively ovevolting things. So, therefore, that regulator relay is not sensing alternator rotation and the "I" terminal won't energize the light if the alternator fails. It's a dumb setup, one that the electronic ACUs fixed. They DO sense an underperforming alternator. In our oldish airplanes we have to monitor the ammeter or loadmeter or voltmeter to see that the system is performing properly.
 
PaulS said:
Maybe a few jumper wires back to the cockpit with a Volt meter to try and find what's failing.
Click to expand...

Get the thing to fail on the ground, and leave everything turned on while you take voltage measurements between ground and these various points: The breaker's bus and output terminals, the ALT switch's terminals, the overvoltage sensor's terminals, and the "S" terminal on the regulator. At some point between the bus and the regulator you'll find a zero indication, and it will immediately become apparent what is failing.

Sometimes wiggling things can trip it. Sometimes it's just heat, and takes time to happen. Perhaps the overvolt sensor is going bad. More likely it's a tired old switch or breaker. Oxidized contacts and all that.
 
Dan Thomas said:
Get the thing to fail on the ground, and leave everything turned on while you take voltage measurements between ground and these various points: The breaker's bus and output terminals, the ALT switch's terminals, the overvoltage sensor's terminals, and the "S" terminal on the regulator. At some point between the bus and the regulator you'll find a zero indication, and it will immediately become apparent what is failing.

Sometimes wiggling things can trip it. Sometimes it's just heat, and takes time to happen. Perhaps the overvolt sensor is going bad. More likely it's a tired old switch or breaker. Oxidized contacts and all that.
Click to expand...

Yup, that's probably the best way to do it.
Based on the wiring diagram he referenced I count about 10 different discrete wires connected together between the electrical bus (looks like from the alternator circuit breaker) and the alternator field, plus who knows how many connectors and splices, I believe they are pictured in the diagram and I would try to find and account for those at a minimum. From his description it sounds like it fails during a left turn which is probably a bad connection some where. I would start at that circuit breaker, tug each wire to make sure a crimp hasn't failed, it should be able to withstand a pretty firm tug, maybe a pound or two of force. Unscrew screw terminals, make sure connections are clean and reassemble. Wiggle wires and look for the voltage to vary at the field. Look that wire insulation too, any crimps or anything that looks weird should be checked. If you are up to it you should do it yourself. I really wouldn't replace any other parts until you are sure the wiring is good.
 
cowman said:
They found something!

The rear bearing in my “new” reman alternator had come apart, needle bearing were free, shaft and brush holder damaged and a brush wire broken. They sent it back, just waiting on the replacement!!!


Finally an actual problem located!
Click to expand...
You must have an electronic regulator or ACU for it to detect that.

One of the first things I would do with any alternator issue is to check the field resistance. Pull the connector off the regulator and stick the ohhmeter leads to ground and the "F" terminal connector. Should see between 3 and 5 ohms,and it should remain relatively steady as you move the propeller a bit to rotate the rotor. Stuff that's broken, or brushes and slip rings contaminated with too much grease from the rear bearing, will show up instantly. Broken is an open circuit, contamination is a high resistance. High resistance means low current flow in the field and a weak electromagnet, so a weak output.
 
So after the replacement for the replacement alternator has been installed I took a test flight. It got through a bunch of touch & gos and steep turns without issue. Next step is a lunch run and if that works out I will declare it trustworthy again.

Of course after weeks of mostly clear weather the storms are rolling in now that I have a fixed plane.
 
cowman said:
So after the replacement for the replacement alternator has been installed I took a test flight. It got through a bunch of touch & gos and steep turns without issue. Next step is a lunch run and if that works out I will declare it trustworthy again.

Of course after weeks of mostly clear weather the storms are rolling in now that I have a fixed plane.
Click to expand...
Did you honestly expect anything different?
The guys at the "Practical Joke Department" aren't finished with you yet.
 
You must log in or register to reply here.
Back
Top