Unusual amp indication

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TrueCourse

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TrueCourse
I’ve got an intermittent and abnormal indication on the loadmeter in a Cherokee 140 and would like to know if you’ve had this issue. I’m thinking I’ve read about this but not sure.

Most of the time when the airplane is operating the load meter has a steady load of amps indicating unless the strobes are selected, then it oscillates some (~15 extra amps?) as expected. However, occasionally something else is going on: a rapid spike back and forth, faster and greater than it does or should for the strobes. When this happens I have cycled the alternator off and on and the spiking has not returned, but not always. Normally it happens with the strobes on, but the other day it was spiking rapidly with the strobes off.

This started one day when a passenger mentioned there was a high pitched squealing sound over the headset and speaker. I glanced down at the load meter and noticed the unusual indication and could terminate the sound when shutting off the alternator. The squealing has gone away as of late. Recent work on the airplane included an annual inspection, inspection of mags, and installation of an adapter/cable on the battery terminals to allow for a battery tender hookup. I don’t believe the alternator (14-volt system) is too old but I’d have to confirm that. The alt belt tension seems ok.

Any thoughts on where a mechanic will start to look?
 
On my Cherokee 140, I would occasionally see oscillations. Eventually I replaced the meter and viola, unexpected oscillations went away.

Caveat: I'm not an A&P, just a (now former) owner.
 
So I searched some more and found some threads and discussions on the "dancing" indications. Sounds like one of several things can be going on. I did see that if a load meter or master switch were to need changing that it wouldn't be easy to find. At least that is the impression I get. Thanks Bob for being the sole reply to this thread.
 
Now that I think about it more, I think I replaced the master switch (not the meter). Sorry about the confusion.

It's been maybe 15 years since I replaced it
 
The two times I got wild swings in the ammeter were shortly followed by alternator failure in flight. I our case there were some bad/faulty connections at the alternator that caused the issue.
 
No problem Bob. Bill, it hasn't come to that yet and hope it never does. At least I haven't been flying it IFR.
 
A pegged ammeter/loadmeter indicates that either the battery is internally shorted (unlikely here) or the alternator is intermittently getting full field voltage. So now you have to go looking for that problem.

The regulator might be worn out, and its eroded and rough voltage regulator contacts are starting to stick shut. They need to vibrate freely.

The voltage regulator might be loose on the firewall and it's not getting a proper, steady ground reference; that makes the regulator think that the voltage has fallen, so it maxes the field current. The regulator rattling around on its bolts will do that.

If there's a short between the alternator field wire and a hot wire such as the "A" wire to the regulator or the alternator output cable, you'd get big loadmeter jumps.

And if there's an intermittent short between the output cable or battery cable and ground, the same indication will show up, but some serious arcing will be burning something somewhere.

Someone with experience needs to go through that system and find the trouble before something catches fire. I'm presuming that the system has no overvoltage protection.
 
It never pegs out. Instead of seeing maybe ~5 amps jumping to ~20 amps with the strobes on, it might be something like 5 amps jumping to 30 or 35 amps, much more rapidly. I agree that it needs to be looked at. Whats good, and frustrating at the same time, it isn't a continuous problem. Just comes and goes occasionally. Yes, it needs to get resolved. The schematic does show an over voltage relay.
 
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I can’t shed light on the cause but I had a similar problem. Initially intermittent no reading to full rapid excursions on the load meter in my Archer2. My IA checked it out and found nothing. He thought that it was a fault in the load meter itself that could be repaired(he was not confidant about the longevity of repairs) or it could be ignored if my other current and voltage indicators we’re good. I flew with it that way for 2 years. However after an annual in the same shop where my annual costs have been interesting getting more expensive, suddenly the meter has been working completely normally for the past 2 years. I suspect a different tech has been looking at the plane with different eyes or just was more fastidious in his approach to cleaning up electrical connections in response to the load meter fluctuations. I never asked about it since it was not supposed to be a problem during the anomaly, and now definitely not since it was gone.
 
May not be related but since you mentioned a squeal in the headset it made me think of it. This was in our Maule, didn't have a load meter but once in a while a breaker would pop and we'd lose the radios. Turned out to be a wire from the audio control panel wasn't properly secured and was laying across the edge of one of the trays which eventually wore through the insulation and caused an intermittent short. Unfortunately intermittent things can be very difficult to locate but you can at least take a look at the routing and make sure everything is secured. On a Cherokee that in itself can be a real chore.
 
MajorTurbulence said:
I can’t shed light on the cause but I had a similar problem. Initially intermittent no reading to full rapid excursions on the load meter in my Archer2. My IA checked it out and found nothing. He thought that it was a fault in the load meter itself that could be repaired(he was not confidant about the longevity of repairs) or it could be ignored if my other current and voltage indicators we’re good. I flew with it that way for 2 years. However after an annual in the same shop where my annual costs have been interesting getting more expensive, suddenly the meter has been working completely normally for the past 2 years. I suspect a different tech has been looking at the plane with different eyes or just was more fastidious in his approach to cleaning up electrical connections in response to the load meter fluctuations. I never asked about it since it was not supposed to be a problem during the anomaly, and now definitely not since it was gone.
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A problem that disappears on its own is a good problem to have!
 
Silvaire said:
May not be related but since you mentioned a squeal in the headset it made me think of it. This was in our Maule, didn't have a load meter but once in a while a breaker would pop and we'd lose the radios. Turned out to be a wire from the audio control panel wasn't properly secured and was laying across the edge of one of the trays which eventually wore through the insulation and caused an intermittent short. Unfortunately intermittent things can be very difficult to locate but you can at least take a look at the routing and make sure everything is secured. On a Cherokee that in itself can be a real chore.
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Interesting. Strangely the squeal eventually went away. Will be opening up the front soon to explore. As you know the cockpit is so small and looking behind the panel is not only a chore but its an eyesore seeing all the wiring. I'm guessing half of it doesn't even need to be there, but that's another project for another day.
 
I have a 76 warrior. I have had the exact symptoms more than once. The first time it eventually led to the failure of the alternator. When it was replaced it disappeared... for a while. It did return. I messed with the wires going to the regulator and disappeared again... for a while. Then on a long cross country it started again and I reached under the dash and wiggled some wires and it would quit for a while. Since bumping cables had an effect I knew it had to be a wiring connection so when I got home I removed the seats and got under the dash to look where the regulator is. On my plane it is mounted to the left wall under there. I tugged on the wires going to it and without much force one came right out of a splice connector. I think it was the ground for the regulator. Changed the splice and re-crimped it. No more problem since.
 
weirdjim said:
I respectfully disagree. A problem that disappears on its own will most probably reoccur in IFR in IMC with bright flashes in all quadrants of the sky.

Jim
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I knew that might elicit a response from someone. I'm not referring to an occasional, reoccurring problem. I've had numerous, unusual, unexplained problems show up and disappear on their own over the years and none reoccurred as you describe. Troubleshooting is started but when they vanish for good, before anything is discovered, they vanish.
 
TrueCourse said:
I knew that might elicit a response from someone. I'm not referring to an occasional, reoccurring problem. I've had numerous, unusual, unexplained problems show up and disappear on their own over the years and none reoccurred as you describe. Troubleshooting is started but when they vanish for good, before anything is discovered, they vanish.
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I'm glad for you that that has been your experience. My experience (not primarily with aircraft, to be fair) is that problems that simply disappear also reappear. Often at inopportune times. And (speaking as the one who's had to hunt down and solve many of these) disappear as soon as the troubleshooter appears. Unless he or she forgot their tools.
 
I hear you. Funny how a "good for you" comment has created this bit of conversation about problems disappearing or not. Out of all the airplane issues I've seen, most are found and fixed or found and explained (if they stop on their own). But, there were numerous others that disappeared and, ironically, they were electrical related on much more complicated airplanes than the Cherokee. I don't believe this issue with the Cherokee will go away on its own. Its intermittent for a reason. I'm leaning on either the master switch or some wiring issue. Found the "Cherokee Charging System" article and that has been helpful.
 
That loadmeter, IIRC, has a shunt somewhere, maybe in the left sidewall. The meter itself is just a milliammeter, and reads the voltage drop across the shunt. A loose connection at the shunt bar will increase and decrease the resistance there. A higher resistance will shunt more current to the loadmeter and make it jump to a higher reading.

Old airplanes are fun. I made a decent living chasing electrical gremlins through them. Oxidation, corrosion, abraded or hardened and cracked insulation, eroded contacts, vibration, oil and grease and dirt, poor repairs: they all contribute to some real frustrations. None of it usually gets inspected nearly well enough.
 
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