Jittery volts/amps

Hang 4

Hang 4

En-Route
PoA Supporter
Joined
Aug 18, 2017
Messages
2,538
Display Name
Display name:
Hang 4
Noticed a pretty erratic volts and amps reading in level flight with normal electrical load. Had a new Plane Power voltage regulator installed in 2020. Nothing noticeable other than reading on gauge. Plane is a 73 Piper Archer. Amps went from 9 - 21, Volts from 14.1 to 14.6 during a ~ 10 second period. Have a video, but troubles attaching.
Have a few other things that will need to go to my A&P, but any initial thoughts?
 
Hang 4 said:
Noticed a pretty erratic volts and amps reading in level flight with normal electrical load. Had a new Plane Power voltage regulator installed in 2020. Nothing noticeable other than reading on gauge. Plane is a 73 Piper Archer. Amps went from 9 - 21, Volts from 14.1 to 14.6 during a ~ 10 second period. Have a video, but troubles attaching.
Have a few other things that will need to go to my A&P, but any initial thoughts?
Click to expand...
Check this thread:

Amp Meter Oscillation

Anyone have any thoughts on my amp meter oscillation? It's done this from day one and I really haven't considered it a discrepancy until flying with a previous co-worker who seemed to think it was concerning. My alternator is from a older Honda, 35 amp and my regulator from an old Ford LTD...
vansairforce.net vansairforce.net
 
Hang 4 said:
Amps went from 9 - 21, Volts from 14.1 to 14.6 during a ~ 10 second period.
Click to expand...
After the 10 seconds it went back to normal?
Is this the 1st time you've seen this?
 
10 seconds was how long I videoed. It seemed to settle down after 20 min or so. It happened on the prior flight as well, which was the first time I noticed it. Had forgotten about it until it did it this time. Twice and I'm getting it fixed before flying again.
No other symptoms, nothing in the headset, instruments were steady etc. Battery is new and was fully charged before installation.
 
Sometimes the alternator belt slips when you first start up then it gets hot from slipping then catches and charges the battery.
 
What was your electrical configuration at the time? Any LED lights or other medium power loads that might be intermittent (bad contacts)?

The fact that you had a decent voltage change for what I'd consider a low change in load (about 10A) makes me think your alternator field circuit might have a problem. Bad brushes/rings, or something as simple as oxidized/dirty contacts on that 50-year old 5A alternator field circuit breaker.
 
Loose connection to the voltage regulator on my C206. Easy fix once discovered.
 
I had a similar on a Cherokee 180. Ring terminal broke at the alternator and the (I think) ground wire was swinging around loosey-goosey inside the cowl, occasionally passing through the electrical field generated by the alternator. Sounds like a loose connection somewhere.
 
Klaus M said:
Sometimes the alternator belt slips when you first start up then it gets hot from slipping then catches and charges the battery.
Click to expand...

Yes! Make sure your alternator belt is tightened to spec. I had an older Ford car that with the belt tightened with the THAR method, it wouldn’t charge running down the Interstate with high beams on, A/C blasting, etc. About every 15 miles I had to pull over, shut everything down ‘cept the tail lights and let it charge at fast idle for 15 minutes or so, then press on until I had to do that routine again. Professional diagnosis: loose belt.

-Skip
 
Anytime I hear jittery or intermittent electrical, I think loose connection or cracked/broken component.

I had an alternator that worked fine on the ground, but cut out in the air. When I landed it worked again. Turned out the plastic brush housing was cracked. The bumpy grass strip would vibrate the field terminals in and out of contact.
 
Some good ideas here. Belt did seem a bit looser than normal. Bunch of connections I can check as well. The one other thing that came up from searching around was a bad master switch. A few things I can fiddle with before turning it over to the pro's.
Thanks
 
A couple oldies but goodies I've posted before. I had both these issues with my Warrior (-161).

1. The field wire to the alternator is thin. In flight it continuously vibrates. This tends to work harden the point at where the wire is crimped into the connector. Over time the strands inside the insulation can break with no external evidence as the insulation remains intact. This can cause intermittent alternator behavior.

2. The alternator engine case mount can break. On my Warrior the mount is just a flat U bracket ( |___| ). One of the wings broke off. I attribute this to a missing strut which I discovered when replacing the engine. In the photo below, you will see a piece of white tape marked "missing strut" which secures the alternator engine case mount point to the starter.
2011-11-17.Front.1024.jpg
 
dbahn said:
This alone sounds like a really bad in-flight problem.
Click to expand...
Not a wing strut. It's a small steel brace that prevents belt tension from pulling the alternator mounting bracket sideways, which stresses the hardware.
 
Once again, from a Cessna service manual:

1724688166374.png

This is less than most mechanics will apply to that belt. Too much tension destroys the belt and can destroy the alternator bearings as well. If the belt is tight and the alternator is still not keeping up, the system has electrical problems and no amount of belt-tightening will fix it.

Poor troubleshooting results in worse damage instead of repair.
 
Dan Thomas said:
Not a wing strut. It's a small steel brace that prevents belt tension from pulling the alternator mounting bracket sideways, which stresses the hardware.
Click to expand...
Not eveyone gets my sarcasm . . .

But I think the wing breaking off would be a bigger problem. ;)
 
Dan Thomas said:
Once again, from a Cessna service manual:

View attachment 132793

This is less than most mechanics will apply to that belt. Too much tension destroys the belt and can destroy the alternator bearings as well. If the belt is tight and the alternator is still not keeping up, the system has electrical problems and no amount of belt-tightening will fix it.

Poor troubleshooting results in worse damage instead of repair.
Click to expand...
No way!!
IMG_4587.JPG
 
So belt was definitely loose, barely took any torque to get it to slip. I had suspected it was getting looser from my pre-flight wiggle. Field wire seemed ok at alternator, but connection was pretty dirty. Cleaned it up, also cleaned the main 12v lead connection. To @Domenick 's point, the field wire was hard as a rock. Suspect it's original from '73. It did seem to be a solid crimp. No way to test with leads I have. Connections at VR were all tight and clean. Too frigging hot in a west facing hangar in FL to do much more. No time or energy to test run. I've got a couple of minor squawks for my mechanic to address, so will add this to the list if the little I did does not address it.
Thanks for all the suggestions.
 
Jittery Volts and Amps? Try switching it to Decaf..........
 
So not sure which of the three things I did solved it, but I suspect belt tension was the answer. Flew today and volts were rock solid at 14.1, amps bumped a little, but +/- 1 vs. the swing of about 10+ before. Tension was too low to measure with a torque wrench. tightened it a bit to ~8ft/lbs (Piper spec is 7-9 for a used belt same as the Cessna one @Dan Thomas posted). I also cleaned the field wire connection which was tight, but lots of crud and did same to the 12V main connection.

Thanks for all the suggestions.
 
Hang 4 said:
So not sure which of the three things I did solved it, but I suspect belt tension was the answer. Flew today and volts were rock solid at 14.1, amps bumped a little, but +/- 1 vs. the swing of about 10+ before. Tension was too low to measure with a torque wrench. tightened it a bit to ~8ft/lbs (Piper spec is 7-9 for a used belt same as the Cessna one @Dan Thomas posted)
Click to expand...
I also found that I needed to tension the belt, then rotate the crank once to seat the belt in the pulleys, then check the tension again. The tension will often fall, especially due to the belt not initially seating in the flywheel pulley. Lots of friction around that arc.

Got to have the plug leads disconnected for this. You don't want that engine to decide to fire.
 
Dan Thomas said:
Got to have the plug leads disconnected for this. You don't want that engine to decide to fire.
Click to expand...
I held the prop still and rotated the alternator pulley nut. The Piper instructions make is sound like its measuring the torque needed for that pulley to slip. Don't see how the engine could fire in that circumstance? It's an existing belt, so didn't need to seat.
 
Hang 4 said:
I held the prop still and rotated the alternator pulley nut. The Piper instructions make is sound like its measuring the torque needed for that pulley to slip. Don't see how the engine could fire in that circumstance? It's an existing belt, so didn't need to seat.
Click to expand...
It won't fire like that, alright. But the belt isn't fully seated in the flywheel pulley at first, used or new. The friction at each end of the arc of contact prevents the rest of it from pulling down into the groove in the rest of the arc.

I have seen the belt a little looser after rotating the prop. Rotating the system is common practice in industrial V-belt installations, to avoid having to retension the belt soon after.
 
Dan, think I see where you're coming from and why it might not be relevant to my situation. My plane had AC, since removed. The belt is tensioned by an idler pulley, not by moving the alternator. So it never was unseated. The belt never moved in the flywheel, just the alternator pulley. I can see how a little rotation might seat it more in the alternator pulley, but I could move the prop with the torque wrench and once I held the prop, there was no slip from the flywheel.
Definitely not arguing, but seeking to understand. Thanks for your feedback.
 
You must log in or register to reply here.
Back
Top