Cherokee 140 Ammeter Bounce

Indiana_Pilot

Indiana_Pilot

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Have you guys ran across Ammeter Bounce?

The plane I am a part owner in is a 1966 Cherokee 140 and has a new Engine and an alternator upgrade that has maybe 200 hours on it. A few weeks ago the mechanic found a "broken wire" on the alternator that caused it not to charge the battery in flight. He fixed that and now shortly after start it bounces then settles down (I think this may be normal)

After flying for a few hours and stating my decent (reducing RPM) it will start bouncing again. then if I blip the throttle and then back down it will stop..

I am thinking voltage regulator. I know it's charging as the battery never dies. :dunno:

Here is a video of the Ammeter bouncing
https://www.youtube.com/watch?v=4H-27TpcsZU&feature=youtu.be

Here is a video after it settles down.
https://www.youtube.com/watch?v=vo6QVT7kvjk&feature=youtu.be

The mechanic is going to look at it next week when he returns from vacation but I am curious what you guys think. (I have seen alot of videos of Piper aircraft that seem to have this bounce)
 
I was going to say yes but the bounce I've seen in the PA28-140 I fly is more like the second video or sometimes slower and usually corresponds to the beacon flashes.

I would call what is displayed in your video an Ammeter Seizure. Never seen that.
 
I thought the same thing but I can turn all equipment off when it's bouncing and it still bounces just a little slower.. I can also control the speed of bounce a little by adjusting the RPM.. (Maybe the rebuilt alternator has bad brushes as well)
 
Firefighter_324 said:
I thought the same thing but I can turn all equipment off when it's bouncing and it still bounces just a little slower.. I can also control the speed of bounce a little by adjusting the RPM.. (Maybe the rebuilt alternator has bad brushes as well)
Click to expand...

Bad brushes, bad brush spring, alternator bearing letting rotor wobble.
Could also be a sick regulator or over-voltage relay.
Check the simple thing first and work from there.
 
There has been more than one thread on this subject. A frequent cause is high resistance contacts in the alternator field switch (the alternator half of the master switch). With the master off, try cycling the field switcha couple of hundred times (Using friction between the switch contacts without interrupting current to clean themselves) and see if it made any difference. Or bypass the switch with a jumper and see if the problem goes away.

The heat generated by the field current flowing through the resistance of the switch contacts makes it act something like the blinker on a turn signal.
 
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You said upgrade. What kind of alternator and what kind of regulator ?
 
Did it have this problem before the "alternator upgrade"? Or did it start after fixing the "broken wire"? Either way, it needs to go back to the A&P to fix whatever he broke, or whatever part is defective out of the box.
 
Yep, the 140 I fly does the same. It's owned by an A&P/AI...I'll have to tip him off to these other threads.
 
It just started a few weeks ago.. Well after the alternator upgrade.. So maybe 200 hours after the upgrade.. This plane only has one master not a alt/battery switch.. Maybe I will suggest the switch and regulator be swapped out next week. I flew it for 2 hours yesterday and it seemed fine.. kind of hit or miss. I would just perfer not to be stuck somewhere needing a jump this weekend!
 
Save money, start with simple things. In your model of Cherokee you may have the single master/alternator switch, if not you have the split switch, in either case try a good shot of contact cleaner into the switch, even try wiggling the switch during operation, if the neddle settles down the switch is the problem. I replaced a customers single switch a few months ago for this exact problem, I think the switch was like $15. We did the trouble shooting above, then jumpered the switch (get your A&P's help if you do this) to take the switch out of the circuit and further verified the location of the problem. This is fairly common in the older Cherokee's.

Russell
A&P, ATP
 
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It could be any number of things but bear in mind that the ammeter in the Cherokee is a load meter rather than a charge/discharge meter as you would find in Cessnas and many other aircraft. What this means is that if there were a problem with the alternator field circuit or the regulator or anything else that might affect it's output the load for the electrical equipment would still be carried by the battery. Furthermore, if the load were to actually go to zero and back like that shown in the video all of your equipment would have to be shutting off and on, there would be all sorts of mayhem and at the very least the lights would be flickering.

So my best guess is that what you have is an indication problem and not an actual problem with the alternator.
 
...our 235 was doing this a while back. I wish I could remember exactly what we did to make it stop. It was really a combo of quite a few things...

We put a new starter in (Sky-Tec) and that exposed a few electrical problems we were having. Our OEM starter was definitely done but once we put the new one in we realized that we needed new solenoids...we replaced the one off the battery box and the one for the starter button (I fly a 64 so it uses the starter button) on the firewall. We also put in a new battery.

Some combo of one or all of those things evened out the ammeter and now it's rock solid.
 
I flew it to Kentucky (about 4 hours total) Sunday and it bounced some but mostly remained steady for the duration of the trip. I did wiggle the master a little and it appeared I could make the bounce speed increase.

I will probably have the master swapped out this week.

Thanks,
 
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