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Topic-icon 1969 PA-28-180 Swinging Ammeter

3 weeks 2 days ago #2451

I had trouble on a 28-140 one time and ended up cleaning some of the connections on the components under the panel. If I’m remembering correctly it seemed like the voltage regulator had to have a good ground connection to the frame where it was mounted; I remember it being up under the pilot’s side instrument panel and it was sort of hard to get to. You might check your field wire to make sure it’s not shorted to ground or broken anywhere, the field wire is routed through the engine compartment and it gets a lot of heat and vibration. You could run a new field wire, it’s a lot of labor to undo all the clamps and tie wraps but if it’s the original wire it prob could use a new one anyhow. If that field wire is shorted to ground it might have messed up your new regulator.

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3 weeks 2 days ago #2450

I applaud your determination and believe you'll find the problem in a loose connection or a corroded wire to terminal connection.
The meter in your airplane is a load meter--it shows how much current is flowing to the airplane. It's normal for it to show a positive number immediately after starting that very quickly falls off. That shows the VR is sensing and adjusting and that the alternator is responding.
The fact that the field CB blew is a pointer to start looking at the field circuit wiring.
It's often quicker to just temporarily install a new "jumper" wire in place of an existing wire when you're tracking this kind of problem. Just make up a wire (correct size) with the right terminals on each end, and after disconnecting the existing wire, put it in the circuit. It's temporary, so the wire does not have to be run through the firewall, run it out the door and to the engine. At this point your looking for the problem. After you discover the resistive circuit, you can replace it with one that has the correct routing.
Of course you can "ring" out wire runs with an ohmmeter, looking for resistance, but that's often tricky when you're working by yourself.
There are not that many connections and/or wires between the field CB and the alternator.
Was anything else done to the engine compartment, electrical system/avionics, etc. at that time that might have an effect on the charging system?

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  • Robert Higgins
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3 weeks 3 days ago #2447

Having a strange problem that has caused the shop working on the plane to give up :whistle:

Problem started with the circuit breaker for the field relay popping in flight resulting in the ammeter going to 0 and the battery not charging. Initially I got a new circuit breaker installed but this didn't fix the problem. Installed a new voltage regulator next and this fixed the first problem, but caused the ammeter to start swinging. The ammeter would start off fine charging at around 30 but then slowly drop to zero and then rise again. This cycle does not seem to change with RPM, however the more electrical load placed on the system (landing lights for example) would cause the ammeter to swing back up to 30 amps and the frequency of the swinging would be increased. The voltage in the system also bounces around frequently.

Here is a list of everything that has been replaced since the problem began (in order):
New Field relay circuit breaker
New Voltage regulator
Overhauled Alternator
New Master Switch

If anybody has had this problem and could explain what they did to fix it that would be much appreciated. Any advice or suggestions are also welcome, as I am going to start going through the system and checking the connections. I would like to have the shop go back through their work since the problem started then, however I would rather find the problem myself than continue throwing money at them.

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