Wonder if the collective wisdom on here can help.
One of the a/c I fly, a 182RG, has developed a very weird alternator issue, that so far (about 4 months!) has beaten all attempts at repair. The alternator checks out fine in the shop, but sometimes fails in flight. The mechanics are unable to find a reason, nor can they reproduce the fault. It happened to me about 3 months ago, by chance on a flight with the owner (I rent the a/c). The alternator was subsequently replaced, but the issue persists.
Yesterday, I was due to fly this a/c again, but was warned by the office guy that the alternator had mis-behaved on an earlier flight. Upon checking (no real preflight, just started the engine), I was greeted with the weirdest indication I’ve ever seen – the ammeter waving it’s needle at me, as if to say – no, don’t fly! Deflection was about 3-4 needle widths either side of neutral. Didn’t go away at higher RPM. Needless to say, I did my trip with another airplane.
Btw, the issue started after a respray job (AFAIK nothing mechanical or electrical was touched at the time).
Any ideas what can cause this recurring fault? Something to do with the field current, perhaps?
Sounds very much like an unreliable contact and there can be a 1000 places for that… I would begin be replacing anything that can relatively easily be replaced, circuit breaker(s) for example. I suppose the ammeter is parallel to a shunt? That shunt is also a candidate for replacement. Annoying of course to replace components that, more than likely, aren’t really broken, only have a faulty connection.
Are the regulators generally located within the alternator?
My caveat is that I know nothing about 182s, but I have seen this problem personally on other aircraft. A voltage regulator needs a “good” connection to the battery so that it knows what voltage is being applied to the battery in order to regulate the voltage.
Having some resistance in this connection makes the voltage control system less stable. Resistance could be a damaged wire, or a bad connection. On some a/c, the feed for the regulator goes directly from the battery, via a separate pole on the master switch, to the regulator, and the switch can cause trouble.
“Less stable” is the waving you see. The resistance causes a lag in the system. I refer to it as being like the charging system gets its own little PIO
It could be that there’s a bad contact that sometimes vibrates/chafes – which is why it is intermittent
I experienced a failure a couple of times. The failure mode was that the voltage went sufficiently unstable as to trigger the over voltage protection and shut down the charging system
Best of luck
It can really be only the voltage regulator, or a bad connection somewhere.
The instability sounds more like a voltage regulator issue.
These components tend to be low grade automotive ones, from the Vauxhall Viva era, and they get affected by moisture etc.
about two weeks ago I read about a similar electric fault on another forum. The problem was solved by cleaning the positive battery leads/ terminal connections which showed a thin layer of oxide/ corrosion. You could troubleshoot it with an electric multi-meter …
If the regulator is separate from the alternator (cheese us, that sounds really prehistoric!) then it is indeed a prime candidate for tentative replacement.
PS any pointer to (the relevant part of) the wiring diagram?
Most problems with alternators are wiring issues, you only have to consider the environment forward of the firewall and you will see that it is very hostile to all the electrical cables.
Having has issues very like the ones described with a C152 all the electrical cables forward of the firewall were replaced on both my C152’s the result has been the end to electrical issues and also given better starting.
I do not agree with the statements previously given.
It will be a seperate regulator, with possible a seperate over voltage protection.
Just start replacing components at random is the most unsenseable option in my opinion. I would use three volt meters (analog prefered), and measure at the SAME time the battery voltage at the bus, the battery voltage at the regulator input and the voltage at the field terminal of the alternator.
A single runup with the setup when it misbehaves will tell you a lot more and points you into the correct direction. As it can be anything, from poor brush contact, bad field wiring, bad regulator, bad over voltage protection, bad alternator switch, bad battery contact.
Troubleshooting will save you money in the long run, especially with intermittend complaints.
You need analog meters as digital meters are slow, and give incorrect readings at fluctating measurements. This is a point a simple analog meter outperforms any DVM. You will need to measure the three voltages at the same time as it seems to be intermittend. Measuring on point at a time could give you false conclusions.
Jesse, if an amateur may criticise the words of a professional:
Your point of view sounds very nice and correct, but perhaps not very practical for everybody. Who can and will fly a plane AND keep a critical eye on 3 analog voltmeters? Must the plane only be flown with a second person on board, preferrably one with a bit of insight in electricity/electronics? And while I agree that a digital multimeter is close to worthless in this diagnosis process, it will not be easy to distinguish between vibration from the mysterious phenomenon vs. vibration from a change in engine regime. &c &c.
The one way to work out your idea reliably would be to install a data logger and analyse its logs when the phenomenon occurs. But who has access to such a device for an extensive period of time?
Admitting the example is extreme, one could even imagine that, by hooking up the voltmeters or the datalogger, one pushes the faulty contact just enough to make the phenomenon disappear – how many megabytes are you going to log before concluding the aeroplane is ok? And what will happen when you remove the test lead? Back to trouble, who knows? Mr. Murphy will do all he can to add to the confusion!
So I see no alternative but to stepwise replace components. Cleaning up/renewing cabling and contacts, as suggested, is an excellent first step, though, and the effort and cost will never be wasted.
