Any electricians out there? Low volts warning.......

[Curlytips]

Picked up aircraft from annual. On subsequent third flight, suddenly got lots of noise on the radios, which then stopped, but then noticed low volts light and ammeter showing serious discharge. Turned everything off and diverted. Still had battery power remaining, and having changed voltage regulator for a new one, could start, but still light on, and no charge happening. System is 14v Cessna. What does the team think? Does the radio noise indicate what happened?:confused:

And what to try next?

[flyingtincan]

I may be wrong but to me it sounds like some wiring has chaffed through and is shorting on the chassis, engine, or some other metal part. That may be the reason for the interference on the radio. Also sparks and fuel may not go well together.
I would disconnect the battery, get a good torch, plenty of time, and have a very good look around for damaged insulation on a cable loom.

What got disturbed on the maintenance? Try looking there first.

But I could well be wrong

[Jan Olieslagers]

Radio noise could have been from an under-voltage relay buzzing at the edge of its limit, but there might be other causes, too.

What to try next: come to terms with the folks who swapped the regulator? For me, they would have to offer solid proof the error was not on their side.

And it never hurts to open up the cowls and check for loose wires and loose connections. Make photographs of any you find, as evidence just for the case your maintenance shop doesn't show reason.

[Curlytips]

Thanks both. The change of voltage regulator was in the hope that it was the cheaper option than changing alternator, so we did this at recommendation of annual provider. But I've done a lot of surfing re how the system works, and realise it may be something else - either broken insulation or switch problems. I really wondered if anyone had experience of the radio noise appearing then going, and what it turned out to be?

Amongst the annual items was adjusting the low volt light which was loose on the panel. Engineer also mentioned he had tightened the alternator belt slightly. I had also asked that he checked whether cigar lighter was live (as I may want to plug something in) and he confirmed it was. Any clues?

[9 lives]

All alternator systems in Cessnas will have an alternator field circuit breaker. However some Cessnas have it hidden in behind, and not accessible, nor inspectable by the pilot. I've had these go wrong, and you'll get a discharge, because it's the same as flying around with the alternator half of the split master switch turned off (that is the control of the field power). Assure that the alternator actually is being powered at the field input.

It is also fairly common that the overvoltage sensor dies, and the outcome will be about the same, as it too controls the power to the field.

Thereafter, Cessna's maintenance troubleshooting for these systems is pretty good, have the maintainer go through the steps. There is a circuit diagram in there to build a test box for the voltage regulator, though the original adjustable ones are the old way of doing things, the newer solid state ones are preferable.

[ShyTorque]

A noise on the intercom is often a pre-cursor to worn brushes on the generator.

I recently experienced this on our aircraft (twin engined) especially during engine start. I predicted the likely cause to the maintainers and sure enough, it was.

[horizon flyer]

Shot gunning a problem by just changing parts is both expensive and dangerous.
As stated first look around for broken or chaffed wiring then all connections are good, then it's time to check the continuity of the wiring, can break inside the shielding.
Breakers are also known to fail.

The next step is obtain a circuit diagram.

Time to get the voltmeter out and check out if volts are getting to the alternator armature. No need to have the engine running to do that.

Don't wear any rings or metal watch straps if working on live 14 volt systems in case of shorting as very high currents can flow causing burns or worse.

On the low voltage light does it actual measure low volts or does it just mean the alternator is off line important to know.

On the radio noise could have been a broken wire making intermittent contact rather than a clean break. https://www.zeftronics.com/ these people make better regulators and somewhere on their web site they have trouble shooting guides.

[India Four Two]

We had a problem last year on my gliding club's C182 which turned out to be a bad ground wire on the alternator.

[A and C]

I think shy torque is correct, time to change the alternator brushes