Alternator issue?

[Rich]

Arnaud, this looks like an improvement, as it seems things are steady. A bit of contamination in the pins of the connector?

The control voltage on the VR looks to be set a bit higher than normal. When you say 28.2 V at idle do you mean actual engine idle (~700 RPM) or the normal 1100-ish RPM. Herewith from the AMM, the expected output of the alternator, as controlled by the VR:

The VM1000 is on the essential bus. When you hit the essential bus switch it takes the alternator (and a lot of other stuff) out of the picture, so you're then reading battery voltage. This is also illustrated in the AMM:

[astaib]

Hi Rich,

For the ess bus, I was expecting these values for the reason that you mentioned.

I don’t feel it like an improvement as the alarms were intermittent during my flights yesterday.
Does the fluctuation between 28.2 and 28.8 normal? I checked some old pictures of the panel during past flights and it was always 28.4.

The tension around 27.5 and maybe less after some minutes at idle were at 700 rpm. At 1200 rpm it is more 28.2.

The amp values that I noticed never went more than 20 when the graph that you attached shows a lot more! But maybe it is what the vr deliver and the vm1000 shows what my plane is draining, right? If yes how can I measure the delivered intensity ?

Arnaud.

[Rich]

The amps in the graph are what the alternator is capable of delivering at the given RPM. What you actually draw depends on what you've got turned on.

The fluctuation you show is more than we actually see. Mine might vary by .1 - .2 V Given you're still seeing alarms and the independent readings aren't totally scary, I'm suspecting something going wrong in the VR.

It's interesting that it's so new. Presumably there were problems a few years back causing the original to be replaced. Alternators are not necessarily changed at overhaul. I think it's odd that the alternator manufacture date isn't on it somewhere. Even so, if were replaced it should have been entered in the aircraft logbook (along with the VR, I might add). But sometimes that doesn't happen.

I may be in a different financial situation than you, but I would replace the VR. Replacing the alternator brushes would be something to try first. They're far cheaper and it wouldn't be such a bad idea, anyway.

[astaib]

Hello,

I get the information this morning from the shop that did the OH of the engine in 2017, and they changed the alternator so we have both “components” very recent !

[Steve]

Arnaud:

It is interesting that they replaced both the alternator and regulator at the time of engine overhaul. Engine mounted accessories (mags, starter, alternator) are typically replaced or overhauled at engine overhaul, and others are overhauled (oil cooler, prop governor). I don't know why they would replace the VR at engine overhaul, unless, perhaps, there was an ongoing issue (like what you are having now). If your logs are "not complete", perhaps you could contact the prior owner to get more information.

If the problem turns out to be your alternator, I would consider replacing it with the PlanePower model. Smaller, lighter, and it charges at near idle RPM. I replaced mine a few years ago, and have been very happy with it.

Steve

[astaib]

Thanks Steve!

In the meantime I get more information: the alternator has been replaced as a standard procedure of this shop (who overhauled the engine), and when the engine came back and was installed on the plane, it seems that there was no charging, after checking everything possible they changed the VR, problem was solved.

This afternoon, I went again to the plane but to fly and check during the flight at different rpm, mp etc.

To make a long story short I can say that the voltage was not stable at all, nor the amp.

When I turned on the engine there was no charging, it triggered the alarms (normal). I switched off and on the alternator and nothing happened, then I set the rpm lower than 1000, and I switched off both mag, and immediately on. The alternator started to charge, but at a low values (alarm again).
While warming up the engine I looked at voltage and amp (both not stable), I already noticed values in the 29v ish.
As it get more and more stable, I decided to try in flight.

During the flight the voltage was changing constantly (but no alarm) from 28.3 to 29.8, even some peak at 30.x and a maxi at 31.1 (still no alarm). Amp was also variating without adding or removing any accessories.
One thing that I noticed (but maybe without any relation). When I flew stable with mp 26.5 rpm 2200 the voltage was more or less stable around 28.6, when I reduced mp and push it back to 26.5, I get an over voltage.

I also noticed that now the parasites in the headsets are almost audible and bothering 90% of the time (when it was only occasional before), when I turn off the alternator the parasites are less audibles but still there.

I don’t know what to do!

Arnaud.

[Rich]

There is a resistor attached at the AUX terminal of the alternator, which feeds the VR. It has been known to be a problem. Check that it's securely in place.

[astaib]

There is a resistor attached at the AUX terminal of the alternator, which feeds the VR. It has been known to be a problem. Check that it's securely in place.

OK, good idea.

Thanks.

[Rich]

Also that it's still 100 ohms and hasn't blown/shorted, etc.

[astaib]

Also that it's still 100 ohms and hasn't blown/shorted, etc.

Of course, can this make behavior like this ?