Question Saratoga intermittent alternator warning light

Hi Andrew;
It doesn't appear as though a standby alternator was a factory option for your Saratoga.
However, there is a STC approved standby alternator from B and C (www.bandc.com).
I suggest you look through your aircraft records to see if there's any information about the installation of a B and C back up alternator system.
You may need to remove the cowling to get a look at the alternator (it mounts on the back of the engine on the accessory section. If the B & C alternator is installed, it has a maximum capacity of 20 amps, so there are some caveats that need to be observed if you ever need to use it.
If it's a B and C system, I suggest you contact B and C for an installation diagram so you and your mechanic can determine if it has been installed correctly.
It may be that when you switch your main alternator off, you are drawing too many amps for the B and C to appear to be on line.
Let me know what you find,
Steve

Hi Steve and thank you so much for taking the time out to answer this query. I have a 2006 PA-32R #3257422 with an Avidyne EX5000 cockpit. Another question, whilst i have your attention; it has a standby alternator, there are no checks for this in the POH and the only indication that it's 'working' is the amber warning light comes on if you turn the main alternator off. However, at the same time i will get a Low BUS voltage warning, and there appears to be no output indicating on the MFD. I have only ever tried this at run up, never in flight, so i don't know whether it needs to be run at higher RPM to produce a sufficient output?
Any feedback will be much appreciated.
best regards
Andy

Hi Andrew;
From your description, it seems as though the fault is in the annunciating system for the alternator.
The obvious conclusion is that a connection is loose between the alternator annunciator wiring and where the power is picked up off the battery solenoid.
The fact that you're not seeing any problem with the main alternator power output is a good sign.
FWIW, the diode bridge in the alternator (there are three) convert the alternator current produced by the alternator into direct current (DC) that can be used in our small airplane system. If you had a bad diode the DC would not be as smooth as before. This is pretty easy to detect as it produces a high pitched whine that increases in pitch at higher RPM. It's easy to hear in your headset.
The fact the behavior of the system changed after the alternator was changed seems to indicate that the intermittent connection could be in the connection between the stator of the alternator and the alternator "out' switch.
At this point it's only a guess; I'll need the serial number of your airplane to dive deeper into the wiring diagrams.
Thanks
Steve

Around two years ago, my 2006 32R 301T started displaying an intermittent alternator warning light, coming on normally during start up. Resetting the alternator occasionally cured the indication, sometimes it would simply go out before departure. Although the light was on, the output voltage and charge was normal - 28.6v dc on the BUS and at no time does the standby alternator kick in.

I thought it might be a rectifier starting to fail, which I believe is on the alternator, so I had my shop change the alternator. This changed the symptoms, the light would come on for perhaps 20 secs on start up but then extinguish. Now the light occasionally comes on on startup, may go out or will stay on through the flight. Still the output is normal even with the warning light on.

Any ideas please?
Andy