Alternator overvoltage

[trackdom]

Hi,
Today I experienced an alternator trouble. During flight GRT Efis sent an alert message , alternator overvoltage . On engine page I read 15 to 16V . 15 mn later total electric failure , all switches are off. 5 mn before landing I switch master switch on, radio on and Efis on to get IAS.
2 hours later I start the engine and get back to home base but without radio, transponder, And Efis.
My question is, can I decrease alternator voltage ? It's a plane power, 40 flight hours , internally regulated.
In the same time I noticed that master switch needs a few minutes before being operative , I am not sure there is a link between both issues.
Before buying a new alternator I would like to know If I am able to fix it by myself...
Thanks

[BobTurner]

The Plane Power unit uses the alternator field line for the sense voltage. If there is high resistance in that line you'll see higher voltages. Start at the main buss, and look for any voltage drops across the switch, any connections, and at the alternator plug itself (this last one being most likely IMHO).

[mbauer]

What type of master switch do you have? Main reason I ask is to verify if you have the old style "Split" switch that had a Batt/ALTernator side.

Many years ago I had an overvoltage/charge condition because someone had removed the one piece Master Switch, replacing it with the old style "Split" switch.

On short flights it wasn't a problem, but on a really long cross-country (Alaska to Idaho) it was a problem. Switch was dropping 8-watts between the contacts, regulator saw this as under voltage and overcharged the battery-destroying it.

Hot electrical smell in the cockpit, lights, nav equipment problems, etc.. Including Hydrogen gas inside the cockpit, from the over charging of the battery.

Was very lucky to find an airport that night!

[F1R]

http://www.vansairforce.com/communit...ernator+fooled
Perhaps not your problem, but a very informative thread.

In agreement with the other help offered.

Also what type and model of battery are you using?

[rapid_ascent]

There is no way a good switch will take a few minutes to become operational. There are two possible options: 1) the switch is bad, 2) you just think the switch is taking a while to become operational and it's actually something else.

What type of switch do you have? Is it rated for the current you are drawing through it? Normally there is a contactor (relay) that is controlled by the master versus switching your loads directly with the master.

[rv8ch]

Salut Dominique,

I have a spare PP alternator if you want to use that. I'm up near Geneva. I can mail it to you by post or you can fly into Bellegarde (LFHN) and I can meet you there.

Mickey

[trackdom]

Hi Mickey,
Thanks for your proposition , Bellegarde is not far from my base. But before changing alternator I'll change master switch which is the beginning of the trouble I suppose .
Rapid ascent,
I bought the master switch from vans catalog , I have no part number.
Today I put away cowlings And look carefully at all connections . I am ordering a new master switch, from vans or stein air or other , what could be the most reliable?
Thanks for your help

[trackdom]

Coming back from the hangar, I noticed nothing special . When switching Master switch it took 6 mn to get a contact . I suppose alternator overvoltage is due to the master relay malfunction .

[climberrn]

As for the master switch, I have the split rocker Cessna style switch but was suggested by B&C to switch it out for a 3 way toggle. They said they have seen lots of failures with the split rockers, and the 3 way toggle holds up better. For what it's worth.

Have not switched mine out yet. Still AOG from my over voltage incident.

[Walt]

If you're looking for the best switch the Honeywell 2TL series is most reliable switch I know of.