some light on odd electric issue

[GMAs]

Hello...

I don't usually get back on this board but we have our own that we maintain tech data on the 337 Skymaster. I was asked if I would comment about your problem.

One can do a lot of trouble shooting of the electrical problems by using a simple volt meter. Here you can measure across the devices and find out if they are in fact bad. By doing so ...if the Ckt Breaker for instance is bad and you close it.. you would see a voltage across it.... if good you would not see any voltage across it.

Now as to your problem. Your mechanic can short across the field ckt breaker if he doesn't own a volt meter and find out if the charge suddenly comes back on line... or he can measure the voltage at the field terminal of the alternator to see if it has the proper setting. (simple)

However, shotgunning is not a acceptable methode to find problems.

As others have said .. voltage settings on the alternators is critical... one does not want the rear and the front set to the same voltage... as Pete has said it will cause osc in the two alternators...one wants the front one set a little lower than the rear.. which should be set a little high. In this way the rear one is always taking the first loading.. once it max'es out then the front one will come on line and pick up the loading from their. Yes the rear will wear faster but it keeps the system in operation. Of course you could just simply shut down the front or rear by pushing the field switch off.. too.

Suggestion...

First off. How long have you had the master Slnoid. We have found that the master ones do go bad after 5 years.. and all should be replaced in the master and engine starters. If the vibration is getting to the master it will cause the battery to come off line and cause the alternators to shut down due to no loading.

Then I would go check the alternator coupler... the drive section of them sometimes go bad... lord ones are natourous for debonding... and while the alterntor will drive at low current it will slip when the power is needed... check by using the turn finger methode on the cooling fins of the alternator rotor...

Last but not least is the battery itself.... how old... if over 2 years... replace.

Most mechanics and IA's right now are not doing the section of the battery "Contenued Airworthness" requirement. One then wonders how they can retrun the aircraft to service AT ANNUAL if they fail to do the load test on the battery once a year as directed by the manufacture. (BUSTED BIG TIME)

Check out the battery manufacture web site and look for the "compliance for Contenued Airworthyness" both Gill and Concord have them in their owners manual... most mechanics are not keeping up with the program and the FAA is now being a bug about it...

Good luck.. thanks Larry for keeping the board up... I owed you for the ride home... what a fun time it was... that customs guy was a hoot... (not to mention the people at TC)
still have that palm hat.... you flew over and trimed the tree with... (smile)

Fly Safe.. GMAs