Hot Wire at Alternator

[rviglierchio]

Can anyone suggest the pros and cons, or reason, for having a connection between the alternator and the battery with no interruptions, i.e. switch or relay, such that the wire out at the alternatior is always hot? We found this today, kind of an exciting discovery near one's elbow when it blew the capacitor near it off the connection, and can't see why it was done that way.
Thank you!

[Lynn Erickson]

Originally Posted by rviglierchio

Can anyone suggest the pros and cons, or reason, for having a connection between the alternator and the battery with no interruptions, i.e. switch or relay, such that the wire out at the alternatior is always hot? We found this today, kind of an exciting discovery near one's elbow when it blew the capacitor near it off the connection, and can't see why it was done that way.
Thank you!

you should have a fuse between the alt. and the battery wire. there should be the master relay between the battery and the wire to the alt. the master relay should disconnect the battery from everything in the plane when off. the battery wire is hot when the master is on and/or if the alternator is on and the engine is turning the alternator

[Waiter]

In the automotive world, they do exactly that.

The "BAT" connection on the alternator is connected directly to the battery.

In aircraft systems, having a "Master Relay" or a "Circuit Breaker" gives the ability to isolate failed components.

Lets take the "Catastrophic alternator short" as an example;

In a car, if this happened, your first clue would be the electrical system seems to die, lights flicker, radio pops in and out, your car stalls. You start getting an oder of something burning. A few seconds later, you see smoke coming from under the hood.

You pull off the side of the road, and turn the key off.

The smoke continues and is getting worst. You open up the hood, and all the sudden, flames erupt from the engine compartment. A few seconds later, a loud explosion as the battery explodes.

If you had a "Master Relay" in the car. Nothing after the "You turn off the key" would have happened.

ONE POSSIBLE ALTERNATIVE

On my system, the Alternator is wired directly to the battery through a 50 amp circuit breaker. I can pull the breaker in the event I suspect a failed alternator. I prefer this over a fuse link or going through a master relay, as it allows me to isolate the alternator from the rest of the electrical system.

You can review my electrical system drawings at:

http://www.iflyez.com/DualSupply.pdf


BOTTOM LINE

Is a master relay or pullable breaker necessary, no. But it does offer you an option in the event of certain electrical system failures.

Have you ever seen a car pulled off beside the road in flames!



Waiter

[rviglierchio]

Thanks Lynn and John.
Mine is also wired through a breaker I've found, but has a test button that has us baffled. If the engine is running and you push the test button the breaker pops and the alternator goes offline....
Any idea what this is all about?
Dave

[argoldman]

Originally Posted by rviglierchio

Thanks Lynn and John.
Mine is also wired through a breaker I've found, but has a test button that has us baffled. If the engine is running and you push the test button the breaker pops and the alternator goes offline....
Any idea what this is all about?
Dave

Dave,

Here's an electron in the dark.

The switch might be a test switch for a "crowbar" overvoltage protection circuit.

I believe these circuits are designed to pop the breaker, rather than fry your radios, when an overvoltage condition is detected.

On the other hand, the builder might have had a strange sense of humor. Do you see any "do not push this button" signs anywhere near???