Alternator OFF until after start a good idea?
 

Hi.

I'm in the process of writing the POH to my -7 and was wondering if it would be a good idea to wait until after engine start before turning on the alternator?
In other words: turn on only the battery switch before engine start.

Then the entire elec system would be protected for "spikes" during start up?

And vice verca on shutdown? (Turn off the alternator before mix is pulled to cutoff)

Or is it something I've missed or don't understand?

I wouldn't
 

I don't honestly think it makes any difference but my preference is to leave the alternator switched on during start up and shutdown.

Reason being is that if ever I have seen an alternator fail its when it has been disconnected from a running engine.

Frank

Nope, turn it all on.... this lets it come online slowly. Turning your alternator on and off while running is not recommended and should be limited to testing only.

I agree with Frank.
 

Do you ever turn off the alternator in your car?

Alf - I have a slightly different view.

I leave it off 'til the engine is running, then turn it on.

What I think is much more important is dont turn it off (if you can) until after the engine has stopped turning. That is where the problems happen.

Have fun, Steve.

Exactly. At my gliding club, I fly the tow plane along with gliders ... unfortunatly with shared aircraft come shared habbits. There was one particular person who had a 'thing' for turning the alternator switch off. The kicker is that it is under a switch cover so that nobody touches it!

I think it is particularly a saftey issue having it off when it comes to numerous pilots as everyone carries out their own checklist. Realistically if you are the only one flying it, and you have it in your checklist ... by all means, do what ever the heck you want .... but think to yourself what the purpose is for it first. That's the difference between a pilot and a good pilot. Pilots do things ... good pilots understand why they are doing the things they do. If you get some electrical engineer to tell you that it will prevent spiking and give longer lasting alternator life. By all means ... and let us know too!

I'm not a fan.

Planepower has an internal regulator like toyota and many other auto type alternators. They say if you turn the field off with the motor running, DO NOT TURN IT BACK ON with the motor running.
http://www.plane-power.com/Tech_Bits_value.htm
BTW.... Van's has the best price on PLane POwer.

I think turning it off for startup and off for shutdown provides an excellent opportunity to forget to do something...your alternator will be fine going through the startup/shutdown...the vast majority of them live their whole lives this way.

I used a Cessna style split master switch and just like all the other planes I have flown, both sides are turned on, the engine is started. It stays on until after I shut down.

One builder in our chapter used to be a co-owner in a 172. He has told me on more than one occasion that one of their co-owners would always turn the master on and off to check the alternator load. He went on to say they replaced three alternators in the two years this guy was flying the plane. After he sold his share they never had another alternator failure.

Who knows if it is cause and effect but since I've never read a POH that suggests testing the alternator by any other method than apply a load (landing lights, fuel pump, etc.) to it and watching the ammeter guage.

Standby Alternator?
 

Looking forward to a final answer on this question.

So what are people doing with a backup alternator? Leave powered all the time, or only operate if the primary fails? With a 2 alternator, single battery setup, I am very interested.

cheers
-10
almost done.