Alternator switch on or off?

[Jim Peace]

I have a 64c with the plane power alt.  I have been turning the alt switch on after start up and off prior to shutdown.  Would it be okay to leave the alternator switch on full time?

I am not sure if turning it on and off is a throw back to older technology that I may not have anymore.  

Does turning it on and off like I do prevent some component from being spiked or working harder than it should and its still good practice?

Thanks in advance

[David Lloyd]

Toilet paper over or under?  Big time opinionated electrical engineer buddy does what you do, wants me to do the same with his airplane.  His reasoning is there is more of a chance of a large power fluctuation at startup than any other time.   I've always tuned the master and alternator on prior to start and turned them off last.

[carusoam]

There is some advantage... one way vs the other...

Depending on sensitivity...

1) turning the alternator on, after start-up, is beneficial to the alternator and it’s controller...

2) the benefit is leaving out all the non-steady state things that can happen during start-up...

3) lots of current spikes, voltage spikes, low voltage situations...

4) better to leave your electronic devices, like the VR, out of this until things have stabilized...

5) On the other hand... Some modern ships seem to turn things on like electronic engine monitors prior to start-up...

As for the TP...

• Over the top allows for ease of use... more space to allow the hand to grab a sheet...
• Around the back allows the sheet to lay against the wall... who needs the added struggle, when you want to get in and get out?
• Some home dwellers find it important from a style point of view... this becomes important for a different reason.

Learning the sensitivity of things can be a challenge... staying conservative can have some benefit, or not... but it won’t hurt...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Jim Peace]

7 hours ago, carusoam said:

Depending on sensitivity...

My girlfriend would tell you I am really not a sensitive guy.  

I am only addressing this because I am doing a total rewrite of my checklist and trying to streamline as much as possible.  I guess I will keep it the way it is unless someone else comes up with a good reason to leave it on.

[Jim Peace]

27 minutes ago, David Lloyd said:

I've always tuned the master and alternator on prior to start and turned them off last.

I forget but isn't that how it is in a Cessna 172 and maybe others.  I remember a combo switch that both halfs would be switched on prior to start.

[carusoam]

Jim,

I finished a couple of thoughts to consider for your checklist... have a read again...   ^^^^

Best regards,

-a-

[jamesm]

I can't speak for a '64 M20C but on my 67'C  the master switch (STDP single throw dual pole) one set contacts provides ground for the battery solenoid  and the other set is the field circuit  for the generator/alternator. I have a Plane Power  alternator installed as well.  Unfortunately my part catalogs only go back to 1965 so I can't tell you what 1964 originally had installed.As far  sequencing when alternator switch is suppose to  be on first or on last . Don't know I can what procedure to advise you. Only to say there is a lot of Mooney's   out there with a single switch turning on battery solenoid  and field for generator/alternator  at the same time.  So the decision has already been made for us  to my knowledge without incident.  I suspect many Cessna's and probably Piper's and Beech's and other aircraft operate in similar fashion . Though I don't  recall on split type master switch on Cessna  for battery and generator/alternator  every having an instructor tell me of certain switch sequencing for master/alternator switch for normal operations.  I suspect have a single switch controlling  both generator/alternator  and battery solenoid or just split switch like a Cessna    is common circuit design among  aircraft designs.  It might depend on voltage regulator since if memory serves me correctly one set of contacts on the master switch connect to field going to voltage regulator. 

Hope this was helpful

James '67C

[Jim Peace]

7 hours ago, jamesm said:

Hope this was helpful

James '67C

yes it was,,,,clear as mud....

I am now going to do something way less complicated and fly to Osaka.

[Jim Peace]

10 minutes ago, jamesm said:

Unfortunately my part catalogs only go back to 1965 so I can't tell you what 1964 originally had installed.As far  sequencing when alternator switch is suppose to  be on first or on last .

I originally had a generator.

[carusoam]

Original 65C, turned the generator and electronics on with the Master switch...

Aged electronics really had sensitivity  to start-up surges...  engine start ,and alternator start surges...

So... adding modern wiring... added  an alternator switch and an avionics master for good reasoning...

Adding super modern electronics may have eliminated the extra safeties provided by the Alt and avionics switches...

Best regards,

-a-

 

[M20C_AV8R]

Great question, just had the plane power conversion done in August and trying to sort out what is best, my current procedure/checklist in respects to this topic that I walked through with the IA that did the install, master on, start plane, once started, make sure temp, pressures etc are where they should be on the JPI 900, I then flip on the alternator field switch, validate that the system is charging as depicted through the JPI, then on to avionics master that covers intercom, GTN etc  and I do just the opposite on shutdown, but, I welcome different perspectives, always learning.

[jamesm]

2 hours ago, Jim Peace said:

I originally had a generator. 

My 67'C had a Generator as well. So  when I converted to a Plane Power alternator several years ago (before Plane Power had kit)  the wiring at the master switch  there were  no changes was necessary.  My point being  (in my case ) the  the Battery and the Alternator come on at the same time. Since are wired to the same switch  just a difference set of contacts. My reference to the generator/alternator comment  is that the switch knows no difference if  it is controlling a field for Alternator or Generator provided you haven't increased current or voltage .

Since many our planes have many different owners over the years sometimes it is hard to tell what is original and what has been modified. 

[0TreeLemur]

4 hours ago, Jim Peace said:

yes it was,,,,clear as mud....

I am now going to do something way less complicate and fly to Osaka.

Hell of a trip in a Mooney.    Fuel-do kudasai!

[Yetti]

From the OWT of old, I was taught in the car world to never spin an alternator without a load (battery) as you would pop a diode.