Alt Field On or Off during engine start and shutdown

[hais]

9 hours ago, ArtVandelay said:

Yes, as Eric points out.

Side note, the G3X (designed to come on with the master) also has a voltage conditioner (GAD 27) which instead of just dropping the voltage down to a safe voltage also will boost the voltage when voltage drops during startup.

Curious why no conditioners on avionics? Surely it can't be for cost reasons given how much these boxes go for.

[ArtVandelay]

Curious why no conditioners on avionics? Surely it can't be for cost reasons given how much these boxes go for.

Generally digital electronics only need 5v so don’t know why G3X needs it.

[EricJ]

29 minutes ago, hais said:

Curious why no conditioners on avionics? Surely it can't be for cost reasons given how much these boxes go for.

Generally there are, they're just inside the boxes these days.   Most modern avionics have power supplies in them that will take in anything from 10-30V and operate just fine, i.e., there's no distinction between between units for 12V or 28V operation, they do all of their conditioning and regulation internally.   They're not immune to powerful transients, but they're generally pretty good.

[carusoam]

Soooo…

History shows… it probably isn’t a big deal.

It’s all about being nicer to the electronics on board….

 

 

I have one of the oldest Os on the planet….

From Transition Training on, it was taught….

1) Master 

2) Start

3) Alternator

4) Avionics

5) + tach/rpm adjustment, OilP, MP adjustment…. Fuel pump off.

Engine start-up is a busy time….

Shutdown is the same, but in reverse order…

where line 5) looks more like this….   Set rpm to 1k, dial out the mixture, while looking for the rpm to rise before the engine dies….

 

If you have an Alt switch… use it.  Because you can.

If you don’t have an Alt switch… don’t sweat it.  You can add one, while installing an avionics switch…

 

Back in the day… we were taught to turn off all of the electronics individually before start…

1) Nothing causes weirder spikes in voltage than starting the engine….  (Save the electronics from this)

2) without the alternator on… the voltage can’t spike above the battery voltage…. (Save the electronics from this)

When the alternator comes on, the voltage regulator tries to catch up with all the data it reads…

3) post Y2K, electronics including primary engine monitors…. Have been designed to handle a fair amount of electrical oddities.

4) Is your primary engine monitor wired to the main bus, or is it accidentally wired to the avionics bus?

 

As long as there are voltage spikes caused by the electric starter motor….

And there are oddities caused by starting up the voltage regulator…

I keep to the five step process… above.

 

But, I also take my time between starting the car’s engine, and turning the lights on…. 

 

It’s OK to be slow and deliberate…  Use the check list.  (Update your checklist properly)

It’s not OK to forget to execute steps of the start-up check list… 

 

Under ordinary conditions… I bet it is hard to tell the difference…

 

When you have a few AMUs in electronics…

You feel better, when you have taken the extra care to not send the known spikes down the line….

This gives the equipment a few extra seconds to adjust, before the next spike or drop comes along…

 

My cars don’t have LED lights yet… 

 

Great… we have discussed what causes the usual spikes and drops in voltage…

But, we don’t have a voltage monitor that is sensitive enough to show us how big the spikes and drops really are during those split seconds that they occur…

For that reason…

I’m sticking with that five step process, and verifying with the checklist when done…

Best regards,

-a-

[hais]

3 hours ago, EricJ said:

Generally there are, they're just inside the boxes these days.   Most modern avionics have power supplies in them that will take in anything from 10-30V and operate just fine, i.e., there's no distinction between between units for 12V or 28V operation, they do all of their conditioning and regulation internally.   They're not immune to powerful transients, but they're generally pretty good.

At least in some airplanes, the avionics reset when engine is started. I assume they are not tolerant to surges/dips. 

[ArtVandelay]

The battery prevents voltage spikes, so you won’t get voltage spikes during startup, just a voltage drop.
Now if you going to turn off the master while the engine is running, you better turn off the avionics first especially if you have a mechanical voltage regulator.
Frankly I would be more worried about a lightning strike frying the electronics, if tied down outside.

[carusoam]

1 hour ago, ArtVandelay said:

The battery prevents voltage spikes, so you won’t get voltage spikes during startup, just a voltage drop.
Now if you going to turn off the master while the engine is running, you better turn off the avionics first especially if you have a mechanical voltage regulator.
Frankly I would be more worried about a lightning strike frying the electronics, if tied down outside.

In case I need to know…
 

What happens if I turn off the master while the engine is still alive?

Now I have to go see where my VR is wired to…. 

 

Best regards,

-a-

[Pinecone]

8 hours ago, hais said:

Curious why no conditioners on avionics? Surely it can't be for cost reasons given how much these boxes go for.

Older avionics, it just wasn't something they did.

Newer stuff should have it.  As mentioned, if no other reason that most of them have a power supply to reduce the voltage to electronics levels.

[hais]

12 hours ago, carusoam said:

without the alternator on… the voltage can’t spike above the battery voltage…. (Save the electronics from this)

With the new boxes. is it safe then to use the order master, avionics, start, alternator? 

 

[jkgyr52]

FWIW,

My 252 is SN-1053 and the POH checklist says "STARTING ENGINE - Alternator Field Switches - ON".

The checklist says - "BEFORE TAXI" - then all the other needed switches are turned on. The next paragraph provides the procedure of checking the dual alternators.

 Apparently the only people who knew what the rationale was for the differing procedure(s) are long gone!

We have lost much of the tribal knowledge regarding Mooney aircraft, and older aircraft in general.

Jeff

[1980Mooney]

Most J's do not have an Alt. Field switch.  The Service Manual with Electrical only shows Alt. Field switch starting with 28 volt system and Serial Number 3000 and up. As noted in the Service Manual, for the 2,999 M20J's without an Alt Field switch, the only way to diagnose the charging system per @M20Doc 's explanation above is to pull the Alt. Field CB. 

The POH for Serial Numbers below 3,000 notes "The master switch operates the battery relay which controls battery power to the main ship bus bar. This switch also cuts the alternator field power - from main bus to the alternator."   The "Normal Procedures - Starting" for those M20J's does not say anything about the Alt. Field.  It does not say to pull the CB.

The POH for Serial Numbers 3,000 and above (28 volt systems) says to leave the Alt Field "On" when starting.  

As noted by @jkgyr52 and others, Mooney has been inconsistent in providing an Alt Field switch and in the instructions for its use across models.  But in 40 years, starting the 3,400+ J's with the Alt Field "on" has not been an issue for old or new avionics.  This seems to be a non-issue.  As @ArtVandelay said "Frankly I would be more worried about a lightning strike frying the electronics...."

[Marc_B]

The general gist I think is that:

1) voltage spikes on old avionics were bad, modern avionics tolerate it better and it's mostly a nonissue

2) the field switch (if you have one) applies power to the alternator field so that when the alternator turns, it produces power

3) there are a variety of POH and traditions that have field switch on as well as field switch off with engine start...all are generally acceptable.

4) BUT the field switch is a good way to check your alternator to see if it's working...and this tidbit is probably what most of us haven't really been using at all.

Personally I'm a start engine, then flip field switches and a avionics off, field switch off, engine off type of guy...but it's just habit and flow, nothing more.  But I will start looking at the volts/amps when I do it in the future!

[Fly Boomer]

5 minutes ago, Marc_B said:

But I will start looking at the volts/amps when I do it in the future!

Me too.  I never thought about this before, but it seems to be a simple way to get a high-level check on the charging system.  And possibly take a tiny bit of load off the engine during start.

[MikeOH]

A few comments from an EE (lawyer warning: worth what you paid for them; YMMV, etc):

1) Transients exist pretty much most of the time.  Magnitude and frequency worse during startup.

2) If you think the battery is going to 'filter' them out...think again!  It's more complicated than that.

3) Modern electronics are MORE immune, but not bulletproof.  It can be a cumulative effect, as well.  And, do you know ALL the protection circuitry and relative susceptibility of ALL of your electronics?  I didn't think so!

4) Just make sure the avionics master is OFF BEFORE startup, and OFF BEFORE shutdown.

5) If you have a voltmeter and ammeter (not a load meter), just look at those to confirm the charging system is operating; no need to turn off the alternator.  You won't see 13.5-14.5 V if the alternator is off-line.  By the time you are done with run-up the ammeter should read 0 (showing the battery has been charged back from starting).

6) If I had a ALT FLD switch I'd follow the POH, but honestly can't imagine it makes any difference to starting.

<end my two cents worth>

 

[kortopates]

Mike nails it above, not only smart but with good common sense! please pay special attention to his #5, a pilot shouldn’t need to flip the alternator off to verifying it’s charging as if we need to rediscover the the difference between battery voltage versus charging voltage. A glance at the voltage meter should be plenty sufficient.

Dual alternators is an exception. But even here you probably don’t need to switch them both off one at a time. If you have the load meter, you can see the belt driven #2 taking the majority of the load, so just flip off the #2 off and see the #1 take up the entire load. That’s sufficient.
If you no longer have the Mooney load meter you won’t have all that good info to go by without turning them off independently.


Sent from my iPhone using Tapatalk

[Oscar Avalle]

Paul and Mike are right on the money. Just make sure that the avionics switch is off and that most electronics (unless otherwise stated in the installation manual) is off when you start the engine and bring the alternator on line. My AOA had been acting up because I had it wired to the main bus and it was losing callibration. I ended up conecting it to the avionics bus and it seems to work now... 

 

[jlunseth]

On 4/2/2023 at 3:53 AM, carusoam said:

 

What happens if I turn off the master while the engine is still alive

Nothing. Your electrical system will be completely dead but that is the point. The main reason for the switch is to stop an electrical fire. All of it goes dead including instruments and engine monitor. Anything electrical. Anything not electrical continues to work such as airspeed (pitot operated). The engine continues to operate like nothing happened. Got to do that once. In that instance the purpose was to save the battery for landing when the alternator failed. I was hoping the engine monitor would keep on keeping on, but no. It’s probably worth doing once for practice, except you will lose some things like digital hour meter tracking the flight hours.

Edit: Let me change that a little. The overhead lights are not connected through the Master in most of our aircraft, so that would not be shut off, it has to be shut off with the overhead switch which is a mistake many have made (leaving it on after departing the aircraft).

My plane also does not have an Alt switch. Just breakers.

Edited April 5, 2023 by jlunseth

[rbp]

On 4/1/2023 at 1:16 PM, kortopates said:

forgetting to turn on the alternator after starting

since the ALT switches are right next to the Avionics Master, it would be hard to forget

[Huckster79]

On 4/1/2023 at 11:08 AM, DCarlton said:

Discussions like this reinforce how great MS is as a forum due to the folks willing share their opinions, experience and knowledge.  You'd never get this level of discussion and interaction on a Facebook site.  

I agree! I’m very heartened by conversation on here. I asked a truly stupid question earlier today, based off misreading something- folks just pointed out my error.  They didn’t call for revocation of my pilots certificate and trash talk me for an error.  
 

I also asked an important to me question a while back and I’ve learned a ton from the replies. 
 

now just gotta buy my Mooney- I think this month, fingers crossed. 

[carusoam]

On 4/2/2023 at 11:10 AM, hais said:

With the new boxes. is it safe then to use the order master, avionics, start, alternator? 

 

No and yes…

1) If we assume everything is modern with built in ruggedness…. Any order you like will work…

especially if your engine instruments are part of the electronics you want to watch during start-up.

2) If we are concerned with minimizing every transition possible… as if we have sensitive equipment… some order would be a benefit…

3) Starting the engine is a big transition…

4) Starting up the charging system comes with its own transition…

5) Our biggest challenge… is the abnormal things that can happen… if the voltage regulator stops regulating… higher voltage can be sent through the system until the battery boils dry…

 

6) I was reviewing a check list from a prior owner earlier today…

He had both the master and the alternator on before start. 

7) Modern electronics have come a long way with their ruggedness!

8) Getting away from the old sticks and stones and springs VR, and going Zeftronics… was a nice way to keep the battery from boiling dry, again… in my old M20C.  Probably eliminates a bunch of transitions as well… 

 

9) Right up there with hitting the brakes before retracting the gear…. The chance of them still rotating is retry slim…. 
 

10) Start-up has a unique oddity… when the starter stays engaged after the starter is de-selected… it becomes a defacto generator with no regulation…

Modern Mooneys have a red light in the annunciator panel dedicated to a stuck starter… one of the things you check right after start… along with OilP.

11) Delaying turning on the voltage regulator until after start… is an attempt to send the nicest condition power to it, before it gets to work…
 

PP thoughts only, not an electrical engineer…

Best regards,

-a-

[carusoam]

On 4/2/2023 at 11:47 AM, jkgyr52 said:

 

We have lost much of the tribal knowledge regarding Mooney aircraft, and older aircraft in general.

Jeff

This is why we have MS! 

Some tribal knowledge is good…

Some wasn’t good the day it was written or orally passed along…

Some has been update after Y2K…

 

It is tough to stay on the path…

when the path goes the wrong way…

 

But, if you don’t know better… following the path is better than guessing, or following bad advice…

Our POHs got better over the years…

There is a good reason to have two POHs some times… the one that matches the year of your plane… and the most recent one written for the last year your plane was built…  speaking of lost  tribal knowledge…  I got this advice when I called the factory in Y2K… I spoke with the engineer who did the flight test on my plane in Augusta of 1965, 35 years earlier…

That was Bill Wheat, aka Mr. Terrible, a wonderful person… 

PP thoughts only, not a CFI…

Best regards,

-a-

[rbp]

I’m gonna get out on a limb here and say that in the grand scheme of things the ALT switch position doesn’t matter one way or another

[carusoam]

2 minutes ago, rbp said:

I’m gonna get out on a limb here and say that in the grand scheme of things the ALT switch position doesn’t matter one way or another

1) Turn it on before you forget…

2) or have a way to make sure it got turned on before departing into IMC…

3) It would suck to baby all of the electronics, then crush them in an accident, because you forgot to supply them power….  

 

We haven’t had very many Red X events post the age of the G1000 introduction…

Or dead back-up batteries for the color screens…

Best regards,

-a-