When do you turn on your Alternator?

[BigTex]

Guys - I've had several conversations with some very respected folks in the Mooney community regarding when they flip on and off the alternator. Both seem to have some pretty good arguments why they turn the alternator on and off when they do. What's everyone else doing as far as when they flip on (and off) the alternator for the start up and shutdown procedures?

[danb35]

In my case, there isn't a separate switch for the alternator, so I'd have to pull the field breaker to turn it off. I don't see any reason to do that.

[Lionudakis]

x2, mine has no on/off, but if it did, on before radio master on, off after radio master off. I would be curious to hear what and why from others.

[Awful_Charlie]

I normally turn one alternator on as soon as the engine is running smoothly at about 1000 RPM, then off, then the other on, and then assuming they're both OK individually, then both on. For some reason until about 1200 RPM my left alternator drops off-line with the right one on, but generates ok on its own. When the charge current has dropped to about 10-15 amps, then fire up the Aspen, wait for it to do the first bunch of its checks, and then turn the avionics mastter on - the delay there allows the Aspen display to wake up before the GNS starts to do its instrument checks. For the first start of the day there is no need to rush, as it takes several minutes to get the CHTs up to temperature.

For shutdown, it will be reduce to 1000RPM, avionics and lights off, record the fuel figures from the Shadin & JPI, then both alternators off, reduce engine to idle, mag checks (would rather know before the next flight if the aircraft is not going to be flyable on the return!), pull the mixtures, and power off the master when the engine stops

Ben

[driller]

If you have an alternator field switch or switches, as in my case, the POH for your model should give you the appropiate proceedure. My book says ON before engine priming, OFF before turning the Master off.

curt

[1964-M20E]

With my former plane I never bothered with turning the alt on or off even though I had a field switch.

[jackn]

If you start the engine with the Alt on, the field will be fully energizing(trying to geneate maximum voltage). This will place an additional load on the battery. The only time this becomes a problem, is when you have a tired battery or the plane has been sitting out in frigid conditions. If you wait until the engine is running to turn on the Alt, you will get a spike through the alternator and and anything not controlled by the avionics master. I leave the alt on while starting, except if I need all the battery power that I can get. I don't think it makes any difference when the alt is turned off.

Ben(Awful Charlie), your system is doing what it's supposed to do. The 'right' Alt is your belt driven one. It spins faster and therefore carries the whole load. The #1(left) is acting as a standby.The VRs are connected and 'tell' each other which one is generating the most voltage, that one gets turned on and the other is turned off.

[driller]

If you start the engine with the Alt on, the field will be fully energizing(trying to geneate maximum voltage). This will place an additional load on the battery. The only time this becomes a problem, is when you have a tired battery or the plane has been sitting out in frigid conditions. If you wait until the engine is running to turn on the Alt, you will get a spike through the alternator and and anything not controlled by the avionics master. I leave the alt on while starting, except if I need all the battery power that I can get. I don't think it makes any difference when the alt is turned off.

Ben(Awful Charlie), your system is doing what it's supposed to do. The 'right' Alt is your belt driven one. It spins faster and therefore carries the whole load. The #1(left) is acting as a standby.The VRs are connected and 'tell' each other which one is generating the most voltage, that one gets turned on and the other is turned off.

I appreciate this info also. I've been wondering why my left alternator drops off at low R's. thanks

curt

[BigTex]

For planes that have a separate alternator switch, whats everyone's thoughts on using a Cessna split master switch to consolidate switches? Would this change require a 337 or is something like this just a logbook entry?

[laytonl]

Jackn is correct, with the alternator "on" the regulator is trying to generate maximum voltage. Also, the alternator is being seen as a heavy load to the battery and is putting an unnecessary load on the battery. I don't think the inductive kick when the alternator is turned on is too bad, but I wouldn't do it with the avionics master on. I follow the POH instruction and just turn on the alternator right after the master. Lee

[larryb]

For planes that have a separate alternator switch, whats everyone's thoughts on using a Cessna split master switch to consolidate switches? Would this change require a 337 or is something like this just a logbook entry?

I would also like to know the answer to this question. Anybody? Is it allowed to replace a simple switch with a different type? I have a standard 2-pole single-throw master/alternator switch. I kinda would like to have the split master.

[65C_flier]

On 1/7/2013 at 7:23 AM, larryb said:

I would also like to know the answer to this question. Anybody? Is it allowed to replace a simple switch with a different type? I have a standard 2-pole single-throw master/alternator switch. I kinda would like to have the split master.

+1. Just giving this old post a bump to get people's thoughts on replacing the Mooney 2 pole single throw with a split switch. Apart from the added benefit of being able to control the alt separately,  they seem a whole lot cheaper. Thanks.

[MikeOH]

My thought is, why bother?  The plane was designed without one; I'd say the engineers didn't see the benefit of separate alternator control.  Never had an issue, never heard of anyone having an issue.  I'm certainly NOT going to mess with mine.

[Rmag]

This...

[MikeOH]

@Rmag

Your point?

[Rmag]

Just now, MikeOH said:

@Rmag

Your point?

Answering the Original Poster’s question:

On 9/30/2012 at 12:17 PM, BigTex said:

What's everyone else doing as far as when they flip on (and off) the alternator for the start up and shutdown procedures?

My answer was my post.

[MikeOH]

Just now, Rmag said:

Answering the Original Poster’s question:

My answer was my post.

Gotcha!

Thought you were trying to answer the why of it....and, didn't see that!

[Guest]

It’s like the RoP/LoP debate.  
 

I’ve always left the alternator field switch off during starting for those that have one.  Once the engine starts, verify oil pressure, vacuum, then alternator field switch on, alternator fail light extinguishes, ammeter show positive rate.

Clarence

[65C_flier]

38 minutes ago, MikeOH said:

My thought is, why bother?  The plane was designed without one; I'd say the engineers didn't see the benefit of separate alternator control.  Never had an issue, never heard of anyone having an issue.  I'm certainly NOT going to mess with mine.

I generally agree; why fix it if it aint broke? My reason is that I am having fluctuating ammeter (as described in the DMax article) on a 78J, but it hasn't been fixed by cleaning the master switch contacts. We have also checked the recently overhauled Prestolite alternator (voltages / resistances across alternator and CBs are good), field wiring, earth, etc all look good. Electrodelta VR seems to be regulating properly (although could have an intermittent internal fault I guess), so we are considering replacing the master switch (in case of internal corrosion). If a split master is (or can be) approved it might be a cheaper option and have added functionality (albeit, not required functionality)

Something like this https://lasar.com/switches/master-switch-688-169 vs something like this https://lasar.com/switches/rocker-switch-master-switch-circuit-breaker-880052-501

[MikeOH]

Just now, 65C_flier said:

I generally agree; why fix it if it aint broke? My reason is that I am having fluctuating ammeter (as described in the DMax article) on a 78J, but it hasn't been fixed by cleaning the master switch contacts. We have also checked the recently overhauled Prestolite alternator (voltages / resistances across alternator and CBs are good), field wiring, earth, etc all look good. Electrodelta VR seems to be regulating properly (although could have an intermittent internal fault I guess), so we are considering replacing the master switch (in case of internal corrosion). If a split master is (or can be) approved it might be a cheaper option and have added functionality (albeit, not required functionality)

Something like this https://lasar.com/switches/master-switch-688-169 vs something like this https://lasar.com/switches/rocker-switch-master-switch-circuit-breaker-880052-501

Well, that makes a lot of sense; if you need to replace the switch anyway, and can save money with the split one, I'd go for it.

[A64Pilot]

Before I replaced the master I’d temporarily jumper it, this bypasses the switch and if it’s the switch it of course will fix the issue.

‘However you lose the CB functionality, if the master is a CB, I’m not sure it is, I wouldn’t think it is.

I’m also having a fluctuating ammeter / voltmeter, cleaning the external contacts seemed to fix it, but then I thought I ought to do it the correct way and put some DC4 on them to prevent future corrosion, and it seems to have returned but at a much lower fluctuation, its intermittent meaning it only does it sometimes

‘So let me know what you do to fix yours. 

‘Whether a split switch is a minor or a major is up to the installer to decide, I’d decide it’s a minor because you only changed from a single to a dual switch, but you should confirm the amp rating of the split switch is as high or higher than the single, for both sides, and confirm it’s not a breaker switch.

‘In Cessna’s I’ve flown the split switch is used as a single switch, meaning alternator off and on with the master. I had always thought it was split in the event of a malfunctioning voltage regulator that gets stuck wide open you have a way to turn off the alternator before it burns something up. Cessna’s seem to favor the type of CB that’s flush and you can’t pull them, I have no idea why perhaps they are cheaper? So you couldn’t pull the field CB on a Cessna, or at least not our old C-210.

 

Edited April 2, 2021 by A64Pilot

[David Lloyd]

I have had airplanes with and without a separate field switch but if having the option, always started the engine with the field switch on.  I've had alternators fail due to worn brushes twice (1 was new, a factory assembly error), a failed bearing, a failed coupler (geared), an internal short (replaced under warranty).  One I exchanged due to old age. None failed due to having the field switch on during start.  Broken wires, improperly crimped terminals, and corroded fuse holder, none failed due to having the field switch on during start.  One regulator due to a bad overvoltage relay, one replaced because the mechanic said it was bad (always wondered if he found a broken wire).  One automotive regulator that truly failed on my home brew circuit due to my home brew crowbar overvoltage relay...I think.  Maybe one other died for an unknown cause.  So, regulators mostly have not failed due to having the field switch on during start.

This has been actively argued on vansairforce.net, along with ROP/LOP and internal primer paint or not.  After reading one of those arguments, I tried leaving the field switch off.  Started the engine, warmed, taxied to runup, went through the checklist, what...no volts.  Better turn this switch on where it belongs.  An it belongs on.

[carusoam]

We can simplify the discussion...

1) Something isn’t working well...

2) Focusing on a split switch?  It either works or it doesn’t. It is two switches in one body... feeding separate relays.

3) Now for the big point... sort of the fun part...

Did you say electrodelta voltage regulator?

4) If the box says Electrodelta on it...  did you take the cover off of it to look inside?

5) Did it look like sticks and stones and springs in there?  Did bats fly out as it opened?  

6) Or were there integrated circuits, and power amplifiers, and other high tech stuff, with LED read outs.?

7) Kind of leads us to a decision point...  

8) Stick with the 20^th century device of the post Apollo era... and adjust performance expectations properly...

9) Move up to the 21^st and get a new voltage regulator with a recognizable brand name...

10) Modern voltage regulator will provide modern performance without a whole lot of effort...

11) There is a maintenance manual for the Electrodelta device... it is a beautiful classic brochure...  posted around here somewhere...

 

Go Zeftronics!

Looking forward to see what I missed...   

Best regards,

-a-

 

 

[carusoam]

Now for the part I missed...

1) Controlling the alternator separately is a good idea...

2) The modern voltage regulator can handle plenty of spikes... 

3) But why send the known start-up irregularities through anything you want to use later..?

4) get a separate switch for your voltage regulator...

5) The split switch is just a different way of getting two switches... in one body...

6) putting two switches in one body is probably a unique way of getting two problems at the same time...

7) Master switches and alternator switches are not CB switches... they are low current, operating a relay mounted elsewhere...

8) Compare to ultra modern airplanes... where some electronics are so robust they are on before engine start happens...

9) Be nice to the electronics... turn them on after the engine starts...  

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[A64Pilot]

19 hours ago, carusoam said:

Now for the part I missed...

7) Master switches and alternator switches are not CB switches... they are low current, operating a relay mounted elsewhere...

 

 

PP thoughts only, not a mechanic...

Best regards,

-a-

LASAR plainly states the single master switch IS a switch / breaker.

https://lasar.com/switches/rocker-switch-master-switch-circuit-breaker-880052-501

They do NOT make that statement for the split switch

https://lasar.com/switches/master-switch-688-169

either their literature is incorrect or the single switch is in fact a breaker as well and the split is not.

So in my opinion if you want a split switch, your going to have to meet the original’s specifications, and it appears that the split switch doesn’t.

I would not think you would want the master to be a breaker, but I didn’t design the thing.