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  #41  
Old 12-21-2010, 01:38 PM
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Ironflight Ironflight is offline
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Just to keep the discussion centered folks, I was NOT talking/asking about Plane power or B&C alternators. Different designs, different operating criteria. I would wire and operate them EXACTLY as the instructions tell you to do, since that is how they were designed.

The Internally regulated ND's were designed to be turned on with the main power, and turned off when the vehicle is shut off, so why not use them that way? The question about twins where you switch the alternator on after start is irrelevant - there are no RV twins, and the certified light twins do not use the ND alternators - again, use them as designed.

As far as the switch in series with the circuit breaker - I am still not convinced that the switch buys you anything except saving an extra second if you have to power things down with a short. If you subscribe to the theory that reducing parts count increases reliability, the breaker should be good enough - as long as you religiously follow your Emergency Procedures (I put a red ring around my alternator field switch). I don't want to belittle that argument BTW, it is a good one - but it is a choice between two "risks", and different folks can choose differently based on their experience.

Paul
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  #42  
Old 12-21-2010, 01:51 PM
JAT JAT is offline
 
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Paul,

First you say you do and then you don't, then you say you will and then you won't, you're undecided now, so what am I gonna do? Say, that would make a good song! Am I back to the original Cessna switch where I turn both on and off at the same time? When the dust settles Paul, just tell me what you have finally decided to do. That will do me just fine and I will follow your lead, as usual!

Thanks, as usual!

Jim
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  #43  
Old 12-21-2010, 02:10 PM
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Fred.Stucklen Fred.Stucklen is offline
 
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Default Split Master or three position toggle

Quote:
Originally Posted by nomocom View Post
Well...when the smoke doesn't stop, you'll remember the field breaker

That is a good point Fred. I have an airplane so equiped, and very infrequently I've shut the master off with the engine running and it does take a few seconds to remember why everything is still lit up. I do get used to the electrons coming and going with the master switch position, but isn't always so.
Another point to ponder. Lets say one were to utilize the split master or three position master switch design. Lets also consider the auto alternator that can not be turned off by interrupting the field circuit. (This does not include Plane Power as it CAN be switched off.)
If the alternator can not be switched off by the pilot, opening the master contactor will only disconnect the battery from the main buss. It will NOT disconnect the alternator, thereby allowing it to continue to supply power to a fault on the main buss (i.e., the fire won't go out!). The pilot now has to pull the alternator output breaker to "put out the fire".....
To complicate matters even more, if this non-field controllable alternator were to somehow fail with an over voltage failure mode, you've just fried all you expensive electronics, even if the pilot could shut the master off and pull the alternator output breaker.....
There's a good safety related reason why all the spam cans had master switches that shut off the alternator output.....

Consider this: You're 20 miles off the coast of North Carolina (over the Atlantic), IFR, North bound to New England. Everything seems to be going just fine, until your passenger comments "Do you smell smo... " Click goes the master, shutting down the whole electrical system, before the comment can be finished. You turn left, direct to Charletton, NC, and start tuning off all electronics, then enable the master again. You see low voltage, not alternator output, are able to raise ATC on a radio (but other equipment seems to also be ON),and land uneventfully. Trouble shooting the failure indicates that the field circuit has "Burned Up", shorting out several other wires in the harness in the process. Yet,from the onset of the first wiff of smoke , to the time everything was disabled, was less than a second... (I'm not going into the stupid reason an electrical engineer allowed this to happen in the first place....)
If the pilot had hesitated any longer, there would have been a bonna fida fire while in flight, especially if he had to take the time to think about what additional steps weere required to shut down the alternator output if the alternator wasn't controllable......
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Last edited by Fred.Stucklen : 12-21-2010 at 02:22 PM. Reason: Added more to the story...
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  #44  
Old 12-21-2010, 03:16 PM
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Ironflight Ironflight is offline
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So Fred, if I understand your argument, you are essentially arguing against the ND alternator, not the concept of using the circuit breaker on the field as a switch - is that correct?

Certainly that is a valid topic for discussion - not the question I asked of course, but one that would be worthy of it's own thread. realistically, if we are depending on the human to turn off the Master switch at the smell of smoke, we can also rely on him or her to pull the field breaker - there is more time lost in going "what's that smell?" than in operating two "switches".
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  #45  
Old 12-21-2010, 04:10 PM
DGlaeser DGlaeser is offline
 
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Default Not to worry . . .

There won't be any passengers to smell the smoke in an RV-3

But to Fred's point, the field breaker won't do anything - you need a breaker on the alternator output.
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Last edited by DGlaeser : 12-21-2010 at 04:12 PM. Reason: update
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  #46  
Old 12-21-2010, 05:43 PM
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L.Adamson L.Adamson is offline
 
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My airplane still has the contactor relay from the day's of the Bob K. over voltage setup. The device that trips the breaker (which disconnects the contactor) has been removed from the circuit. I left the contactor in, as I have no desire to re-wire the alternator B-lead.

However, this contactor is energized by the alt-switch. If the alt-switch or master switch is turned off, that heavy wire from the alternator is disconnected at the firewall. Could be a good thing..........or just extra weight.

These day's my alternator is a Plane Power.

L.Adamson --- RV6A
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  #47  
Old 12-21-2010, 05:58 PM
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Chino Tom Chino Tom is offline
 
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Quote:
Originally Posted by Fred.Stucklen View Post
Ok guys, here's an electrical question for you to ponder. I'm Assuming that you do not have a field switch, just an alternator field circut breaker.. You start the engine normally, but sometime, while the engine is running (maybe in flight) you have the need to shut off the master (maybe due to an electrical fire!). What causes the alternator to stop putting out power?
In this case, the battery has been disconected from the main power bus. Because it was never shut off, the alternator starts to supply it's own field current trough the regulator as it has never shut down. (this might be unstable as the buss has lost the battery capacitence to make if more stable). Your main electrical bus is still hot! You electrical fire continues to burn until you pull the breaker in the field circut.......
So to stop the alternator from supplying energy to the fire, you have to shut off the master AND pull the field breaker (IF you remember in the heat -pun intended - of the moment)....
I would rather have just one function to perform to eliminate my main buss power.... The split master or three position switch does that....
I set my system up so this won't happen. My alternator field CB/switch
get its power from the main bus. When the master is turned off the alternator
field power is shut down. I also have a constant current relay
between the B power from the alternator and the main bus which is also
controlled by the Alternator field CB/Switch. I believe once you have excited
the field, and the alternator is spinning, turning off the field doesn't guarantee
that the alternator will quit producing power. Thus the reason for the
constant current relay. With the master switch on, turning on the Alt field
supplies current to the field and closes (allows power to pass through, I always confuse myself
with open or closed) the constant current relay. Of course
as posted by Paul, a simple Circuit breaker would accomplish the same
thing.
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Last edited by Chino Tom : 12-21-2010 at 06:17 PM.
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  #48  
Old 12-21-2010, 08:20 PM
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Walt Walt is offline
 
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One of the reasons I prefer the externally regulated B&C is the positive shutdown of the of the Alt with the master switch (OFF-BAT-ALT).

With the Alt switch off, you shut off the regulator (which supplies field current) so the alternator WILL positively shut down.
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  #49  
Old 12-21-2010, 09:01 PM
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Ron Lee Ron Lee is offline
 
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I think I have a goal for 2011. Understand what is being said here.

I have a master rocker switch and an alternator (Field) rocker switch. Due to an indication of higher than normal output voltage, I removed the 14684 type ND alternator and had it tested by an AI who does build engines. It is working around 14.2 volts.

Initial startup on the test stand shows zero alternator output. Energize the field and it outputs 14.2 volts. Remove the jumper and it cuts the alternator output.

This appears to be inconsistent with other comments made. I will test it more tomorrow after reading these posts, but for now I will install my backup alternator and see what happens.

I am pondering adding over voltage protection.
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  #50  
Old 12-22-2010, 06:48 AM
DGlaeser DGlaeser is offline
 
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Default Cool!

Quote:
Originally Posted by Ron Lee View Post
I think I have a goal for 2011. Understand what is being said here.
I have a master rocker switch and an alternator (Field) rocker switch. Due to an indication of higher than normal output voltage, I removed the 14684 type ND alternator and had it tested by an AI who does build engines. It is working around 14.2 volts.
Initial startup on the test stand shows zero alternator output. Energize the field and it outputs 14.2 volts. Remove the jumper and it cuts the alternator output.
This appears to be inconsistent with other comments made. I will test it more tomorrow after reading these posts, but for now I will install my backup alternator and see what happens.
I am pondering adding over voltage protection.
Not inconsistent, just not always the case. I also have an IR alternator which works that way (chosen because it has that feature). With that control, adding OV protection is easy and straightforward. I did because I have no idea whether the IR has OVP built-in or not. To me it's worth $$ to protect $$$$$ in radios.
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uAvionixEcho ADSB in/out with GRT Safe Fly GPS
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