RVG8tor

RVG8tor

Well Known Member
I am brain storming here while I work on my electrical system design (Z12). I wonder why there is a switch for the Alt Field. From my reading on the forums internally regulated alternators get their life shortened if one turns them on under load, (they should be on before start until after start to get the most life out of the alternator). The B&C alternator is externally regulated and can handle the switching under load. But operationally there is no reason to switch the alternator on and off, if you have an abnormal situation and need to turn the alternator off you can do that just as easily with a circuit breaker as you can with a switch. So why not leave the switch out of the loop and wire the alternator field directly to circuit breaker so it is always on, in case of alternator problem, pull circuit breaker. On less switch a few ounces and dollars saved. So, am I missing something obvious here?
 
I have a PLANE POWER ALT. and that's how I did it. Been working great for 250 hours. And you don't need that split hard to install master switch. Drill another hole and install your master sw.............
 
If regulator fails youi can then shut off the Alternator. Of course fuse and/or circuit breaker will allow same thing. If you have crowbar overvoltage protection it will happen automatically.
 
You are probably already doing this but...

Be sure that when the master switch is off, so is the field circuit. In other words, if you are using an essential bus, make sure you attach it to the main bus, not the essential bus. If you can energize it from the essential bus, there would be current being used by the alternator even if it is not generating electricity.

If you are following Aeroelectric connection drawings you can run the field circuit throught the master switch and it shuts down the master solenoid and field circuit at the same time on separate circuits.
 
Clarification.

N999BT said:
Be sure that when the master switch is off, so is the field circuit. In other words, if you are using an essential bus, make sure you attach it to the main bus, not the essential bus. If you can energize it from the essential bus, there would be current being used by the alternator even if it is not generating electricity.

If you are following Aeroelectric connection drawings you can run the field circuit through the master switch and it shuts down the master solenoid and field circuit at the same time on separate circuits.
Click to expand...

I am not sure I understand, if I have my alternator field going to just a circuit breaker on the main bus and it is IN, and I shut off the battery master (de-energize the main bus). I then turn on my E-bus alternate feed to power the E-bus from the battery. Would this cause trouble? If I need the alternator field off, I can do this with a switch or without the switch pull the CB. What I am asking about is wiring according to the AEC Z12 but I would not have the alternator field go to a switch it would just go to the main bus CB. My master switch would really be a "battery switch".
 
I'm not using a ALT switch on my rocket. I have one in my RV-6, and in over 1100 hours of flying I've never found a need to shut the alternator off. Of course if you were flying on battery alone, you can switch the field off which would drop the 3A draw off the bus if you have the switch...but if your fuses or breakers are accessible then its just a simple matter of pulling the breaker to disconnect the field.
 
Another reason is that if you have a primary and a backup alternator, you need a switch to select which one to use.
 
Another reason, if your running the battery master but not the engine you don't have the drain of the alternator field.

Peter
 
If you have an under or overvoltage system installed you can reset by turning off the field. It worked very well in my PA32 & 172 I have the split sw in my RV8.
 
Z12 is Stby Alt

MCA said:
Another reason is that if you have a primary and a backup alternator, you need a switch to select which one to use.
Click to expand...


I will have a Stby alternator, it is on all the time but its regulator is adjusted to kick on only when bus voltage gets below a certain value. If the main alternator dies, it just picks up the load. It will be up to me to load shed equipment to remain with in the stby alternator capacity. Again I see no reason to have a switch, I can take either alternator offline by pulling the CB>
 
Cycle CB

N184JG said:
If you have an under or over voltage system installed you can reset by turning off the field. It worked very well in my PA32 & 172 I have the split sw in my RV8.
Click to expand...

On the very rare occasion this type of reset is required, I can pull the CB. So far no one has told me why the switch is in the design, unless all of the Z designs are predicated on using fuses which are not accessible in flight.

I am just at a loss to figure why there is a switch, everyone puts one in. I know it is experimental and I can do what I want, I am really trying to get an education here and understand why the switch is there, it must be for something other than convenience.
 
Bob Nuckolls answer

I received this answer from Bob on the AEC forum.

Bob Nuckolls replies:

An urban (or perhaps hangar) legend. I've been
working with alternators and generators for 40+
years. There is no basis in physics to support
the legend. In fact, it has always been a design
goal of every TC aircraft electrical system to
offer any time, any conditions, positive ON/OFF
control of alternators and/or generators without
concern for degradation of performance or damage
to equipment.

The B&C alternator is externally regulated and can handle the
switching under load.

As can ALL other skillfully designed alternators. One
of the foundations upon which the hangar-myth was
built had to do with alternators ostensibly
wired per Z-24 . . .

http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z24-Interim.pdf

. . . and apparently switched off (B-lead
broken) while the alternator was under load.

This started a hysterical kerfuffle about "turning
alternators on or off under load". Numerous
authors have posited the same hypothesis before.
However, the special case presented by a b-lead disconnect
contactor energized efforts by the in-experienced
and un-informed to stoke the fires anew and stir
the pot of misunderstanding.

I enjoyed a two-day tour of a LARGE scale alternator
remanufacturing operation about a year ago. Details
of this visit can be discovered at:

http://aeroelectric.com/R12A/03_Alternator_12A1.pdf

During that visit I witnessed a demonstration
of a full load, max rpm, hot-alternator b-lead
disconnect that liberated kilojoules of energy
in the ensuing arc . . . 5 times in a row. The
flash of fire was so great that it was impossible
to photograph or record on video. Their chief engineer
asserted that all of their reman products (2800+
line items) were tested to the same design goals.
These alternators were demonstrably immune from
self-induced load dump damage.

But operationally there is no reason to switch the alternator on and
off, if you have an abnormal situation and need to turn the
alternator off you can do that just as easily with a circuit breaker
as you can with a switch.

Suppose you have two alternators like Z-12 or
Z-13? Is it not useful to test the two alternators
independently of each other irrespective of all
other conditions?

Suppose you have smoke in the cockpit? How
about an unruly regulator? Our brothers in
the TC aircraft world have adopted any-time,
any-conditions, ON/OFF control as a design
goal.

So why not leave the switch out of the loop and wire the alternator
field directly to circuit breaker so it is always on, in case of
alternator problem, pull circuit breaker. On less switch a few ounces
and dollars saved. So, am I missing something obvious here?

Perhaps not obvious . . . but certainly not
'secret'. Any student of contact physics for
things like relays, switches and CIRCUIT BREAKERS
will understand that depending on a breaker
like . . .

http://aeroelectric.com/Pictures/Breakers/Klixon_1.jpg

. . . to open the 100 volts plus, b-lead of a runaway
alternator is quite likely to experience a hundreds-of-
kilojoules arc in the gap of relatively slow moving
contacts that are guaranteed to produce a lot of smoke
in the cockpit. BREAKERS are not intended to serve
as commanding manual control devices. Breakers for
aircraft are designed to break faults of several
thousand amps at 32 VOLTS or less. See paragraph
4.7.14 of . . .

http://www.aeroelectric.com/Reference_Docs/Mil-Specs/5809G.pdf

Since the first generators (and then alternators) went
aboard an airplane, the pilot has been offered positive
control of those electrical energy sources by breaking the
FIELD lead. At no time did anyone consider the main power
output feeder protection to be a control device. In fact,
b-lead protection on TC aircraft isn't even on the panel . . .

http://aeroelectric.com/Pictures/Wiring_Technique/A36_Firewall_A.jpg

I have posted this on VAF, but thought since this forum is more on
point I should post it here.

Please post this reply to VAF. Thanks!

Bob . . .

And there you have it from an expert.
 
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Switched Field

I don't think you HAVE to have one, but I would put one in anyway. Typically to reset an overvolatge you turn off the field and then back on.
When I have had a tough time starting (like a hot start), I shut off everything including the alt field.
Now, you can do all this with a pull type CB, but they are not designed to be used as a switch (think in terms of number of cycles). Consider a circuit breaker switch combo, and you'll have both. Leave it on all the time if you care too.
 
Too late

Luca,

I have already drilled my holes so I will have to live with my 1.5 inch spacing, how far apart are yours, I can see what you mean things might get tight with my spacing. I am using 3/4" between breakers based on what Stein and other panel builder use. I will let you know how goes, I can always make anew panel and try again. I am in Amsterdam this month and the weather today has been great, hope you are having the same in Trento.


There was much more discussion about the alternator field switch on the Aeroelectric list forum. I decided to go with switch for two reasons, it is convenient and circuit breakers are not built to be switches. We do use them that way for a lot of things with my airline but I figure my Klixon breakers are not as robust so I don't want to use them as switches. The short answer is you could do away with the switch but a breaker might fail and would be more trouble to replace.

Ciao.
 
try it, you can re-do it later

Mike,

here's my spacing, 3/4 is standard. I choose 2 inches because .... I did a tighter one panel spacing :rolleyes:

but you can try yours and re-do it later.

cbpanel.jpg


this is the wiring, 2 inches is ok for me - 1 half maybe

http://www.rv8.it/log/electrical_system/Breaker_switches_panel/Pages/11.html

My buss bar is a copper piece 1/16 thick and 1/2 inch large

Only for sharing this is my CBs map :

http://www.rv8.it/vansairforce/swich&cb.pdf

IMHO : for future maintenance changing a CB or a switch is the same problem (perhaps the CB is more difficult due it's locked to the buss bar)

Trento weather, nice fall day 73?F. Spent a good sunday morning as CFI in a Falco F8L and flew a SF260. Can't wait to fly my 8.
 
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For anyone that has ever studied user interface design, just about the worst thing you can do is create a long row of evenly spaced things that the user must interact with. It is much better to put items in groups. Want an example? Just take a look at the function keys on your computer keyboard. They are grouped like that for a reason. Also look at the cb panels in certificated airplanes. In all of the airplanes I can think of breakers are grouped in some way or another.

This is one of the reason I chuckle when people say things like "you need to put those trim servos on a breaker for an emergency" and then they proceed to bury the breaker in a long row of other breakers. If your trim runs away it happens fast and you will not find the breaker before the trim hits the stop.

Me personally I handled this is another way. My trim is not on my e-buss (neither is my autopilot). I also do not have breakers for either (I have fuses). They are only on my main buss. If either of them goes nuts, I energize the e-buss and shut off the master switch. For me it was the simplest, most cost-effective solution and doesn't compromise safety in any way.
 
Straight Line Breakers

Jamie said:
For anyone that has ever studied user interface design, just about the worst thing you can do is create a long row of evenly spaced things that the user must interact with. It is much better to put items in groups. Want an example? Just take a look at the function keys on your computer keyboard. They are grouped like that for a reason. Also look at the cb panels in certificated airplanes. In all of the airplanes I can think of breakers are grouped in some way or another.
Click to expand...

You're right in that a little intelligence needs to go in to the design of switch and breaker layouts Jamie, but there are ways to group things and still have straight lines. I have three lines of breakers on my sub-panel - each represents a bus. OK - Avionics, Essential, Main - I can pull all breakers in a row and completely isolate a bus. Breaking up a "long line" with an extra space is a good idea - separate items by functionality. Another trick is to throw in a switch guard on specific items - that provides a "finger-findable" option for an important breaker. One other idea is to use colored rings on the breaker caps to identify specific groups - pull all the RED breakers to get rid of high load items, for instance.

One reason lines of breakers are popular is because you can hook a solid bus bar to the feed side of a row, and have a very solid and trouble-free connection.

Paul
 
logical options

Jamie, you're right in general.

But I studied my logical idea, thinking to my sequence that depends from : space to put things, wanting to put the buss bar(s) only in one place, fight with Italian FAA engineer and ... a good check list when in flight.

The key in general is, like Paul said, the coloured ring for CBs.

This my CBs panel thought :

- first row : standard way, last one is for avionics

- second row : CBs in decreasing order, firts one is for Electronic Equipment, last one (easy to reach) is A/P.

- third row : after single avionic and electrical equipment, roll trims CBs are in the perfect place (for my size) to reach just in case [ergonomy] others are minor/low amp stuff. Last CB is for a future smoke system.

With the side panel I can easily check if a white internal CB ring has popped.

My switches are :

side panel - master/alt field/avionics/electronic stuff/nav lights/strobe/flood light

left panel - fuel pump / land light

trims, a/p disengage, PTT, flaps are on my infinity stick

This works for me, absolutely better that in each and every every general aviation airplane I flew :)

http://www.rv8.it/vansairforce/swich&cb.pdf

Thanks for your advice.
 
Agree completely with both of you guys. My main point is that there needs to be some sort of difference in otherwise similar things in order to call attention to them.

Also remember that this must be done at night too, and the we often times use colored lights to illuminate our panels so items are different colors then. :)
 
Back to the original question

One good reason you need either a circuit breaker you can pull manually or a switch is so you can troubbeshoot on the ground. If switch on the master switch and the field is always live, you will drain your battery fasterwhen the engine is not running.

I have also had to switch off the field in the air because the insulation on my alternator output post disinegrated (sp?) and the battery wire was grounding intermittently on the the case of the alternator. This is when an ebus is very handy.
 
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