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tomblejwas(at)yahoo.com
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 Posted: Wed Oct 23, 2013 5:19 pm Post subject: Alternator without a Battery |
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In designing the electrical system for my Zenith Zodiac with a Viking engine, I thought I would start with Z-19 and modify - add OVP for the alternator, a relay to prevent run-on of the starter, and maybe more. Recent discussions on this site about contactors and the Z-19 philosophy have me rethinking things. Also, the Viking has an alternator that can run without a battery. I remember driving an overloaded old Dodge Colt on a long evening trip (Christmas eve) and having the headlights go dimmer and dimmer. Fortunately, I made it to a gas station next to a motel, because the battery that had easily started the engine 4 hours earlier was very shorted. (I was able to get a used battery installed on Christmas Day by a great farmer with a tow truck.). Why don't we worry about this in airplanes? Shouldn't we be able to fully disconnect the battery or batteries, if the alternator can run without a battery? Thanks.
Tom
Sent from my iPad
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nuckolls.bob(at)aeroelect
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| Posted: Thu Oct 24, 2013 5:20 am Post subject: Alternator without a Battery |
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At 08:18 PM 10/23/2013, you wrote:
<tomblejwas(at)yahoo.com>
In designing the electrical system for my Zenith Zodiac with a Viking
engine, I thought I would start with Z-19 and modify - add OVP for
the alternator, a relay to prevent run-on of the starter, and maybe
more. Recent discussions on this site about contactors and the Z-19
philosophy have me rethinking things.
Good critical review is always a good thing, if only
to confirm the validity of our faith in legacy
philosophies. Such confirmation fosters understanding.
Also, the Viking has an alternator that can run without a
battery. I remember driving an overloaded old Dodge Colt on a long
evening trip (Christmas eve) and having the headlights go dimmer and
dimmer. Fortunately, I made it to a gas station next to a motel,
because the battery that had easily started the engine 4 hours
earlier was very shorted. (I was able to get a used battery
installed on Christmas Day by a great farmer with a tow truck.). Why
don't we worry about this in airplanes? Shouldn't we be able to
fully disconnect the battery or batteries, if the alternator can run
without a battery?
. . . the Barons and Bonanzas do it, perhaps other airplanes
too. Your mission, if you choose to accept it, is to evaluate
the science and risks for adopting this philosophy yourself.
A discussion and study of stand-alone alternator operation
would be a good thing.
Bob . . .
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uuccio(at)gmail.com
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| Posted: Thu Oct 24, 2013 5:52 am Post subject: Alternator without a Battery |
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| Quote: | A discussion and study of stand-alone alternator operation would be a
good thing.
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Yes. I think the internal rotax 912 alternator/ducati regulator combination
will do this but I wouldn't want to do any damage by just disconnecting the
battery and seeing what happens. What's a safe way to test this?
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Thu Oct 24, 2013 7:12 pm Post subject: Alternator without a Battery |
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From the Rotax Installation Manual, Section 24-00-00, page 7:"A capacitor (see fig. 11, pos 14) of at least 22000 uF/25V is necessary to protect the correct function of regulator and to flatten voltage. The regulator is not designed to store any electrical charge. If for any reason the battery or bus system is disconnected from the regulator while the engine is running (i.e. the master switch is shut off) the capacitor will safely absorb and dissipate the electrical charge produced by the generator. Otherwise the regulator would be damaged."
Rick Girard
On Thu, Oct 24, 2013 at 8:52 AM, Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "Sacha" <uuccio(at)gmail.com (uuccio(at)gmail.com)>
> A discussion and study of stand-alone alternator operation would be a
good thing.
Yes. I think the internal rotax 912 alternator/ducati regulator combination
will do this but I wouldn't want to do any damage by just disconnecting the
battery and seeing what happens. What's a safe way to test this?
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tomblejwas(at)yahoo.com
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| Posted: Fri Oct 25, 2013 3:30 pm Post subject: Alternator without a Battery |
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Yes, I accept the mission - I'm responsible for the safety of my aircraft and I see potential benefits in having the ability to disconnect the batteries. Unfortunately, my last formal education in electronics was a freshman physics class many, many years ago. To fill some of the void, I read the AeroElectric Connection, but sometimes struggle with cognition and retention. I'm counting on Bob and others on the list for critical evaluation.
I see risks in 3 areas: physical risk associated with the actual operation of the alternator without a battery, i.e., damage to the alternator itself or other components; risks associated with circuitry changes to allow for operation without a battery; and risks in operational changes, i.e., people engineering or cockpit management. I'll leave the first of these to last, because I feel least confident with my understanding.
Since the batteries (I'm planning on 2 in my system) are no longer "always on," they are logically each connected through a contactor or other type of switch. I won't rehash the recent discussions of contactors, but with two batteries and contactors, the risk of contactor failure is small compared to the additional redundancy (assuming operational recognition and response) of an alternator without a battery. For my system, the steady-state load will be on the order of 15 amps, which shouldn't overly challenge a traditional style contactor, e.g., from B&C. Although I need to design and evaluate the entire electrical system, I don't see any other inherent circuitry changes. My basic approach is a ocircuit to which the batteries and alternator may or may not be connected. The buses may be physically connected to the circuit near a particular power source, but the primary purpose of multiple buses is to allow critical redundant devices (primarily fuel pumps and ECUs) to be connected in such a way that the loss of a single connection will not cause loss of power or, at worst, can be recovered by one or two switches.
With the potential for one battery to be disconnected in "normal flight," operations need to be established to ensure both batteries are charged and available. This could be as simple as connecting both into the charging circuit, but then power is being drawn from both and neither is a traditional "backup." My preference is for one to be connected for one leg of a trip and the other for the return or next leg. This works particularly well if I choose to use lithium phosphate batteries, because their unused discharge rate is extremely low. (I'm periodically checking online for fires with Shorai batteries, because these are widely used on motorcycles. So far, mishaps are few and not explosive. Also, one of the areas under my purview in a past position was a battery destructive-test lab. I'll be trying to get non-proprietary info from the people at this lab.) I also think it is prudent to monitor each battery during flight with instruments like the MGL BAT-1, which provide both voltage and current.
If the engine stops in flight, I don't want to have to remember how the electrical system works to recover. If no electrical power, check the battery monitors and change contactors to the unused one. If there is electrical power, switch fuel pumps and switch ECU power source (both changing to a different bus and associated connections) and finally switch to backup ECU. For me this is simpler than determining what to switch at the top of Z-19, but that probably just shows my lack of familiarity with aero-electrical speak. I don't see using the alternator without a battery except for the following. Monitoring of the batteries shows a problem with a battery and the other one replaces it. (Or maybe it is the standby battery with a problem.) Before being able to land, the second battery starts acting up. Now, switch both off and do a precautionary landing ASAP.
Now, what about the risks to the alternator or other critical devices because an alternator is running without a connected battery? First, Viking has claimed that the alternator can be so run. A capacitor was initially required, which makes sense in that it would "smooth" the output; but, curiously, engine owners were later instructed to remove the capacitor. I could find no explanation for the change and my memory is that an inquiry was ignored. I'll make my own attempt at finding out why. At this point, I plan to design with the option and test the output after completion. I can see no harm in having a capacitor in the circuit, but hopefully others will correct me if I'm wrong.
Sorry if I've missed the point of your suggestion or gone off on too many tangents. I realize that a schematic would have been helpful for this discussion, but I'm just starting to teach myself TurboCAD and who knows how long that will take.
Tom
Sent from my iPad
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nuckolls.bob(at)aeroelect
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| Posted: Fri Oct 25, 2013 6:49 pm Post subject: Alternator without a Battery |
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At 06:29 PM 10/25/2013, you wrote:
| Quote: |
<tomblejwas(at)yahoo.com>
Yes, I accept the mission - I'm responsible for the safety of my
aircraft and I see potential benefits in having the ability to
disconnect the batteries. Unfortunately, my last formal education
in electronics was a freshman physics class many, many years
ago. To fill some of the void, I read the AeroElectric Connection,
but sometimes struggle with cognition and retention. I'm counting
on Bob and others on the list for critical evaluation.
|
The only time I think one deliberately shuts off batteries
in flight is for smoke in the cockpit . . . which means
alternator needs to be off too.
| Quote: | I see risks in 3 areas: physical risk associated with the actual
operation of the alternator without a battery, i.e., damage to the
alternator itself or other components; risks associated with
circuitry changes to allow for operation without a battery; and
risks in operational changes, i.e., people engineering or cockpit
management. I'll leave the first of these to last, because I feel
least confident with my understanding.
|
Many alternators run fine without a battery. They may
not start but once in operation, they produce useful energy
with a disconnected battery. Bonanzas and Barons have offered
this feature for decades.
| Quote: | Since the batteries (I'm planning on 2 in my system) are no longer
"always on," they are logically each connected through a contactor
or other type of switch.
|
Why two batteries?
| Quote: | I won't rehash the recent discussions of contactors, but with two
batteries and contactors, the risk of contactor failure is small
compared to the additional redundancy (assuming operational
recognition and response) of an alternator without a battery. For
my system, the steady-state load will be on the order of 15 amps,
which shouldn't overly challenge a traditional style contactor,
e.g., from B&C. Although I need to design and evaluate the entire
electrical system, I don't see any other inherent circuitry
changes. My basic approach is a ocircuit to which the batteries
and alternator may or may not be connected. The buses may be
physically connected to the circuit near a particular power source,
but the primary purpose of multiple buses is to allow critical
redundant devices (primarily fuel pumps and ECUs) to be connected
in such a way that the loss of a single connection will not cause
loss of power or, at worst, can be recovered by one or two switches.
|
Have you been following the thread on Fred's project?
Check the drawings I published earlier today and assess
potential for missing your design goals. The question is,
suppose a contactor DOES fail, how does that impact risks
for comfortable termination of flight?
Bob . . .
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uuccio(at)gmail.com
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| Posted: Sun Oct 27, 2013 12:37 pm Post subject: Alternator without a Battery |
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From the Rotax Installation Manual, Section 24-00-00, page 7:
"A capacitor (see fig. 11, pos 14) of at least 22000 uF/25V is necessary to protect the correct function of regulator and to flatten voltage. The regulator is not designed to store any electrical charge. If for any reason the battery or bus system is disconnected from the regulator while the engine is running (i.e. the master switch is shut off) the capacitor will safely absorb and dissipate the electrical charge produced by the generator. Otherwise the regulator would be damaged."
[quote]Thanks Rick… I had missed your post. sacha Do not archive[b]
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tomblejwas(at)yahoo.com
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| Posted: Wed Oct 30, 2013 6:22 pm Post subject: Alternator without a Battery |
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Bob,
It has taken days for me to respond because I couldn't get the website to respond to my enquiries and, consequently, I was unable to open your new drawing. Today I could! Thanks for your response.
You state that you wouldn't shut down a battery unless there is smoke in the cockpit and, in which case you would shut down the alternator as well. If a battery is shorting and drawing more and more current from the alternator, why wouldn't you disconnect it or do you consider this too unlikely to design against?
You ask why two batteries? I'm reconsidering. If the battery can be disconnected and the engine continues to run on only the alternator, then one battery probably meets my design goals. Thanks for the question.
As you suggested, I've looked at your new drawing, but I don't think it meets all my design goals. A shorted battery can't be disconnected. I'll continue to study it w.r.t my other design goals. Thanks.
Tom
Sent from my iPad
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nuckolls.bob(at)aeroelect
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| Posted: Fri Nov 01, 2013 4:06 am Post subject: Alternator without a Battery |
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At 09:21 PM 10/30/2013, you wrote:
<tomblejwas(at)yahoo.com>
Bob,
It has taken days for me to respond because I couldn't get the
website to respond to my enquiries and, consequently, I was unable to
open your new drawing. Today I could! Thanks for your response.
No problem. I started at Cessna last Monday
and the IT Spirits have yet to honor me with
a CAT5 portal to the outside world . . . So
I've been 'disconnected' to some degree as
well . . .
You state that you wouldn't shut down a battery unless there is smoke
in the cockpit and, in which case you would shut down the alternator
as well. If a battery is shorting and drawing more and more current
from the alternator, why wouldn't you disconnect it or do you
consider this too unlikely to design against?
First, how does such a fault become known
to you? You would need a battery-specific
ammeter combined with a bus voltage indicator
combined with the skills to monitor and
interpret those readings for signs of failure.
You ask why two batteries? I'm reconsidering. If the battery can be
disconnected and the engine continues to run on only the alternator,
then one battery probably meets my design goals. Thanks for the question.
A design goal for discussions on this List is
to identify drivers of risk based on useful
study and exploitation of the physics.
As you suggested, I've looked at your new drawing, but I don't think
it meets all my design goals. A shorted battery can't be
disconnected. I'll continue to study it w.r.t my other design goals. Thanks.
Have you identified any instance where a 'shorted
battery' took a system down? A battery is like
a house plant. Given attention tailored to its
needs, it will thrive and perform with great
predictability . . . and reliability. Instances
of battery failure are generally driven by failure
to track the battery's condition and to service
or replace it when performance falls below limits.
I've not heard the phrase "shorted battery" uttered
or written over the course of my career where the
battery was not first subjected to abuses of
poor system architecture and/or poorly implemented
operation and maintenance.
We're encouraged to change oil, plugs, add
magic potions, install engine analyzers, and
read voraciously from every author that claims
to offer words of wisdom for getting the most
from an engine. Now the battery is becoming
an integral component of the system that spins
the prop. I suggest that it be treated with
no less curiosity and respect for capabilities
and limits than your engine.
I will suggest that design goals for your system
include crafting and implementation of an
architecture and maintenance that recognizes
the role of the battery and optimizes conditions
for it to perform.
Bob . . .
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