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Sifting design goals and establishing protocols

 
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nuckolls.bob(at)aeroelect
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PostPosted: Sat Jan 05, 2019 7:29 am    Post subject: Sifting design goals and establishing protocols Reply with quote

To: aeroelectric-list(at)matronics.com
Subject: Re: Re: Alternator/shunt question
Cc: it


Quote:
No alternator should be run at greater than 80% of its rating for any length of time.

That is a legacy rule of thumb (a very sore one at that)
left over from the days when a full-up electrical
system was driven with a generator . . . perhaps
as small as 25A . . . and batteries offered
a small fraction of today's products.

The idea was that you didn't want to launch
into the blue with a partially discharged battery
with running loads that used all of the generator
output leaving the battery un-attended.

Later the rule was modified to suggest that
the engine driven power source be capable
of running all necessary loads while recharging
the battery in some time frame . . . I don't
recall the number.

At least this change called for doing
purposeful load analysis and testing
to meet the 'time' irrespective of
any 'percentage'.


Quote:
So don't figure the backup at more than 24 amps.

Hold that thought . . .

Quote:
Even an AGM battery will charge (perhaps slowly) at any
voltage over 13 volts. Almost all 14 V aircraft electrowhizzies
will operate fine on 13V.

They DO160 qualify down to 10.0 volts

[img]cid:7.1.0.9.0.20190105092748.05ce8da8(at)aeroelectric.com.0[/img]


Quote:
If you intend to limp home on the back up alternator, know what
you need electrically and assume you get only partial
recharge of battery after starter draw.

If you've lost primary alternator minutes
after departure, given the performance of
modern batteries the order of the day
is return home. There is almost no scenario
where one would be electrically deprived
of energy to do the task whether the
battery is being recharged or not . . . what
is the operational incentive for arriving
back home with a dead main alternator and
100% charge on the battery?

Starting an engine (200A x 12.5v x 10 sec)
takes something on the order of 25,000
Watt seconds, 7 Watt-hours or 0.5 Ampere-hours
of battery capacity. On some airports that
would be replaced before you launched.
Assume you used another 0.5 Ah fiddling
with stuff before engine start . . . what
risk is added to your flight by departing
with 90 to 95 percent of battery capacity
remaining and TWO alternators?

<snip>
Of course if battery fails where only certified aircraft batteries
are available, the Concorde will bolt right in. If you are trying
to power two electronic ignitions, you may want to think about 2 batteries.

In my never humble opinion, anyone who suffers
battery failure away from home should be flogged
with his own headset cord.

EVERY away-from-home battery replacement is
foretold HOURS of operation before the
battery fails to crank an engine. If there's
an insidious down-side to dual alternators,
it has roots in the idea: "got two alternators,
I can run the battery until it craps
completely."

In the years of this List we've studied
'Dark-n-Stormy' night stories published in
the popular journals. The stories told
a great deal about the pilot's ignorance of
system condition and operations; very
little about emergency management.

I've often opined that the educated pilot
flying a MAINTAINED electrical system matched to
the mission has about 0.01% chance of suffering
an EMERGENCY with foundation in an electrical
failure.

Things break in airplanes all the time . . .
were it not so, FBO shops would be out of
business. The key to bullet-proofing yourself
and your airplane against bad days in the
cockpit starts with LOAD ANALYSIS with
scenarios divided up into the various flight
conditions, picking an architecture that
reduces FAILURE MODE EFFECTS ANALYSIS outcomes
to acceptable risks and finally MAINTAINING
the equipment to minimum performance standards
set by YOU.

No single failure of any electro-whizzy should
be cause for breaking a sweat in the cockpit.

Here's are exemplar load analysis in Excel
and paper forms that go to the same exercise . . .

https://tinyurl.com/9rt6ymn

Falling short on any of those points
only serves to make you more a passenger
and less a pilot-in-command of your aircraft.

This fellow had dual alternators, batteries out
the wazoo and STILL wound up being a passenger
in his own airplane:

https://tinyurl.com/yckwghyv

Quote:
Quote:
I understand, the system wasn't designed with my plan in mind. The question is: Is it possible to apply my idea as requested or won't physics allow it?
When I look at the gear driven main B&C 462H (60amp) alternator -it is supposed to deliver 41.3Amps at cruise RPM 2450. This is 11.3 Amps more than the 30Amps Stby Alt. This would not leave me with 2 identical alternators either.

You can answer that question with due
diligence to planning and operations.
There are airplanes flying around out there
with a single 8A alternator on a vacuum
pump pad as the PRIMARY source of electrical
energy. Those airplanes operated within
LIMITS have probably never suffered an
electrical emergency.


Quote:
Quote:
One can wait for a week or more before the replacement unit arrives in Europe. We have a completely different network here. Further, you will hardly find a service center willing to touch an experimental.

A critical component of your design and
operations protocols. One of the columns
in your load analysis should include a study
of electrical demands for 'minimized' loads
with the largest alternator inop. No amount
of discussions here about rules-of-thumb
will replace the need for matching hardware
and operations to design goals. Unlike the
stuff rolling off the line at Textron, we are
NOT working with cookie-cutter airplanes and
textbook missions.

In your case, it is entirely practical to task
the 'standby alternator' with routine flight
duties. In this case, you have alternator #1 and
and alternator #2. Each is capable of operating
the aircraft within limits defined by a
considered load analysis. In this instance,
both controllers would be LR3C set for 14.2 Volts.

Quote:
Quote:
It is quite common in airlines that items get on MEL (minimum equipment list) if they fail and the airplane can depart for another flight although limited by weather or any other restriction. It doesn't mean that you are grounded as soon as something fails, provided there is a backup system available and functional. Not to compare to cars..


Exactly. I've never owned an airplane.
I've always rented. Up-side: got a lot
of experience in various models. Down-side:
seldom if ever knew the finer details of
the ship's electrical/avionics systems.
Hence, my personal protocols for use of
these aircraft called for certain items
in the flight bag.

https://tinyurl.com/yc26xryh

I could always plan to get where I wanted
to go even if the panel was completely
dark . . .


Bob . . .



Bob . . .


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supik



Joined: 22 Aug 2018
Posts: 44

PostPosted: Sun Jan 06, 2019 2:05 am    Post subject: Re: Sifting design goals and establishing protocols Reply with quote

nuckolls.bob(at)aeroelect wrote:
To: aeroelectric-list(at)matronics.com
Subject: Re: Re: Alternator/shunt question
Cc: it

In your case, it is entirely practical to task
the 'standby alternator' with routine flight
duties. In this case, you have alternator #1 and
and alternator #2. Each is capable of operating
the aircraft within limits defined by a
considered load analysis. In this instance,
both controllers would be LR3C set for 14.2 Volts.


Bob,

What would then be the method to recognize an alternator failure except for a preflight check? As long as the remaining alternator is capable of handling the actual load, there would be no warning to the pilot..


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Igor

RV10 in progress
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alec(at)alecmyers.com
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PostPosted: Sun Jan 06, 2019 7:40 am    Post subject: Sifting design goals and establishing protocols Reply with quote

Twin piston engined aircraft routinely have two alternators online simultaneously and it is widely accepted that due to different set points on their respective regulators that only one with carry a load when both are operational. It is immaterial which.

Preflight procedures are to isolate each alternator in turn and verify that in either case the remaining alternator carries the electrical load demanded of it.

Sent from my iPhone

Quote:
On Jan 6, 2019, at 05:05, supik <bionicad(at)hotmail.com> wrote:




nuckolls.bob(at)aeroelect wrote:
> To: aeroelectric-list(at)matronics.com
> Subject: Re: Re: Alternator/shunt question
> Cc: it
>
> In your case, it is entirely practical to task
> the 'standby alternator' with routine flight
> duties. In this case, you have alternator #1 and
> and alternator #2. Each is capable of operating
> the aircraft within limits defined by a
> considered load analysis. In this instance,
> both controllers would be LR3C set for 14.2 Volts.


Bob,

What would then be the method to recognize an alternator failure except for a preflight check? As long as the remaining alternator is capable of handling the actual load, there would be no warning to the pilot..

--------
Igor

RV10 in progress




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=486764#486764











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skywagon185(at)gmail.com
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PostPosted: Mon Jan 07, 2019 12:24 pm    Post subject: Sifting design goals and establishing protocols Reply with quote

"....When utilizing LR-3 regulators for both alternators set at the same volts output will they share the loads equally? 50:50?....."
Paralleling/matching the regulators might work "one" time during the set-up.  But, environmental changes will make each reg. system respond slightly differently.  The point is, they will never stay in balance as you would expect as a 50/50 balance.  Then, there is the chance that the one, low power, system will be handling all or most of the electrical load.

On Mon, Jan 7, 2019 at 9:17 AM Bill Watson <Mauledriver(at)nc.rr.com (Mauledriver(at)nc.rr.com)> wrote:

Quote:
On 1/6/2019 8:43 PM, Robert L. Nuckolls, III wrote:
>
>   Do a Z-14 and make them totally independent
>   of each other.

This is what I implemented on my RV-10.  I did a very straight up Z-14
with 40 and 20 amp alternators.  For the first 500 hours or so I've
flown with the 2 buses interconnected.  Regulator voltage levels were
staggered but not on purpose.  My usual operational procedure was to
start on 1 battery with my (3) power hungry, unswitched MFDs running on
the other battery.  Bob helped me understand that this was exactly the
opposite of the way I should be running things.

After swapping out the light weight starter that came with the Van's
engine package (too high a momentary current draw turning over the
IO540), I began doing all starts with both batteries and buses
interconnected.  Then I disconnect them for flight.   I've run that way
for the last 600 hours.

Running on 2 separate batteries, alternators and buses makes most any
failure both readily apparent and easily recoverable in flight.  At one
point I had a LRC3 fail but the Z-14 made it reasonable for me continue
my multi-leg trip, VFR-only,  before returning  to my home shop for repair.

The Z-14 is  a very robust design and easy to implement in the RV-10.






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