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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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 Posted: Sat Apr 27, 2013 6:57 am Post subject: Dual Batteries |
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| Quote: | If you have dual, battery powered, electronic ignition
and single alternator, a second battery will improve system
reliability numbers. |
Bob,
The above quote is from yesterday's AeroElectric daily digest. Did you inadvertently leave the word "NOT" out? Or are you recommending that aircraft with electrically dependent engines with single alternators have dual batteries?
Modern AGM batteries are very unlikely to short out. Good workmanship will minimize the danger of an open circuit. In the event of an open battery circuit, the alternator is capable of providing power without the battery. I think that a second battery adds unnecessary weight, cost, and complexity.
Joe
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Joe Gores |
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jluckey(at)pacbell.net
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| Posted: Sat Apr 27, 2013 8:08 am Post subject: Dual Batteries |
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Joe,
I disagree. When you add the second battery, you add redundancy to the whole power train [battery, master solenoid, shunt, wiring, etc]. If any one of those components fails, the associated battery is off-line.
Another consideration is how long you can run after an alternator failure. IIRC, the Odessy-type batteries have about a 20 amp-hour rating which, depending on your buss load, is probably 45-60 minutes of flight time after alt failure. My personal preference is to have 100% reserve for emergency situations.
Jeff Luckey
--- On Sat, 4/27/13, user9253 <fransew(at)gmail.com> wrote:
[quote]
From: user9253 <fransew(at)gmail.com>
Subject: Dual Batteries
To: aeroelectric-list(at)matronics.com
Date: Saturday, April 27, 2013, 7:57 AM
--> AeroElectric-List message posted by: "user9253" <[url=/mc/compose?to=fransew(at)gmail.com]fransew(at)gmail.com[/url]>
| Quote: | If you have dual, battery powered, electronic ignition
and single alternator, a second battery will improve system
reliability numbers.
|
Bob,
The above quote is from yesterday's AeroElectric daily digest. Did you inadvertently leave the word "NOT" out? Or are you recommending that aircraft with electrically dependent engines with single alternators have dual batteries?
Modern AGM batteries are very unlikely to short out. Good workmanship will minimize the danger of an open circuit. In the event of an open battery circuit, the alternator is capable of providing power without the battery. I think that a second battery adds unnecessary weight, cost, and complexity.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=399486#399486
http://www.matronics.com/Navigator?AeroElectric-List --> [quote][b]
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tim2542(at)sbcglobal.net
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| Posted: Sat Apr 27, 2013 8:56 am Post subject: Dual Batteries |
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I think a lot of us, me included tend to over engineer these systems to some extent. Unless you really are going to follow C-130s into hurricanes or similar, Id suggest adding one layer of protection over what your Cessna/Piper had and call it good. Ebus, second alternator OR battery, PMAG or any one thing to add a layer over a bare bones system. If you lose both of those you're one un-lucky guy.
Tim
From: Jeff Luckey <jluckey(at)pacbell.net>
To: aeroelectric-list(at)matronics.com
Sent: Sat, April 27, 2013 9:20:40 AM
Subject: Re: Dual Batteries
Joe,
I disagree. When you add the second battery, you add redundancy to the whole power train [battery, master solenoid, shunt, wiring, etc]. If any one of those components fails, the associated battery is off-line.
Another consideration is how long you can run after an alternator failure. IIRC, the Odessy-type batteries have about a 20 amp-hour rating which, depending on your buss load, is probably 45-60 minutes of flight time after alt failure. My personal preference is to have 100% reserve for emergency situations.
Jeff Luckey
--- On Sat, 4/27/13, user9253 <fransew(at)gmail.com> wrote:
| Quote: |
From: user9253 <fransew(at)gmail.com>
Subject: Dual Batteries
To: aeroelectric-list(at)matronics.com
Date: Saturday, April 27, 2013, 7:57 AM
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
| Quote: | If you have dual, battery powered, electronic ignition
and single alternator, a second battery will improve system
reliability numbers.
|
Bob,
The above quote is from yesterday's AeroElectric daily digest. Did you inadvertently leave the word "NOT" out? Or are you recommending that aircraft with electrically dependent engines with single alternators have dual batteries?
Modern AGM batteries are very unlikely to short out. Good workmanship will minimize the danger of an open circuit. In the event of an open battery circuit, the alternator is capable of providing power without the battery. I think that a second battery adds unnecessary weight, cost, and complexity.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=399486#399486
http://www.matronics.com/Navigator?AeroElectric-List -->
|
[quote]
[b]
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bicyclop(at)pacbell.net
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| Posted: Sat Apr 27, 2013 7:20 pm Post subject: Dual Batteries |
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I'm doing dual Lightspeed Plasma 3 on my RV. I chose to run each directly off a separate PC680 with a fuselink. Either battery can be run on the main buss, or on the ebuss which also has a diode feed from the main. The 680 is rated at 17ah and my ebuss minimum comfortable load will be about 4 amps plus 2 more amps for the ignitions. Assuming day VFR, if I turn off one both battery contactors and have one battery supporting the ebuss, I should be able to run for about 3 plus hours while keeping the second battery in reserve except for the one amp I was drawing for the other ignition. That should leave me about 13 -14ah with which to run out my fuel with at least one ignition assured. This also assumes that I have tested the batteries recently and know how much they will really do at low draw rate. Putting a backup alternator on top of all that seems a little over the top, but maybe I'll add it before I undertake a Bahamas trip or something like that.
The option I didn't select was for one battery and two alternators. Seems viable, and is lighter, but I just liked the separate feeds to the ignitions and being able to start from one battery and have no brownout problems with EFIS run from the other one. I will need to remember to close the contactor on the non starting battery after engine start so it will charge. I don't see that as a problem, just a post start checklist item. Push comes to shove, I can use both batteries for starting, too. If I do need both to start, it's time to do another capacity check and maybe replace one or both batteries.
Ed Holyoke
On 4/27/2013 9:56 AM, Tim Andres wrote: [quote] I think a lot of us, me included tend to over engineer these systems to some extent. Unless you really are going to follow C-130s into hurricanes or similar, Id suggest adding one layer of protection over what your Cessna/Piper had and call it good. Ebus, second alternator OR battery, PMAG or any one thing to add a layer over a bare bones system. If you lose both of those you're one un-lucky guy.
Tim
From: Jeff Luckey <jluckey(at)pacbell.net> (jluckey(at)pacbell.net)
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Sent: Sat, April 27, 2013 9:20:40 AM
Subject: Re: Dual Batteries
Joe,
I disagree. When you add the second battery, you add redundancy to the whole power train [battery, master solenoid, shunt, wiring, etc]. If any one of those components fails, the associated battery is off-line.
Another consideration is how long you can run after an alternator failure. IIRC, the Odessy-type batteries have about a 20 amp-hour rating which, depending on your buss load, is probably 45-60 minutes of flight time after alt failure. My personal preference is to have 100% reserve for emergency situations.
Jeff Luckey
--- On Sat, 4/27/13, user9253 <fransew(at)gmail.com> (fransew(at)gmail.com) wrote:
| Quote: |
From: user9253 <fransew(at)gmail.com> (fransew(at)gmail.com)
Subject: Dual Batteries
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Date: Saturday, April 27, 2013, 7:57 AM
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
> If you have dual, battery powered, electronic ignition
> and single alternator, a second battery will improve system
> reliability numbers.
Bob,
The above quote is from yesterday's AeroElectric daily digest. Did you inadvertently leave the word "NOT" out? Or are you recommending that aircraft with electrically dependent engines with single alternators have dual batteries?
Modern AGM batteries are very unlikely to short out. Good workmanship will minimize the danger of an open circuit. In the event of an open battery circuit, the alternator is capable of providing power without the battery. I think that a second battery adds unnecessary weight, cost, and complexity.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=399486#399486
http://www.matronics.com/Navigator?AeroElectric-List -->
|
[b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Apr 29, 2013 4:23 am Post subject: Dual Batteries |
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At 09:57 AM 4/27/2013, you wrote:
| Quote: |
> If you have dual, battery powered, electronic ignition
> and single alternator, a second battery will improve system
> reliability numbers.
Bob,
The above quote is from yesterday's AeroElectric daily digest. Did
you inadvertently leave the word "NOT" out?
|
No, the architecture cited is right out of
Lightspeed's installation instructions for
dual electronic ignitions wherein he suggests
a diode isolated, second battery dedicated to
powering the second ignition system. It was this
this train of thought that prompted the ABMM (Aux
Battery Management Module) some years back.
But Z-13/8 offers a third source for power which
diminishes the value of a second battery. Of course,
P-mags go a step further and relieves the need
for any external sources for back-up power.
| Quote: | Or are you recommending that aircraft with electrically dependent
engines with single alternators have dual batteries?
|
Not as a blanket recommendation but the question
should be carefully considered. If you're flying
a day-vfr pleasure machine, perhaps your plan-B
with a carefully maintained battery is sufficient.
But Z-13/8 or the auxiliary battery lets one approach
the question with a 'less sharp' pencil.
| Quote: | Modern AGM batteries are very unlikely to short out. Good
workmanship will minimize the danger of an open circuit. In the
event of an open battery circuit, the alternator is capable of
providing power without the battery. I think that a second battery
adds unnecessary weight, cost, and complexity.
|
Agreed. An SD-8 alternator is light, exceedingly
reliable and low cost of ownership. It beats
auxiliary batteries without even breathing hard.
Bob . . .
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Mon Apr 29, 2013 6:09 am Post subject: Re: Dual Batteries |
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Thanks for the reply Bob.
A friend of mine is building an airplane and will install a Viking engine which is electrically dependent. The Viking does not have two independent ignition systems, although it does have a backup ECU in the same enclosure as the primary ECU. The ECU has provisions for two power inputs. However, those two power sources are connected together internal to the ECU. If both power sources are turned on simultaneously, they will be shorted together. Thus an electrical system isolating diode will effectively be shorted.
One solution is to use mechanically interlocked ECU power switches which might not look good and will complicate operation, increasing pilot workload.
Another option is to use a legacy TC electrical system with the addition of a relay (similar to E-Bus relay) to feed the opposite end of the power bus. The goal is to keep it simple while having a backup in case any one component fails.
Joe
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Apr 29, 2013 3:17 pm Post subject: Dual Batteries |
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On the way home from Wichita I had some further thoughts
on this thread . . .
| Quote: | > Modern AGM batteries are very unlikely to short out. Good
> workmanship will minimize the danger of an open circuit. In the
> event of an open battery circuit, the alternator is capable of
> providing power without the battery. I think that a second
> battery adds unnecessary weight, cost, and complexity.
Agreed. An SD-8 alternator is light, exceedingly
reliable and low cost of ownership. It beats
auxiliary batteries without even breathing hard.
|
Sometimes its hard to sift the bits-and-pieces
with consideration for the time frame of their
conception and popular incorporation. For example,
the original Endurance Bus was installed in a LongEz
with a design goal for sizing/maintaining a battery
and crafting an en route energy profile that offered
electrical endurance equal to or greater than fuel
aboard. Back then, the E-bus target loads were on the
order of 2 amps or less. Even then, you were likely
to arrive at destination with a depleted battery.
Then the vacuum pumps started disappearing and the
SD-8 was no longer limited to day-vfr power source
in a simple airplane . . . it became a heavy duty
player in the crafting of a much more robust endurance
mode. Now the e-bus could jump to 8A and you now arrive
with a battery held in total reserve for approach and
landing. A BIG change over the 20+ years.
The dual battery idea proffered by Lightspeed pre-dates the
e-bus. I think it pre-dates the great SVLA take-over
for aircraft batteries. I recall seeing two wet motor
cycle batteries installed in an 'Ez about 20 years
ago. The ABMM became a product on my website about 2003
and the article I did for Sport Aviation pre-dated the
product by a year or two.
Today, April 29, 2013 it is my considered opinion that
an architecture like Z-13/8 and Z-12 COMBINED with a
well maintained SLVA battery is EVERYTHING you need for
securing a reliable source of energy for ALL of the ship's
electro-whizzies. This assertion is offered in spite of
the fondest wishes for anyone's electro-whizzy installation
instructions suggesting or recommending adding any sort
of stand-by or back-up battery.
The elegant solution for an architecture calls for a minimum
parts count, lowest practical weight and lowest cost of
ownership while making sure that items necessary for comfortable
termination of flight have energy sources with higher
reliability than the device itself.
With one MSVLA (Maintained SLVA) battery, and two
alternators the likelihood of total loss of power is
a tiny fraction compared to loss of the gizmo you're
worrying about. You are more likely to benefit from having
two such gizmos than for having a plethora of "emergency"
power backups.
A favorite question I used to ask the seminar attendees
was, "What is the value of having lots of energy sources
for a landing light bulb that you KNOW has a 10-50 hour
service life?" If you often return home to a marginally
illuminated field after dark then having two landing lights
will offer a greater boost to system reliability than adding
another energy source. With the advent of LED landing
lights, perhaps that question needs to be updated.
So getting back to the opening paragraph of this posting,
let's not lose our grip on the manner in which many of
the ingredients that went to legacy recipes for success
came about . . . and be mindful of their applicability
in the current kitchen.
Does this mean there is no longer a valid reason to add
a second battery? No, some electro-whizzies like to reboot
during a starter inrush brown-out event. So having really
small, brown-out protection battery might still be part
of the elegant solution. On the other hand, one might simply
PLAN pre-flight procedures for powering these items
up after the engine is started. It's YOUR airplane, YOUR
decision. Do what works best for you.
Bob . . .
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