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is battery filter or dead weight?

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jan_de_jong(at)casema.nl
Guest

Posted: Sun Jan 02, 2011 9:31 am Post subject: is battery filter or dead weight?

A question.

Is a fully charged 12V lead-acid battery held at 14V a voltage stabiliser?

People seem to think so but I doubt it.

If you disconnect the battery while the alternator consistently puts out 

over 13V will there be much difference in AC components on the bus?

Is there an AC on top of DC internal impedance measurement out there 

somewhere that I can't find a reference to?

I hope somebody knows more.

Thank you.

Jan de Jong

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Jan 02, 2011 2:37 pm Post subject: is battery filter or dead weight?

The battery in the circuit will help dissipate voltage spikes.  If your

generator goes into an overvoltage charge situation it won't take long to

boil the battery.  Once that happens the buss will go overvoltage too,



Noel 



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 03, 2011 4:34 am Post subject: is battery filter or dead weight?

At 11:23 AM 1/2/2011, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl>



 A question.

 Is a fully charged 12V lead-acid battery held at 14V a voltage stabiliser?

 People seem to think so but I doubt it.

 If you disconnect the battery while the alternator consistently puts out over 13V will there be much difference in AC components on the bus?

 Is there an AC on top of DC internal impedance measurement out there somewhere that I can't find a reference to?

 I hope somebody knows more. 	


   I think you've already identified the battery

   filter myth . . . a myth I once propagated.

   There was a sort of "giant capacitor" quality

   ascribed to batteries that kind of made sense.

   Batteries are indeed a huge energy source/sink

   for their size.



   If you study battery behavior you'll discover

   that they are very non-linear devices. The term

   "internal impedance" does not describe a simple

   resistive or reactive loss. While a battery

   is being heavily discharged (say 12.0v and below)

   it can be said to have a very low internal impedance

   on the order of tens of milliohms. But while

   being charged at 14.0 volts and above, that

   impedance value rises. Worse yet, when

   the battery is fully charged, it's internal impedance

   goes waaayyyy up.



   This is why Mil-Std-704 tells us to EXPECT bus voltage

   excursions of 3v pk-pk over the range of

   1000 to 5000 Hz on a 28v system (1/2 that

   on a 14 volt system). The expected/permissible

   levels drop off on either side of that band:



 [img]cid:.0[/img]



 

     Further, 704 is silent as to whether or not there is a battery

     present.  And it makes sense. A fully charge battery floating

     on a normal bus is electrically 'transparent'.



     If you experience an alternator runaway, the battery will offer

     a significant mitigating load that joins with system loads to

     drive the alternator into a current limited mode. This is helpful

     in holding down bus voltage while the ov protection system

     takes a few tens of milliseconds to shut it down.



     Obviously, when the alternator fails, the battery can be 

     expected to provide the alternate source of energy albeit at

     reduced voltage. But as a "filter" small transients that we

     call noise, the battery is of no practical value. Dead weight?

     Hope not. The thoughtfully maintained battery is the most

     reliable source of energy on the airplane. 



   Bob . . .

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jan_de_jong(at)casema.nl
Guest

Posted: Mon Jan 03, 2011 4:45 am Post subject: is battery filter or dead weight?

Thanks.

I realise that the battery will not allow excursion below 12.5V and will 

be an increasing load above 15.5V as long as it lives.

I wonder about its filtering role around 14V when it's neither drawing 

or supplying current which is the standard situation.

What might be an equivalent load of capacitor, resistor and inductor 

combination?

Jan



The question is not urgent

[quote] Time: 02:37:38 PM PST US

 From: "Noel R.C. Loveys" <noelloveys(at)yahoo.ca>

 Subject: RE: is battery filter or dead weight?

 The battery in the circuit will help dissipate voltage spikes.  If your

 generator goes into an overvoltage charge situation it won't take long to

 boil the battery.  Once that happens the buss will go overvoltage too,



 Noel 



 --

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 03, 2011 6:38 am Post subject: is battery filter or dead weight?

At 06:42 AM 1/3/2011, you wrote:

 	  Quote: 	
		  



Thanks.

I realise that the battery will not allow excursion below 12.5V and 

will be an increasing load above 15.5V as long as it lives.

I wonder about its filtering role around 14V when it's neither 

drawing or supplying current which is the standard situation.

What might be an equivalent load of capacitor, resistor and inductor 

combination?


	


    I've never considered researching an "equivalency" . . .

    It would depend heavily both on size of the battery

    and its physical condition. Given that noise values

    for battery-in versus battery-out are indistinguishable

    from each other says that noise mitigation benefits,

    if any, are insignificantly small.



   Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Jan 03, 2011 6:40 am Post subject: Re: is battery filter or dead weight?

It is a little hard to discover if big commercial aircraft have batteries at all. My guess is that they have some efficient small battery to start the APU, and not much more. Can an airplane be built without a battery? Sure. There is a large Russian airplane that can be parked all Winter, then started with the compressed air stored from a previous flight. If it doesn't start, you have your prisoners hand-pump in more compressed air.



So having a battery is convenient for starting the airplane, and seems to be a stabilizing load for the alternator. If the battery is disconnected, plan on some other stabilization for the alternator, because what comes out of the alternator is a bumpy DC whose bumps are proportional the the alternator RPM. Modern electronics are perfectly capable of doing this as well as a big battery, but modern electronics are going to POL (Point-of-Load), where the "main" power supply is no longer forced to provide various voltages at various currents and various stabilities. Instead a single (and perhaps higher voltage) power line runs around the aircraft, and is then changed at the load to whatever the load needs by tiny little ICs. This has advantages from several angles, perhaps the main one being that the system supply and buses don't easily become obsolete.



In my little airplane a-building, I plan an internally-regulated ND alternator and a power filter using a capacitor, and inductor, Zener and just a few other parts to give far better filtering than standard Cessnas. Why this is not routine practice mystifies me. 



I might also find a reason to put in a 1.0 F supercapacitor sitting on my shelf. Such a reason might be that it would reduce the wire size between my battery and the starter, while (it has been shown) cause the battery life to soar.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 03, 2011 2:13 pm Post subject: is battery filter or dead weight?

At 08:41 AM 1/3/2011, you wrote:

 	  Quote: 	
		  



It is a little hard to discover if big commercial aircraft have 

batteries at all. My guess is that they have some efficient small 

battery to start the APU, and not much more. Can an airplane be 

built without a battery? Sure. There is a large Russian airplane 

that can be parked all Winter, then started with the compressed air 

stored from a previous flight. If it doesn't start, you have your 

prisoners hand-pump in more compressed air.


	


    The first time I saw the B-57 Canberra,

    it was preparing to leave an air show at

    McConnell AFB



http://www.b-57canberra.org/b-57sounds.htm



    Those were late 40s engines too. It was

    amazing to think that a thing which made so

    much smoke and noise was doing all that

    because it was the best-they-knew-how-to-

    do at the time.



    Other airplanes have used a variety of

    energy sources for engine cranking. I

    was once invited to crank up the flywheel

    on the engine for getting it started without

    success. It's not mean task.



    Our J-3 at 1K1 would start on the first

    pull of a blade . . . IF you carried out

    the right combination of preparation (and

    had the prop clocked right on the hub).



    Each system left the factory having met certain

    design goals. Those goals might be driven by

    some combination of customer specs, weight,

    costs, space, etc. Some of them caught on in

    the consumer markets, others were relegated to

    the annals of historical curiosities.



 	  Quote: 	
		  So having a battery is convenient for starting the airplane, and 

seems to be a stabilizing load for the alternator.


	


    I think we've discussed and demonstrated that

    batteries are not "stabilizers" in the common

    sense of the word. The battery will assist a

    wound field alternator in getting started.

    However, the alternator doesn't need the battery

    to provide useful output. They will run self-excited

    as long as you don't hit the machine with a

    hi inrush load that exceeds it's output

    current rating thus stalling it.



    At Cessna in 1967 or so, we fiddled with ways

    to kick start alternators on the 337 should the

    battery become unavailable. Ideas included (1) array

    of D-cells OR (2) a 3-phase rectifier off the tach

    generator. These small energy sources could be

    tapped by means of a panel mounted push button

    to get the alternators on-line. They were operated

    in parallel with one regulator.



    Neither idea made it to production as I recall.

    We were sandbagging a failure that was very low

    on the ladder of probability. That was about

    20 years before the idea of a dual feed e-bus

    blossomed. THAT would have been a very simple,

    low cost alternative to the dragons of the day.

 	  Quote: 	
		    If the battery is disconnected, plan on some other stabilization 

 for the alternator, because what comes out of the alternator is a 

 bumpy DC whose bumps are proportional the the alternator RPM.


	


    Have you ever put a 'scope on the bus of

    your car, started the engine, and taken trace

    pictures of the battery-connected versus

    battery disconnected? I was hard pressed

    to see any differences. System load had more

    effect on noise than the presence of a battery.

    I'd like to put a spectrum analyzer on the system

    sometime and get some real numbers.

 	  Quote: 	
		    Modern electronics are perfectly capable of doing this as well as 

 a big battery, but modern electronics are going to POL 

 (Point-of-Load), where the "main" power supply is no longer forced 

 to provide various voltages at various currents and various 

 stabilities. Instead a single (and perhaps higher voltage) power 

 line runs around the aircraft, and is then changed at the load to 

 whatever the load needs by tiny little ICs. This has advantages 

 from several angles, perhaps the main one being that the system 

 supply and buses don't easily become obsolete.


	


    What supplies and busses have or are becoming

    obsolete? Especially those which have or currently

    find favor in small airplanes? What are the design

    goals driving that "obsolescence"? Do these proposed

    technologies portend lower cost, higher reliability,

    less weight, increased performance?



    I recall visiting a booth at OSH about 15 years ago

    where the proprietor was demonstrating an advanced

    power distribution and control system. He had a control

    box with switches on it for nav, strobe, landing and

    taxi lights. One power/data wire came out of the box

    and ran to each of those fixtures. Digital data was

    transmitted to smart controllers over the power wire

    to turn them on/off. What could be simpler? One wire

    does it all.



    The implications for single points of failure, increased

    parts count, increased cost of ownership, etc were

    profound. I didn't see him there the next year.



    I have perhaps a dozen tools that will set a nail or

    stable style fastener. Some electric, some air driven.

    But sometimes the best way to drive a nail is with a

    hammer. Hammers have been around for a long time.

 	  Quote: 	
		  In my little airplane a-building, I plan an internally-regulated ND 

alternator and a power filter using a capacitor, and inductor, Zener 

and just a few other parts to give far better filtering than 

standard Cessnas. Why this is not routine practice mystifies me.


	


    In what way? Cars, trucks and all manner of ground

    based vehicle have been doing these things for over

    100 years to the tunes of hundreds of millions of

    examples. Airplanes to hundreds of thousands of

    examples. Is it your assertion that the designers

    of these vehicles have stubbed their intellectual

    toes and failed to exploit some process that

    promises improved performance at lower costs of

    ownership?  As you fly along in any airplane of

    any age, are you painfully aware of some deficiency

    of performance that cries out for a quieter bus.

 	  Quote: 	
		  I might also find a reason to put in a 1.0 F supercapacitor sitting 

on my shelf. Such a reason might be that it would reduce the wire 

size between my battery and the starter, while (it has been shown) 

cause the battery life to soar.


	


    Haven't heard of that one. Can you enlighten us

    as to the simple-ideas in physics that support

    these assertions? 1 Farad hit with a 100A load

    discharges at 100 volts per second. This means

    that the capacitor will support the battery for

    something on the order of 30 milliseconds after

    onset of a start cycle. How is this beneficial

    to battery life?

   Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Mon Jan 03, 2011 4:30 pm Post subject: Re: is battery filter or dead weight?

 	  Quote: 	
		  Haven't heard of that one. Can you enlighten us 

as to the simple-ideas in physics that support 

these assertions? 1 Farad hit with a 100A load 

discharges at 100 volts per second. This means 

that the capacitor will support the battery for 

something on the order of 30 milliseconds after 

onset of a start cycle. How is this beneficial 

to battery life? 	




Batteries are electrochemical are are thus affected by temperature. SuperCaps, being electrostatic have no such problem. Thus they are fastened near the starter and help immensely starting engines in cold climates, or with weak batteries one might suppose. 



Starting an engine is usually separated into three phases: Breakaway, takes the greatest current as the starter overcomes the static friction of the cold engine. A SuperCap helps enormously in this breakaway and load shares with current from the battery, albiet for a short time. Nobody said the initial current was 100A. In fact the SuperCap has the ability to discharge much faster than the battery--they are very low ESR.



In my earlier life a problematic solenoid attached to a limited supply would just have a capacitor attached to it (and a diode and a resistor to discharge it fast and recharge it slowly) so that the capacitor would dump current through the coil. The plan I mentioned is similar.



But hey, nobody said I suggest this for everyone. But I just might do it.

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 03, 2011 7:27 pm Post subject: is battery filter or dead weight?

Batteries are electrochemical and thus affected by temperature. 

SuperCaps, being electrostatic have no such problem. Thus they are 

fastened near the starter and help immensely starting engines in cold 

climates, or with weak batteries one might suppose.



    I'm having trouble calibrating "immensely" . . .



Starting an engine is usually separated into three phases: Breakaway, 

takes the greatest current as the starter overcomes the static 

friction of the cold engine. A SuperCap helps enormously in this 

breakaway and load shares with current from the battery, albiet for a 

short time. Nobody said the initial current was 100A. In fact the 

SuperCap has the ability to discharge much faster than the 

battery--they are very low ESR.



   Absolutely . . . but while capacitors have a greater ability

   to deliver CURRENT, their ability to deliver ENERGY is

   the fact I'm wrestling with. Total energy stored on a

   1F capacitor at 12v is CE(squared)/2 or 72 watt-seconds.

   The capacitor can deliver energy into the cranking task

   only until its terminal voltage drops to some value equal

   to the battery terminal voltage . . . lets assume a cold

   weather worst case of 8v whereupon the capacitor still

   contains 1*8^2/2 or 32 watt-seconds. Hence, the paralleled

   capacitor can offer 40 watt-seconds of stored energy to the

   task of getting the engine started for about 50 milliseconds

   topes . . . . Assume 100A (small engine) and 9 volts average

   for 10 seconds gives 100 * 9 * 10 = 9000 watt-seconds. So

   perhaps we see the capacitor contributing less than 1/2 of

   1% into the first 1/20 of a second of a cranking scenario.

   Does this agree with your calibration of "immensely"?

In my earlier life a problematic solenoid attached to a limited 

supply would just have a capacitor attached to it (and a diode and a 

resistor to discharge it fast and recharge it slowly) so that the 

capacitor would dump current through the coil. The plan I mentioned is similar.



   But of course . . . you're getting a boost for the

   purposes of aiding an event that takes perhaps 10

   milliseconds total and a current level on the order

   of tens of amps . . . not ten seconds for hundreds of

   amps. These are not similar energy transfer

   scenarios.

But hey, nobody said I suggest this for everyone. But I just might do it.



   Understand. You brought forth an idea that suggested

   "soaring battery life" . . . I'm just making sure

   I've not overlooked some new discovery.



   Bob . . .

jan_de_jong(at)casema.nl
Guest

Posted: Tue Jan 04, 2011 8:39 am Post subject: is battery filter or dead weight?

Thank you very much for confirming my model of lead-acid battery.

So battery is:

- backup energy source

- engine starting energy source

- overvoltage slowdown load

- negligible filter



Ultracap is fascinating but it is hard to find a compelling use.

With http://www.maxwell.com/docs/DATASHEET_K2_SERIES_1015370.PDF

one could make a 100F, 16.2V, 5mOhm capacitor weighing 1 kg for $500 or so.

Multiple seconds of starting amps.

Leakage 1.5 mA or more than 1Ah per month though.

And would need six 2.75V 0.5A or so power zeners made and very reliable OVP.



For $150 or so one could make a 8Ah, 13.2V, 8mOhm LiFePO4 battery 

weighing 1.5 kg or so:

http://www.evassemble.com/index.php?main_page=index&cPath=2&zenid=s0l174nirkm5s4ltndf75rt9f2

Minutes of starting amps.

Leakage 0.3 mA or so.

Would need four 3.75V full charging current power zeners made and a 

heatsink temperature controlled alternator switch.

Function then automatically includes 15V OVP.

Alternator needs set at 14.6V.

And not very good at low temperatures:

http://www.lifebatt.com/sandiareport.pdf



Jan de Jong

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 04, 2011 10:11 am Post subject: is battery filter or dead weight?

At 11:36 AM 1/4/2011, you wrote:

 	  Quote: 	
		  



Thank you very much for confirming my model of lead-acid battery.

So battery is:

- backup energy source

- engine starting energy source

- overvoltage slowdown load

- negligible filter


	


    <snip>



    What you have discovered is that not every

    "problem" is begging to be solved. A proposed

    advancement to the state of our art needs to be

    evaluated for a host of unknowns . . .



    What's the impetus for 'solving' this 'problem'?

    Will anything on the airplane work better if the

    bus noise is reduced? What is the probability

    that making this change will add any observable

    or measurable value for the way I use my airplane?

    What does it cost to own this feature over the next

    10 years?



    Burt Rutan beat us up for grams of weight savings

    but didn't care if the system was any quieter than

    what you might find in a C-172. I don't know what

    size batteries he ended up with . . . but you can

    bet it was a carefully considered decision. When

    I was asked to convert a LongEz into a spook airplane

    loaded with sensitive receivers, noise became the

    paramount issue. Whole different mission.



    The point is that latching onto the latest and

    greatest electro-whizzy may or may not have a

    return on investment. Throughout our culture,

    there's an almost primal urge to step up to

    the new and improved but without regard to

    whether or not the thing being replaced really

    needs to be replaced.



    If I were to rent an airplane tomorrow, I'd be

    just as comfortable navigating to intended

    destination using the Wallmart Magellan

    GPS I introduced to The OBAM aircraft industry

    13 years ago.



http://aeroelectric.com/articles/nailgun.pdf



    But MOST important, make sure that the proposed

    change is integrated into the system with thoughtful

    understanding of all the simple-ideas that makes

    the thing work. It will reduce if not eliminate those

    "Aw #$#%" moments in the cockpit.

   Bob . . .

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Wed Jan 05, 2011 6:21 am Post subject: Re: is battery filter or dead weight?

The 1 Farad cap I mentioned is pitifully small (Hell, it shows my age that I was impressed). Here is a 3000F (-0/+20%!) Cap:

maxwell.interconnectnet.com/ultracapacitors/datasheets/DATASHEET_K2_SERIES_1015370.pdf



On Ebay a guy is selling five cases of these (2.7V) 15 per case, for $775/case OBO. You'd need 5-6 of these to make a proper cell. (In series total capacitance is 1/(n/C), but you'd still get 500 F at 14V or so)



A few years ago the caps were used more for starting purposes, now they are advertised more for "energy saving" applications, like stop-start engines, and providing a boost when starting hybrid cars from a standstill.



See also: maxwell.com/products/ultracapacitors/applications/cold_starting.aspx

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 05, 2011 2:18 pm Post subject: is battery filter or dead weight?

At 09:21 AM 1/5/2011, you wrote:




The 1 Farad cap I mentioned is pitifully small (Hell, it shows my age 

that I was impressed). Here is a 3000F (-0/+20%!) Cap:



maxwell.interconnectnet.com/ultracapacitors/datasheets/DATASHEET_K2_SERIES_1015370.pdf



   Okay, that's a whole new paradigm.



http://www.greencar.com/articles/ultrabattery-combines-battery-supercapacitor-power.php



http://www.technologyreview.com/biztech/18086/

On Ebay a guy is selling five cases of these (2.7V) 15 per case, for 

$775/case OBO. You'd need 5-6 of these to make a proper cell. (In 

series total capacitance is 1/(n/C), but you'd still get 500 F at 14V or so)



A few years ago the caps were used more for starting purposes, now 

they are advertised more for "energy saving" applications, like 

stop-start engines, and providing a boost when starting hybrid cars 

from a standstill.



    Ultracaps been proposed and even advertised for a host

    of "new and improved" performance . . . but compared

    to what product and for what purpose?



See also: maxwell.com/products/ultracapacitors/applications/cold_starting.aspx



     I think it was Mallory that proposed a capacitor

     replacement for a lead-acid battery a few years ago

     for cranking over the road truck engines. I think

     I saw some catalog sheets on product. Maxwell is offering

     catalog items with interesting specs . . .



http://www.aeroelectric.com/Mfgr_Data/Capacitors-UltraCaps/Maxwell_BMOD-Series_Ultracaps.pdf



     These or similar products may very well be the

     solution to engine cranking design goals. Right

     now, an OBAM airplane using a $75, 17 a.h. lead

     acid battery can plan to support a 4 a load for

     3 hours when new, 2.4 hours at end of life. 2.4

     hours at 11 volts average and 4 amps is 380KJ of

     standby energy.



     A capacitor being discharged from 14 to 10.5 volts

     delivers 47 Joules/Farad. The equivalent storage

     for a lead-acid replacement is something on the

     order of 8000 Farads or 16 of the Maxwell modules

     connected in parallel for about 800 cubic inches.



     Methinks 16 of these critters is larger and a lot

     more expensive than the 17 a.h. battery.



     I worked lead-acid battery project for HBC a couple

     years ago that proposed to used lead-plated carbon

     fibers . . . MUCH lighter. Thinner plates with really

     good performance numbers. That product turned

     out to be made mostly of smoke, mirrors, and computer

     models that 'neglected' a few important variables.



     I have no doubt that somebody will replace or even

     augment the SVLA battery somewhere sometime. If a sense

     of history serves us well, it will be years after

     Honda, Kia or Chrysler puts a few millions of

     consumer road-miles on them before they become

     an economic practicality for the OBAM aircraft.



     I don't expect to live to see it . . . but I'd be

     tickled pink to be proven wrong.

   Bob . . .

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