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current limiting an alternator

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bob.verwey(at)gmail.com
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Posted: Tue Dec 04, 2012 12:28 am Post subject: current limiting an alternator

Listers,



Is it economically and relatively simple to limit charging current from an alternator in a 12v system? The automotive alternators have relatively high initial output and looking at my small electrical loads, I don't see the need for a massive battery...or have I got it all wrong?? <grin>

 



Bob Verwey

IO470 Bonanza A35 ZU-DLW

V6 Chevy Safari ZU-AJF  



  [quote][b]

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nuckolls.bob(at)aeroelect
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Posted: Tue Dec 04, 2012 6:34 am Post subject: current limiting an alternator

At 02:26 AM 12/4/2012, you wrote:

Listers,



Is it economically and relatively simple to limit charging current 

from an alternator in a 12v system? The automotive alternators have 

relatively high initial output and looking at my small electrical 

loads, I don't see the need for a massive battery...or have I got it 

all wrong?? <grin>



    While an alternator has the CAPABILITY of delivering

    energy at relatively high rates, it can do so only

    if the LOAD is willing to accept it based on

    VOLTAGE DIFFERENTIALS and total loop resistance.



    When you hook an energy consumer across the bus,

    the current it requires is relatively constant and

    only slightly dependent on bus voltage. But an

    energy storage device (battery) may present a

    load to the bus that is initially several volts

    lower than the bus voltage set point.



    Now, you have the POTENTIAL for some serious

    currents to flow but even that's limited by the

    internal resistance of the battery. Intuitively

    one sees a potential hazard to, let us say, a 2 a.h.

    SLVA battery being totally discharged and then connected

    across a bus capable of delivering 40+ amps

    at normal bus voltages. Indeed, the itty-bitty

    battery's acceptance will 'spike' on initial

    connection but probably no where near 40 amps

    and it will fall rapidly. The risk to the battery

    is not so much from 'hammering energy into a

    chemical conversion'; the greatest potential

    for damage is from heating of the internals

    as a result of I(squared) x R watts being

    dissipated within the small mass. This is

    made worse by the fact that the dissipation

    is not necessarily spread evenly throughout

    the battery's chemistry.



    The battery will not necessarily drown

    upon experiencing its first 'drink from the

    firehose' but a series of such events will

    chip away at battery performance and severely

    shorten its potential service life.



    It would help to know more about your design

    goals. What size battery are you wanting to

    use? Is this battery going to be your only

    source of energy during failure of the boss-

    hog alternator? Have you established endurance

    goals for alternator-out operations?  Aside

    from engine cranking, ENDURANCE goals are the

    big driver of battery size. Can you give

    us more numbers as to size of battery you

    want to use and how this battery fits into

    your consideration for a comfortable Plan-B

    termination of flight after an alternator

    failure?

   Bob . . .

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bob.verwey(at)gmail.com
Guest

Posted: Tue Dec 04, 2012 8:37 am Post subject: current limiting an alternator

Hi Bob, As usual, you have put much more thought into your answer than I did into my question!

My craft is powered by a Chevy V6 with a single aftermarket ignition coil, specifically designed for "high vibration environments". My endurance goals for alternator-out operations would be 30 minutes, as I will be strictly day VFR, and with a cruise speed of 100 knots I will have some options.

  Electrical loads are the usual ignition system, 2 comms, GPS, landing light, but really the very basics required. No fuel pump, high wing with carb. I had the H35 battery in mind, same as in the Bonanza.



 

I am not considering an endurance bus.





Bob Verwey

 IO470 Bonanza A35 ZU-DLW

V6 Chevy Safari ZU-AJF  



  



On 4 December 2012 16:33, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  [quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

   

 At 02:26 AM 12/4/2012, you wrote:

 Listers,

 

 Is it economically and relatively simple to limit charging current from an alternator in a 12v system? The automotive alternators have relatively high initial output and looking at my small electrical loads, I don't see the need for a massive battery...or have I got it all wrong?? <grin>

   

    While an alternator has the CAPABILITY of delivering

    energy at relatively high rates, it can do so only

    if the LOAD is willing to accept it based on

    VOLTAGE DIFFERENTIALS and total loop resistance.

 

    When you hook an energy consumer across the bus,

    the current it requires is relatively constant and

    only slightly dependent on bus voltage. But an

    energy storage device (battery) may present a

    load to the bus that is initially several volts

    lower than the bus voltage set point.

 

    Now, you have the POTENTIAL for some serious

    currents to flow but even that's limited by the

    internal resistance of the battery. Intuitively

    one sees a potential hazard to, let us say, a 2 a.h.

    SLVA battery being totally discharged and then connected

    across a bus capable of delivering 40+ amps

    at normal bus voltages. Indeed, the itty-bitty

    battery's acceptance will 'spike' on initial

    connection but probably no where near 40 amps

    and it will fall rapidly. The risk to the battery

    is not so much from 'hammering energy into a

    chemical conversion'; the greatest potential

    for damage is from heating of the internals

    as a result of I(squared) x R watts being

    dissipated within the small mass. This is

    made worse by the fact that the dissipation

    is not necessarily spread evenly throughout

    the battery's chemistry.

 

    The battery will not necessarily drown

    upon experiencing its first 'drink from the

    firehose' but a series of such events will

    chip away at battery performance and severely

    shorten its potential service life.

 

    It would help to know more about your design

    goals. What size battery are you wanting to

    use? Is this battery going to be your only

    source of energy during failure of the boss-

    hog alternator? Have you established endurance

    goals for alternator-out operations?  Aside

    from engine cranking, ENDURANCE goals are the

    big driver of battery size. Can you give

    us more numbers as to size of battery you

    want to use and how this battery fits into

    your consideration for a comfortable Plan-B

    termination of flight after an alternator

    failure?

 

 

   Bob . . . 

 

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 le, List Admin.

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 -List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

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 ====================================

 

 

 

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Dec 04, 2012 9:57 am Post subject: current limiting an alternator

At 10:35 AM 12/4/2012, you wrote:

 Hi Bob, 

 As usual, you have put much more thought into your answer than I did into my question!



 My craft is powered by a Chevy V6 with a single aftermarket ignition coil, specifically designed for "high vibration environments". My endurance goals for alternator-out operations would be 30 minutes, as I will be strictly day VFR, and with a cruise speed of 100 knots I will have some options.

 Electrical loads are the usual ignition system, 2 comms, GPS, landing light, but really the very basics required. No fuel pump, high wing with carb. I had the H35 battery in mind, same as in the Bonanza.



 I am not considering an endurance bus.  Okay. According to this posting



   http://tinyurl.com/cryc6w3



  The battery on an H35 is a 12 volt, rated at 29 a.h. for a one-hour rate. At 30 pounds this is not a wimpy device. On the certified airplane, it's paired with at least a 60A alternator. There might have been an larger alternator offered as an option.

  Many of our brothers are flying 17 a.h. batteries with alternators of 40 amps or more.

  Can you articulate a foundation for your concerns? Even if you don't have an E-bus, consider a battery bus that supplies power for the ignition system. You should be able to fly this airplane with the battery master and alternator switches OFF.

    Bob . . .    [quote][b]

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bob.verwey(at)gmail.com
Guest

Posted: Wed Dec 05, 2012 12:38 am Post subject: current limiting an alternator

Bob, thanks for the insights; my concern was clearly born of ignorance. I will implement the battery bus as suggested.



Best...

 Bob Verwey

IO470 Bonanza A35 ZU-DLW

 V6 Chevy Safari ZU-AJF  



 



On 4 December 2012 19:55, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

  [quote]  At 10:35 AM 12/4/2012, you wrote:

 Hi Bob, 

 As usual, you have put much more thought into your answer than I did into my question!



 My craft is powered by a Chevy V6 with a single aftermarket ignition coil, specifically designed for "high vibration environments". My endurance goals for alternator-out operations would be 30 minutes, as I will be strictly day VFR, and with a cruise speed of 100 knots I will have some options.

 Electrical loads are the usual ignition system, 2 comms, GPS, landing light, but really the very basics required. No fuel pump, high wing with carb. I had the H35 battery in mind, same as in the Bonanza.



 I am not considering an endurance bus.  Okay. According to this posting



   http://tinyurl.com/cryc6w3



  The battery on an H35 is a 12 volt, rated at 29 a.h. for a one-hour rate. At 30 pounds this is not a wimpy device. On the certified airplane, it's paired with at least a 60A alternator. There might have been an larger alternator offered as an option.

  Many of our brothers are flying 17 a.h. batteries with alternators of 40 amps or more.

  Can you articulate a foundation for your concerns? Even if you don't have an E-bus, consider a battery bus that supplies power for the ignition system. You should be able to fly this airplane with the battery master and alternator switches OFF.





    Bob . . .     	  Quote: 	
		  



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.com" target="_blank">www.buildersbooks.com

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ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

tp://forums.matronics.com



	


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