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Shunt/Hall Sensor placement

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Tue May 11, 2010 10:50 am Post subject: Shunt/Hall Sensor placement

In Z-13, I would like to place a Hall Sensor for the AUX Alternator between the battery contactor and the Batt Bus to locate it in the cabin and within it's recommended ambient temperature operating envelope. 

Ditto for the Primary Alternator between the Batt Contactor and the Main Bus.

Any caveats here?



If only one alternator will be online at a time, is there any reason why I should not run the alternator outputs through just one Hall Sensor?



John

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Tue May 11, 2010 11:48 am Post subject: Re: Shunt/Hall Sensor placement

After looking long enough at my proposed HS placement, I can see that one of the shortcomings is that in the intended location, the sensors would only show alt throughput to the bus. In the case of the main bus, I could see alt output to the bus if the main contactor was open. But if it's closed, I'd have no way of knowing for sure if the alt was functioning at all because battery current throughput  could be masking a dead alternator.

On the batt bus there would be no way to know if the Aux alt was contributing or not.



RETHINK time.

Sorry for the bother.



J

nuckolls.bob(at)aeroelect
Guest

Posted: Tue May 11, 2010 9:17 pm Post subject: Shunt/Hall Sensor placement

At 02:48 PM 5/11/2010, you wrote:




After looking long enough at my proposed HS placement, I can see that 

one of the shortcomings is that in the intended location, the sensors 

would only show alt throughput to the bus. In the case of the main 

bus, I could see alt output to the bus if the main contactor was 

open. But if it's closed, I'd have no way of knowing for sure if the 

alt was functioning at all because battery current throughput  could 

be masking a dead alternator.



     Check the chapter on batteries in the 'Connection

     again . . .



     Batteries deliver energy at 12.7 volts and BELOW

     while alternators deliver energy at 13.8 volts

     and ABOVE.



     If an alternator is working, it will have a

     positive indication of output current consisting

     of aircraft system loads PLUS anything the battery

     is asking for in order to replenish a discharge.

     Alternators mask dead batteries . . . but batteries

     don't mask anything.



     Further if the alternator is working, then the bus

     voltage is high enough to keep low voltage warning

     lights out which are calibrated at 13.0 volts.



On the batt bus there would be no way to know if the Aux alt was 

contributing or not.



     Same principals apply for both alternators.



     Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Wed May 12, 2010 12:04 pm Post subject: Re: Shunt/Hall Sensor placement

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 02:48 PM 5/11/2010, you wrote:



     If an alternator is working, it will have a

     positive indication of output current consisting

     of aircraft system loads PLUS anything the battery

     is asking for in order to replenish a discharge.

     Alternators mask dead batteries . . . but batteries

     don't mask anything.

	




I re-read CH2 on Batteries, but it seems that with the sensor on the contactor-main bus leg, the sensor would only see the current(amps) going through that leg to the main bus.  The bus voltage would show up on the voltmeter indicating alternator condition, but I don't see how the HS could detect current going to the battery if it is located on a branch of the system. 



So I'm happy that I can at least verify that the alternator is working with the sensor inside the cabin, but it seems that if I want to know how hard, I will need another sensor at the alternator, or use a shunt per Z-13 and forget the hall sensor.



J

nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 12, 2010 5:18 pm Post subject: Shunt/Hall Sensor placement

I re-read CH2 on Batteries, but it seems that with the sensor on the 

contactor-main bus leg, the sensor would only see the current(amps) 

going through that leg to the main bus.



    Correct.



The bus voltage would show up on the voltmeter indicating alternator 

condition, but I don't see how the HS could detect current going to 

the battery if it is located on a branch of the system.



    How would you use that information if you had

    it?



So I'm happy that I can at least verify that the alternator is 

working with the sensor inside the cabin, but it seems that if I want 

to know how hard, I will need another sensor at the alternator, or 

use a shunt per Z-13 and forget the hall sensor.



    You KNOW how hard the alternator is working

    before you ever fly the airplane. I.e., it

    HAS to be large enough to carry all of system

    loads PLUS recharge a battery.



    If your low volts warning light is out, the

    alternator IS WORKING.  If the battery cranked

    your engine to get you airborne and you're

    confident of its CAPACITY, then the battery

    IS WORKING. If in the rare instance that you

    loose either alternator or battery contactor,

    the e-bus alternate feed gives you a means by

    which you get comfortably on the ground . . .

    preferably at airport of intended destination.



    Ammeters of any style installed connected to

    measure any current flow in the aircraft are

    diagnostic tools where the data offered is best

    considered on the ground. Ammeters are

    not particularly useful for making Plan-A/Plan-B

    decisions in flight.



    Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Thu May 13, 2010 5:35 am Post subject: Re: Shunt/Hall Sensor placement

jonlaury,

You can place the current sensor wherever it will give you the most useful information.  The current sensors in Z-13/8 provide the total current produced by each alternator.  Some builders locate the current sensor between the battery and main contactor.  In that location and under normal conditions, the ammeter will show battery charging current, which is not very useful information.  Other builders locate the current sensor in the wire that feeds the main power bus.  In this location, the ammeter shows the total current used by the aircraft (except for current used for battery charging and for devices connected directly to the battery bus).  It can be useful to know the total aircraft electrical load and the power consumed by each device.  In case of alternator failure, a knowledgeable pilot can shut off unneeded devices that consume the most power.  Given a choice between a voltmeter and an ammeter, a voltmeter is more useful.  With a modern EFIS, one can monitor both voltage and current without having extra gauges on the panel.  It does not matter where the current is monitored (or if it is monitored).  Just be aware of the advantages and disadvantages of different locations.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu May 13, 2010 7:45 am Post subject: Shunt/Hall Sensor placement

jonlaury,



You can place the current sensor wherever it will give you the most 

useful information.  The current sensors in Z-13/8 provide the total 

current produced by each alternator.



     Joe is quite correct . . . and I would like

     to apologize for my terse responses earlier.

     There are reasons but they are not excuses . . .

     I'll attempt to make amends.



Some builders locate the current sensor between the battery and main 

contactor.  In that location and under normal conditions, the ammeter 

will show battery charging current, which is not very useful information.



     It is also more difficult to do and requires

     that the alternator b-lead be brought to the

     main bus instead of tying it into the fat-wire

     network on the firewall.



     Since one of the design goals for Z-figures

     is to eliminate bringing the alternator b-lead

     into the cockpit, implementation of the battery

     ammeter is more difficult. We don't want to

     apply cranking current stresses to the ammeter

     equipment and still expect it to be well calibrated

     for normal operation.



     Finally, interpreting the readings of a battery

     ammeter take some study and understanding of

     what the readings show under various operating

     conditions.



Other builders locate the current sensor in the wire that feeds the 

main power bus.  In this location, the ammeter shows the total 

current used by the aircraft (except for current used for battery 

charging and for devices connected directly to the battery bus).  It 

can be useful to know the total aircraft electrical load and the 

power consumed by each device.  In case of alternator failure, a 

knowledgeable pilot can shut off unneeded devices that consume the most power.



Given a choice between a voltmeter and an ammeter, a voltmeter is 

more useful.  With a modern EFIS, one can monitor both voltage and 

current without having extra gauges on the panel.  It does not matter 

where the current is monitored (or if it is monitored).  Just be 

aware of the advantages and disadvantages of different locations.



    Exactly. Jonlaury was wrestling with the trade-offs

    of the various ammeter locations and getting a

    handle on the significance/usefulness of the

    readings.



    When we put an instrument on the panel that

    offers up NUMBERS that represent performance

    values, the cognizant system designer considers

    when and how those numbers are useful. In

    the case of the Z13/8, normal operations may

    load the e-bus to greater than 8A and it's

    no problem as long as the main alternator is

    functioning. An alternator loadmeter

    in the SD-8 feed line allows the pilot to

    do an as-needed load reduction on the e-bus

    when conditions require a shift to Plan-B.



    The legacy placement for ammeters has been

    in either (1) battery ammeter like your grandpa's

    Piper, Cessna and '52 Chevy, or (2) alternator/

    generator loadmeters like the rest of general

    aviation. But no matter where they are placed,

    they'll offer very low-value data. In other

    words, it's entirely possible and practical

    to craft a system with no ammeters at all.



    Active notification of low voltage combined

    with what ever electrical system instrumentation

    comes with your modern electro-whizzies

    can be quite adequate to the task of airborne

    electrical system management and crafting

    of Plans A and B.



    Plan-A says, "I can operate THIS list of

    electro-whizzies." Plan-B says, "I can

    operate THAT list of electro-whizzies."

    It's better that you craft the two plans

    before first flight rather than "on the

    fly", no pun intended.



    Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Thu May 13, 2010 10:11 am Post subject: Re: Shunt/Hall Sensor placement

Joe and Bob,



"Joe is quite correct . . . and I would like

to apologize for my terse responses earlier.

There are reasons but they are not excuses . . .

I'll attempt to make amends. "



Thank you both for your learned observations and attempts to understand my thinking on this.



Bob, your prodigious and continuing contribution to the OBAM aircraft community on this forum unequivocally qualifies you as the most patient teacher I've ever encountered. I didn't think your response was "terse". I thought it was patient, good-natured disgruntledness or self-effacing comic exasperation of having explained, about a gazillion times on this forum, that knowing how many amps your system is using is not very useful. 

When I read your response, the annunciator light went on that says "oh yeah, I've read this before" and felt foolish for wasting forum space. 

And in spite of knowing how many amps are careening about my system, I also know that it's only useful in making me feel like I'm more in control. Yet the control freak in me wants to know.  So with your and Joe's clarifications about what the different placements of the current sensor mean, I will confidently sally forth to appease my inner demons.



John

nuckolls.bob(at)aeroelect
Guest

Posted: Thu May 13, 2010 8:18 pm Post subject: Shunt/Hall Sensor placement

And in spite of knowing how many amps are careening about my system, 

I also know that it's only useful in making me feel like I'm more in 

control. Yet the control freak in me wants to know.  So with your and 

Joe's clarifications about what the different placements of the 

current sensor mean, I will confidently sally forth to appease my inner demons.



    Everyone learns differently. If some new light

    bulbs have lit up for you, then what we've done

    here is a good thing.



    Bob . . .

Speedy11(at)aol.com
Guest

Posted: Fri May 14, 2010 6:05 pm Post subject: Shunt/Hall Sensor placement

John

 I also appeased my "demons" and inserted current detections where I wanted  it.  I'm not an aero electric expert, but I've been flying numerous  aircraft for 35 years and I know what info I like to have displayed in the  cockpit.  I wanted current measurements.

 So, I inserted a HE device along the wire from the alternator to the #1  battery and a shunt on the wire from the #2 battery.  My thinking was that  I could monitor the amps going to the #1 battery to see how much load was on the  alternator.  It works great in that function and shows the high amps used  to recharge the battery and then once it is recharged, it shows the load being  used by the entire aircraft.  The shunt will indicate the amps being drawn  from the #2 battery should the alternator and #1 battery fail.

 I like having information in the cockpit.  Control freak?   Perhaps.  Guess I've been a control freak for 35 years and didn't realize  it.

 For me, just as I like to know what my fuel flow is, what my oil pressure  is, what my system voltage is, - I also like to know my amperage  load.

 Build it the way you like it.

 Stan Sutterfield

  	  Quote: 	
		  So with    your and Joe's clarifications about

what the different placements of the    current sensor mean, I will confidently sally

forth to appease my inner    demons.

	


 

  

  [quote][b]

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