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dvanlanen

Joined: 25 Jul 2006
Posts: 122
Location: Madison, WI

Posted: Thu Apr 10, 2008 7:23 am Post subject: Shunts

I am reading through the AeroElectric Connection manual as I have time, but I am having trouble comprehending some of the concepts presented.  I just read about the use of shunts in an electrical system to allow the measurement of large currents with small meters.  One thing I don’t understand is, if a shunt is used in the circuit to be measured, what prevents a reduction in energy in the circuit on the downstream side of the shunt?  Can someone help me better understand this?  

Thanks,  

Dave Van Lanen  

601XL – Tail        [quote][b]

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dan(at)familybrown.org
Guest

Posted: Thu Apr 10, 2008 7:50 am Post subject: Shunts

Quoting Dave VanLanen <davevanlanen(at)sbcglobal.net>:



 	  Quote: 	
		   understand is, if a shunt is used in the circuit to be measured, what

 prevents a reduction in energy in the circuit on the downstream side of the

 shunt?  Can someone help me better understand this?


	


Nothing prevents it; there is in fact such a reduction.  However, it's  

such a minuscule reduction that it's not noticeable in ordinary  

operation.  A shunt typically is designed for a 50 mV voltage drop at  

full capacity.  So, a 100A shunt will cause a 50 mV drop at 100A.  In  

a 14V circuit, 100A represents 1400W, and the shunt will consume 5W of  

that.



-- 

Dan Brown, KE6MKS, dan(at)familybrown.org

"Since all the world is but a story, it were well for thee to buy the

more enduring story rather than the story that is less enduring."

  -- The Judgment of St. Colum Cille

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mprather(at)spro.net
Guest

Posted: Thu Apr 10, 2008 8:32 am Post subject: Shunts

Hey Dave,



Nothing prevents loss of energy downstream of the shunt.  But, a properly

selected shunt will have a relatively small voltage drop at full scale

current - reducing the power consumption of the device.  Typical shunts

drop 50mV at full scale.  On a 100A peak current circuit that's 5W = 100A

* 50mV.  If you figure you're dropping the rest of the 13V supply into the

100A load, you're only losing 5W out of 1300W or 0.3%.  Not too terrible. 

At lower currents the percentage of power lost is less: 10A through the

same shunt will drop 5mV which is 50mW of the 130W delivered to the load -

or 0.03%.



Many aircraft engine monitors are setup to use Hall Effect sensors - which

do not consume any current from the measured circuit.

Regards,



Matt-



 	  Quote: 	
		   I am reading through the AeroElectric Connection manual as I have time,

 but

 I am having trouble comprehending some of the concepts presented.  I just

 read about the use of shunts in an electrical system to allow the

 measurement of large currents with small meters.  One thing I don't

 understand is, if a shunt is used in the circuit to be measured, what

 prevents a reduction in energy in the circuit on the downstream side of

 the

 shunt?  Can someone help me better understand this?



 Thanks,

 Dave Van Lanen

 601XL - Tail

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mprather(at)spro.net
Guest

Posted: Thu Apr 10, 2008 8:33 am Post subject: Shunts

Hey Dan



That's funny..  We used much of the same verbiage.  Even most of the same

example.



Matt-



do not archive



 	  Quote: 	
		   



 Quoting Dave VanLanen <davevanlanen(at)sbcglobal.net>:



> understand is, if a shunt is used in the circuit to be measured, what

> prevents a reduction in energy in the circuit on the downstream side of

> the

> shunt?  Can someone help me better understand this?



 Nothing prevents it; there is in fact such a reduction.  However, it's

 such a minuscule reduction that it's not noticeable in ordinary

 operation.  A shunt typically is designed for a 50 mV voltage drop at

 full capacity.  So, a 100A shunt will cause a 50 mV drop at 100A.  In

 a 14V circuit, 100A represents 1400W, and the shunt will consume 5W of

 that.



 --

 Dan Brown, KE6MKS, dan(at)familybrown.org

 "Since all the world is but a story, it were well for thee to buy the

 more enduring story rather than the story that is less enduring."

   -- The Judgment of St. Colum Cille

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gmcjetpilot

Joined: 04 Nov 2006
Posts: 170

Posted: Sat Apr 12, 2008 3:38 am Post subject: Shunts

The AMP meter is really a VOLT METER. Yep it has nothing to do with AMPS. (There is an AMP and VOLT relation).

   

  How does it work. The shunt causes a voltage drop across the shunt (due to resistance). That resistance is a known calibrated value. The volt gauge is reads volt drop. Since voltage drop is proportional to current (amps) the gauge can read the volt drop as current or amps, as follows:

   

  This is the famous OHMS law:

   

  V = I x R

   

  OR

   

  Volts = Current (amps)  X Resistance (ohms)

   

  So what?

   

  We know a shunt is "calibrated" to drop a certain volt for every every amp of current. Shunts vary, but a typical 50 amp shunt has a 50 millivolt drop at 50 amps. 

   

  If you have 50 amps at 14 volts  entering the shunt, the volts leaving the shunt at 50 amps will be 50 millivolts (0.050v) lower or 13.95 volts. 

   

  One millivolt drop = one amp. So you need a gauge that is labeled from 0 to 50 amps (but has a range from 0 to 0.050 volts). 

   

  With a volt gage that reads millivolts from 0 to 50 millivolts (but labeled amps) we have an AMP METER!

   

  Again the meter is measuring voltage drop not amps. It just happens OHMS LAW is handy and linear (usually); where current and volts are proportional based on the resistance of the shunt. 

   

  Shunts can have higher or lower resistance. Not all have the 1 amp to 1 millivolts ratio. That is OK as long as the scale and range of the gauge (analog or digital) compatible or calibrated for that shunt. The 1 amp to 1 millivolt ratio is handy since many volt gauges are calibrated in  [quote][b]

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echristley(at)nc.rr.com
Guest

Posted: Sat Apr 12, 2008 11:06 pm Post subject: Shunts

gmcjetpilot(at)yahoo.com wrote:

 	  Quote: 	
		   The AMP meter is really a VOLT METER. Yep it has nothing to do with AMPS. (There is an AMP and VOLT relation).

    

   


	


Aahh!  But is it?  Maybe the VOLT meter is really an AMP METER!!



If using a swinging arm type meter, the voltage across the inputs drives 

a current that energizes an electromagnet, the forces the deflection.  

You're using current to measure a voltage, that's caused by the current 

across the shunt, which is caused by a voltage.



Aahiiieee!!



8*)



-- 



http://www.ronpaultimeline.com

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nuckolls.bob(at)cox.net
Guest

Posted: Sun Apr 13, 2008 6:31 am Post subject: Shunts

At 03:05 AM 4/13/2008 -0400, you wrote:



 	  Quote: 	
		  

<echristley(at)nc.rr.com>



gmcjetpilot(at)yahoo.com wrote:

>The AMP meter is really a VOLT METER. Yep it has nothing to do with AMPS. 

>(There is an AMP and VOLT relation).



Aahh!  But is it?  Maybe the VOLT meter is really an AMP METER!!


	




 	  Quote: 	
		  If using a swinging arm type meter, the voltage across the inputs drives a 

current that energizes an electromagnet, the forces the deflection.

You're using current to measure a voltage, that's caused by the current 

across the shunt, which is caused by a voltage.



Aahiiieee!!


	


   A very astute observation sir. Allowing a coil

   of wire to move within the field of a permanent magnet

   was the brainchild of a fine fellow named D'arsonval

   who conceived the design about 130 years ago. There's

   an excellent description of the details of this idea

   offered over several pages beginning at:



http://www.tpub.com/neets/book3/7.htm



   Hit the "-> next" buttons to access the series.



   One may also craft a moving magnet instrument . . .

   a good example is Van's ammeter. Unlike the more

   fragile and difficult to calibrate moving coil

   movement typical of:



http://www.aeroelectric.com/Pictures/Instruments/Loadmeter_2.jpg



   Vans ammter shown at:



http://www.aeroelectric.com/Pictures/Instruments/VAM10_Interior_View



   moves a barrel shaped magnet in the center of TWO coils

   positioned at right angles to each other. This movement

   doesn't need springs and is NOT calibrated with respect

   to current flowing in the coils. In this case

   two coils are excited with a current proportional

   to the sine and cosine of the applied stimulus. The magnet

   and pointer are often free to rotate 360 degrees. Van's

   instrument is "pegged" at -45 amps and has a light spring

   that drives the pointer to the peg when the instrument is

   powered down. But you could remove the peg and spring.

   The pointer would rotate freely and still properly indicate

   the mechanical result of the ratio of two currents applied

   to the coils. This style of meter movement can be used to

   drive something like a compass card for displaying a

   heading not unlike that offered by the DG.



   This instrument is interesting because it can be

   electronically conditioned to display a host of stimuli

   and it takes advantage of the full rotational scale

   of the instrument. D'arsonval movements get VERY

   hard to build beyond 90 to 110 degrees of pointer

   swing.



   Because they deal with the results of a magnetic

   interaction between coil(s) of wire and fixed magnets

   both instruments are indeed displays of the effects

   of CURRENT.



   However, if one considers the internal resistance of

   the instrument as being part of the overall circuit,

   the raw device can be used to display the effects

   of very small voltages. A good example is the classic,

   non-amplified CHT instrument. An example is shown

   here:



http://www.aeroelectric.com/Pictures/Instruments/CHT%20Gauge.jpg



   This puppy reads full scale when something on the order

   of 7 MILLIVOLTS is applied to its terminals. This is

   the voltage generated by K-type thermocouple wire

   at 350F. In this case, the moving coil can be crafted

   of few turns of relatively large wire (low resistance)

   because while a thermocouple doesn't offer much VOLTAGE,

   it is a very low impedance source of energy and can

   produce considerable CURRENT at the relatively small

   voltage.



   All moving coil devices are dependent upon the force

   against a spring which is proportional to the current

   flowing in a coil of wire. Of course the coil has resistance

   of its own so any basic meter movement calibrated for

   the measurement of a current may also be said to be

   a "voltmeter" . . . typically, rudimentary movements will

   indicate full scale with voltages on the order of 10

   to 200 millivolts. The instruments designed to work in

   conjunction with shunts are generally crafted so that

   the CURRENT induced in the coil produces full scale

   torque when 50 milliVOLTS (standard shunt calibration)

   is applied to the terminals.



   Van's instrument is fitted with electronics such that

   the stuff sensed at the input terminals is indeed

   a voltage . . . the considerable current required

   to position the pointer comes from the electronics

   power supply and not from the voltage stimuli being

   monitored.



   I've done some preliminary testing on the Van's

   ammeter . . . by modern aviation design goals it

   is exceedingly sensitive to local RF fields. I'm

   working on an article to explore this condition.

   I'll also see if I can craft an easily fabricated

   filter or shield as a workaround for this product's

   shortcomings.



   Bob . . .

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gmcjetpilot

Joined: 04 Nov 2006
Posts: 170

Posted: Mon Apr 14, 2008 6:13 am Post subject: Shunts

Oh my my. This is why people make fun of tech geeks and nerds, ha-ha. Yes voltage, current and EMF are all magically intertwined. Even the magic of the hall effect sender puts out proportional volts to current. But you all are right, there are coils in those mechanical gauges. However a digital meter will read directly off a shunt? Huha? What? Doha! ha-ha. 

   

  Bob your "VAM10_Interior_View link" is not working?

   

  Cheers

   

   

  do not archive



            [quote][b]

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nuckolls.bob(at)cox.net
Guest

Posted: Mon Apr 14, 2008 7:16 am Post subject: Shunts

At 07:07 AM 4/14/2008 -0700, you wrote:



 	  Quote: 	
		  Oh my my. This is why people make fun of tech geeks and nerds, ha-ha.


	


     Interesting . . . it seems that the same folks would also

     make fun of neurosurgeons, master chefs and physicists.



    Individuals who poke fun at the assemblage of simple-ideas

     into useful inventions are themselves at-risk for not

     enjoying the benefits that arise from understanding . . .

     a kind of self imposed exile to ignorance that leaves

     them dependent upon those who DO understand.



 	  Quote: 	
		    Yes voltage, current and EMF are all magically intertwined.


	


     Nothing magic about it. But the conditions under

     which they interact are not consistent. For example,

     just because there is voltage to be measured doesn't

     automatically translate to a current flow. Similarly,

     there are conditions where huge magnitudes of current

     flow with zero impressed voltage.



 	  Quote: 	
		  Even the magic of the hall effect sender puts out proportional

volts to current.


	


     Sort of . . . volts is proportional to the intensity

     of a magnetic field. The magnetic field can come from

     a variety of sources not the least of which is the

     field surrounding a current carrying conductor.



 	  Quote: 	
		  But you all are right, there are coils in those mechanical gauges.

However a digital meter will read directly off a shunt? Huha? What?

Doha! ha-ha.


	


     Yes, the digital voltmeter takes advantage of the

     voltage drop impressed across a shunt as a result

     of current flow. The measurements obtained by this

     method are independent of simple-ideas involving

     magnetics.



 	  Quote: 	
		  Bob your "VAM10_Interior_View link" is not working?


	


     Yes, I corrected it in the posting that followed

     a few minutes after the first. The working link

     is . . .



http://www.aeroelectric.com/Pictures/Instruments/VAM40_Interior_View.jpg



        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

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