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Shunt Questions

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Paul Valovich

Joined: 11 Jan 2006
Posts: 75

Posted: Sat Aug 09, 2014 8:18 am Post subject: Shunt Questions

RV-8A, 420 total hours. Electrical design based on Z13/8 architecture. AFS 4500 EFIS taking ammeter current readings from 50 MV / 60 amp shunt. 

  

Ammeter reading suddenly became very intermittent – mostly inop. Replaced wires, D-sub pins, connectors. Extensive troubleshooting with Advanced Flight Systems has led to questions about whether shunt is working properly. 

  

How does one troubleshoot a shunt? No moving parts; no visible damage; All other electrical systems operating normally.  

Paul Valovich 

Ridgecrest, CA 

N192NM 

  

    [quote][b]

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enginerdy(at)gmail.com
Guest

Posted: Sat Aug 09, 2014 8:45 am Post subject: Shunt Questions

Could you hook it up temporarily to a good quality volt meter (at the remote end)?

That could help eliminate some things.



Daniel Hooper



On Aug 9, 2014, at 11:16 AM, "Valovich, Paul" <pvalovich(at)dcscorp.com (pvalovich(at)dcscorp.com)> wrote:

[quote]      <![endif]-->   <![endif]-->    

RV-8A, 420 total hours. Electrical design based on Z13/8 architecture. AFS 4500 EFIS taking ammeter current readings from 50 MV / 60 amp shunt. 

  

Ammeter reading suddenly became very intermittent – mostly inop. Replaced wires, D-sub pins, connectors. Extensive troubleshooting with Advanced Flight Systems has led to questions about whether shunt is working properly. 

  

How does one troubleshoot a shunt? No moving parts; no visible damage; All other electrical systems operating normally.  

Paul Valovich 

Ridgecrest, CA 

N192NM 

  

     	  Quote: 	
		  



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[b]

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jluckey(at)pacbell.net
Guest

Posted: Sat Aug 09, 2014 9:11 am Post subject: Shunt Questions

How does one troubleshoot a shunt? 



Great question - shunts are about as "solid-state" as they come.



Based on you conversations w/ Advanced, we assume that it's not  something in their system.  Have you tried swapping-in a known-good  shunt?

As you may already know, a shunt is really just a highly-calibrated, very low-resistance resistor.  On many shunts the main element is soldered between the connection posts.  I'm wondering if there is some kind of mechanical problem in there somewhere.  I assume there are no visible cracks or other damage.



To test a shunt you could:



1.  hook-up a test circuit (on the bench) with a battery and some small load - maybe a couple of automotive brake lights (or equivalent).  You want a load of around 5 amps for this test.



2. Hook-up a DVM to the shunt on the mili-volt scale.  Your shunt you should be reading just about 1 mV per Amp of current in the circuit. (technically that's 5/6 mV per Amp, but that's really splitting hairs)



3. While the circuit is on, agitate the shunt: bang in on the bench top or hit it w/ a plastic mallet and see if the reading remains steady.  Perhaps some part of the shunt is damaged/cracked and it is having intermittent connection problems. (you will want to have good solid connections on the shunt terminals for this test - alligator clips probably won't do it)

4. It would be fun to test w/ high load, something like 40-50 amps, but I can't think of an easy way to create a load like that - maybe other Listers have some ideas...



Good Luck & keep us posted,



-Jeff



 

     On Saturday, August 9, 2014 9:28 AM, "Valovich, Paul" <pvalovich(at)dcscorp.com> wrote:  

             RV-8A, 420 total hours. Electrical design based on Z13/8 architecture. AFS 4500 EFIS taking ammeter current readings from 50 MV / 60 amp shunt.

    

  Ammeter reading suddenly became very intermittent – mostly inop. Replaced wires, D-sub pins, connectors. Extensive troubleshooting with Advanced Flight Systems has led to questions about whether shunt is working properly.

    

  How does one troubleshoot a shunt? No moving parts; no visible damage; All other electrical systems operating normally. 

  Paul Valovich

  Ridgecrest, CA

  N192NM

    

  

     	  Quote: 	
		  http://www.matronics." class="" rel="nofollow" target="_blank" href="http://forums.matroollow" target="_blank" href="http://www.matronics.com/contribution">htt


	


  

 

  

 

 [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Aug 09, 2014 11:33 am Post subject: Shunt Questions

At 12:10 PM 8/9/2014, you wrote:



 	  Quote: 	
		  How does one troubleshoot a shunt?



Great question - shunts are about as "solid-state" as they come.



Based on you conversations w/ Advanced, we assume that it's not 

something in their system.  Have you tried swapping-in a known-good shunt?



As you may already know, a shunt is really just a highly-calibrated, 

very low-resistance resistor.  On many shunts the main element is 

soldered between the connection posts.  I'm wondering if there is 

some kind of mechanical problem in there somewhere.  I assume there 

are no visible cracks or other damage.


	


   The only shunts I've seen 'fail' were

   destroyed by gross over-current. If the thing

   is not discolored and the screws are tight,

   it's good.



   Bob . . .

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voltar(at)vx-aviation.com
Guest

Posted: Sat Aug 09, 2014 3:08 pm Post subject: Shunt Questions

I destroyed a Dynon supplied shunt because the plastic base melted.  It was located FWF.



The fix was to fabricate a new base out of Bakelite.  I remember the day when they were all made that way...



Vern



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

Sent from my iThing. It is responsible for all gramma and typo terrors.



 	  Quote: 	
		   On Aug 9, 2014, at 12:32 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

 

 

 

 At 12:10 PM 8/9/2014, you wrote:

 

> How does one troubleshoot a shunt?

> 

> Great question - shunts are about as "solid-state" as they come.

> 

> Based on you conversations w/ Advanced, we assume that it's not something in their system.  Have you tried swapping-in a known-good shunt?

> 

> As you may already know, a shunt is really just a highly-calibrated, very low-resistance resistor.  On many shunts the main element is soldered between the connection posts.  I'm wondering if there is some kind of mechanical problem in there somewhere.  I assume there are no visible cracks or other damage.

 

  The only shunts I've seen 'fail' were

  destroyed by gross over-current. If the thing

  is not discolored and the screws are tight,

  it's good.

 

 

 

  Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1922
Location: Riley TWP Michigan

Posted: Sun Aug 10, 2014 5:53 am Post subject: Re: Shunt Questions

See the attached picture from Dynon's installaiton manual.  Is the shunt

located in position A or B or C?  When the shunt is located in position "A", 

which measures current into or out of the battery, as you know, very little

current flows through the shunt when the battery is fully charged.

  The following pertains to a shunt in position "A".  The engine needs to be

off while troubleshooting.  If the electrical system operates normally, the

shunt must be good.  If the shunt has a higher than normal resistance,

then there would be a larger voltage drop across the shunt.  This would

show up as lower system voltage and a higher ammeter reading.

  Since the electrical system operates normally, I suspect a bad connection

between the shunt and EFIS, or a problem within the EFIS.

  Even though the EFIS displays amps, it actually measures millivolts.

I would test the EFIS by applying a millivolt signal to the ammeter input.

This millivolt signal could be provided by a resistor network or by an almost

dead flashlight battery.

Joe

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Joe Gores

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Aug 10, 2014 8:49 am Post subject: Re: Shunt Questions

Shunts and Hall Effect sensors.



Hall effect sensors seemed to be quite nice since they were small and could directly interface with other electronics. But it is harder and harder to justify their use over a simple shunt.



As for troubleshooting a shunt, cracks can be very hard to detect, so bolting another in its place is a good approach. Shunts are ultra-reliable, but everything fails sometime.



There is another way to measure current, and that is to measure the voltage at each end of the wire in question. This is done by running a small (like AWG 26) wire from each end of the high-current conductor (whose current you want to know) to some voltmeter. The technique works because ESSENTIALLY NO CURRENT flows in the tiny sense wires. The voltage sensor then measures the voltage drop through the fatwire. Of course, you need to know something else, like the true current/voltage drop, or true fatwire resistance. But this technique is the preferred way for really big and reasonably long power conductors.



And there is no separate shunt or Hall Effect sensor.

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_________________
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: Sun Aug 10, 2014 9:20 am Post subject: Shunt Questions

There is another way to measure current, and that is to measure the voltage at each end of the wire in question. This is done by running a small (like AWG 26) wire from each end of the high-current conductor (whose current you want to know) to some voltmeter. The technique works because ESSENTIALLY NO CURRENT flows in the tiny sense wires. The voltage sensor then measures the voltage drop through the fatwire. Of course, you need to know something else, like the true current/voltage drop, or true fatwire resistance. But this technique is the preferred way for really big and reasonably long power conductors.



 And there is no separate shunt or Hall Effect sensor.



   I have used this technique in several applications

   where calibration is not an issue. The ammeter shunt's

   resistor is made from a special alloy7 called 'manganin'.



  http://tinyurl.com/3f79fgy



   This is an alloy crafted both for it's practical

   resistance and very low temperature coefficient of

   resistance. The ordinary conductors used to wire

   things up tend to have higher temperature

   coefficients. Which makes their use as an ammeter

   rather squirrely. As the wire heats up, it's temperature

   goes up, resistance goes up, power dissipated goes up,

   temperature rises some more and so it goes. If one

   plots current versus voltage drop in a wire in free-

   air (waiting for temperature to stabilize after each

   new current setting), you get a rather non-linear curve

   that isn't even repeatable except when the ambient

   conditions in which the wire operates are held constant.



   One practical way to use wiring as a 'shunt' is to

   detect lamp failure or perhaps failure in some other

   load like pitot heat. In this case, it is sufficient

   to simply know that current is flowing in the

   wire . . . or not. It is not necessary to know how

   much current flows.



     



 

 

   Bob . . .    [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Aug 10, 2014 9:56 am Post subject: Shunt Questions

Even though the EFIS displays amps, it actually measures millivolts.

 I would test the EFIS by applying a millivolt signal to the ammeter input.

 This millivolt signal could be provided by a resistor network or by an almost

 dead flashlight battery.



 



  Even an 'almost dead' battery is probably too much . . .

  Suggest you craft a millivolt test source from a couple of resistors and a good flashlight cell. Any other combination of resistors can be used as long as you hit the 'output target' in the upper half of a 50mV full scale input to the EFIS.



   



 [img]cid:.0[/img]  This is not an 'accurate' source, only a practical source for carrying out a divide-and-conquer experiment to isolate your fault.

 





    Bob . . .

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