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ammeter shunt

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klolson(at)wwestsky.net
Guest

Posted: Thu Apr 30, 2015 8:02 am Post subject: ammeter shunt

Hello,  

I’m installing Dynon’s Flight DEK D180. The instructions show the ammeter shunt installed in one of three locations on the positive side of the system. Taking a page from AeroElectric Connection book, I asked tech support if I could install the shunt on the ground side of the battery. I’m not getting a cogent answer. Is there any reason I cannot install the shunt on the ground side or is there something going on in the inside the D180 “box” that won’t allow this?  

Thanks,  

Ken  

       [quote][b]

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jluckey(at)pacbell.net
Guest

Posted: Thu Apr 30, 2015 9:23 am Post subject: ammeter shunt

Ken,

The current flow coming out of the positive terminal is equal to the flow going back in to the negative terminal so the shunt really doesn't care.  



HOWEVER

Without seeing a diagram of your proposed installation, it's hard to provide more analysis, but here are some things to consider:



There are several legitimate places to put a shunt in an electrical system.  If you are considering, for lack of a better term, a "battery" shunt, which measures current flow into & out of the battery, consider this.

The starter circuit is not typically run thru the shunt. So when wiring a shunt in the conventional way, it is usually put down-stream of the starter.  



If you put the shunt in the big negative wire, it will see starter current.  Something you probably do not want.

There are other issues with ground return paths that might get complicated... ( and require a lot of typing 



Now the big question: Why are you considering this?

-Jeff

  



     On Thursday, April 30, 2015 9:16 AM, Ken Olson <klolson(at)wwestsky.net> wrote:

  

  



                  Hello,

   I’m installing Dynon’s Flight DEK D180. The instructions show the ammeter shunt installed in one of three locations on the positive side of the system. Taking a page from AeroElectric Connection book, I asked tech support if I could install the shunt on the ground side of the battery. I’m not getting a cogent answer. Is there any reason I cannot install the shunt on the ground side or is there something going on in the inside the D180 “box” that won’t allow this?

   Thanks,

   Ken

   

        	  Quote: 	
		  



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jdubner

Joined: 17 Jul 2012
Posts: 35
Location: Independence, OR

Posted: Thu Apr 30, 2015 9:30 am Post subject: ammeter shunt

Ken,



Short and simple: Don't do it.  Here's why:



1.  You didn't mention what type of airplane you have but there's a good chance 

it has a starter.  The starter current will have to go through it.  Chances are 

also good that the shunt isn't rated for more than 50-100A.



2.  The shunt will be a additional point of failure for the battery system (like 

the battery ground cable, but in addition to it).  Flight without a battery 

ground connection will be a lot "less good" than flight without, say, an 

alternator B-lead connection.



I've been very satisfied with the ammeter shunt located in my RV-8A's alternator 

B-lead output.  It shows only the output of the alternator, which is what I care 

about (although I can appreciate that you may feel differently).  The downside 

of this location is the requirement for protection  of the wires from the shunt 

to the instrument but that's easily handled with fusible links.



--

Joe

Independence, OR

Ken Olson wrote, On 4/30/2015 09:01:

 	  Quote: 	
		   Hello,

 

 I'm installing Dynon's Flight DEK D180. The instructions show the ammeter

 shunt installed in one of three locations on the positive side of the

 system. Taking a page from AeroElectric Connection book, I asked tech

 support if I could install the shunt on the ground side of the battery. I'm

 not getting a cogent answer. Is there any reason I cannot install the shunt

 on the ground side or is there something going on in the inside the D180

 "box" that won't allow this?

 

 Thanks,

 

 Ken

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_________________
Independence, OR

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Fri May 01, 2015 3:22 am Post subject: Re: ammeter shunt

 	  Quote: 	
		  Hello, 

I’m installing Dynon’s Flight DEK D180. The instructions show the ammeter shunt installed in one of three locations on the positive side of the system. Taking a page from AeroElectric Connection book, I asked tech support if I could install the shunt on the ground side of the battery. I’m not getting a cogent answer. Is there any reason I cannot install the shunt on the ground side or is there something going on in the inside the D180 “box” that won’t allow this? 

Thanks, 

Ken 	




The D-180 does not care where the shunt is located or what the polarity is.  If the D-180 ammeter display has the wrong polarity, then just switch the 2 small ammeter sensor wires.  As others have pointed out, the shunt should NOT be in the starter circuit because it is not rated for starter current and because starter performance will be degraded.

  Here is a quote from the Dynon D-180 installation manual:

 	  Quote: 	
		  Note that the ammeter shunt is not designed for the high current required by the starter and must

not be installed in the electrical path between the battery and starter. 	


Joe

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Fri May 01, 2015 6:42 am Post subject: ammeter shunt

At 06:36 2015-05-01, you wrote:



 

  	  Quote: 	
		   Hello,

 I’m installing Dynon’s Flight DEK D180. The instructions show the ammeter shunt installed in one of three locations on the positive side of the system. Taking a page from AeroElectric Connection book, I asked tech support if I could install the shunt on the ground side of the battery. I’m not getting a cogent answer. Is there any reason I cannot install the shunt on the ground side or is there something going on in the inside the D180 “box” that won’t allow this? 	


   Say you DO put it in the (-) side of the battery . . .

   how would you use the information presented?



   Ammeters are pretty worthless in the cockpit.

   They WERE originally installed as a go/no-go

   indicator of system performance. The zero

   center, un-calibrated instruments were

   battery-ammeter clones of the instruments

   found in cars. As long as the needle was at

   or above 'zero' all was right with the

   universe.



 [img]cid:.0[/img]



 

   If your DEK180 has a voltage display

   function . . . and better yet, a low volts

   warning function, the usefulness of the

   panel mounted ammeter as a flight management

   instrument goes to zero.



   If you become aware of a low voltage condition

   that mitigates with reduction in load, then

   the alternator is CRIPPLED and you reduce loads

   to keep voltage at or above battery discharge

   level of 12.5 volts. If no mitigation is

   possible, alternator is CRAPPED and your

   plans are necessarily modified.



   Values of CURRENT under all conditions

   of flight are predictable and should be known

   as part of your load analysis and  system design

   goals. The idea that having a continuously

   monitored current will assist with a aw-S%$T-

   flip-a-switch situation in the cockpit is

   unrealistic and easily replaced with PLAN-B

   that calls for flipping at most 2 switches

   with predictable result that does not depend

   on an ammeter for confirmation.



   Recommend you put the shunt in the alternator

   b-lead. That will be most useful as a GROUND

   diagnostics tool AFTER plan-b got you comfortably

   on the ground.

   



 



 

   Bob . . .

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