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Compatable Shunt

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fedico94(at)mchsi.com
Guest

Posted: Sun Sep 30, 2012 7:17 pm Post subject: Compatable Shunt

My RV9-A uses the Z-12 drawing.  I installed a G3X unit (two Garmin GDU's 37x).  The ammeter does not read but the voltmeter does.  Reviewing the schematic provided by Garmin for connecting the two instumentation wires to the Shunt and comparing this to the Z-12 schematic I see both are essentially the same.  The shunt sent to me by the Avionics shop for use with the Garmin is 100 amp/50mv and the one B & C supplied and installed in the plane is 60 amp at 50mv.  My confusion and question concerns the schematic from Garmin that says the shunt is rated at 0.0005 Ohm.  The B & C supplied system with its shunt is 50mv/60 amp gives me 0.00083 Ohm.



First are my calculations correct and second does this have any bearing on the inability to display the ammeter reading ?  If the above is not contributing to the problem should I look elsewhere in the system for the problem ?  (Prior to turning on the field of the 60 amp alternator I get the main volts waring light flashing and goes off after the field is activated.  Remainder of G3X works fine)

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 01, 2012 5:57 am Post subject: Compatable Shunt

 	  Quote: 	
		     The shunt sent to me by the Avionics shop for use with the Garmin 

 is 100 amp/50mv and the one B & C supplied and installed in the 

 plane is 60 amp at 50mv.  My confusion and question concerns the 

 schematic from Garmin that says the shunt is rated at 0.0005 

 Ohm.  The B & C supplied system with its shunt is 50mv/60 amp gives 

 me 0.00083 Ohm.



First are my calculations correct and second does this have any 

bearing on the inability to display the ammeter reading ?  If the 

above is not contributing to the problem should I look elsewhere in 

the system for the problem ?  (Prior to turning on the field of the 

60 amp alternator I get the main volts waring light flashing and 

goes off after the field is activated.  Remainder of G3X works fine)


	


    The size of the shunt is relative only to calibration

    of the display. If you have no display, then the problem

    is not with the shunt. If the display is present but

    inaccurate, THEN you probably have a shunt problem.



    A shut is just a high power resistor . . . abeit a special

    resistor manufactured from amazium alloy with a near

    zero temperature coefficient of resistance. The material

    is actually Manganin.



http://tinyurl.com/3f79fgy



    When your current display is a LOADMETER calibrated

    in 0-100%, then the shunt is sized to what ever that

    100% value is . . . in case of the 60A alternator,

    you would use a 60A shunt. If it were a 100A alternator,

    then a 100A shunt. Interestingly enough, using a 100A

    shunt in ALL installations converts the 0-100% display

    to a 0-100A display.



    I suspect that the 100A shunt recommended by the

    avionics shop is based on some knowledge that the

    EFIS calls 50mv drop 100Amps and that size shunt

    will read ANY practical current up to 100A accurately.



    Substitution of a 60A shunt would simply mean that

    your 100A display was really a 100% display.



    Looking past calibration issues, if your display is

    non-reading, the difficulty lies elsewhere.



   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Mon Oct 01, 2012 7:27 am Post subject: Re: Compatable Shunt

Your calculations look correct to me.

What is the aircraft electrical load?  It might be too small to show up on the ammeter.  Turn on the landing light or other heavy load.

The engine needs to be running for the following test.

Measure the voltage drop across the shunt with a milli-voltmeter.  With a 60amp shunt and a 10amp load, the voltage drop will be about 8mv.

Then measure the voltage drop across the ammeter input.  It should be the same as at the shunt.

If there is a millivolt input signal to the ammeter but it still does not display, perhaps the ammeter needs to be calibrated.  See Page 12-20 G3X Installation Manual - Engine Sensor Configuration

Joe

_________________
Joe Gores

fedico94(at)mchsi.com
Guest

Posted: Mon Oct 01, 2012 6:45 pm Post subject: Compatable Shunt

The G3X manual you refer to lists the calibration procedure for Hall effect sensor on page 12020.  Cn this be used with the Shunt ?  I suspect there is no calibration for the shunt.

Thanks for the reference, I have to keep up on the manual revisions as they add new devices all the time.  After initial test flights I will have to update the software as well.

---

fedico94(at)mchsi.com
Guest

Posted: Mon Oct 01, 2012 6:45 pm Post subject: Compatable Shunt

again thanks for the pointers so I can proceed with some confidence.

---

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 01, 2012 7:53 pm Post subject: Compatable Shunt

At 09:43 PM 10/1/2012, you wrote:

 	  Quote: 	
		  



The G3X manual you refer to lists the calibration procedure for Hall 

effect sensor on page 12020.  Cn this be used with the Shunt ?  I 

suspect there is no calibration for the shunt.

Thanks for the reference, I have to keep up on the manual revisions 

as they add new devices all the time.  After initial test flights I 

will have to update the software as well.


	


   I downloaded the g3x manual. A search of the book

   cites 82 instances of the word "shunt" where the

   expected device is a 50mv/100A device. There

   are also 8 instances of Hall Effect where it appears

   you can use AmpLoc KEY100 style sensors.



   Paragraph 8.3 speaks to the use of either. I was

   unable to find any schematic references to hall

   devices. They have 3 wire connections and need a

   source of clean power. Also, hall effect sensors

   are noted for their variability in both offset

   and scale factor . . . they require individual

   calibration for accuracy. Shunts are precision,

   two wire devices that are very predictable. Suggest

   you stay with the 100A shunt.



   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Tue Oct 02, 2012 2:52 am Post subject: Re: Compatable Shunt

 	  Quote: 	
		  The G3X manual you refer to lists the calibration procedure for Hall effect sensor on page 12020. Cn this be used with the Shunt ? I suspect there is no calibration for the shunt. 	


I do not know if the calibration procedure is for only Hall Effect sensors or for both Hall Effect and Shunts.  The manual is not clear on this point.  You could ask Garmin support.  If there is no calibration procedure for shunts, then only a +/-50mV, 100amp shunt can be used, if you want the display to be accurate.

  Easier than calling Garmin would be to try calibrating per page 12-20.  What do you have to lose except a little time?  If it doesn't work, you can reset the parameters back to default.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 02, 2012 8:20 am Post subject: Compatable Shunt

At 05:52 AM 10/2/2012, you wrote:

 	  Quote: 	
		  

 > The G3X manual you refer to lists the calibration procedure for 

 Hall effect sensor on page 12020. Cn this be used with the Shunt ? 

 I suspect there is no calibration for the shunt.



I do not know if the calibration procedure is for only Hall Effect 

sensors or for both Hall Effect and Shunts.  The manual is not clear 

on this point.  You could ask Garmin support.  If there is no 

calibration procedure for shunts, then only a +/-50mV, 100amp shunt 

can be used, if you want the display to be accurate.


	




   In a customer's airplane, cutting wires and splicing

   back requires different levels of inspection than simply

   Pushing the pin out of a connector to route a wire

   through the hall device.



   The AMPLOC hall sensors are really handy. I've used

   them many times especially when I needed to measure

   current in a wire for which I was discouraged from

   doing damage.



   Over the years, I developed some tools that offered

   a quick-n-dirty access to current-in-the-wire . . .



http://tinyurl.com/8n6fo2n



http://tinyurl.com/8zqqetc



   The KEY series AMPLOC devices



http://tinyurl.com/8gtrsru



   Are more user friendly for getting electrons-per-second

   counted in fat wires.



   They do have the disadvantage of needing power to

   operate . . . and it must be well regulated since

   the output is ratiometric to the supply voltage.

   They are bi-directional devices . . . meaning that

   zero amps is some value close to 1/2 that of the

   applied power. Hence the need for a wide range

   of offset programming to move from shunts (zero volts

   at zero amps) to hall effect sensors (some volts

   at zero amps).



http://tinyurl.com/8suspug



   I suspect that the Garmin display value for AMPS is

   derived from analog data which is then massaged

   for offset and scale factor. Given the extensive references

   for 50mv/100A shunts for both wiring and discussion

   of AMPS sensing, I'd bet that the default programming

   assumes a 50mv/100A shunt. The resolution of their

   a/d system would allow the 100A shunt to be used

   virtually anywhere . . . even in series with an

   SD-8, without adjustment to default offset and

   scale factors.



   I don't recall if the subject problem was "no reading"

   or inaccurate reading. Of course, no reading could be

   either wiring error . . . or there's no actual current

   flowing to be measured and displayed. Inaccurate reading

   could be due to 60A shunt being used without re-calibration

   for the higher scale-factor value.



   A more detailed study of symptoms and conditions is

   called for. I suspect that either of the shunts in

   hand will do the job . . . just need to learn the

   correct incantation and wave of the wand to get the

   hardware's attention.

   Bob . . .

cwjazun(at)aol.com
Guest

Posted: Tue Oct 02, 2012 11:37 am Post subject: Compatable Shunt

Hello Bob,

 

 Got the book, good job, I'm really enjoying it. 

 

 Quick question, how do I un-suscribe from the forum??? I get about 30 emails an hour! hard to keep up with it. 

 

 Thanks

 

 Regards

 

 Walter 

    

  

     

  

     

  

    --

user9253

Joined: 28 Mar 2008
Posts: 1925
Location: Riley TWP Michigan

Posted: Tue Oct 02, 2012 12:02 pm Post subject: Re: Compatable Shunt

 	  Quote: 	
		  Of course, no reading could be 

either wiring error . . . or there's no actual current 

flowing to be measured and displayed. 	


It is too bad that we are so far from the aircraft.  It would be fun to do some troubleshooting in person.

The original posting said that there was zero amperage displayed.  And he said that the 60amp shunt was installed.  If anything, the 60 amp shunt should read higher current than a 100amp shunt.

 It would be helpful to know the millivolts across the shunt compared to the millivolts at the input to the G3X.  If those voltages are equal and above zero and there is no amperage displayed, then the problem is the G3X, perhaps a software setup problem.

Joe

_________________
Joe Gores

fedico94(at)mchsi.com
Guest

Posted: Tue Oct 02, 2012 6:07 pm Post subject: Compatable Shunt

With the 80 pin (read delicate) connector I am reluctant to pull it.  The information I have from Garmin implies that the G3X will not read unless it has 5 milliohm resister (rather than 8.3)

Job one is to test fly with voltmeter. andswap out the shunt in the next few weeks.  will recheck wiring tomorrow

---

fedico94(at)mchsi.com
Guest

Posted: Tue Oct 02, 2012 6:09 pm Post subject: Compatable Shunt

The readout has a red "X" through it meaning inoperable, no scale is displayed

---

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 02, 2012 6:11 pm Post subject: Compatable Shunt

At 02:36 PM 10/2/2012, you wrote:

  	  Quote: 	
		  Hello Bob,



 Got the book, good job, I'm really enjoying it. 



 Quick question, how do I un-suscribe from the forum??? I get about 30 emails an hour! hard to keep up with it. 



 Thanks



 Regards



 Walter 

 	


    30 an hour? I don't think I get 30 a day. In

    any case, they're very easy to delete if the topic is

    uninteresting to you. I have submitted an

    un-subscription request. When it arrives in

    your email, click on the link within the e-mail

    to confirm your request.



 

 

   Bob . . .    [quote][b]

eschlanser

Joined: 08 Apr 2010
Posts: 60

Posted: Wed Oct 03, 2012 5:12 am Post subject: Re: Compatable Shunt

Walter, 



 If you are really enjoying it, then don't unsubscribe. Rather, change your setting to receive a daily digest rather than individual e-mail messages. That way you will receive only one message per day. 



Eric



 	  cwjazun(at)aol.com wrote: 	
		  Hello Bob,

 

 Got the book, good job, I'm really enjoying it. 

 

 Quick question, how do I un-suscribe from the forum??? I get about 30 emails an hour! hard to keep up with it. 

 

 Thanks

 

 Regards

 

 Walter 

    

  

     

  

     

  

    --

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Oct 03, 2012 6:49 am Post subject: Compatable Shunt

At 09:05 PM 10/2/2012, you wrote:




With the 80 pin (read delicate) connector I am reluctant to pull 

it.  The information I have from Garmin implies that the G3X will not 

read unless it has 5 milliohm resister (rather than 8.3)

Job one is to test fly with voltmeter. andswap out the shunt in the 

next few weeks.  will recheck wiring tomorrow



The readout has a red "X" through it meaning inoperable, no scale is displayed



   Aha! Then the difficulty is not with the size of

   the shunt. Shunt size has only to do with scale

   factor . . . calibration.



   Substitution of a 60A vs. 100A shunt without

   re-calibrating the instrument means only that

   readings displayed will be 1.66 times higher

   than true.



   The fact that your display does not show a

   numerical value suggests that something in

   the software has detected an error in wiring

   or in setup. The instrument has no way to

   deduce shunt size, only that a shunt appears

   to be present. This strongly suggests a

   wiring problem.



   You can leave the 60A shunt in place and

   re-calibrate per instructions . . . or swap

   out for the 100A shunt where the instrument

   will probably read correctly . . . AFTER

   the big red X goes away.



   Bob . . .

fedico94(at)mchsi.com
Guest

Posted: Wed Oct 03, 2012 2:36 pm Post subject: Compatable Shunt

SUPRISE Bob

A fellow EAA'r came out and we easily swapped out the 50mc 60amp shunt for the Garmin provided 50mv/100amp shunt and connected the wires back up as they were previously.  Turned on master switch and the Garmin screens came up.  Went to engine page on MFD screen and would you believe that the red "X" was gone and it was reading amp draw.  Later I will do same for EBus shunt.

It appears with Garmin its their way or the highway.  You would think it would read with just any old shunt in there, but as I was advised by Tim Larberg at Garmin, that is not the case.

---

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Oct 03, 2012 3:36 pm Post subject: Compatable Shunt

At 05:35 PM 10/3/2012, you wrote:




SUPRISE Bob



A fellow EAA'r came out and we easily swapped out the 50mc 60amp 

shunt for the Garmin provided 50mv/100amp shunt and connected the 

wires back up as they were previously.  Turned on master switch and 

the Garmin screens came up.  Went to engine page on MFD screen and 

would you believe that the red "X" was gone and it was reading amp 

draw.  Later I will do same for EBus shunt.

It appears with Garmin its their way or the highway.  You would think 

it would read with just any old shunt in there, but as I was advised 

by Tim Larberg at Garmin, that is not the case.



   That's more than a surprise, it's a mind bender . . .

   I would REALLY like to understand the intelligence

   built into the system for making that determination.



   Low resistance measurements are not easy to do

   even when you can attach 4-wires directly to the

   shunt . . .



http://tinyurl.com/4l3tuj6



   . . . looking at a .0005 ohm resistor on the

   end of lead wires several feet long having a

   resistance of 0.010 to 0.015 ohms PER foot

   is magic.



   I may have occasion to enjoy some face-time with

   a Garmin techno-wienie next summer. I'll put this

   on my list of questions to ask.



   In any case, I'm delighted that your problem has

   been resolved . . . even if we don't understand

   just how it all came to pass. Must be pixie dust.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Oct 03, 2012 5:28 pm Post subject: Compatable Shunt

 	  Quote: 	
		  

It appears with Garmin its their way or the highway.  You would 

think it would read with just any old shunt in there, but as I was 

advised by Tim Larberg at Garmin, that is not the case.


	


    Do you have a phone number for Mr. Larberg. I'd

    like to talk to him.

   Bob . . .

fedico94(at)mchsi.com
Guest

Posted: Wed Oct 03, 2012 7:06 pm Post subject: Compatable Shunt

Hope this is not a serious discussion.  Garmin has their own way of setting up the software and when I install the next shunt for the auxillary alternator, if the red "X" is gone then I will be two for two.  Tim Larberg  1-888- 606-5482  press 3 for the first phone prompt and then press 3 for the second phone prompt (G series glass panels)

---

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Oct 03, 2012 7:56 pm Post subject: Compatable Shunt

At 10:04 PM 10/3/2012, you wrote:

 	  Quote: 	
		  



Hope this is not a serious discussion.  Garmin has their own way of 

setting up the software and when I install the next shunt for the 

auxillary alternator, if the red "X" is gone then I will be two for 

two.  Tim Larberg  1-888- 606-5482  press 3 for the first phone 

prompt and then press 3 for the second phone prompt (G series glass panels)


	


    Nothing tense. Just one techno wienie talking to another

    one. It behooves suppliers of any product to spread the

    knowledge around. Cuts down on calls to field service.



    An amazed and inquiring mind just wants to know . . .



   Bob . . .

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