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Shunt Questions

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon May 25, 2020 6:39 am Post subject: Shunt Questions

At 07:25 PM 5/24/2020, you wrote:

  	  Quote: 	
		  Bob, I hope you and yours are well!



 I have a question on shunts, but for my camper, not an aircraft.  I thought maybe you prefer I don't clutter up the AeroElectric list with non-aircraft topics!  (But tell me if you'd rather I send this to the list.) 	


  Not that far off-topic. No doubt there

  are other List members with at least

  an academic if not practical interest

  in DIY data acquisition. A pretty smart

  cookie once opined:



    "I often say that when you can measure what you

    are speaking about, and express it in numbers,

    you know something about it; but when you cannot

    measure it, when you cannot express it in numbers,

    your knowledge is of a meagre and unsatisfactory kind.”

       -- Lord Kelvin 



  	  Quote: 	
		  I would like to build some data logging for the DC system in my VW camper.



  https://sbw.org/sbwsty/



 There's a photo of my van's (messy) wiring closet here:



  https://sbw.org/westybattery/



 I have two lead-acid batteries, starting and house.  Right now, just two charging sources, the alternator and a ProSport marine charger. Thinking of adding solar.



 I'd like to monitor several current flows:



 - From the alternator to the house battery.

 - From the ProSport to the house battery.

 - From the house battery to the appliances.

 - In future, from the solar charge controller to the house battery.



 I don't NEED all of those, of course.  Just curious.  So I'll need several shunts.  B&C offers only one, 50mv at 20A, if I understand.  So 2.5 milliohms?



 I think a different shunt might be better, because I'm planning to use this breakout board:

 

  https://www.adafruit.com/product/904



 It comes with a 100 milliohm shunt (a 1% resistor), intended to measure up to 3.2A at the INA219B chip's max differential 320mv.  The resolution at 3.2A is .8mA.  I would put a shunt in parallel to measure a higher current, ideally one that produces close to 320mv for good resolution.



 For example, the if the alternator can produce 60A, would I maybe choose this 20A/100mv shunt (5 milliohms), which would produce 300mv at 60A?



  https://www.newark.com/canadian-shunt/la-20-100/shunt/dp/73K4805

 

 Is it silly to give up 300mv just to get higher resolution?



 Will it get too hot, dissipating 18W vs. the 2W it's rated for?



 B&C sells their shunt for $5, where the shunts from Newark are much more spendy.  Is there somewhere better to buy them?



 Is there a simpler way to do this?



 Another interesting part of the project will be how to get the data up to the cloud: I'm thinking WiFi when it's available and APRS otherwise. And maybe BLE to an app on my phone.  Adafruit has lots of radios I can experiment with.



 But first I need to gather the data.



 Thanks! 	


   I have all but abandoned metallic shunts for current

   measurement - especially when the millivolt data

   is to processed in low level digital electronics.



   We can revisit your shunt questions but I'll

   suggest you consider this product:



  https://tinyurl.com/yaxv58ax



   These are closed loop, hall-effect sensors priced

   about the same as the metallic shunts. Beauty

   of these critters is total isolation, very

   good linearity, repeatability and accuracy.



   Best yet, one device can measure a huge

   range of currents. 



   I stock the 6A version for about all applications.

   I can run 5 passes of 22AWG wire through the

   aperture and get plus/minus 1.2A full scale.

   Alternatively, a single pass of 22AWG 1 foot

   long through the aperture spliced in parallel

   with 10AWG 1 foot long outside the aperture

   gives me approx 10x multiplier for plus/minus

   60A full scale.



   You can situate the sensor local to the stimulus

   of interest and extend the leads on a shielded,

   twisted pair for direct interface with your

   a/d converter. You don't need those high common

   mode gain chips to do achieve an interface.

   You WILL need some a/d ports to process your

   hall sensor data.



   I've acquired high quality data at the ends

   of 40' leads in all manner of noisy environments.

   The attached photo is one example of one

   application. This board includes a 5v, 3-terminal

   regulator enabling me to use the device

   'barefoot' with a digital VOM at the observation-

   end of the leads. For applications such as yours,

   I'd probably solder a shielded pair directly to

   the module pins and 'pot' the connections with

   E-6000.



   If you'd like some boards to mount and terminate

   the wires in a connector, I think I've got a

   few laying around. Also, if you'd like to

   go for the metalic shunts, I think I've

   got a few dozen 20A shunts available for the

   asking . . . but you don't want to overload

   these things by much . . . maybe 50%. They're

   easy to 'smoke'.



   LONG time no hear my friend! Pleased to know

   that you're still alive, kicking and curious!



 

 

   Bob . . .

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Eric Page

Joined: 15 Feb 2017
Posts: 245

Posted: Mon May 25, 2020 10:44 am Post subject: Shunt Questions

Gents,

Another good option is Allegro MicroSystems' line of Hall effect sensors.  You can get them from all of the usual suspects on eBay, Amazon, AliExpress, etc., mounted on a small PCB.  You just feed your current of interest through the screw terminals, connect the output to an ADC input on your micro and scale the reading in your code.  They work well, are very small, generate virtually no heat and cost very little.

The unidirectional sensors output 0V with no current flow, while the bidirectional sensors output half the supply voltage with no current flow (5V supply = 2.5V no-current output; current in one direction produces output >2.5V and current in the other direction produces output <2.5V).

A couple of caveats.  1. Avoid laying another current-carrying wire over the surface of the sensor IC, as it can disturb the Hall sensor inside.  2. The zero-current output of the bidirectional ICs is ratiometric with the supply voltage, so be sure your sensor supply is the same as your ADC reference.

Search links for sensor modules on eBay:



-- ACS712 (5A, 20A and 30A sensors): https://preview.tinyurl.com/ybc556k5

-- ACS724 (40A and 50A sensors): https://preview.tinyurl.com/y9xfbehu

-- ACS758 (50A and 100A sensors): https://preview.tinyurl.com/ybqcwoqt

Sensor IC datasheets:

-- ACS712: https://preview.tinyurl.com/ybbckmf5

-- ACS724: https://preview.tinyurl.com/yafr2oms

--ACS758: https://preview.tinyurl.com/yxoukcv4



Eric





                  

                                               At 07:25 PM 5/24/2020, you wrote:



  	  Quote: 	
		  I'd like to monitor several current flows:



 - From the alternator to the house battery.

 - From the ProSport to the house battery.

 - From the house battery to the appliances.

 - In future, from the solar charge controller to the house battery.

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)aeroelect
Guest

Posted: Mon May 25, 2020 2:06 pm Post subject: Shunt Questions

At 01:40 PM 5/25/2020, you wrote:

  	  Quote: 	
		  Gents,



 Another good option is Allegro MicroSystems' line of Hall effect sensors.  You can get them from all of the usual suspects on eBay, Amazon, AliExpress, etc., mounted on a small PCB.  You just feed your current of interest through the screw terminals, connect the output to an ADC input on your micro and scale the reading in your code.  They work well, are very small, generate virtually no heat and cost very little.



 The unidirectional sensors output 0V with no current flow, while the bidirectional sensors output half the supply voltage with no current flow (5V supply = 2.5V no-current output; current in one direction produces output >2.5V and current in the other direction produces output <2.5V).



 A couple of caveats.  1. Avoid laying another current-carrying wire over the surface of the sensor IC, as it can disturb the Hall sensor inside.  2. The zero-current output of the bidirectional ICs is ratiometric with the supply voltage, so be sure your sensor supply is the same as your ADC reference.

  	  Quote: 	
		  	
	
 

   I've used these with success. They are

   not quite so 'tight' for accuracy, etc. but

   if your error budget will tolerate them, they

   perform as advertised.



 

 

   Bob . . .

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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sbw(at)sbw.org
Guest

Posted: Tue May 26, 2020 9:40 am Post subject: Shunt Questions

Bob and Eric, thanks for pointing out a much more elegant solution than 

a shunt farm!



Bob, I re-read the section of Chapter 7 on Hall effect sensors.  I'm 

sure I read it around 30 years ago, but I had forgotten.



One way this is more elegant is that it can be inserted into the ground 

path without disrupting the ground, which makes the physical wiring 

safer.  (The shunt and fuse block in my van's wiring closet are a bit 

vulnerable right now.)



The microcontrollers I'm planning to use have lots of A/D pins, so 

that's not a problem.  They're Arduino compatible, but at 3.3V, so I 

wonder whether the LTS 6-NP must have a 5V supply voltage?  If so, 

that'll factor in to the multiplier produced by the parallel wires, to 

make full scale no more than 3.3V.



I skimmed the data sheet on the LTS 6-NP.  I'll have to read it more 

closely before I'll be able to put it to use!  I believe I understand 

how the six primary leads are configured to the application, but not so 

much passing a conductor (or turns!) through the aperture.



Other than your clever 10X scaling, how does one choose between a 

conductor through the aperture vs. the primary leads?



And I'll want to understand more about the physical considerations: Does 

this device require some minimum clearance from other wiring/components?



I assume you specify a 1 foot length for each of the parallel 22AWG and 

10AWG wires because 10AWG has a cross section about 9X 22AWG?  Why 1 

foot?  What about just a shorter length of each, from one side of the 

sensor to the other?  (I'm picturing a printed circuit board with the 22 

AWG soldered near Fast-Ons or threaded studs to attach the 10AWG and the 

wires to ground and load/battery.  Or, heck, just a bolt through to the 

chassis, like the ground block.)



I wonder whether one could achieve the same multiplier (and current 

capacity) using a shorter wire through the aperture together with a 

generous area of printed circuit foil to carry the other 90% of the 

current?  (I've never learned anything about the current capacity of 

printed circuit foil or how to predict its resistance.)  Could that 

assembly be calibrated somehow?  Would it be stable?



Thanks, as always, for being so generous with your time!



On 5/25/2020 7:38 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		      I have all but abandoned metallic shunts for current

    measurement - especially when the millivolt data

    is to processed in low level digital electronics.

 

    We can revisit your shunt questions but I'll

    suggest you consider this product:

 

 https://tinyurl.com/yaxv58ax

 

    These are closed loop, hall-effect sensors priced

    about the same as the metallic shunts. Beauty

    of these critters is total isolation, very

    good linearity, repeatability and accuracy.

 

    Best yet, one device can measure a huge

    range of currents.

 

    I stock the 6A version for about all applications.

    I can run 5 passes of 22AWG wire through the

    aperture and get plus/minus 1.2A full scale.

    Alternatively, a single pass of 22AWG 1 foot

    long through the aperture spliced in parallel

    with 10AWG 1 foot long outside the aperture

    gives me approx 10x multiplier for plus/minus

    60A full scale.

 

    You can situate the sensor local to the stimulus

    of interest and extend the leads on a shielded,

    twisted pair for direct interface with your

    a/d converter. You don't need those high common

    mode gain chips to do achieve an interface.

    You WILL need some a/d ports to process your

    hall sensor data.

 

    I've acquired high quality data at the ends

    of 40' leads in all manner of noisy environments.

    The attached photo is one example of one

    application. This board includes a 5v, 3-terminal

    regulator enabling me to use the device

    'barefoot' with a digital VOM at the observation-

    end of the leads. For applications such as yours,

    I'd probably solder a shielded pair directly to

    the module pins and 'pot' the connections with

    E-6000.

 

    If you'd like some boards to mount and terminate

    the wires in a connector, I think I've got a

    few laying around. Also, if you'd like to

    go for the metalic shunts, I think I've

    got a few dozen 20A shunts available for the

    asking . . . but you don't want to overload

    these things by much . . . maybe 50%. They're

    easy to 'smoke'.

 

    LONG time no hear my friend! Pleased to know

    that you're still alive, kicking and curious!

 

 

    Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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