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Volt / Ammeter



 
 
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  #1  
Old February 17th 06, 03:09 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter

How is a shunt determined for a digital volt meter to determine amp? Can a
voltmeter that is using the measured voltage for its own power be set up on
a shunt to measure amps?

Charlie


  #2  
Old February 17th 06, 11:58 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter

On Thu, 16 Feb 2006 21:35:15 -0800, "RST Engineering"
wrote:

Yes, rather trivially.

Jim

"ccwillwerth" wrote in message
. ..
How is a shunt determined for a digital volt meter to determine amp? Can
a voltmeter that is using the measured voltage for its own power be set up
on a shunt to measure amps?

Charlie


I disagree with Jim here; most calibrated shunts that one would
purchase are either 50mV or 100mV at full load, and 0V at no load. I
don't know of any meter that relies on measured variable for its power
which will work with zero input. That is sorta sarcastic; I also know
of none that will work with 100mV, full scale on a higher than common
shunt.

As for the determination, Jim is 100% correct; you would want a
voltmeter with a very low input range, 50 or 100mV. Assuming oyu
wanted 50mV to correspond to 50A, using Ohms law, R=E/I you get
0.001=0.05/50 so you want a 1 milliohm shunt. You have #10 wire? It
is about 1 Ohm/1000ft, or 1 milliohm/ft. Stick 2 pins through the
insulation about a foot apart and hook them to the meter.
  #3  
Old February 17th 06, 03:06 PM posted to rec.aviation.homebuilt
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Default Volt / Ammeter

I'll bite here. I'll agree that the first part of the post is easy, using a
shunt and a meter across the shunt, but the second part of the post requests
that it measure the current while being powered from the same supply.

I can easily set this up with a battery powered meter, to measure the
current in the supply, but to power the meter from the same supply stumps
me......

Assuming this is for a meter to monitor the aircraft's power use after say
the master switch, then the only way I see to have the unit self powered is
to use a normal analogue moving needle gauge where it is self powered.

Peter


  #4  
Old February 17th 06, 07:07 PM posted to rec.aviation.homebuilt
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Default Volt / Ammeter

Yeah, I'll give you that I missed the "powered from the measured voltage"
part. It becomes a bit less trivial. Practically impossible.

As for sticking pins through the wire a foot apart, you are going to get
more contact resistance (and corrosion as time goes on) than the shunt
itself. If you are using the primary wire as the shunt, I'd break the wire,
use a terminal strip with a shorter piece of thinner wire a few inches long,
then back to the larger wire.

Jim


"GeorgeB" wrote in message
...
On Thu, 16 Feb 2006 21:35:15 -0800, "RST Engineering"
wrote:

Yes, rather trivially.


Stick 2 pins through the
insulation about a foot apart and hook them to the meter.



  #5  
Old February 18th 06, 02:42 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter

I have been making shunts for years using a box of paper clips. I measured
the resistance of the full clip as .025 ohms, so part of a clip is less
resistance in a linear relationship. Larger paper clips have less
resistance. Depending upon the current drawn and the sensitivity of the
meter used, you may need to consider heat dissipation and of course consider
the insulation. I solder taps and they work fine.

Far easier than using so many feet of wire.

Colin


  #6  
Old February 18th 06, 02:57 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter ENOUGH OF THIS!!!!

Please, either change the subject title or quit this thread...

You know how you can be in a room filled with people all talking at once
but you'll instantly hear when someone mentions your name?? Well, I'm
getting tired of seeing my name posted every day on RAH...

How about changing the name of the thread to "ammeter"? At least, with
the lower case it isn't so obvious to me.

BTW, if you can believe it... I retired from the Meter Department of a
large public Electric Utility as the Crewchief for all
Commercial/Industrial Metering for our very large city.... I've had
enough references to my name and what I did to last several lifetimes....

John Ammeter

COLIN LAMB wrote:
I have been making shunts for years using a box of paper clips. I measured
the resistance of the full clip as .025 ohms, so part of a clip is less
resistance in a linear relationship. Larger paper clips have less
resistance. Depending upon the current drawn and the sensitivity of the
meter used, you may need to consider heat dissipation and of course consider
the insulation. I solder taps and they work fine.

Far easier than using so many feet of wire.

Colin


  #7  
Old February 18th 06, 03:44 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter ENOUGH OF THIS!!!!

I got a charge out of your reply. You must have fun when the FAA does a
ramp check to see if you are current.

If we are talking about volt/amps with direct current, we could simply
replace the heading with watts and be done with it.

Colin


  #8  
Old February 18th 06, 03:58 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter ENOUGH OF THIS!!!!

("COLIN LAMB" wrote)
If we are talking about volt/amps with direct current, we could simply
replace the heading with watts and be done with it.



http://www.geocities.com/thereaganyears/environment.htm
James Watt... :-)


Montblack, a woman, two Jews and a cripple

  #9  
Old February 18th 06, 04:09 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter ENOUGH OF THIS!!!!

I used to be known as "amprobe".... "probe" to my friends...

Probe


Morgans wrote:
"John Ammeter" wrote


Please, either change the subject title or quit this thread...



So you have changed your name at some time, and wanted to keep it, like some
girls that get married? You went from Volt to Ammeter? You could have just
dropped the " / " from the name change, so it didn't look like
"Volt/Ammeter." That really is a silly name, I think.

Could you not have gone to something a little further away from the
electrical world for the new name, like aardvark, or something?

You know, my old computer that I used when I first started reading this
group had terrible resolution. For a while, I thought you name was
ant-eater, or something.

Really, you have to be less paranoid. Just go by Ammeter, from now on, and
drop the Volt. That way, you won't think that everyone is out to get you.

They really are, though. g

Bwwaaahhaahaahaa!!!

  #10  
Old February 18th 06, 04:19 AM posted to rec.aviation.homebuilt
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Default Volt / Ammeter ENOUGH OF THIS!!!!


"John Ammeter" wrote

Please, either change the subject title or quit this thread...


So you have changed your name at some time, and wanted to keep it, like some
girls that get married? You went from Volt to Ammeter? You could have just
dropped the " / " from the name change, so it didn't look like
"Volt/Ammeter." That really is a silly name, I think.

Could you not have gone to something a little further away from the
electrical world for the new name, like aardvark, or something?

You know, my old computer that I used when I first started reading this
group had terrible resolution. For a while, I thought you name was
ant-eater, or something.

Really, you have to be less paranoid. Just go by Ammeter, from now on, and
drop the Volt. That way, you won't think that everyone is out to get you.

They really are, though. g

Bwwaaahhaahaahaa!!!
--
Jim in NC

 




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