Volt / Ammeter

[ccwillwerth]

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

[GeorgeB]

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.

[Bushy Pete]

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

[RST Engineering]

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.

[COLIN LAMB]

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

[John Ammeter]

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
>
>

[COLIN LAMB]

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

[Montblack]

("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

[John Ammeter]

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!!!

[Morgans]

"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

[Rip]

John Ammeter wrote:
> 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
>>
John, you have nothing on my grade school shop teacher. His name was
....drum roll...Woody Rafters. Swear to God! And speaking of which, he
was the local Episcopal minister's son.

Rip

[Dan]

Montblack wrote:
> ("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

Thank you Secretary Watt.

Dan, U.S. Air Force, retired

[Dan]

RST Engineering wrote:
> 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.
>
>
Would AC amps and DC amps read the same given a single meter switched
between the two?

Dan, U.S. Air Force, retired

[ELIPPSE]

Paper clips? When Digikey has all these nice 3%, 0.005 to 0.10 current
sense resistors for $0.42?

[Morgans]

"John Ammeter" > wrote in message
news:5oidncI8B55FEmvenZ2dnUVZ_vidnZ2d@cablespeedwa .com...
> I used to be known as "amprobe".... "probe" to my friends...
>
> Probe

That would be milli amp probe, I would think! <g>

Jim <Ducking and Running> in NC

[Bushy Pete]

> Would AC amps and DC amps read the same given a single meter switched
> between the two?

>Dan, U.S. Air Force, retired

G'day Dan,
they will normally read pretty close, but the meter (and you get what you
pay for...) will read an average of the applied AC or voltage.

This difference in reading will apply more to non-sinusoidal waveforms.

Some of the fancy meters will read "True RMS", but for most typical
applications a cheap meter will be close enough. To check the alternator
output in an aircraft....... Well, you could always log the data and apply a
calibration correction if you needed to be super-accurate.......

Hope this helps,
Peter

[Rich S.]

"John Ammeter" > wrote in message
news:5oidncI8B55FEmvenZ2dnUVZ_vidnZ2d@cablespeedwa .com...
> I used to be known as "amprobe".... "probe" to my friends...
>
> Probe

That's pronounced Pro-bee as in Rookee or Newbee. . .

Rich "I knew someone at City Light" S.

[Morgans]

"Rich S." > wrote in message
. ..
> "John Ammeter" > wrote in message
> news:5oidncI8B55FEmvenZ2dnUVZ_vidnZ2d@cablespeedwa .com...
> > I used to be known as "amprobe".... "probe" to my friends...
> >
> > Probe
>
> That's pronounced Pro-bee as in Rookee or Newbee. . .
>

I know, but I just couldn't pass on the obvious joke!
--
Jim in NC

[Roger]

On Fri, 17 Feb 2006 10:07:50 -0800, "RST Engineering"
> wrote:

>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.
>
I'm wondering if the OP may have mis worded, or mis understood.

As you say the measurement is trivial, however I'm wondering if he
didn't think of powering the meter from the same source as was
*providing* the current rather than the current being measured. That
would make sense. Then it'd be easy and as you said, practically
impossible if powered from the *measured* current.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

>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.
>

[Capt. Geoffrey Thorpe]

"Roger" > wrote in message
...
> On Fri, 17 Feb 2006 10:07:50 -0800, "RST Engineering"
> > wrote:
>
>>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.
>>
> I'm wondering if the OP may have mis worded, or mis understood.
>
> As you say the measurement is trivial, however I'm wondering if he
> didn't think of powering the meter from the same source as was
> *providing* the current rather than the current being measured. That
> would make sense. Then it'd be easy and as you said, practically
> impossible if powered from the *measured* current.

What am I missing here? A good old fashioned analog ammeter is powered from
the "measured current".
Or, you can use a Simpson panel meter with your shunt. No power required. Of
course, they cost a fair bit of change nowadays.

http://www.simpsonelectric.com/pdf/webpdfe/Wide-Vue%20ADC.pdf

You only need "power" if you want some kind of fancy pants digital readout.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

[RST Engineering]

Go back to the original post and read it.

Jim





"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message >
> What am I missing here? A good old fashioned analog ammeter is powered
> from the "measured current".

[Capt. Geoffrey Thorpe]

"RST Engineering" > wrote in message
...
> Go back to the original post and read it.
>
> Jim
>
> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
> >
>> What am I missing here? A good old fashioned analog ammeter is powered
>> from the "measured current".

oops, missed the word "digital". Never mind.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.