As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

In article ,
writes:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

You probably don't want resistance wire for this sort of current,
and you don;t want anything like 1 ohm resistance.

As a teenager, I made a multimeter (moving needle type back then),
and I used a length of wire coat-hanger as the shunt resistor with
a 50microamp meter movement. Just needed a few inches IIRC, although
I don't now recall what the current was for full scale deflection.

Later, I made a car battery charger, and used a length of plain
copper wire as the shunt, folded back and forth a few times.

One important thing - make sure your sense wires are connected to the
shunt wire only, and not to the shunt wire terminals/ends. Otherwise
variation in the terminals will generate more noise than the voltage
drop measurement in the shunt wire you're looking for, and it removes
the risk of the shunt wire terminal failing such that the shunt drops
out and everything passes though your sense circuit (for a millisecond
or so until it burns out).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Jan 1, 8:19*pm, wrote:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Made_Shunt_for...
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better *eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

Using copper wire for a shunt is fine if the temperature does not vary
much. The link
you posted overcomplicates things a bit.
1) You don't need to worry about the resistance of the meter if you
use a voltmeter
and calculate the current.
2) You can calibrate the shunt by first using a long length of wire
and passing a current that
one of your existing meters can measure. Then shorten the wire and
scale the
readings proportionately.

Make sure you use 4-terminal measurements. In other words, pass the
high current through
the sensing wire and add a pair of connections soldered onto that
wire, one near each end.
The millivoltmeter is connected to those soldered tappings.

John

On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC measurements.



I have a couple of multimeters ... but obviously not going to be
any good for around 80-100A

Ouch! That's a serious current.

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use
a 1 ohm shunt, anybody made one of these ?

Ahem. Let's review those school physics lessons shall we?

Volts = Ohms x Amps

So 80A through 1 ohm will generate 80V. Further, the definition of
volts is:
Watts = Volts x Amp

So your shunt resistor is going to be dissipating
80 x 80 = 6400 W = 6.4 kW.

That's a serious amount of energy!

(Of course, what I expect will happen is that your shunt resistor
will have much higher resistance than the rest of the circuit,
and bring the current way down - or possibly kill it altogether.)

I suggest you need something more like 1 milli-ohm, which will produce
a voltage of 80 mV (perfectly within the range of digital volt meter),
and an energy output of 6.4W

http://uk.farnell.com/jsp/search/pro...=1292504&N=401
(for example) ?

wrote:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

A much more elegant (and still DIY) method is to use a Hall Effect
device, no direct connection to the circuit being measured at all. The
bigger devices (from 50 amps or so upwards) are just toroids through
which you feed the current carrying wire.

Available from CPC, Farnell and others. Devices such as HTFS200-P and
LTFS 50-NP should take you where you need.

--
Chris Green

wrote:
As part of another project, would like to take some High Current DC measurements.

Depending how accurate they need to be, you can get a cheapish DC only
current meter with ranges of +- 100A and +-600 Amps from most decent
motor factors. Mine's made by Durite, Part No. 0-534-00.

They're sold for checking charging and starter currents without breaking
the circuit, you just put the wire into a channel on the back of the meter.

http://uk.picclick.com/2-X-VINTAGE-D...999596420.html

The e-bay auction's ended, but you get the idea...

I bought mine a few years ago, though. And no, it's not for sale, it's
too useful. :-)


--
Tciao for Now!

John.

On 1 Jan,
Martin Bonner wrote:

On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC
measurements.



I have a couple of multimeters ... but obviously not going to be any good
for around 80-100A

Ouch! That's a serious current.

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm
shunt, anybody made one of these ?

Ahem. Let's review those school physics lessons shall we?

Volts = Ohms x Amps

So 80A through 1 ohm will generate 80V. Further, the definition of volts
is:
Watts = Volts x Amp

So your shunt resistor is going to be dissipating
80 x 80 = 6400 W = 6.4 kW.

That's a serious amount of energy!

(Of course, what I expect will happen is that your shunt resistor will have
much higher resistance than the rest of the circuit, and bring the current
way down - or possibly kill it altogether.)

I suggest you need something more like 1 milli-ohm, which will produce a
voltage of 80 mV (perfectly within the range of digital volt meter), and
an energy output of 6.4W

http://uk.farnell.com/jsp/search/pro...=1292504&N=401 (for
example) ?

I'd just use a hall effect clamp on ammeter. CPC do a good one for up to
400A.

--
B Thumbs
Change lycos to yahoo to reply

On 01/01/13 20:59, Martin Bonner wrote:
On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC measurements.



I have a couple of multimeters ... but obviously not going to be
any good for around 80-100A

Ouch! That's a serious current.

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use
a 1 ohm shunt, anybody made one of these ?

Ahem. Let's review those school physics lessons shall we?

Volts = Ohms x Amps

So 80A through 1 ohm will generate 80V. Further, the definition of
volts is:
Watts = Volts x Amp

So your shunt resistor is going to be dissipating
80 x 80 = 6400 W = 6.4 kW.
whichwici leads you directly there.

That's a serious amount of energy!

(Of course, what I expect will happen is that your shunt resistor
will have much higher resistance than the rest of the circuit,
and bring the current way down - or possibly kill it altogether.)

I suggest you need something more like 1 milli-ohm, which will produce
a voltage of 80 mV (perfectly within the range of digital volt meter),
and an energy output of 6.4W

http://uk.farnell.com/jsp/search/pro...=1292504&N=401
(for example) ?

Problem with resistors that low is the leads themselves start to make a
difference.

This is car starter motor type territory..think of the battery leads to THAT




--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

In message ,
Martin Bonner writes
On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC
measurements.



I have a couple of multimeters ... but obviously not going to be
any good for around 80-100A

Ouch! That's a serious current.

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use
a 1 ohm shunt, anybody made one of these ?

Ahem. Let's review those school physics lessons shall we?

Volts = Ohms x Amps

So 80A through 1 ohm will generate 80V. Further, the definition of
volts is:
Watts = Volts x Amp

So your shunt resistor is going to be dissipating
80 x 80 = 6400 W = 6.4 kW.

That's a serious amount of energy!

(Of course, what I expect will happen is that your shunt resistor
will have much higher resistance than the rest of the circuit,
and bring the current way down - or possibly kill it altogether.)

I suggest you need something more like 1 milli-ohm, which will produce
a voltage of 80 mV (perfectly within the range of digital volt meter),
and an energy output of 6.4W


That'd be two coathangers in parallel then ... or one 6" nail

--
geoff

wrote:

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'

I made up some ammeters that read up to 30A and the shunts were pieces
of copper about 30mm long x 8 x 1, with terminal holes at each end. I'm
remembering this from 2001 so I might be a bit out with the dimensions.

Bill

wrote in message
...
As part of another project, would like to take some High Current DC
measurements.

I have a couple of multimeters ... but obviously not going to be any good
for around 80-100A

if you are to do the measurements more than once, and would like to keep a
log of them.... you might want to try something like :

http://www.giantshark.co.uk/power-13...-p-406644.html

it's a power meter for the radio controlled plane bods, they are using
brushless motors and lithium polymer batteries nowadays pulling/producing
upto 100 amps, (my plane's motor is a tiddler, pulling 28 amps peak, and
using a battery pack that weighs next to naff all... thank bod the days of
ni-cads and brushed can motors are over

Anyway, check the voltage range of the meter suits your application if you
decide to go for one of those meters, and the time they can handle the
current you want to pull,


If you really want a shunt, i bought one off ebay a while back, something
like 6 quid, was sold for motorhome/boat use, to measure the current being
drawn from the leisure batteries,

On Jan 1, 8:19*pm, wrote:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Made_Shunt_for...
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better *eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

These shunts are very low resistance and made by the manufacturers to
very exact values. So you have no chance of making your own and
expecting accurate amps readings.
You will have a job to even determine the value of the internal
resistance of your meter and hence find out what value the shunt
should be.

On Jan 1, 11:58*pm, John Williamson
wrote:
wrote:
As part of another project, would like to take some High Current DC measurements.

Depending how accurate they need to be, you can get a cheapish DC only
current meter with ranges of +- 100A and +-600 Amps from most decent
motor factors. Mine's made by Durite, Part No. 0-534-00.

They're sold for checking charging and starter currents without breaking
the circuit, you just put the wire into a channel on the back of the meter.

On 01/01/2013 20:19, wrote:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'

A 1R shunt will drop 100V at 100A and have to dissipate 10kW!
Even a 0.01R dropping 1V will need to handle 100W at 100A without
getting too warm (and so altering its own resistance). Forced air
ventilation on a chunky heatsink would seem to be the best bet.

You would be much better off buying a 10x high power 0.1R resistors and
a suitably large aluminium heatsink.

Are you absolutely sure you want to do this ? You don't sound at all
safe. 10 of these on a decent heat sink ought to just about hack it.

http://www.rapidonline.com/Electroni...sistor-62-8071

ISTR Zetatalk is a bunch of delusional nutters led by "Nancy" that
expected the world to end around 1996 when the "Radish" planet X
arrived. World ending cults go quiet for a while after it doesn't.

Yes.
Indeed it is the same bunch of delusional nutters see the home page:

http://www3.zetatalk.com/

Unless you want to be first in line for a Darwin Award you would do well
to ignore anything they say on that site!

Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

http://www.rapidonline.com/Electroni...esistors-79897

But nothing with the sort of power handling rating you would want.

--
Regards,
Martin Brown

harry wrote:
On Jan 1, 11:58 pm, John Williamson
wrote:
wrote:
As part of another project, would like to take some High Current DC measurements.
Depending how accurate they need to be, you can get a cheapish DC only
current meter with ranges of +- 100A and +-600 Amps from most decent
motor factors. Mine's made by Durite, Part No. 0-534-00.

They're sold for checking charging and starter currents without breaking
the circuit, you just put the wire into a channel on the back of the meter.

http://uk.picclick.com/2-X-VINTAGE-D...999596420.html

The e-bay auction's ended, but you get the idea...

I bought mine a few years ago, though. And no, it's not for sale, it's
too useful. :-)

--
Tciao for Now!

John.

The cheap high current ammeters have no coil but a bit of resistance
wire where the length changes due to the heating effect. Very
inaccurate and subject ambient temperature.
Some have a bimetal strip to work the needle.

This one has an internal magnet working against a spring. It works by
sensing the magnetic field round the wire. Think of the way a Hall
effect sensor is used, but without the electronic bit. It has no
electrical connection at all to the circuit under test and has no
internal electronics. Not terrifically accurate, but good enough for its
intended application.

--
Tciao for Now!

John.

On Jan 2, 11:48*am, The Natural Philosopher
wrote:
On 02/01/13 08:56, harry wrote:







On Jan 1, 8:19 pm, wrote:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ....http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Made_Shunt_for...
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better *eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

These shunts are very low resistance and made by the manufacturers to
very exact values. *So you have no chance of making your own and
expecting accurate amps readings.
You will have a job to even determine the value of the internal
resistance of your meter and hence find out what value the shunt
should be.

it is in fact not hard at all, and if its a moving coil meter it will be
in the spec as so many ohms per volt. If its digital you dont really
care. You are using it as a voltmeter anyway, measuring millivolts.

--
So if it's measuring milivolts, the internal resistance will be
miliohms. And the shunt will be smaller resistance still. Micro ohms.
So, a futile pursuit trying to make one.
Which is why your multimeter manufacturers don't even try.

On 02/01/2013 16:55, harry wrote:

So if it's measuring milivolts, the internal resistance will be
miliohms. And the shunt will be smaller resistance still. Micro ohms.
So, a futile pursuit trying to make one.

Not futile in the slightest.
As long as the shunt is capable of carrying the maximum drawn current
it's just a matter of trial and error with a know load.
Very simple actually. You could probably make one from a bit of
automotive jump-lead or car battery earth strap etc. Hammered flat 15mm
copper pipe (or several lengths in parallel) perhaps?

Presumably anything DIY measuring 100 amps isn't going to be matter of
extreme accuracy so a margin of error of a few % should be perfectly
acceptable and easy to achieve.

Pete

--
http://www.GymRatZ.co.uk - Fitness+Gym Equipment.
http://www.bodysolid-gym-equipment.co.uk
http://www.trade-price-supplements.co.uk
http://www.water-rower.co.uk

In article ,
www.GymRatZ.co.uk wrote:
On 02/01/2013 16:55, harry wrote:

So if it's measuring milivolts, the internal resistance will be
miliohms. And the shunt will be smaller resistance still. Micro ohms.
So, a futile pursuit trying to make one.

Not futile in the slightest.
As long as the shunt is capable of carrying the maximum drawn current
it's just a matter of trial and error with a know load.
Very simple actually. You could probably make one from a bit of
automotive jump-lead or car battery earth strap etc. Hammered flat 15mm
copper pipe (or several lengths in parallel) perhaps?

Presumably anything DIY measuring 100 amps isn't going to be matter of
extreme accuracy so a margin of error of a few % should be perfectly
acceptable and easy to achieve.

In practice I found it pretty difficult. Best thing to do is check Ebay to
see if a ready made one is available. You'd need to know the exact
parameters of the material you are using and make it by measuring size -
measuring the actual resistance at 0.00001 ohms or whatever isn't easy.

--
*What hair colour do they put on the driver's license of a bald man? *

Dave Plowman London SW
To e-mail, change noise into sound.

In article om,
newshound wrote:
Pico Technology used to do a "clamp" type ammeter which you connect to a
normal DVM, and which does DC as well as AC amps, but it looks as though
this has been discontinued. ISTR it was about £50. Occasionally very
handy for car diagnostics (I think it gives 1 mV per amp).

I have one of these, and it's not really accurate enough on DC. Or rather
not for my purposes. Although one which was would be handy.

--
*How many roads must a man travel down before he admits he is lost?

Dave Plowman London SW
To e-mail, change noise into sound.

On 02/01/2013 18:08, Dave Plowman (News) wrote:

In practice I found it pretty difficult. Best thing to do is check Ebay to
see if a ready made one is available. You'd need to know the exact
parameters of the material you are using and make it by measuring size -
measuring the actual resistance at 0.00001 ohms or whatever isn't easy.

Here's one I made earlier... (around 1988 for my Radio Amateur rig)
https://www.dropbox.com/s/2vt7igvz4g...2018.05.34.jpg
13.8v Home-Grown PSU

https://www.dropbox.com/s/k0dss3b7hr...2018.12.48.jpg
Subtly modified meter with "danger zone" added.

The heart of the beast
https://www.dropbox.com/s/w8tncjzumf...2018.08.19.jpg

And.... the shunt! (it's the doubled up wiggly blue wire)
https://www.dropbox.com/s/vjoyl9omua...2018.09.35.jpg

I think it only took 3 or 4 tweaks in length to get the meter calibrated
to the load being drawn.

Pete@

--
http://www.GymRatZ.co.uk - Fitness+Gym Equipment.
http://www.water-rower.co.uk

On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC measurements.
I have a couple of multimeters ... but obviously not going to be any good for around 80-100A
Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0
The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'
Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.


Stable R metals like constantan wire have too much R for this. Low resistance metals like copper change R as they heat up. A simple diy solution when making a shunt from something like copper is to dip it in water, then temp changes are far smaller. In principle you could probably also use a cup-like shape.


NT

On 01/01/2013 20:59, Martin Bonner wrote:


I suggest you need something more like 1 milli-ohm, which will produce
a voltage of 80 mV (perfectly within the range of digital volt meter),
and an energy output of 6.4W

http://uk.farnell.com/jsp/search/pro...=1292504&N=401
(for example) ?



Or even micro ohms
http://www.farnell.com/datasheets/887640.pdf

Also from Farnell/CPC
http://uk.farnell.com/vishay-dale/ws...5-5/dp/1858295


http://electronics.stackexchange.com...nce-has-3-line

--
mailto:news{at}admac(dot}myzen{dot}co{dot}uk

On 02/01/13 19:53, wrote:
On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC measurements.
I have a couple of multimeters ... but obviously not going to be any good for around 80-100A
Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0
The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'
Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.


Stable R metals like constantan wire have too much R for this.

Not if they are solid bars, which many ammeter shunts are.


Low resistance metals like copper change R as they heat up.

A simple diy solution when making a shunt from something like copper is
to dip it in water, then temp changes are far smaller.

In principle you could probably also use a cup-like shape.


NT



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On 01/01/2013 20:59, Martin Bonner wrote:
On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
As part of another project, would like to take some High Current DC measurements.



I have a couple of multimeters ... but obviously not going to be
any good for around 80-100A

Ouch! That's a serious current.

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use
a 1 ohm shunt, anybody made one of these ?

Ahem. Let's review those school physics lessons shall we?

Volts = Ohms x Amps

So 80A through 1 ohm will generate 80V. Further, the definition of
volts is:
Watts = Volts x Amp

So your shunt resistor is going to be dissipating
80 x 80 = 6400 W = 6.4 kW.

That's a serious amount of energy!

(Of course, what I expect will happen is that your shunt resistor
will have much higher resistance than the rest of the circuit,
and bring the current way down - or possibly kill it altogether.)

I suggest you need something more like 1 milli-ohm, which will produce
a voltage of 80 mV (perfectly within the range of digital volt meter),
and an energy output of 6.4W

http://uk.farnell.com/jsp/search/pro...=1292504&N=401
(for example) ?


Hadn't done the maths yet ... I used 1 ohm as that was the example in
the Doc I posted

On 02/01/2013 01:15, The Natural Philosopher wrote:


Problem with resistors that low is the leads themselves start to make a
difference.

This is car starter motor type territory..think of the battery leads to
THAT



Agree ...That was the problem I saw with a really low value shunt ...
leads are going to have appreciable resistance

On 02/01/2013 00:28, wrote:
On 1 Jan,
Martin Bonner wrote:



I'd just use a hall effect clamp on ammeter. CPC do a good one for up to
400A.



I don't have such a clamp meter, and impractical to buy one for just one
set of measurement.

On 01/01/2013 21:35, wrote:
wrote:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

A much more elegant (and still DIY) method is to use a Hall Effect
device, no direct connection to the circuit being measured at all. The
bigger devices (from 50 amps or so upwards) are just toroids through
which you feed the current carrying wire.

Available from CPC, Farnell and others. Devices such as HTFS200-P and
LTFS 50-NP should take you where you need.



Never used these ... are they passive and direct interfacing to a DVM,
or do you need driver circuitry ?

On 02/01/2013 12:11, newshound wrote:
On 02/01/2013 12:09, newshound wrote:
On 01/01/2013 20:19, wrote:
As part of another project, would like to take some High Current DC
measurements.

I have a couple of multimeters ... but obviously not going to be any
good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor
...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1
ohm shunt, anybody made one of these ?
The WEB ref
page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf


details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better eg Nichrome around
10.58" for 1 ohm.
Welcome to any better ideas.


Other posters have covered shunt design and issues in plenty of detail.

Pico Technology used to do a "clamp" type ammeter which you connect to a
normal DVM, and which does DC as well as AC amps, but it looks as though
this has been discontinued. ISTR it was about £50. Occasionally very
handy for car diagnostics (I think it gives 1 mV per amp).


Oh yes, here it is

http://www.picoauto.com/current-clamp.html

(Web site search facility is crap!)



Now one of those would be good ... but not at that price :-)

On Wednesday, January 2, 2013 9:15:09 PM UTC, The Natural Philosopher wrote:
On 02/01/13 19:53, wrote:

Stable R metals like constantan wire have too much R for this.

Not if they are solid bars, which many ammeter shunts are.

obviously, I was addressing the idea of using wire as a homemade shunt

Low resistance metals like copper change R as they heat up.
A simple diy solution when making a shunt from something like copper is
to dip it in water, then temp changes are far smaller.
In principle you could probably also use a cup-like shape.

On 02/01/2013 21:50, Rick Hughes wrote:

Agree ...That was the problem I saw with a really low value shunt ...
leads are going to have appreciable resistance


As long as the connecting leads can handle the current and are "low"
resistance, the resistance of the leads makes no difference to the
measurement.

The voltage drop is only measured across a fixed known resistor in
series with the connecting leads. The voltage drop in the connecting
leads carrying, say, 100Amps is not being measured.

Cheap and commercially available low value shunt resistors (milli or
micro Ohms) come with 4 terminals. Two terminals will handle the 100Amps
and the other two connect to a high impedance volt meter. The current in
the connecting leads to the voltmeter is vanishly insignificant.

http://en.wikipedia.org/wiki/Four-terminal_sensing

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On Tuesday, January 1, 2013 8:19:55 PM UTC, wrote:
The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?

You don't "make" a shunt, you find or acquire one, then you calibrate it, according to whatever resistance it turned out to have. Otherwise it's a right sod of a job to adjust one.

If you want one calibrated to give easy round numbers as an output, just use a potentiometer across its output. If your display meter has a modern high impedance, this is easy.

Andy Dingley wrote
wrote

The issue will be obtaining a suitable shunt ... assuming
I use a 1 ohm shunt, anybody made one of these ?

You don't "make" a shunt,

You can do, most obviously from whatever suitable wire is handy.

you find or acquire one, then you calibrate it, according
to whatever resistance it turned out to have.

Otherwise it's a right sod of a job to adjust one.

Not if you make one out of suitable wire,
you just vary the length of wire used.

If you want one calibrated to give easy round
numbers as an output, just use a potentiometer
across its output. If your display meter has a
modern high impedance, this is easy.

On Jan 2, 6:01*pm, "www.GymRatZ.co.uk"
wrote:
On 02/01/2013 16:55, harry wrote:

So if it's measuring milivolts, the internal resistance will be
miliohms. And the shunt will be smaller resistance still. Micro ohms.
So, a futile pursuit trying to make one.

Not futile in the slightest.
As long as the shunt is capable of carrying the maximum drawn current
it's just a matter of trial and error with a know load.
Very simple actually. You could probably make one from a bit of
automotive jump-lead or car battery earth strap etc. Hammered flat 15mm
copper pipe (or several lengths in parallel) perhaps?

Presumably anything DIY measuring 100 amps isn't going to be matter of
extreme accuracy so a margin of error of a few % should be perfectly
acceptable and easy to achieve.



So how are you going to calibrate it?

On Jan 2, 6:47*pm, "www.GymRatZ.co.uk"
wrote:
On 02/01/2013 18:08, Dave Plowman (News) wrote:

In practice I found it pretty difficult. Best thing to do is check Ebay to
see if a ready made one is available. You'd need to know the exact
parameters of the material you are using and make it by measuring size -
measuring the actual resistance at 0.00001 ohms or whatever isn't easy.

Here's one I made earlier... (around 1988 for my Radio Amateur rig)https://www.dropbox.com/s/2vt7igvz4g...2018.05.34.jpg
13.8v Home-Grown PSU

https://www.dropbox.com/s/k0dss3b7hr...2018.12.48.jpg
Subtly modified meter with "danger zone" added.

The heart of the beasthttps://www.dropbox.com/s/w8tncjzumfzdnih/2013-01-02%2018.08.19.jpg

And.... the shunt! (it's the doubled up wiggly blue wire)https://www.dropbox.com/s/vjoyl9omua...2018.09.35.jpg

I think it only took 3 or 4 tweaks in length to get the meter calibrated
to the load being drawn.

So how do you know it is accurate?

In article ,
alan wrote:
As long as the connecting leads can handle the current and are "low"
resistance, the resistance of the leads makes no difference to the
measurement.

Swapping leads on my various DVMs - using what appears to be decent
quality leads - will give different resistance readings for very low
values. Try it.

--


Dave Plowman London SW
To e-mail, change noise into sound.

On Jan 3, 11:05*am, "Dave Plowman (News)"
wrote:
In article ,
* *alan wrote:

As long as the connecting leads can handle the current and are "low"
resistance, the resistance of the leads makes no difference to the
measurement.

Swapping leads on my various DVMs - using what appears to be decent
quality leads - will give different resistance readings for very low
values. Try it.

The connecting leads referred to are clearly those to the shunt, hence
the reference to the current rating. They make no difference to the
reading across the shunt for a given set of test leads and DVM.

MBQ

On 03/01/2013 09:34, harry wrote:

I think it only took 3 or 4 tweaks in length to get the meter calibrated
to the load being drawn.

So how do you know it is accurate?

You'd need to define the degree of accuracy required.

For my own needs calibrating to a know fixed load was good enough.
+ or - 10% would have been fine so more precise "tuning" wasn't needed.

Running the PSU on the fixed load for +60 minutes soak test (to check
overall stability of unit and heat dissipation of transistors /
auto-cooling fan etc saw no deviation in meter reading which pretty much
ruled out inaccuracies from varying shunt temperature which presumably
remained pretty constant.

Everything is relative to exactly what level of accuracy the OP actually
needs, which I don't believe has ever been stated.

Cheers
Pete@

--
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http://www.bodysolid-gym-equipment.co.uk
http://www.trade-price-supplements.co.uk
http://www.water-rower.co.uk

Rick Hughes wrote:
On 01/01/2013 21:35, wrote:
wrote:
As part of another project, would like to take some High Current DC measurements.

I have a couple of multimeters ... but obviously not going to be any good for around 80-100A

Now going back to school physics lessons I could use a Shunt resistor ...
http://www.societyofrobots.com/robot...?topic=13900.0

The issue will be obtaining a suitable shunt ... assuming I use a 1 ohm shunt, anybody made one of these ?
The WEB ref page:http://www3.zetatalk.com/docs/Electr...Meter_2007.pdf
details using 12guage copper wire .. based on 1.619 ohm per 1000'

Although maybe a resistance wire may be better eg Nichrome around 10.58" for 1 ohm.
Welcome to any better ideas.

A much more elegant (and still DIY) method is to use a Hall Effect
device, no direct connection to the circuit being measured at all. The
bigger devices (from 50 amps or so upwards) are just toroids through
which you feed the current carrying wire.

Available from CPC, Farnell and others. Devices such as HTFS200-P and
LTFS 50-NP should take you where you need.


Never used these ... are they passive and direct interfacing to a DVM,
or do you need driver circuitry ?

They vary a little in their requirements but the simplest just need a
5 volt supply and then you can measure the output with a DVM. Take a
look at the data sheets at Farnell.

--
Chris Green

In article
,
Man at B&Q wrote:
On Jan 3, 11:05 am, "Dave Plowman (News)"
wrote:
In article ,
alan wrote:

As long as the connecting leads can handle the current and are "low"
resistance, the resistance of the leads makes no difference to the
measurement.

Swapping leads on my various DVMs - using what appears to be decent
quality leads - will give different resistance readings for very low
values. Try it.

The connecting leads referred to are clearly those to the shunt, hence
the reference to the current rating. They make no difference to the
reading across the shunt for a given set of test leads and DVM.

Well, yes. But my point is in practice they will make a difference.

--
*It's a thankless job, but I've got a lot of Karma to burn off

Dave Plowman London SW
To e-mail, change noise into sound.

On 03/01/2013 11:05, Dave Plowman (News) wrote:
In article ,
alan wrote:
As long as the connecting leads can handle the current and are "low"
resistance, the resistance of the leads makes no difference to the
measurement.

Swapping leads on my various DVMs - using what appears to be decent
quality leads - will give different resistance readings for very low
values. Try it.


It doesn't matter if the measuring leads are 0.01ohms or 1 ohm when
measuring the _Voltage_ across a shunt resistor with a DVM (or
voltmeter) with a high impedance input. There may be 100s of Amps
flowing through the shunt resistor but microAmps in the measuring leads.



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