Test your skills boys

[boscoe99]

Rodnut has been critical of a Yamaha article that he read in a magazine. Anyone care to read the following and offer any comments? Good, bad, or ugly.

[99yam40]

I have had a few cold ones already while BBQing 25 briskects and some sausage and chickens at the church today, and it has been years since I worked on large DC circuits.
We used devices called halimar units(I believe) that read 0 to 80K amps DC on large buss bars from very large recitifires feeding cell lines.
Any where from 15kv inputs to 138 kv fed through transformers that split out the phases to more than the 3 phase inputs and regulated the voltages ,then rectified the a/c to DC either through high current fuses and diodes or thyristers that con*****ed the voltage and current.

these Hallimar units around the large buss bars sent out a Dc current to nulify the magnetic field around the buss bar it was seeing, and that cuurrent was sent through shunts that in turn fed instruments or meters that took that input and related that a certain amount of DC current flowing through the Buss bar
Those shunts were not wire but small busses or say strips on copper/brass that were calibrated(ground downto proper resistance) to make the proper resistance needed,
So the amount of DC current through it relates to so much MV drop across the shunt

Depending on the unit the MV out represented some amount of DC current.
Not necessarily 1 amp to 1 MV.

but I may be very confused right now

[zenoahphobic]

Rodnut has been critical of a Yamaha article that he read in a magazine. Anyone care to read the following and offer any comments? Good, bad, or ugly.

My brain is familiar with Ohm's Law etc. My brain also hurts when I think too hard.

Volts don't get consumed; but I suspect the figures given and the multimeter settings will be unhelpful in a large current situation. At first glance all the volts (only got 12 of them) will be "consumed" across the shunt at any meaningful current. At any rate, the shunt will share significant voltage (power) making the measurement wildly inaccurate.

[zenoahphobic]

To make a shunt to suit your particular multimeter, just measure with another meter the resistance of the meter shunt (don't just measure across red and black lead, as you might wreck the electronics. Open it up and disconnect the metal strip and then measure it.)

If you have a 10amp range, and you want to read say 100Amp you need to parallel up the resistance to one tenth the resistance. But:

1. the extra shunts need to be heavy duty to carry 100Amps (not a tiny low ohm resister), and
2. you will need heavy duty leads, and connections otherwise their resistance will make the measurement false, and if the current is routed thru your meter, it will fry your meter.
3. you will need to alter (recalculate) your meter scale.

[bajakeith]

Lol..

Ya ..Right,,, millivolts...GET A GRIP !!

[rodbolt17]

amazingly.
the shunt article was correct.
two others are wrong.

[boscoe99]

I have had a few cold ones already while BBQing 25 briskects

but I may be very confused right now

You are confused. Brisket is beef. BBQ is not beef. BBQ is pork.

With a mustard based vinegar sauce. Not that girlyman catsup and sugar based shit that Kalifornians put on ribs in an oven and call it BBQ.

[boscoe99]

My brain is familiar with Ohm's Law etc. My brain also hurts when I think too hard.

Volts don't get consumed; but I suspect the figures given and the multimeter settings will be unhelpful in a large current situation. At first glance all the volts (only got 12 of them) will be "consumed" across the shunt at any meaningful current. At any rate, the shunt will share significant voltage (power) making the measurement wildly inaccurate.

That was the first thing that jumped out at me. I have never heard about volts getting consumed. Voltage drop yes, voltage consumption no.

The other thing that I noticed, while picking fly shit out of the pepper, was the sentence "The shunt must be placed in series with the circuit being tested." A shunt by one definition is to parallel. Quite different from series. The actual meter when measuring current is not in series but is in parallel to the current flow. Actually, it is a volt meter that is being used to measure voltage drop with is converted to current flow.

[boscoe99]

amazingly.
the shunt article was correct.
two others are wrong.

I will get to those in due course.

[ausnoelm]

I do believe that to measure "amps" (current) the measuring device is in series, but to measure ( say) the 100amps listed, you would need battery cables, or the meter leads will be frizzled, so, what the artical is explaining is how to measure high amps without using the device in series, by measuring the known voltage drop over a load in this case called a "shunt" and thereby eliminating the need for very heavy cables and equipment.

[zenoahphobic]

Yes the word shunt means across, but "current" is tested in series, or has to be part of the circuit being tested.

From a pure physics point of view there really isn't such a thing as current. There is electromotive force(EMF) simplistically, that creates some sort of energy shift.

Historically the only way we could detect or define what we refer to as current, is by voltage measurement and then determine (calculate) current. So our current is calculated by introducing some resistance in the circuit being tested (in series) and measuring the voltage drop across that resistance.

For those people that might take issue with me saying there is no such thing as current think of this example:

Your power is AC at 60 Hertz. That is, electrons are pushed some distance one way and then back again 60 times every second. (how long does a conductor have to be for the first electron to reach the other end before it is forced to go back again?)

Now imagine using gigahertz, which is commonly used today. Not really knowing how these things translate to in some countries , to me that is a million times faster than 60; so how short does this conductor have to be now to allow that electron to reach the end??

[tmann45]

You are confused. Brisket is beef. BBQ is not beef. BBQ is pork.

With a mustard based vinegar sauce. Not that girlyman catsup and sugar based shit that Kalifornians put on ribs in an oven and call it BBQ.

You must have missed 99yam40's location, "middle Texas coast", I'd call it smoking.

[tmann45]

The other thing that I noticed, while picking fly shit out of the pepper, was the sentence "The shunt must be placed in series with the circuit being tested." A shunt by one definition is to parallel. Quite different from series. The actual meter when measuring current is not in series but is in parallel to the current flow. Actually, it is a volt meter that is being used to measure voltage drop with is converted to current flow.

The shunt is in series, the DVM is parallel as you said. The twisted pair leads in the diagram go to the milli-volt meter. I guess the translation of the Yamaha stuff makes it more difficult to comprehend what they are describing.

Diagram is from the Cruising Equipment Co E-Meter Owner's Manual, innovative at the time but now long gone, but here is the manual:
http://www.evalbum.com/tech/e-mtrpdf.pdf

[bajakeith]

milliV VS Amps

Big story there, I've had a FLUKE 88A for 25+ years and make my living with it.. if your checking Amps in millivolts,,, somethings WRONG !! most DVM's are fused at 10 Amps... Carry On............

[rodbolt17]

baha
the shunt works
awkward but it works.
and yes you use the millivolt scale.

but the clamp on inductive amp meter works better and requires no battery terminal access.