To shunt or not to shunt

[JimMann]

Hello

I've been redoing my boat electrics and got a bit confused when it got to my cva amp meter as Ive been told I need a shunt but there was no shunt before?

Is the bridged connection a shunt?

Thanks in advance

[HankOnthewater]

Not sure what you mean with your question, Did you have the Amp meter before? Then you must have a shunt.
Here is pic (borrowed from the net).
Generally it is close to the battery, and between the negative post and the negative busbar. It has 2 thick wires, and then 2 thin wires that is used to measure the voltage drop over the shunt, often 50 or 75 mVolt, at full capacity of the shunt.

[GordMay]

That depends upon the ammeter.
Some DC ammeters have built-in shunts, some meters have external shunts, but, they all have shunts.

The basic mechanism for a ammeter is a voltmeter, with a [shunt] resistor, in parallel with the volt meter, producing a calibrated voltage, proportional to the current flowing.

[JimMann]

https://ibb.co/F4rNYNC]

This is a pic of the unit

I realize it needs one, it was working before without one as far I know, hence me wondering if the bridge is the shunt.

just making sure I didn't miss something

Thanks

[Wotname]

A fair chance the ammeter shown in the image has an internal shunt. As GordMay rightly says, all ammeters have a shunt. Your one has (most likely) the shunt inside the meter housing.

What is the bridge connection you mention, do you have picture of it?

[JimMann]

Thanks for that

Does this wiring diagram look anywhere near correct?

https://ibb.co/5hC7tXS

[JBP]

That diagram shows the ammeter measuring how much current the alternator is producing, not how much you are using nor other sources, which is correct for an engine ammeter.

While it used to be true that all ammeters have shunts, the newer Hall effect ammeters don't. They have a coil instead of the shunt. Same purpose, but they look different.

[JimMann]

I'm only wanting to see how many amps the alternator is producing as I have another system for monitoring everything else

Thanks

[Wotname]

Originally Posted by JimMann

Thanks for that

Does this wiring diagram look anywhere near correct?

https://ibb.co/5hC7tXS

It is near correct.

The ignition switch wiring is shown (presumably) incorrectly. The way it is drawn, there is no OFF position. I suspect there is an OFF position in practice.

The rest looks OK.

[JimMann]

Originally Posted by Wotname

It is near correct.

The ignition switch wiring is shown (presumably) incorrectly. The way it is drawn, there is no OFF position. I suspect there is an OFF position in practice.

The rest looks OK.

The off is the unturned key position, wasn't sure what it called 😊

[Wotname]

Originally Posted by JimMann

The off is the unturned key position, wasn't sure what it called 😊

I may have misunderstood the drawing - thinking there is a key start position. If so, my apologies.

Perhaps you have a seperate start switch or haven't shown the START position on the Ignition switch.

[GordMay]

Originally Posted by JBP

... While it used to be true that all ammeters have shunts, the newer Hall effect ammeters don't. They have a coil instead of the shunt. Same purpose, but they look different.

Not exactly - Hall effect ammeters [often clamp-on, not panel mount], don't have a coil, they have a magnetically permeable core, with an air gap, in which the Hall effect sensor sits

The resistive shunt is a calibrated resistor, placed in a current path, that produces a voltage drop, proportional to the current flow according to: V = IR.

Hall effect and induction coils are both non-contact technologies, based on the principle that, for a given current flow, a proportional magnetic field is produced around the current-carrying conductor. Both technologies measure this magnetic field, but with different sensing methods.

The Hall effect sensor has a magnetically permeable core, whereas the inductive sensor has a wire-wound core.

The Hall effect sensor consists of three basic components: the core, the Hall effect device, and signal conditioning circuitry. The current conductor passes through a magnetically permeable core, that concentrates the conductor's magnetic field. The Hall effect device is mounted in a small slit [air gap] in the core, at a right angle to the concentrated magnetic field. A constant current in one plane excites it. When the energized Hall device is exposed to a magnetic field from the core, it produces a potential difference (voltage) that can be measured. The output of the Hall sensor is a voltage, proportional to the core magnetic field, which is also proportional to the input current.
The core’s air gap length directly affects the maximum current that can be measured. In addition to the gap length, there are other factors, such as the core material, core dimensions, and core geometry, that determine the efficiency of a magnetic core.
Depending on the design, Hall effect transducers can measure frequencies from DC to several kilohertz. Because they tend to be more expensive than shunts, or inductive transducers, their use is generally limited to measuring DC power.

The inductive sensor consists of a wire-wound core, and a signal conditioner. The current conductor passes through a magnetically permeable core, that magnifies the conductor's magnetic field. AC current constantly changes potential, from positive to negative, and back again, generally at the rate of 50 Hz or 60 Hz. The expanding and collapsing magnetic field induces current in the windings. This is the principle that governs all transformers.
The secondary current is converted to a voltage and conditioned to output process-level signals such as 4-20mA. Inductive sensors are designed to measure AC power and typically operate between 20 Hz and 100 Hz, although some units will work in the kilohertz range.

I hope I didn't mangle that too badly - I wrote my thesis ["Meters & Measuring Instruments"] about 45 years ago.
BTW: I didn't cover Hall effect metering.

Maybe these guys will do better:


“Six ways to sense current and how to decide which to use” ~ Texas Instruments
➥ https://e2e.ti.com/blogs_/archives/b...e-which-to-use

“Selecting the Most Effective Current Sensing Technology”
➥ http://www.power-mag.com/pdf/feature...Technology.pdf

[JimMann]

Originally Posted by Wotname

I may have misunderstood the drawing - thinking there is a key start position. If so, my apologies.

Perhaps you have a seperate start switch or haven't shown the START position on the Ignition switch.

The issue will be my discription.. 😂

Off is key unturned, on is key turned supplying power to instruments and ignition
Is engine start

[oleman]

Originally Posted by GordMay

That depends upon the ammeter.
Some DC ammeters have built-in shunts, some meters have external shunts, but, they all have shunts.

The basic mechanism for a ammeter is a voltmeter, with a [shunt] resistor, in parallel with the volt meter, producing a calibrated voltage, proportional to the current flowing.

Many years ago the fancy pants engineers invented a device that became known as a HALL EFFECT SENSOR It senses the magnetic field that current running through a conductor produces. It is the basis of the clamp on ammeter probe used on an oscilloscope and was always primarily used in AC circuits BUT there are now DC probes that also use that sensor. Being an old tech I personally don't trust them especially in above a 100A range for DC. I have used them in AC panel meter circuits and they track very closely with the analog/resistive shunt meters.

[Adelie]

Originally Posted by oleman

Many years ago the fancy pants engineers invented a device that became known as a HALL EFFECT SENSOR It senses the magnetic field that current running through a conductor produces. It is the basis of the clamp on ammeter probe used on an oscilloscope and was always primarily used in AC circuits BUT there are now DC probes that also use that sensor. Being an old tech I personally don't trust them especially in above a 100A range for DC. I have used them in AC panel meter circuits and they track very closely with the analog/resistive shunt meters.

I’m an engineer. I want some of these fancy pants.
Are they engineering specific fancy pants or just run of the mill fancy pants?