How Many Ammeters Can Be Connected to One Shunt?

Er, could two shunts be used instead?

The two ammeters must be wired in series, but clearly the length of cable run will have an effect on the readings.

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Please note: A shunt driven ammeter includes its shunt and calibrated leads and is a matched set for accuracy purposes, so any changes to this setup will decrease the accuracy of the readout. Is this shunt the one furnished by the charger maker or did you buy a good (accurate) one as are made by Simpson or Crompton, for example? Are the meters "decent" ones ($50 to $90 range) or the "cheapies" furnished in the charger? Do you want this for accurate metering of Amps or for just a general idea of what the charger output is doing? You should parallel identical shunt-driven voltmeters (usually 25 to 125 mV range, depending upon manufacturer) without too much loss of accuracy, but as pointed out above, one shunt for its matched meter and calibrated leads, with shunts connected in series, is better.

If you measure the voltage across the shunt it can easily be converted to amperes by I=E/R or amperes = voltage on the meters divided by the resistance of the shunt, using 2 voltmeters will not affect the accuracy of the reading they must be connected in parallel.

In parallel, but expect that there will be errors. This is not good instrumentation but if you have no choice, the mechanical meters and the lead resistances should be matched as best you can and terminated at the shunt. Expect an under-registration meter error.

Note: Using electronic (digital type) meters would be preferred. They are such high impedance that the lead resistance would have little effect.

Originally, shunts operated mechanical DeArsonaval movement meters that were 250 ohms per volt (millivolt meters).

As I have stated, Not a very good application....

Ps. The guy that said in series either dose not understand meters and shunts or isn't too bright in his thinking.

These quick to speak people that have all this knowledge (probably from their many years of experience in power engineering) are extremely frustrating to us that only have 20 to 30 years.

Good Luck.

A shunt is a known resistance put into the current path. You measure the voltage across the shunt to determine the current. The shunt needs to have a low enough resistance that it doesn't significantly change the current in the circuit.

How many voltmeters you can use across (in parallel) the same shunt would depend on the input impedance of the meters and the allowable error. For most applications, using a normal high impedance digital meter, and without any great need for accuracy, you could put in as many meters as you wanted.

Years of experience ~0, Years of knowledge of ohms law ~ 30 Happy cooking Jeff

Correctly spoken if you measure current with a shunt then the meter (or meters) are primary no amperemeters but (milli)voltmeters with an amp-scale and so have to be connected in parallel.

The higher the impedance of your meters is (perhaps by using an impedance converter located nearby the shunts and powered by the battery voltage with few milliamps) the lower your errors determined by leads will be.
Regards Uwe

Correctly spoken if you measure current with an external shunt then the meter (or meters) are primary no amperemeters but (milli)voltmeters with an amp-scale and so have to be connected in parallel.

The higher the impedance of your meters is (perhaps by using an impedance converter located nearby the shunts and powered by the battery voltage with few milliamps) the lower your errors determined by leads will be.

If your ampmeter has an internal shunt it is of course a real ampmeter and two of those have always to be connected in series, of course (regarding that you have twice the shunt voltage missing at the load voltage of your battery).

Shunts of this measurement range have par example 60mV full scale so your voltage drop between loading source and battery is max. 120mV.
Regards Uwe

The 2 remote reading ammeters should be connected in parallel across the shunt. They really are reading the voltage developed across the shunt as a result of the current through it. Use meters with the lowest burden you can get.

A amperemeter with a shunt is actually a millivoltmeter,with a full scale sensitivity of 200mV if it's a digital circuit, or if its a galvanometer,most probably 20 to 50mV full scale,with a resistance of a few hundred ohms.
The resistance of a 100 Ampere shunt with a drop-out of 50mV is 0,5milliohms.

If you use 100 ohms galvanometers,even 100 meters in parallel would introduce an error of only 0,05%,which is below the true acciracy of such meters(1,3 to 3%).

If you put in serie two meters,they should be of equal resistance,or scaled according to their resistance,but this is of no practical utility.
You can measure using the Hall effect:using a As-Ga Hall sensor KSY13 or 14 made by infineon,with an iron gap of 1,8mm,you get about 70mV Hall voltage at 100 Amperes,and could measure as easily tens of thousands of amperes.
You can even induce Hall effect into your own wire using a strong magnet.

At the start I would like to describe briefly how Ammeters & Shunts work.

Ammeter itself is only a mAmeter. Its Spec normally indicated as:

FSD in mA/ MicroA [& its Internal Resistance in Ohms.]

or

in mV [& its Internal Resistance in Ohms actuually in m-Ohms .]

So a Shunt which matches these Specs can only be connected in parallel with it.

The Shunt is a Hi-Power very low resistor, having sufficiently wide strips connected in parallel to attain very low resistance with a good Temperature coefficient [actually does not heat @ full load to aviod variations in resistance].

Has two Main Terminals for power connection & two small terminals quite inside the main connections.

This is basically to aviod the burning of meter in case Shunt is disconnected

or any of the connection is loose. Had the meter connected at pionts of main-connections there is a such chance.

In single-strip shunts one of meter-connetions is just inside of main connection & the other is searched for coarse-calibration while the slots are cut in strip for fine calibration.

In multy-strips shunt the meter connections are on main connection post but well inside.

slots are cut in strip for calibration.

---------------------------

Now I come to the question:

1. More than one Ammeters with internal Shunts is not recommended to be connected in series of Mains cable. Actually the Ammeter itself is not recommended to be connected as such. Instead the Shunt is connected in series of main-circuit & Ammeter [Which is actually a mA meter] is connected in Panel thru Leads having neglibible drop at Ammeter's FSD [in mA / MicroA].

2. To connect more than one Ammeter All the shunts of individual Ammeters should be connected in series & their leads brought to panels.

Mind that Shunts are designed for as low as 20 to 200mV drop across them. so connecting of more shunts is no problem & niether accuracy is effected if the Main supply drop is not a problem [ie at very low supply voltage, say less than 12V or so].

Thanks everyone. I can see now that meters and shunts should be bought as a calibrated matched pair for ultimate accuracy.

But if purchased separately, it looks as though I need to make sure of the precise value of the design resistance and volt drop of the shunt for the load, and then match this to the design voltage of the meter to obtain a true scale reading of amps.

The second identical meter (connected in parallel) will upset the readings by a fractional amount - but to my mind that does not matter much.

A little bit of ohms law will show that the shunt resistance for a 100mv meter will be 0.001 ohms. The resistance of the meter will be (say) 10k. Thus when the second meter is connected in parallel with the shunt to a 100 amp load - which is the same as connecting another resistance in parallel - the overall resistance of the shunt will reduce marginally to cause the first meter to read 99.9999 amps - which in my case is nothing to worry about.

I doubt if original 'resistance' of the shunt would have been that accurate anyway.

That's it for the moment. Thanks