Please excuse my awful math/s. Can anyone please help me calculate/convert the mV reading from a 50A shunt? For example if i was reading 1.5mv how do i convert please. Please keep it simple as math is (obviously) not my strong point!
Thank you
Slightly embarrassed at the state of my maths but thank you all for comments. However going with (50/75) x the Amp reading isnt agreeing with my two ammeters!
The ammeters are reading 2.06 and 2.12, and the DMM is reading 12.0mV – so – (50/75)x12 =8 oops. Any ideas folks?
It is a series circuit 12v battery, fuse holder with cheap ammeter plugged here, switch, bulb, earthed through chinese shunt with second ammeter reading here along with DMM. Appreciate shunt and cheap ammeters may not be 100% but im not getting close even. How might ammeters not be reading total circuit current pls?.
Schematic (description below)
The two ovals at (a) represent a fuse holder (fuse removed). into this is inserted an ammeter (c) which accepts the removed fuse (b).
(d)represents the shunt with the other ammeter attached and this is where the voltmeter reading are taken off either side of shunt.
Excuse poor schematic drawing/symbols etc.
simulate this circuit – Schematic created using CircuitLab
Schematic added by Transistor. OP to edit / correct.
Update – PROBLEM SOLVED Brilliant – I was taking the mV reading from the wrong place, on the large, outer terminals when I should have been reading from the the smaller terminals. Here I get 3.5mv which then gives me a close amperage figure (50/75*3.5=2.4).
Lesson learnt – thanks to all – admin please feel free to edit this to make it more useful to others.
Best Answer
The calculation of measured A = Vm * 50A/75mV is correct (Vm measured in mV).
You need to connect the meter directly to the shunt and you need to use the "inner" terminals on the shunt (usually they are smaller screws) to go directly to the meter (and nowhere else) and the outer terminals on the shunt carry the high current.
It should look like this:
simulate this circuit – Schematic created using CircuitLab
The resistors marked "?" represents wiring resistance and internal resistance of the shunt.
If you were to (say) connect the meter to ground rather than directly to the shunt then the resistance of the connections would add to the shunt resistance and you would get a significant error most likely.