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Hey EVeryone,

Somebody gave me a shunt marked "50mv".

My understanding of an ammeter is that you run your full current through the shunt, put your volt meter/multimeter on the little side parts, put it to measure millivolts, and it tells you how many amps you are pulling.

Since this shunt is marked "50mv" does that mean I need to have the multimeter set to measure millivolts, and then DOUBLE whatever the display says to get the actual number of amps?

(Yes I know I can go out and buy an actual amp meter, but I am trying to keep costs as low as possible for now, and maybe buy actual parts later, once I figure everything out.)

Please advise, -Thanks

-Ben
 

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Somebody gave me a shunt marked "50mv".
My understanding of an ammeter is that you run your full current through the shunt, put your volt meter/multimeter on the little side parts, put it to measure millivolts, and it tells you how many amps you are pulling.
there are two basic ways to measure amps; with a shunt, or a 'hall effect' sensor.

shunts are calibrated resistors essentially... when current runs thru, there will be a proportional voltage difference across the shunt. your shunt will have another number on there.... like 100-50, or perhaps 500-50, telling you that the full scale current that should generate the 50mv difference.

analog ammeters are only about $60 brand new, and sometimes you can find used ones in the classifieds. Most of the high-amp ones like 0-500 amps accept 0-50mV input. Digital displays might be even cheaper, but I find them hard to read while driving....
 

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Yes you set the multimeter to millivolts (or the lowest voltage range if no millivolt setting) then use ohms law to figure out how to "read" it.
First you take the current rating at 50mv (this is usually marked on it) IE 500A 50mv shunt.
R=V/I R=50mv/500A R=0.0001ohms
Now that you know the resistance of the shunt flip the equation around and you get I=V/R, so at 25mv for example you would have I=25mv/0.1mohm I=250A

To sum it all up, 1mv = 10A or 0.1mv = 1A

It gets a little harder to read it it was say a 250A 50mv shunt, then you have:
R=50mv/250A R=0.0002
In that case 1mv = 5A or 0.1mv = 0.5A (1A = 0.2mv, 100A = 20.0mv etc.)
 

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The "short and skinny is" a 50mv shunt is used with a 100mA meter to indicate 500Amps full scale.
5x100 = 500 (10mV is a 100-Amp full scale with a 100mA Ammeter)
Dave
 

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The shunt indicates it is designed to read 50mv at some number of amps, but I don't know how many amps. If it is a 500 amp shunt then it will read 50mv at 500 amps and so every 1mv is 10 amps. If it was a 50 amp shunt then every millivolt would be and amp of current.
 
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