High current shunt question

[recumpence]

Hey Guys,

I just switched from a 200 amp 50mohm shunt to a 500 amp 75mohm shunt and I need to know what to tell the CA (what the ohm rating is). With the 200 amp shunt, the CA was set as a resistance of .25. I have no idea what to program the CA for with my bigger shunt.

I am sure it is easy to calculate. But, I do not know how.

How do I calculate this?

Matt

 

[teklektik]

...a 200 amp 50mohm shunt to a 500 amp 75mohm shunt and I need to know what to tell the CA (what the ohm rating is).
With the 200 amp shunt, the CA was set as a resistance of .25

Hey Matt-
I think you have your shunt units a bit mixed which is causing the confusion (mV not mOhm).

A shunt is specified in terms of the voltage it develops at the rated amps.
A little Ohm's laws gets the resistance (Voltage = Current x Resistance or Resistance = Voltage/Current)

So for your old shunt (50mV @ 200A) we get:

• .050V/200A = .00025Ohm = 0.25mOhm

For your new shunt (75mV @ 500A) we get:

• .075V / 500A = .00015Ohm = 0.15mOhm

The minimum CA shunt resistance on Hi Range is 0.0752mOhm so you are good to go.