Current Sensing of 100 + amps

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
Hey guys,

What is the most effective way to sense amperages over 100 amps? Using a milliohm resistor for shunt based sensing would still cause 10watts of heat. Is there a better way to do this than a current sense/shunt resistor?

-Khan
 

recklessrog

Joined May 23, 2013
985
If you want a reasonably accurate indication, depending on the gauge of the conductors you are using, at a hundred amps there will be some resistance in the wires. you could use a volt meter between two points and use ohms law to work out the current.
For ac use a clamp meter.
 

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
If you want a reasonably accurate indication, depending on the gauge of the conductors you are using, at a hundred amps there will be some resistance in the wires. you could use a volt meter between two points and use ohms law to work out the current.
True, but in my circuit, with such amperages, I am trying to keep the conductors as short and large as possible so the voltage based on resistance maybe too low. I am then trying to read the voltage to an arduino.
 

recklessrog

Joined May 23, 2013
985
True, but in my circuit, with such amperages, I am trying to keep the conductors as short and large as possible so the voltage based on resistance maybe too low. I am then trying to read the voltage to an arduino.
well unless you are using super conductors or extremely short leads, even a cheap digital multimeter will show some millivolts. remember I did say reasonably accurate, as temperature changes either ambient or due to current flow will affect the accuracy.
You can become disproportionately over complicated very quickly if you want high resolution and accuracy, Make it fit for purpose.
 

Thread Starter

bkhan10000

Joined Jan 18, 2017
31
well unless you are using super conductors or extremely short leads, even a cheap digital multimeter will show some millivolts. remember I did say reasonably accurate, as temperature changes either ambient or due to current flow will affect the accuracy.
You can become disproportionately over complicated very quickly if you want high resolution and accuracy, Make it fit for purpose.
My circuit can't use a dmm indefinitely. It is to be left alone to sense via microcontroller. In order to keep heat production down, the total resistance of the circuit is low. I realize that there will be voltages to be sensed in the millivolts range. How do I sense this with an arduino?
 

recklessrog

Joined May 23, 2013
985
I'm not the most qualified to ask about Arduino, but they have analogue inputs so I guess even if you have to amplify the millivolts first, the Arduino should be able to interpret the changes and a suitable program could be written to perform whatever function you require.
I am not sure if it helps, but there is a system called cayenne which apparently has some quick programs that can do a whole lot more than the standard libraries.

Probably someone else on here could advise you better than me in that respect.
 

crutschow

Joined Mar 14, 2008
34,201
If you want to avoid the expense of a hall-effect device you could use a low-offset op amp, such as the common 0P07 to amplify a few mV of signal to a several volt level, assuming you can monitor the current in the ground leg of the circuit.
A resistance value of 0.1 mΩ gives 10 mV of drop at 100A and dissipates 1W.
That's about 10 inches of #1 AWG copper wire.
What size wire will you use to carry this current?
 
Last edited:

ian field

Joined Oct 27, 2012
6,536
Then you could use a Hall-effect device current sensor, which requires no direct contact with the wire.
There are even made for the job Hall sensors, basically a heavy bussbar set in regular encapsulation and has separate terminals for the Hall sensor. AFAIK: these are usually available off the shelf ready calibrated. There's probably a choice of ratiometric analog or digital in a variety of serial format outputs.
 
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