sensor current limits looking in the chart

Thread Starter

vlobo

Joined Jul 30, 2017
9
Hi! I need to meassure 0 to 82A with a sensor current. I found the LEM HLSR40-P which can meassure up to 100A. But I am not sure because looking in the datasheet (http://docs-europe.electrocomponents.com/webdocs/1272/0900766b81272eb1.pdf) i see the IP(A) vs Vref(V) chart, and it looks like if it is only possible to measurre currents from -25 to -125A and from 100 to 125A. So if i am not wrong I can't meassure 0 to 82A. Althought it is strange. Am I wrong?
 

#12

Joined Nov 30, 2010
18,076
I believe you are mistaken in reading the graphs, but I caution about the average current allowed. It seems to me that the -40 device and the -50 device have a limit on "nominal" current. Please wait for a second opinion.

Here it comes now:
Page 10/13 Max continuous DC current = 50A
 
Last edited:

ebeowulf17

Joined Aug 12, 2014
2,942
IMG_2190.PNG I could be wrong, but I believe those lines represent the upper and lower bounds, so any current in between the lower line and the appropriate upper line has a valid output voltage. You choose which upper line to read based on what supply voltage you're using (4.5 to 5.5V.) Then, on the x-axis find the reference voltage you intend to use (it looks like default is 2.5V if you don't supply an external reference voltage.) Then just read the upper and lower amperage limits at that point on the x-axis.

So, for the 40 amp model you've chosen, if you use a 5V supply and the default reference, the sensor can read -125 to +125A. If you supplied an external reference at 0.5V, you'd be limited to -25 to +125A.

But, keep in mind what #12 pointed out. This unit can only continuously handle 40A DC or 40A AC RMS. So, if you're measuring brief, instantaneous peaks, you should be ok up to your 82A range, but if it's 82A continuously, this sensor won't handle it.

What are you measuring? Is the current continuous or intermittent?
 
That's what I see it as too. +-150 AMP is your supply is 5 V and Vref =2.5 V or 1/2 Vcc. It may not exactly be able to measure +-150 A. It really depends on how close the output can get to the rails and your A/D resolution.

Remember, quantization error, where at the low end of the measurement, you gain % error.
 

Thread Starter

vlobo

Joined Jul 30, 2017
9
View attachment 131957 I could be wrong, but I believe those lines represent the upper and lower bounds, so any current in between the lower line and the appropriate upper line has a valid output voltage. You choose which upper line to read based on what supply voltage you're using (4.5 to 5.5V.) Then, on the x-axis find the reference voltage you intend to use (it looks like default is 2.5V if you don't supply an external reference voltage.) Then just read the upper and lower amperage limits at that point on the x-axis.

So, for the 40 amp model you've chosen, if you use a 5V supply and the default reference, the sensor can read -125 to +125A. If you supplied an external reference at 0.5V, you'd be limited to -25 to +125A.

But, keep in mind what #12 pointed out. This unit can only continuously handle 40A DC or 40A AC RMS. So, if you're measuring brief, instantaneous peaks, you should be ok up to your 82A range, but if it's 82A continuously, this sensor won't handle it.

What are you measuring? Is the current continuous or intermittent?
It is for continuous current, charging and discharging a battery pack. Ok. I understand. So I must search a sensor current with 100A Nominal rms current. Thanks!
 
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#12

Joined Nov 30, 2010
18,076
It is for continuous current, charging and discharging a battery pack. Ok. I understand. So I must search a sensor current with 100A Nominal rms current. Thanks!
This is not a simple request. Wire sizes to avoid overheating are in the range of AWG 1 @ 8.072 feet per milliohm and diameter = .2893 inches
Why would I say that? Because 0.001 ohms times 100A = 0.1 volt, a very measurable voltage and an acceptable loss in a battery charger system. If you can budget for a whole volt of loss, you could use 0.8072 feet (9.6864 inches) of AWG1 wire and amplify the results with an op-amp.

There does exist a Hall Effect method to measure DC current in an existing wire. I suggest you explore that method because a 100 amp shunt is something I have never seen available in retail offerings.
 
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