Author Topic: What resistance is a 0m30 shunt resistor?  (Read 941 times)

0 Members and 1 Guest are viewing this topic.

Offline Alex_BakerTopic starter

  • Frequent Contributor
  • **
  • Posts: 262
  • Country: us
What resistance is a 0m30 shunt resistor?
« on: June 03, 2023, 07:01:03 pm »
Hello, quick question here!

I am designing a current sense circuit and referencing other designs. I keep seeing shunts marked 0m30, what resistance is this? I have had trouble finding resources to figure out what code this uses. My guess is that this is 3 miliohms, but I am not 100% sure.

Thanks!
 

Offline Dave

  • Super Contributor
  • ***
  • Posts: 1352
  • Country: si
  • I like to measure things.
Re: What resistance is a 0m30 shunt resistor?
« Reply #1 on: June 03, 2023, 07:55:53 pm »
0.3 milliohms or 300 microohms.
You will often find the unit prefix used in place of the decimal point in electronics, be it on schematic diagrams, PCB silkscreens, or on the components themselves.
Supposedly it originates from the time when schematic sheets were hand drawn and copied back and forth. Degradation of image quality meant that decimal points had a tendency of disappearing, so the simple solution was to avoid using them entirely.
« Last Edit: June 03, 2023, 08:02:23 pm by Dave »
<fellbuendel> it's arduino, you're not supposed to know anything about what you're doing
<fellbuendel> if you knew, you wouldn't be using it
 

Offline Alex_BakerTopic starter

  • Frequent Contributor
  • **
  • Posts: 262
  • Country: us
Re: What resistance is a 0m30 shunt resistor?
« Reply #2 on: June 03, 2023, 08:53:06 pm »
Cool, Thanks!
 

Offline DavidAlfa

  • Super Contributor
  • ***
  • Posts: 5802
  • Country: es
Re: What resistance is a 0m30 shunt resistor?
« Reply #3 on: June 03, 2023, 09:28:28 pm »
Can you really handle 300uOhm accurately?
I mean, even the solder will affect the value at such low value.
Hantek DSO2x1x            Drive        FAQ          DON'T BUY HANTEK! (Aka HALF-MADE)
Stm32 Soldering FW      Forum      Github      Donate
 

Online langwadt

  • Super Contributor
  • ***
  • Posts: 4384
  • Country: dk
Re: What resistance is a 0m30 shunt resistor?
« Reply #4 on: June 03, 2023, 09:33:26 pm »
Can you really handle 300uOhm accurately?
I mean, even the solder will affect the value at such low value.

at such low values, hopefully, the resistor and footprint has a kelvin connection for the sense
 

Offline coppice

  • Super Contributor
  • ***
  • Posts: 8574
  • Country: gb
Re: What resistance is a 0m30 shunt resistor?
« Reply #5 on: June 03, 2023, 09:39:47 pm »
Can you really handle 300uOhm accurately?
I mean, even the solder will affect the value at such low value.
Most of the applications for such low value resistors are as current sensing shunts. The accuracy of the resistance is frequently not that important, as there will be a calibration performed after assembly. Many times such low resistances will be 4 terminal, but 2 terminal ones are very common, as they are cheaper. The key issue is not solder, but copper in the sensed path. Its awful temp coeff (0.4%/C) ruins any calibrated accuracy over even a modest temperature range.
 

Online Benta

  • Super Contributor
  • ***
  • Posts: 5817
  • Country: de
Re: What resistance is a 0m30 shunt resistor?
« Reply #6 on: June 03, 2023, 09:44:32 pm »
Is this for a 1000 A current shunt?
 

Offline coppice

  • Super Contributor
  • ***
  • Posts: 8574
  • Country: gb
Re: What resistance is a 0m30 shunt resistor?
« Reply #7 on: June 03, 2023, 09:48:31 pm »
Is this for a 1000 A current shunt?
You would generally use a much lower resistance for 1000A. 300 micro-ohms will dissipate 300W.
 

Online langwadt

  • Super Contributor
  • ***
  • Posts: 4384
  • Country: dk
Re: What resistance is a 0m30 shunt resistor?
« Reply #8 on: June 03, 2023, 10:09:12 pm »
Can you really handle 300uOhm accurately?
I mean, even the solder will affect the value at such low value.
Most of the applications for such low value resistors are as current sensing shunts. The accuracy of the resistance is frequently not that important, as there will be a calibration performed after assembly. Many times such low resistances will be 4 terminal, but 2 terminal ones are very common, as they are cheaper. The key issue is not solder, but copper in the sensed path. Its awful temp coeff (0.4%/C) ruins any calibrated accuracy over even a modest temperature range.

most metals are roughly 0.4%/C
 

Online Zero999

  • Super Contributor
  • ***
  • Posts: 19286
  • Country: gb
  • 0999
Re: What resistance is a 0m30 shunt resistor?
« Reply #9 on: June 03, 2023, 10:25:29 pm »
Is this for a 1000 A current shunt?
You would generally use a much lower resistance for 1000A. 300 micro-ohms will dissipate 300W.
I would use a Hall effect sensor for 1000A.

300µOhm is fine for up to 100A or so. The source impedance is low, so it doesn't matter if the amplifier has a low input impedance and relatively high bias currents, making low offset easier to design, or use a chopper amplifier.
 

Offline coppice

  • Super Contributor
  • ***
  • Posts: 8574
  • Country: gb
Re: What resistance is a 0m30 shunt resistor?
« Reply #10 on: June 03, 2023, 11:08:33 pm »
Can you really handle 300uOhm accurately?
I mean, even the solder will affect the value at such low value.
Most of the applications for such low value resistors are as current sensing shunts. The accuracy of the resistance is frequently not that important, as there will be a calibration performed after assembly. Many times such low resistances will be 4 terminal, but 2 terminal ones are very common, as they are cheaper. The key issue is not solder, but copper in the sensed path. Its awful temp coeff (0.4%/C) ruins any calibrated accuracy over even a modest temperature range.

most metals are roughly 0.4%/C
True, but follow the guidelines in https://www.analog.com/en/analog-dialogue/articles/optimize-high-current-sensing-accuracy.html and the metals with a horrible coefficient can have a minimal effect. The contacts on the resistor itself should be made of a material with a good coefficient.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf