Really low-ohm resistors are difficult to do, because even the solder
connections to the part change the resistance. Individual calibration of
each sensor becomes mandatory if you want any decent accuracy.
Have you thought of using the Allegro hall-effect sensors (like the
ACS750SCA-100) instead? I use them all the time with great results.
I use one op-amp to move the normal Vcc/2 offset to near gnd, and
amplify the output by about 1.8. I then take that output and feed it
into my PICs A/D. I have a "calibrate" button that takes the A/D
reading at zero current and stores that value in EEPROM. All subsequent
readings subtract out that value.
No pots, no adjustments and 2% accuracy to 100A.
Charles Linquist
PicDude wrote:
{Quote hidden}> I need to measure DC current up to 100A (at 12V) at multiple points and
> planning to use the ZXCT1010 current monitor and a sense resistor for this.
> A drop of 100mV or even a bit more is acceptable; few percent error/accuracy
> preferred.
>
> (a) Calculated ideal is a 0.001-ohm, 10W, 1% sense resistor, or .0005-ohm 5W,
> but can't find either at the usual sources (Digikey, Mouser, etc).
>
> (b) I can use 4 sense resistors in parallel -- 0.005-ohm, 3W resistors, but
> these add up to ~$6. Replicating this a few more times adds up fast.
>
> (c) Shunts are and option, but are really expensive ($19 ea. at All
> Electronics).
>
> (d) The other option is to use a couple inches of say 10-ga wire, but I'm not
> sure how consistent this wire/resistance is. Google hasn't found me any info
> on this accuracy. I do have the option of calibrating these individually,
> but without any specific calibration equipment, I'd like to avoid doing this.
> I'm also not sure if I should be running 100A through a piece if 10-ga wire.
>
> (e) Finally, I thought of using a PCB trace for this, which is an elegant
> solution, but some high-level calcs of 1oz or 2oz copper yield some large
> trace sizes -- ~2 inches wide and 5+" long and really high temps.
>
> Any ideas on this? Or perhaps a source for the ideal sense resistor in (a)?
>
> Cheers,
> -Neil.
>
>
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:
Charles Linquist email (remove spam text)