Using standard copper as a shunt - FAIL - Page 1
Forum section: electronics / projects

author: BiOzZ
author_rank: Regular Contributor
timestamp: April 26, 2013, 03:28:48 pm
content: i made a post a few days back about using 14 AWG house hold grounding solid copper wire as a high current shunt and i would like to fowlow up on my trialssomeone posted that the temp co of the wire is simply too high to be useful and the wire will heat up way to fast to be usefulyes and no! ... yes the tempco was so high it was unusable short of calibrating it before every useno the shunt wire did not heat up at all at 9.5 amps for 1 hour (seeing how it was thinner than the wires used to connect it ... it was not a real concern)here is the rig that i used to test itit is all messy so let me explainthe large meter is my reference ... its on the low side and in amp modefor current regulation i use a SIMPLE mosfet on a fanned heatsinc with SIMPLY a pot on the gate ... i adjust the pot untill i have the current desired ... this was VERY stable not drifting at all in 1000 countsEDIT: for the power supply i used a standard 250 watt benchtop PSU modified HEAVILY ... big inut chokes, big output chokes and filters, slightly larger caps and ground isolated (shorted to ground here tho ...)here is the circuit i usedi used a simple instantiation amp that i had sitting in my parts bin that i use on all sorts of things ... but im sure it worked just fine for thisResultsi dont remember what i had the pot set as but the gain should be ~ 200 ishat room tempature for a full hour the voltage out at 9.5 amps was 2.415v and only drifted by 4 on the LSDas SOON as i applied heat to the copper it jumped up to 3.2ish volts than slowly bleed downCONCLUSIONif its not being constantly adjusted for temperature or in a temperature controlled environment ITS USELESSsorry to whoever i doubted!

author: Alana
author_rank: Frequent Contributor
timestamp: April 26, 2013, 06:35:45 pm
content: How about janking 10A current shunt from those 5$ Chinese DMMs then?

author: croberts
author_rank: Regular Contributor
timestamp: April 26, 2013, 06:54:32 pm
content: Can you epoxy a temperature sensor to the shunt wire and then use it to temperature compensate the output.

author: jeroen74
author_rank: Frequent Contributor
timestamp: April 26, 2013, 07:37:45 pm
content: Wouldn't it be easier, cheaper and less complex to just use the proper kind of wire

author: C
author_rank: Super Contributor
timestamp: April 26, 2013, 07:38:13 pm
content: If your copper current shunt was the wires needed anyway, like the wires from a motor drive circuit to the motor, it would be dual use and not waste power.An old car I had did just that for a charge/discharge indicator.The problem is if you want/need a more calibrated reading.If this was a temp sensing resistor and you wanted accuracy, you would use a 4 wire kelvin setup to measure it's resistance.what if you combine that idea with a way to sense the temp indirectly.For example, say you took a 10 gage magnet wire and in parallel put two 30 gage magnet wires The two 30 gage wires in close contact would have almost the same temp. as the 10 gage wire, so the resistance of the 30 gage wires would change almost the same ratio as the 10 gage wire. Connect all three at remote end and cover with some heat shrink. By using 2 wires you can get the voltage at the remote end and use the resistance change to help calibrate out the temp change.C