Low Cost milliohm meter

[temperance]

As noted by dobsonr741:

I only need it for a few quick checks to confirm that short lengths of copper wire (sometimes as short at 10cm with a wire OD of 0.3mm and 0.5mm) aren’t shorted together.

What's missing? You don't need a milliOhm meter to find shorts. Or do you want to locate the place where the short might be?

[PCB.Wiz]

.... I just need it for a couple of quick measurements of small coils to make sure none of the turns are shorted.

That's a slightly different problem.
Copper has a high temperature coefficient, and coils also vary from unit to unit, so trying to find adjacent turns shorted by milli-ohms readings will be doomed to fail.
You might catch adjacent layers shorts, with more confidence, especially if you measured each unit before failure to get a known good point.

You may be better with a simple AC driven bridge, that compares a good coil with a suspect one. 

[temperance]

.... I just need it for a couple of quick measurements of small coils to make sure none of the turns are shorted.

That's a slightly different problem.
Copper has a high temperature coefficient, and coils also vary from unit to unit, so trying to find adjacent turns shorted by milli-ohms readings will be doomed to fail.
You might catch adjacent layers shorts, with more confidence, especially if you measured each unit before failure to get a known good point.

You may be better with a simple AC driven bridge, that compares a good coil with a suspect one. 

Is there a problem with using insulated wire?

[Gyro]

Is there a problem with using insulated wire?

He's trying to test inductors so of course they use insulated wire. He's looking for shorted turns, ie. damaged insulation.                   

[wraper]

Is there a problem with using insulated wire?

He's trying to test inductors so of course they use insulated wire. He's looking for shorted turns, ie. damaged insulation.                   

It could be a silver plated copper wire that is not insulated.

[MariuszD]

Hi,
I’m looking for a low-cost sub-milliohm meter, ideally under £100. I only need it for a few quick checks to confirm that short lengths of copper wire (sometimes as short at 10cm with a wire OD of 0.3mm and 0.5mm) aren’t shorted together.

Any recommendations?

Thank you

If you want to detect short circuits in coils, measuring the quality factor using the ringdown method might be more effective.

This method can detect a single shorted turn in coils with hundreds of turns. In the case of coils, a ohmmeter is useless because the measurements are inaccurate for the following reasons:

A short circuit in a coil does not always have zero resistance; it is often nonlinear and manifests at higher voltages or temperatures. A change in the coil's temperature by 10°C will change the resistance by 4%, which complicates accurate measurements. Even factory-wound coils do not have exactly the same wire length.

[temperance]

Maybe the op can explain the real problem. Perhaps there is no problem.


This is kind of funny. Many people who responded didn't understand the question or questioned the somewhat strange or incomplete question. But they all keep on writing...on and on and on. Just like in real life. Except that here it is not about listening but about reading and reading comprehension and in real life you can apply corrective feedback must faster.

[mikerj]

Since you don't need to do this often or in the field, I hope this is not too simple a solution:
Do you have a lab-power supply that allows current limiting? Do you have a voltmeter?
Just inject current into the wires and measure the voltage. Keyword is "4-wire"- or "Kelvin"-connection.

Now you have moved the problem to measuring current and voltage to the required precision.

[Randy222]

I didnt read the full thread, but the Subject seems to lean 4W, but a 2W is probably ok for the need.

Use a precision uAmp constant current IC (LT3092 1%). It will auto adjust voltage to maintain the uAmp, from there it's just math and a display.

Can be made for a "few" dollars, less the case, zero BOM cost if you have 3D printer, etc.

[temperance]

I didnt read the full thread,

Maybe you should.

[Randy222]

I didnt read the full thread,

Maybe you should.

??
What posts did I not read?

[temperance]

A milli Ohm meter is not a solution for the problem stated in the original post.

[gamalot]

Why are you guys still arguing here?  The OP isn't even responding anymore. 

[Randy222]

A milli Ohm meter is not a solution for the problem stated in the original post.

Hmmm. Ok.