mΩ resistance of your DMM leads probes

Batteries and Chargers Chargers
1

easy task, please could you share some values of your shortened DMM probes. here are some of mine.

I don't have any FLUKE leads or FLUKE leads w/ installed F crocodile clips.

Thanks for sharing!!

EDIT:

Oh shoot. it makes sense not to plug in the leads but to take 'external' measurements of the probes by delta'ing out all resistances to zero, i.e. of the dmm internal resistance plus of the plugged in leads. Then we get a fair measurement of the second pair of leads, which must be shortened of course.

Let me try it!

stock leads plugged in, delta'ing zero, measuring resistance of diy leads w/ crocos: "0.02Ω"

stock leads plugged in, delta'ing zero, measuring resistance of hc leads w/ crocos: "0.03Ω"

stock leads plugged in, delta'ing zero, measuring resistance of BG leads: "1.54Ω"

hc leads w/ crocos plugged in, delta'ing zero, measuring resistance of diy leads w/ crocos: "0.02Ω"

hc leads w/ crocos plugged in, delta'ing zero, measuring resistance of stock leads: "0.19Ω"

hc leads w/ crocos plugged in, delta'ing zero, measuring resistance of BG leads w/ crocos: "1.57Ω"

BG leads w/o crocos plugged in, delta'ing zero, measuring resistance of diy leads w/ crocos: "0.02Ω"

BG leads w/o crocos plugged in, delta'ing zero, measuring resistance of hc leads w/ crocos: "0.03Ω"

BG leads w/o crocos plugged in, delta'ing zero, measuring resistance of stock leads: "0.19Ω"

diy leads w/ crocos plugged in, delta'ing zero, measuring resistance of hc leads w/ crocos: ~"0.05Ω"

diy leads w/ crocos plugged in, delta'ing zero, measuring resistance of stock leads: ~"0.20Ω"

diy leads w/ crocos plugged in, delta'ing zero, measuring resistance of BG leads w/ crocos: ~"1.57Ω"

My diy leads have a loose connection in the DMM socket and it is almost impossible to get a reliable or reproducible reading with them!

Summary:

the Ohms measurements are very consistent and it does not make a difference how one measures the resistance. the delta button of the DMM comes in handy but one can just insert the leads in the DMM socket and short the probes: whatever the DMM displays, that's the resistance of your set of leads. Although the DMM device itself must have an internal resistance, its value does not show in the displayed Ohms number … as if the DMM internally delta zero'ed it beforehand, i.e. DMM internal resistance ≡ 0.00Ω, for the user's viewing convenience! :D

The order of resistances of my four sets of leads are:

diy leads w/ diy crocos (~20mΩ)

< hc leads w/ hc crocos (~30mΩ)

< stock leads (~190mΩ)

< BG leads w/ bg crocos (~1570mΩ)

The high resistance of the stock leads is disappointing. Wondering how good FLUKE leads are!

2

haha :frowning: :slight_smile:

my DMM has only 0.1Ω resolution… :stuck_out_tongue:

3

Very low. :stuck_out_tongue: (It is under 1 milliohm but the meters have greater internal resistance 30-40 milliohm).

4

I use 1/0 welding cable.

5

That is impressive.

I have measured a few test leads and they are in the 20-40 mOhm range each for quality leads. This includes one connection resistance.

Shorting them on the DMM and checking the reading, does not say much about the resistance in the test leads.

6

i expanded my tests, see OP. the meter's internal resistance does not show on the display ;)

under 1 miliohm for test leads? my best are between 20-40mΩ, e.g. ~30mΩ for the set of hc leads with hc crocos.

i don't mean to contradict but after my extended tests, see edited OP, i can claim that on my UT61E i get the same reading either way.

and i am glad that i did this kind of work ;)

7

One additional hint:
These lead resistance is essential if we measure current, the current is measured with a shunt resistor inside of DMM….so you need to measure the resistance in A mode.
I like to use a power supply and push some A through the meter measuring current and measure the voltage drop over the meter to find out how the resistance is….

My stock from all the cheapo dmm leads are also in the 150-200mOhm range, I also have some thin multifunctional leads from banggood with serious resistance as long as some crococlipcables which are all junk. That’s why I build my own crodileclips with low resistance.

8

Check the specifications for the DMM, it has +/-10 in tolerance on the last digit.

You might fairly get correct result with your DMM (It looks like it), but there is no guarantee for it.

9

Yes, measuring small currents in low voltage systems is a challenge. I am aware of the shunt resistor phenomenon in dmm's and i'd always measure in the A mode, thanks. Yesterday i got the Fasttech precision screwdriver 25pcs set, awesome stuff, thanks again for the tip!!

HKJ, did you buy Dave Jones uCurrent Gold?

10

I did already have the old uCurrent, but I did get the gold, due to the better precision, better band width and higher current capability.

I do not use it often, I have other meters that can do nearly the same.

11

Would it be possible to recalibrate your uCurrent Gold unit in future (by you, by Dave, by ..), if needed, or do the users assume that, with proper storage at constant humidity/constant temperature, they won't need to recalibrate the device at all?

Afaik the uCurrent has potentiometers(?) inside to finetune recalibration, is that correct? :)

12

No, it cannot be recalibrated (Except by replacing resistors).

It has no adjustments, but uses precision (0.1%/0.05%) resistors. It will stay calibrated for a long time, except if it is overloaded.

13

thanks HKJ!

i will try to buy one when they are available again :)

14

You do not have to wait: http://eevblog.myshopify.com/

15

:D

16

I misread the request, thinking you meant ‘custom/shortened’ probes. >.< The stock probes are higher resistance on both meters, and much longer: 0.2 - 0.3 ohms (that’s cheap probes for you).

Better to measure the voltage drop across leads than shorting probes together, for a more accurate idea.