Why is that?Ideally, you want R1 and R2 to be about the same order of magnitude.
While trying this method I realized my multimeter is no good, the resistance values are all over the map and the slightest touch or repositioning of components gives wildly different results.. I almost certainly ruined the guts of the thing by accidently measuring the resistance of voltage sources (haha) including having bypassed the fuse months agoAs pointed out, you can do this using the 4-wire measurement method.
Here is a similar technique along the same idea using a battery, resistor and your DMM.
Firstly, you need a known low resistance. For example, suppose you have a 1Ω ±10% resistor.
You create a circuit with your battery in series with the 1Ω resistor R1 and your 0.1Ω DUT R2 (device under test).
View attachment 234037
With your DMM in voltage range, measure the voltage V1 across R1 and V2 across R2.
By Ohm's Law analysis:
I = V1 / R1 = V2 / R2
R2 = R1 x V2 / V1
independent of the voltage of the battery.
I only did it because the fuse blew and I was planning to get a 10A meter, normally I'm a safety nut but I read a lot on the issue that suggested that the voltage I'm working with will at most ruin the meter which is what has come to pass..Safety mechanisms are there for a reason. Bypass safety mechanisms at your own peril.
Live and learn.