Current-sense shunts, 1–47 mΩ, 0.5%, from Isabellenhütte

As a continuation of my series on components, I decided to post a review of current-sense shunts from the well-known Isabellenhütte. I also needed these shunts for the power module of an electronic load. Since I was ordering from the same seller, I decided to get a variety of them and ended up ordering six values.
I'll say right away: these are interesting shunts, but as always, more on that in the review.


First, two things are worth mentioning:
1. I already reviewed similar shunts in my milliohmmeter review, and I really liked them.
2. Before this, I had checked the milliohmmeter I use to test shunts against other shunts, which had themselves been checked before the tests.

I ordered a bunch of different ones at once, partly because I'm a hoarder who likes to stock up, and partly because I'm frugal: I only had to pay the forwarding service once to ship the seller's entire parcel to me. I received six bags, one value per bag.


And to settle the questions about price, weight, and quantity right away, here's the table from the forwarding service, showing the price (excluding their shipping fee to me) and all the details mentioned above.


There is a really wide selection of these shunts on Taobao. The price depends on both the seller and the value. For example, the 2.2 mΩ shunts are cheaper, and the price hardly depends on whether the tolerance is 0.5% or 1%. Also, all the shunts are used.
In the end, I ordered shunts with these values (all with 0.5% tolerance):
1 mΩ
2.2 mΩ
6.8 mΩ
10 mΩ
41.6 mΩ
47 mΩ

Here and below, the photos are arranged in order of increasing resistance.


What makes these shunts special? First of all, they have a four-terminal connection from the outset and can be mounted on a heatsink to reduce their temperature, and therefore minimize the effect of temperature on their resistance.
In my milliohmmeter review, I included an image from the datasheet for these shunts to explain how they work. I'll include it here too.


For a rough idea, here's another example. But really, it's easier to check out the review where I explained four-terminal connections in detail, for example here and here.


With a shunt, this connection ensures that neither the length of the PCB traces, nor the quality of the solder joints, nor anything else affects the voltage measured across the shunt, since the connection is made inside it.
A similar method is also used with an ordinary wire-wound shunt, but the result still depends on the factors mentioned above. You can even add a little solder to the shunt's contact and get a different result—I had that happen once. And the lower the shunt's resistance, the more significant the effect.

The classic shunt connection is on the left; the four-terminal connection is on the right.



Now for the inspection and measurements.
Value: 1 mΩ
Tolerance: 0.5%
Price: $0.28, link.

Two shunts, paint markings, average quality. The bases on the back also differ slightly in appearance.


Both have the specified resistance.


Value: 2.2 mΩ
Tolerance: 0.5%
Price: $0.09, link.

I bought seven, partly because of the price—they cost only about $0.09 each—and partly because the value suited my needs. I figured they might come in handy.
Four shunts (on the left) have laser markings, while three are marked with paint. The bases also differ slightly; the ones on the left have a rougher finish.


The values are within +/-0.01 mΩ. Even when a reading is 2.19 or 2.21, it usually fluctuates between 2.19 and 2.20. I didn't try to get it to show exactly 2.20, although one or two resistors consistently read 2.19.


Value: 6.8 mΩ
Tolerance: 0.5%
Price: $1.09, link.

These are the most expensive shunts in the review. I bought them because their resistance was a better fit for my needs. They have laser markings but no company name, just its logo. To me, these resistors look “more genuine.”


All three readings were mostly very stable: two read exactly 6.8, and one read 6.79 mΩ.


Value: 10 mΩ
Tolerance: 0.5%
Price: $0.44, link.

A very handy value. I probably should have bought more. Laser marking, not very deep and rougher than on the previous ones. They’re also noticeably dirtier, so they may actually be used originals, though who knows.


One pair measured 9.9 mΩ, another pair 10 mΩ, and one measured 10.1 mΩ. Of course, you could say that’s closer to 1%, but the meter doesn’t have enough resolution to measure values like these accurately enough.


Nominal resistance: 41.6 mΩ
Tolerance: 0.5%
Price: $0.55, link.

I bought it more or less “for the collection,” since this is a very unusual, uncommon value. The marking is painted on and very rough.


And I’m glad I bought it: the resistor has clearly been relabeled or is a fake. Its actual resistance is 54 mΩ. I checked it several times; I could hardly believe it was possible, especially after the measurements of the previous ones.


Nominal resistance: 47 mΩ
Tolerance: 0.5%
Price: $0.27, link.

These resistors aren’t very suitable for me as shunts because their resistance is too high, so I bought them mainly as samples for checking meters.
Laser marking, very neat.


The measured resistance matches the stated value.


Different marking styles. You can see that they vary considerably from one type to another. I can’t say which ones are genuine, but personally, I trust the laser-engraved ones more.


But let’s get back to the strange resistor marked 41.6 mΩ, which actually measures 54 mΩ.
Here it is next to the others, which also had painted markings. You can see that both the print quality and the marking itself are different. After the company name, there are three letters: Dbg.


It turned out that the resistor had clearly been relabeled (at first I thought it had simply overheated). Proper painted markings usually withstand even acetone, and certainly don’t react to alcohol. I rubbed both resistors with a cotton swab dipped in alcohol, and the marking on the one on the right started to come off. Go figure...


This next test is more interesting: measuring how resistance changes with temperature. I positioned the resistor and soldering iron so the resistor would heat up without touching the heating element directly, while monitoring its case temperature with an IR thermometer. I didn’t test every value, just the main ones.

1, 2. 1 mΩ nominal, heated to 90 degrees. No issues, although the meter started switching a little more often between readings of 1.00 and 0.99.
3, 4. Same as the previous one; case temperature was 95 degrees.


1, 2. 47 mΩ nominal; after heating to 94 degrees, it dropped to 46.9 mΩ.
3, 4. This was the most interesting test for me. I thought they might have put an ordinary resistor inside this strange one, then simply filled it with compound and added the marking. Chinese sellers can be quite inventive sometimes...
But it turned out that when heated to 95 degrees, the resistor performed no worse than the previous one, so no issues there.


It’s strange, really. Why take a perfectly good resistor, relabel it as something else, and then sell it for basically the same price as the other similar ones? That’s probably the biggest mystery to me.

Anyway, I decided to fix this little mix-up.
1. Grab a cotton swab and some alcohol, and wipe off the old marking.
2. I didn’t have any paint at home, so I got out my laser engraver, quickly put together some text, and made a new marking that better reflects reality.
3. Wiped off the engraving residue with alcohol.
4. I agree, it came out a little crooked and rougher. But really, this was my first try: I just threw together some text, set the power to 20%, and went for it. The main thing is that this marking will be much harder to remove.
I think I could get something closer to the original after 4 or 5 tries, but I’d need the right fonts and would also have to engrave in vector mode rather than raster mode, as I did.


By the way, each resistor has some kind of code in addition to its value and type, so almost all the resistors in this review have different codes (there are two identical ones at 1 mΩ). Some have L34, P21, V19, and so on in the upper right; others have 0.12, 7.9, 8,11 in the lower right. Does anyone know what these are? I think this is some kind of calibration mark, perhaps indicating how much the resistance changed from its original value as a result of trimming.



And that’s pretty much the whole review. I don’t have much else to say. In short, I’m happy with the resistors, even the odd one that was relabeled for reasons I can’t figure out.



That’s all. I hope you found the review useful, and as always, I’ll be happy to answer any questions.