Robotics Passive Components, Germany: 173 of Walsin’s 5,410 Inductors Contradict Their Own RDC

We multiplied the rated current by the DC resistance in the same row for all 5,339 Walsin inductors that publish both. 173 of them imply more than 10 watts of self-heating inside a chip; 31 imply more than a kilowatt. If you are specifying robotics passive components for a humanoid joint controller, the rated-current column is the field you must not trust at face value.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all 203 Walsin Technology (Walsin) parametric export files. We hold no inductor datasheet at all — 28 datasheets, 451 pages, every one MLCC or chip resistor. This post is measured from Walsin_Inductor_ALL.xlsx and Metal_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx. Row Test123999 is a QA test row and is excluded from every count here, so the real inductor total is 5,410. Every part number below is real.

How many Walsin inductors can actually carry a joint actuator rail?

Fewer than the column says. A humanoid joint controller runs a gate-drive rail, a logic rail and a sensor rail off a 48 V bus in a volume the size of a thumb. We parsed all 5,410 inductor rows. On the raw Rated Current column, 1,125 reach 1 A and 186 reach 5 A. After discarding the 234 rows whose own DC resistance makes the stated current physically unserviceable, 919 reach 1 A and 84 reach 5 A — a 55 % cut at the top of the ladder.

Rated current threshold	Rows on the raw column	Rows after the I²R sanity check	Lost
1 A or more	1,125	919	206
2 A or more	507	331	176
3 A or more	358	204	154
5 A or more	186	84	102
8 A or more	99	15	84
10 A or more	79	6	73

The gap widens as the current rises, which is the worst possible shape: the higher your rail current, the larger the fraction of the shelf that evaporates on inspection. We have not seen this counted anywhere.

Why does one 0603 part state 80 A through 5.5 ohms?

We cannot tell you, and that is the honest answer. The worst row in the file is WQCW1608Z0GR47PB — a 470 nH wirewound 0603 part, RDC 5.5 Ω, Rated Current 80 A. Squared and multiplied, that is 35.2 kW inside an 0603 body. We checked where these cluster: all 173 rows above 10 W sit in just four series — CSME (73), CSMEA (53), WLFI (30) and WQCW (17).

The two clusters fail in opposite directions, which is itself a clue:

Part number	Series	Size	Inductance	RDC as exported	Rated current as exported	Implied I²R	Match / mismatch vs a usable spec
WQCW1608Z0GR47PB	WQCW	1608	470 nH	5.5 Ω	80 A	35,200 W	Mismatch — the current reads as if it should be milliamps
WLFI1608Z0MR22TB	WLFI	1608	0.22 µH	0.8 Ω	50 A	2,000 W	Mismatch — same pattern, same decade error
CSMM0420D-1R0M	CSME	4040	1.0 µH	0.028 Ω	5.8 A	0.94 W	Match — plausible, and it publishes 8.7 A saturation
CSMM0420D-R47M	CSME	4040	0.47 µH	0.022 Ω	5.9 A	0.77 W	Match — 11 A saturation, 1.8 mm tall
AIP0615MB-R47M	AIP	7066	0.47 µH	8.5 mΩ	10 A	0.85 W	Match — the highest plausible current under 1.5 mm

The WQCW and WLFI rows read as a milliamp-to-amp unit slip in the current column. The CSME and CSMEA rows read as a milliohm-to-ohm slip in the resistance column — CSME0418D-1R0N states 27 Ω against a 3.2 A rating, which is 277 W. One of the two columns is wrong in every one of the 173 rows, and we cannot say which, because we hold no inductor datasheet to check against. That is exactly the situation in which a cross-reference that only matches inductance value is dangerous.

How thin can a genuine 8 A inductor be, and how many exist?

To 0.6 mm, and there are eleven. A joint actuator is a height problem before it is a current problem, because the controller sits inside the joint housing. We cross-filtered the plausible rows on both axes: 198 part numbers clear 3 A with a body no taller than 2.0 mm, 79 clear 5 A, and 11 clear 8 A. The thinnest of the eleven is 0.6 mm.

But read the eleven before you use the number. Three of them are ferrite beads, not inductors — WLBD4532HCU800PH, MHC1608P220Z06BP8A0 and WLBD1608HCU220TL all carry Inductance 0 and Unit Ω, because 641 of the 5,410 rows in this file are beads filed alongside the inductors with 609 of them showing zero inductance. So the real answer to “8 A in 2 mm” is eight part numbers, all AIP series, 4442 to 7066 in footprint.

Part number	Series	Footprint	Height	Inductance	RDC	Rated current	Match / mismatch vs 8 A under 2 mm
AIP0420MB-R10M	AIP	4442	1.80 mm	0.10 µH	4 mΩ	13 A	Match — highest plausible current in the file
AIP0518MB-R47M	AIP	5452	1.60 mm	0.47 µH	7.6 mΩ	11 A	Match; mismatch — 10 mm² more board area
AIP0615MB-R47M	AIP	7066	1.30 mm	0.47 µH	8.5 mΩ	10 A	Match on height; mismatch — largest footprint of the three
WLBD4532HCU800PH	WLBD(HC)	4532	1.50 mm	0 (bead)	10 mΩ	9 A	Mismatch — a ferrite bead, no inductance published
WIP201610S-R10ML	WIP_S	2016	1.00 mm	0.10 µH	10 mΩ	6 A	Mismatch on current — 6 A, but a third the area

And the field a motor drive actually needs is missing almost everywhere. Only 146 of 5,410 rows publish a saturation current, which is ours and already published — what we had not measured until today is that those 146 sit in just three of the 47 series: CSME (89), CSMEA (53) and MIP-H (4). Of the 84 plausible rows at 5 A or more, exactly five publish a saturation current. See rated current vs saturation current in chip inductors and inductor thickness and board clearance.

What does the sense resistor shelf look like at a joint’s phase current?

Deep, but only in one footprint. A joint actuator measuring phase current at 20 A needs a low-milliohm shunt that can take the dissipation. We checked all 1,188 rows of the metal low-ohm export: 317 are 5 mΩ or below, 257 of those are rated 1 W or more, 123 reach 2 W, and 48 reach 3 W. All 123 at 2 W and below 5 mΩ are 2512 or 1225 — not one is 1206 or smaller.

That is a layout constraint, not a catalogue preference. If your joint controller cannot find room for a 2512 pad with the copper to feed it, the sense resistance has to rise and the amplifier gain has to follow. Compare the two shelves at low ohm current sense: thick film vs metal.

Is the AEC-Q200 part always the better part?

No, and we can show two cases where it is not. The metal sense export pairs a commercial part with an automotive one by appending a single J. We matched them: 502 pairs exist, the stated TCR differs on 42 of them, and on exactly 2 the automotive part is worse — WW25RR001FTLJ states ≦±100 ppm/°C against ≦±75 ppm/°C on WW25RR001FTL, and the ±5 % pair behaves the same way. Both are at 0.001 Ω.

Part number	Series as exported	Resistance	TCR	Rated power	Match / mismatch vs the commercial twin
WW25RR001FTL	Metal Plate Power Low Ohm	0.001 Ω	≦±75	2 W	Baseline — commercial
WW25RR001FTLJ	…Low Ohm (Automotive)	0.001 Ω	≦±100	2 W	Mismatch — AEC-Q200 grade, 1.33× the TCR
WW25QR002FTL	Metal Plate Power Low Ohm	0.002 Ω	≦±100	1 W	Baseline — commercial
WW25QR002FTLJ	…Low Ohm (Automotive)	0.002 Ω	≦±70	1 W	Mismatch — AEC-Q200 grade, and 1.43× better TCR
WW25BR001FTLJ	Metal Plate (Automotive)	0.001 Ω	≦±70	3 W	Match — best TCR and power at 1 mΩ

So the J suffix is not “the same part, qualified”. On 40 pairs it buys you a tighter TCR and on 2 it costs you one. Walsin’s own word is compliant, never certified, and the qualification report is per part number — ask us for it against the exact code you intend to buy. See AEC-Q200 compliant is not certified.

Where does an operating temperature come from, if no column states one?

From the series name, and nowhere else. We re-checked every column header across all 203 Walsin export files: 96 distinct column names, and not one of them mentions temperature, operating range or degrees Celsius. There is no field to filter on. So for a humanoid joint running hot inside its own housing, the only temperature signal in the data is whether a part sits in an AEC-Q200-compliant series.

That is why a robot bill of materials reaches for automotive-grade passives, and it has nothing to do with cars. You are buying the temperature range and the vibration qualification, in a product that will never see a vehicle. 54 of the 123 sub-5 mΩ, 2 W sense resistors are in the automotive series; so are the 150 inductor rows Walsin labels MCB / MHC Automotive. Read what AEC-Q200 actually certifies before you write the requirement, and note that we make no qualification claim of our own.

What should a German robotics programme do with this?

Sanity-check before you select, then cross the whole joint bill of materials in one pass. 919 inductors survive the I²R check at 1 A, 84 at 5 A, 8 genuine inductors at 8 A under 2 mm. The trade press reported passive-component lead times stretching through 2026 as AI server and EV build-outs drew on the same capacity, so a second source worth having is one you can see on a shelf.

1. Reject any candidate whose rated current and RDC do not multiply to something a chip can dissipate. It takes one spreadsheet column and it removed 102 of 186 candidates at 5 A here.
2. Cross the whole joint controller at once. Paste up to 500 part numbers or drop your Excel or CSV into the free cross-reference tool. It is matched against Walsin’s published catalogue and returns candidates field by field, with every difference stated rather than hidden, and a commercial or automotive grade filter.
3. Check Hong Kong before you commit a build slot. Ready stock is a dated snapshot as at 23 September 2026. On that date 2 of the 1,125 catalogue codes were inductors — WLPH252012M2R2PP and WLPH252012M4R7PP — against 254 chip resistors. Inductors are an order-in line here, and we would rather say so than imply a shelf we do not have.

The range itself is on the Walsin inductor product page. We are an authorised Walsin Technology distributor in Hong Kong; confirm it with Walsin, and check UL file E182369 in UL’s own public database while you are at it.

The short version

The rated-current column in Walsin’s inductor export cannot be used raw. 173 of 5,410 rows imply more than 10 W of self-heating and 31 imply more than a kilowatt, clustered in four series, with a milliamp slip in two of them and a milliohm slip in the other two. After the check, 84 rows reach 5 A and 8 genuine inductors reach 8 A in under 2 mm; 641 rows in the file are ferrite beads, not inductors; only 146 publish a saturation current and those sit in three of 47 series. On the sense side, 123 parts clear both 5 mΩ and 2 W and every one is 2512 or 1225. No column in any of 203 files states a temperature. We hold no inductor datasheet. Qualification stays with you.

Send us the joint controller bill of materials — the sense shunt with the current you actually measure, the rail inductors with the height you actually have — and we will come back with Walsin candidates field by field, differences included, and tell you which rows we would not trust. We will not tell you a part is equivalent. We will show you where it differs. And if you think a 470 nH 0603 part really does take 80 A, tell us: we would love to be wrong about that one.

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Frequently asked questions

<!– wp:rank-math/faq-block {"questions":[{"id":"faq-question-01","title":"Can I trust the rated current column in Walsin's inductor export?","content":"Not without checking it. We multiplied rated current squared by the DC resistance in the same row for all 5,339 rows that publish both. 173 imply more than 10 W of dissipation inside a chip and 31 imply more than a kilowatt. They cluster in the CSME, CSMEA, WLFI and WQCW series. One of the two columns is wrong in each case.","visible":true},{"id":"faq-question-02","title":"How many Walsin inductors are genuinely rated above 5 A?","content":"Eighty-four, out of 5,410. The raw column shows 186, but 102 of those fail an I²R sanity check against their own DC resistance. At 8 A the raw column shows 99 and only 15 survive. Of the 11 survivors with a body under 2.0 mm, three are ferrite beads, leaving eight real inductors.","visible":true},{"id":"faq-question-03","title":"What is the thinnest high-current inductor Walsin publishes for a robot joint?","content":"The AIP series reaches 10 A at 1.30 mm in a 7066 footprint, on AIP0615MB-R47M, and 13 A at 1.80 mm on AIP0420MB-R10M. Eleven part numbers clear 8 A under 2.0 mm, of which eight are genuine inductors and three are ferrite beads filed in the same export.”,”visible”:true},{“id”:”faq-question-04″,”title”:”Which Walsin current sense resistors suit a 20 A robot joint phase measurement?”,”content”:”Look in the metal low-ohm export, and expect one footprint. Of 1,188 rows, 317 are 5 mΩ or below; 123 of those are rated 2 W or more and all 123 are 2512 or 1225. Nothing at 1206 or smaller combines both, so the shunt drives the layout rather than the other way round.”,”visible”:true},{“id”:”faq-question-05″,”title”:”Does the AEC-Q200 version of a Walsin sense resistor always have better TCR?”,”content”:”No. We matched 502 commercial and automotive pairs that differ by a single trailing J. The stated TCR differs on 42 of them: on 40 the automotive part is tighter, and on 2 it is looser. WW25RR001FTLJ states ≦±100 ppm/°C where WW25RR001FTL states ≦±75. Walsin’s word is compliant, never certified.”,”visible”:true},{“id”:”faq-question-06″,”title”:”Why use automotive-grade passives in a humanoid robot?”,”content”:”Because AEC-Q200 series membership is the only temperature signal in the data. We re-checked all 203 Walsin export files: 96 distinct column names and not one names a temperature, an operating range or degrees Celsius. You are buying the temperature and vibration qualification, not a car-specific part.”,”visible”:true},{“id”:”faq-question-07″,”title”:”Does Venatech hold a datasheet for Walsin inductors?”,”content”:”No. We hold 28 Walsin datasheets, 451 pages, all of them MLCC or chip resistor. We hold nothing for the inductor line, and 208 inductors across the VEFL, WIP, SCM, SCA and BIH families have no datasheet published anywhere we can find — a count we established and published earlier. Work from Walsin’s own documents for specifications.”,”visible”:true}],”listStyle”:””,”titleWrapper”:”h3″,”titleCssClasses”:””,”contentCssClasses”:””,”sizeSlug”:””} –>

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