Current Sense Resistor Value and TCR for India’s Electric Two-Wheelers: a Worked 3 mΩ Example, and the 612 Walsin Metal Shunts at ±50 ppm/°C From Venatech

Choose a current sense resistor value from the amplifier’s full-scale voltage divided by peak current, then check power and TCR. For an Indian electric two-wheeler, that often lands at 1 to 3 mΩ in 2512, and Walsin Technology (Walsin) lists 612 metal shunts at ±50 ppm/°C from 3 mΩ up, from Venatech, the authorised Walsin distributor in Hong Kong.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, wrote this for a battery management or motor controller engineer in India who has to size the shunt that measures pack or phase current. We parsed Walsin’s metal low-ohm current sense export, Metal_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx (1,188 distinct part numbers), and its thick film low-ohm file, read Vishay’s D/CRCW thick film datasheet for comparison, and checked our stock list as at 23 September 2026. The market figures name their source and the day we fetched them, 11 November 2026.

Why is current sense resistor selection a live question in India’s EV two-wheeler market?

Because volumes are climbing. According to Autocar India on 9 November 2026, electric two-wheeler retail sales in India reached 2,24,064 units in October 2026, up 48.5% year on year, with TVS at 60,490 units, Bajaj at 49,126 and Ather at 31,833.

Those are the publication’s figures, not ours. Every one of those scooters and motorcycles has a battery management system and a motor controller, and each measures current through a shunt. Range estimates, state-of-charge, over-current protection and torque control all depend on that one resistor reading true across temperature. We say nothing about any company’s designs or suppliers.

How do you choose a current sense resistor value?

From the amplifier and the peak current. The value is the amplifier’s full-scale input voltage divided by the peak current you must measure: a 50 mV full-scale input at 40 A gives 1.25 mΩ, so you pick the next value down, 1 mΩ, which reads 40 mV at 40 A and dissipates 1.6 W.

Then check four things in order:

1. Power: I squared R at the RMS current, with margin. Our working rule is no more than half the rated power, so 1.6 W calls for a 3 W part.
2. Signal: a lower value wastes less power but gives a smaller signal, so amplifier offset becomes a larger share of the reading at low current.
3. Tolerance: ±1% for metering and protection thresholds, ±5% only where you calibrate in production.
4. TCR: how far the value moves as the shunt heats, covered below.

A second example: a 15 A BMS discharge path with the same 50 mV amplifier gives 3.3 mΩ; at 3 mΩ it reads 45 mV and dissipates 0.68 W, so a 2 W part keeps it under half rating. These worked figures are ours, from Ohm’s law.

How much does TCR add to the current sense error?

TCR times temperature rise. A shunt at ±70 ppm/°C that heats 60 °C above its calibration temperature can move ±0.42%; at ±50 ppm/°C, ±0.30%; a thick film part at ±300 ppm/°C moves ±1.8% over the same rise.

That arithmetic is ours. Self-heating matters as much as ambient: at 1.6 W in a 2512, the resistor body runs well above the board, so specify TCR at the temperature it actually reaches. For comparison, Vishay’s D/CRCW thick film datasheet (document 20035) specifies ±100 ppm/K for its ±1% parts and ±200 ppm/K for ±1% parts from 1 to 9.76 ohm, which shows why metal element shunts dominate milliohm sensing. Use four-terminal (Kelvin) pads where the layout allows, since solder and copper add their own resistance and their own temperature coefficient.

Which Walsin metal current sense resistors fit a 1 mΩ or 3 mΩ brief?

Dozens at each value. We counted 48 Walsin metal current sense part numbers at 1 mΩ and 64 at 3 mΩ; across the file, 612 of 1,188 list a TCR of ±50 ppm/°C or better, available from 3 mΩ up, and 1,188 cover 66 values from 0.5 mΩ to 700 mΩ.

Walsin part	Series	Value	Size	Rated power	TCR (ppm/°C)	Match / mismatch for the worked brief	On the shelf, 23 Sep 2026
WW25BR001FTL	Metal plate	1 mΩ ±1%	2512	3 W	±70	Match, 40 A brief	request a quote
WW25AR001FTL	Metal plate power	1 mΩ ±1%	2512	3 W	±70	Match, 40 A brief	request a quote
WW25BR001FTLJ	Metal plate (automotive)	1 mΩ ±1%	2512	3 W	±70	Match, automotive series	request a quote
WW25NR001FTL	Metal plate power	1 mΩ ±1%	2512	2 W	±70	Mismatch: 1.6 W is over half rating	request a quote
WW25NR003FTL	Metal plate power	3 mΩ ±1%	2512	2 W	±50	Match, 15 A brief	request a quote
WW25MR003FTL	Metal plate power	3 mΩ ±1%	2512	1 W	±50	Mismatch: 0.68 W is over half rating	request a quote
WW12NR005FTLJ	Metal plate (automotive)	5 mΩ ±1%	1206	1 W	±50	Mismatch on value, smaller footprint option	request a quote

We checked each row against the export and our snapshot. At 1 mΩ, the export lists TCR from ±70 to ±100 ppm/°C; the ±50 ppm/°C parts start at 3 mΩ, with 8 at 3 mΩ and 21 at 5 mΩ. For these lines, request a quote and we source them through our authorised Walsin channel. Our low-ohm current sense: thick film vs metal guide covers the construction difference.

When is a thick film current sense resistor good enough?

When the value is higher and the accuracy budget is looser. Walsin’s thick film low-ohm file lists 10,428 part numbers starting at 5 mΩ, 8,730 of them with TCR between ±100 and ±500 ppm/°C; 3 were on our shelf as at 23 September 2026, including WW08WR270FTL, 0.27 ohm ±1% at ±100 ppm/°C in 0805.

• Good fit: fault detection, over-current trip points with margin, LED and small motor drives at a few amps, where a 1 to 2% drift is acceptable.
• Poor fit: pack current integration for state of charge, where TCR error accumulates into range error.
• Rule of thumb from our counts: below 5 mΩ, metal is the only Walsin route; from 5 mΩ to about 1 ohm, choose by accuracy budget.

How can Venatech help an Indian team pick the Walsin shunt?

How Venatech helps: send the current, the amplifier full scale and your current part, and we return the Walsin shunts that fit. Venatech Limited is Walsin’s authorised distributor in Hong Kong; our free VenaMatch tool decodes 18 manufacturers’ part numbers and crosses 800,000+ parts to Walsin, with value, size, power and TCR differences stated.

Paste up to 500 part numbers into the cross-reference tool or upload a BOM. The ready-stock list is a Hong Kong snapshot dated 23 September 2026; for the metal shunts above, request a quote and we source them through our authorised Walsin channel. Small lots from Hong Kong, no lead-time or stock promise, and no customs advice; confirm import requirements with your compliance team. The chip resistor range lists the families.

The short version

Value equals full-scale voltage over peak current; then size power at half rating and budget TCR times temperature rise. For an Indian e-two-wheeler, a 40 A path lands on a 1 mΩ, 3 W 2512 such as WW25BR001FTL, and a 15 A path on a 3 mΩ, 2 W, ±50 ppm/°C part such as WW25NR003FTL, from 1,188 Walsin metal shunts.

Send us your peak current, amplifier and current shunt part number, and we will return the Walsin options with power and TCR side by side. How hot does your shunt run at full load?

Related reading

• Low-ohm current sense: thick film vs metal
• What resistor TCR actually buys you
• Cross-referencing chip resistors to Walsin
• Free cross-reference tool and ready-stock snapshot

Last reviewed 11 Nov 2026.

Sources

Fetched 11 November 2026 unless stated.

• Autocar India, “TVS leads electric two-wheeler sales in October 2026 as sales nearly double”, 9 November 2026: https://www.autocarindia.com/bike-news/tvs-leads-e2w-sales-in-october-2026-as-sales-nearly-double-441292
• Vishay, D/CRCW e3 Standard Thick Film Chip Resistors datasheet, document 20035, revision 14 April 2026: https://www.vishay.com/docs/20035/dcrcwe3.pdf
• Walsin exports Metal_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx and Thick_Film_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx, and the Venatech stock list as at 23 September 2026, counted by us.

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Frequently asked questions

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