MOV varistor peak current does not scale with disc size. Dividing all 379 Walsin parts by nominal disc area gives 5.1 to 69.2 A per square millimetre, a 13.6x spread, and the Standard series re-rates the same disc by 3.25x to 5x between 40 and 50 Vac. We have not seen this counted anywhere.
Venatech Limited, an authorised Walsin distributor in Hong Kong, holds the metal oxide varistor parametric export published by Walsin Technology (Walsin): 379 rows, and no datasheet for any varistor. This post is written from that one file. Every part number below is real. Nobody in this catalogue states a surge rating per unit area, so we computed one from the two fields the file does give, Size and Peak Current, to see whether the diameter in the part’s name tells you what the part will survive.
How much peak current does a Walsin varistor carry per square millimetre of disc?
Between 5.1 and 69.2 A. We parsed all 379 rows, took the nominal disc area from the Size column (a circle for the diameters, a square for the 34 mm square disc) and divided each part’s peak current by it. The lowest is SR180K05D at 5.1 A per square millimetre and the highest is the 80,000 A square disc SR201K34RD at 69.2, a spread of 13.6 times.
| Series | Parts | Footprints | Lowest A per mm² | Highest A per mm² | Match / mismatch against “peak current scales with disc area” |
|---|---|---|---|---|---|
| Standard (D) | 170 | 6 | 5.1 (SR180K05D) |
36.7 (SR181K25D) |
Mismatch — a 7.2x spread inside one series |
| High Energy (E) | 48 | 3 | 35.4 (18 mm) | 45.5 (7 mm) | Mismatch — the 7 mm disc beats the 18 mm disc |
| Super High Energy (V) | 60 | 3 | 41.4 (20 mm) | 52.0 (14 mm) | Mismatch — the 14 mm disc beats the 20 mm disc |
| Industrial | 101 | 4 diameters, 5 ratings | 31.7 (53 mm) | 69.2 (34 mm square) | Mismatch — the 53 mm disc is the lowest |
If rating scaled with area, every row would be one number. In none of the four series is it. In High Energy, Super High Energy and Industrial, the largest disc is the lowest or near the lowest per unit area, which is what you would expect if a large disc is rated for its energy and not for its area, but we hold no varistor datasheet and cannot say that is Walsin’s method.
Where does the Standard series re-rate the same disc?
Between 40 Vac and 50 Vac, on every Standard footprint that spans both. We listed the peak current of each Standard disc down its voltage ladder. Five of the six Standard footprints carry two peak current values, and the break is at the same place on all five: 36 of the 170 Standard parts, at 11 to 40 Vac, are rated 3.25 to 5 times lower than the same disc at 50 Vac and above.
| Footprint | Last low-voltage part | Rating | First 50 Vac part | Rating | Step | Match / mismatch |
|---|---|---|---|---|---|---|
| 5 mm | SR680K05D (40 Vac) |
100 A | SR820K05D |
400 A | 4.0x | Mismatch on peak current, same diameter |
| 7 mm | SR680K07D (40 Vac) |
250 A | SR820K07D |
1,200 A | 4.8x | Mismatch |
| 10 mm | SR680K10D (40 Vac) |
500 A | SR820K10D |
2,500 A | 5.0x | Mismatch |
| 14 mm | SR680K14D (40 Vac) |
1,000 A | SR820K14D |
4,500 A | 4.5x | Mismatch |
| 20 mm | SR680K20D (40 Vac) |
2,000 A | SR820K20D |
6,500 A | 3.25x | Mismatch; the 20 mm ladder starts at 25 Vac, so only 4 low-voltage parts |
| 25 mm | none; ladder starts at 120 Vac | none | SR181K25D |
18,000 A | n/a | Match — a single rating |
Read the first two columns together. A buyer who filters on “7 mm, Standard, 250 A” gets 8 parts that all stop at 40 Vac. A buyer who filters on “7 mm, 1,200 A” gets 19 parts that all start at 50 Vac. The same diameter is two different surge devices. Our series post said so in one sentence in the D, E, V and Industrial comparison; the numbers here are the new part.
Does disc diameter change the varistor voltage to working voltage ratio?
No. We checked every one of the 35 working voltage steps. Each Vac step maps to exactly one varistor voltage across every diameter that offers it: 35 working voltages, 35 varistor voltages, zero steps with two answers. The ratio runs from 1.500 at 120 Vac (180 Vdc) to 1.700 at 40 Vac (68 Vdc), and it does not depend on the disc.
| Diameter group | Parts | Lowest varistor-to-working ratio | Highest | Match / mismatch against the 1.50 to 1.70 file-wide band |
|---|---|---|---|---|
| 5, 7, 10, 14, 20 mm | 237 | 1.500 | 1.700 | Match — whole band |
| 18, 25 mm | 41 | 1.500 | 1.655 | Match, upper end narrower — nothing at 40 Vac |
| 32, 34 mm square, 40, 53 mm | 101 | 1.538 | 1.655 | Match, narrower still — nothing below 130 Vac |
The ratio band narrows with diameter only because large discs exist only at high voltage: nothing above 20 mm is offered below 120 Vac. The disc is not what narrows it; the ladder is. The practical effect is that a clamping estimate built from the file’s two voltage fields carries the same ratio at 5 mm and 53 mm, and any difference in let-through voltage between them is a property the export does not publish. The export has no clamping voltage column at all. Our earlier post on the choice of a varistor covers the selection steps that follow.
Which series gives the most surge rating per square millimetre?
Industrial, but only because of one suffix. We ranked all 22 distinct (series, footprint, rating) groups by A per square millimetre. The top three are the 80,000 A square disc at 69.2, the Super High Energy 14 mm at 52.0 and the Super High Energy 10 mm at 50.9; the bottom five are all Standard-series low-voltage groups, at 5.1 to 6.5.
| Rank | Group | Peak current | A per mm² | Example part | Match / mismatch against “same diameter, same rating” |
|---|---|---|---|---|---|
| Highest | Industrial 34 mm square, 34RD |
80,000 A | 69.2 | SR201K34RD |
Mismatch with SR201K34R, same 34 mm disc at 40,000 A (34.6) |
| 2 | Super High Energy 14 mm | 8,000 A | 52.0 | SR201K14E |
Mismatch with SR820K14D, same 14 mm at 4,500 A (29.2) |
| 3 | Super High Energy 10 mm | 4,000 A | 50.9 | SR201K10E |
Mismatch with SR820K10D, same 10 mm at 2,500 A (31.8) |
| Lowest | Standard 5 mm, 11 to 40 Vac | 100 A | 5.1 | SR180K05D |
Mismatch with SR820K05D, same 5 mm at 400 A (20.4) |
The 34 mm square disc exists twice at every voltage, as 34R and 34RD, and the second carries exactly double the rating. That doubling is the entire difference between rank one and the middle of the Industrial range. Neither the suffix nor the rating tells you which is which unless you read both. Check the whole thing against the 40,000 A versus 80,000 A comparison.
What should a selector do with a peak current filter?
Filter on peak current, diameter and voltage together, because the file holds 21 distinct peak current values and five of six Standard footprints carry two of them. The export is the only source we hold. Three rules follow.
- Never infer surge capability from diameter. The same 10 mm disc is rated 500 A, 2,500 A or 4,000 A depending on series and voltage.
- Never filter a Standard-series disc on a peak current figure without a voltage. The rating changes between 40 Vac and 50 Vac on five of six footprints.
- Never read the 69.2 as an area law. The area is our arithmetic, the pulse waveform is unstated, and we hold no varistor datasheet.
None of the 379 varistor part numbers appears in our ready-stock snapshot of 1,125 part numbers as at 23 September 2026, so the ready stock page will not list one today; ask us for availability on the part you need. The family page is varistors, and our free cross-reference tool states the differences from your original rather than hiding them behind a tick.
The short version
Walsin’s varistor peak current per square millimetre of disc runs from 5.1 to 69.2, a 13.6x spread, with a Standard series that re-rates five of six footprints by 3.25x to 5x between 40 Vac and 50 Vac. 36 of 170 Standard parts sit below the break. All 35 working voltage steps map to one varistor voltage, so diameter does not move the 1.50 to 1.70 ratio. The export has no clamping voltage column. We hold no varistor datasheet, so every figure is the file’s, not Walsin’s published statement. We will not tell you a varistor matches on surge. We will show you the rating the file holds. Qualification stays with you; confirm against both datasheets and qualify in your own circuit.
Send us the varistor on your board, its diameter and the surge you design to, and we will show you which Walsin rows differ and by how much. And a question back: when your selector said “14 mm, 4,500 A”, did it tell you the same disc is 1,000 A below 50 Vac?
Frequently asked questions
Does a larger Walsin varistor disc always carry more peak current?
Not per unit area. Across 379 parts the peak current per square millimetre of nominal disc area runs from 5.1 to 69.2, a 13.6x spread. In the High Energy series the 7 mm disc at 45.5 beats the 18 mm disc at 35.4, so diameter alone does not rank surge capability.
Where does the Walsin Standard series change its peak current rating?
Between 40 Vac and 50 Vac. Five of the six Standard footprints carry two ratings with the break at that point, and 36 of the 170 Standard parts sit below it. The 7 mm disc is 250 A up to 40 Vac and 1,200 A from 50 Vac, a step of 4.8x.
Does disc diameter change the varistor voltage to working voltage ratio?
No. Each of the 35 working voltage steps maps to exactly one varistor voltage across every diameter offering it, from 1.500 at 120 Vac to 1.700 at 40 Vac. The band looks narrower on large discs only because they are not offered below 120 Vac.
Does the Walsin varistor export publish a clamping voltage?
No. The file has ten columns, and none is a clamping voltage, a let-through voltage or an energy rating in joules. The only surge figure is Peak Current, with 21 distinct values and no pulse waveform stated. Confirm clamping voltage against Walsin’s published catalogue.
Why does the 34 mm square disc appear twice at each voltage?
It is published as 34R at 40,000 A and 34RD at 80,000 A, each at 21 voltage steps, 42 parts in all. The two share every voltage point and differ only in peak current, which is double on the D version. The suffix is the only visible difference.
Are Walsin varistors in your ready-stock snapshot?
None of the 379 varistor part numbers appears in the snapshot of 1,125 part numbers as at 23 September 2026. That is a dated snapshot, not a live feed. Send us the part numbers you need and we will confirm availability directly.