A colleague sent me two links last week. One was 29.9 yuan, the other 329. Both were round pads, both claimed 15W, both had the Qi logo printed on the box, and he wanted to know what justified a tenfold gap. You cannot answer that from outside the case, so we opened them. I lined up the published teardowns I could find against a comparison test run by the Shanghai consumer council, and the answer turned out to be blunter than expected: the price difference sits almost entirely in four places — the controller chip, the shielding sheet and coil winding underneath, the thermistor stuck at the centre of the coil, and whether foreign object detection is real or just printed on the box.

Start with the part that actually matters: foreign object detection. In 2024 the Shanghai consumer council ran a comparison test on phone wireless chargers, buying 18 units — four bundled originals from Huawei, Apple, Xiaomi and vivo, and 14 third-party models from brands such as Bull, Ugreen and Baseus. Prices ran from 29.9 to 329 yuan, with third-party units averaging 90 yuan. Tested against GB 4943.1-2022, all 18 passed on heating and charge protection, with peak temperatures during charging landing between 29.7°C and 67.0°C. But six failed foreign object detection: they kept pushing power with a metal object nearby, and that object's temperature blew past the standard's limit. A one-in-three failure rate is not trivial for a product category where people toss their keys onto the desk without thinking.

So what should a competent board carry? Open a 15W disc like the Baseus BS-W526 and the inside is mostly empty: one transmitter coil in the middle, with the PCB squeezed into less than half the remaining area. Everything that belongs there has to be there — a reasonably integrated wireless charging SoC (this one uses a Maxic MT5811; OPPO's 50W unit uses a Renesas IDTP9247), four MOSFETs forming a full bridge, a few paralleled NPO resonant capacitors, a 16MHz crystal, a shielding sheet under the coil, and an NTC thermistor planted right at the coil's centre. That last part costs about a cent, yet it is the only temperature source over-temperature protection has. Leave it out and the phrase 'smart thermal control' on the listing page means nothing at all.

The coil winding matters too, and teardown photos make it obvious. Native Union's SNMAG01 magnetic pad is wound with Litz wire, thinner than the conventional served wire, which is how the whole unit comes in at 8.4mm thick. vivo's 50W stand has room to spare inside, so it still uses served wire. Magnetic models also add a neodymium magnet ring in the top cover with a shielding sheet at the centre. So a magnetic wireless charger costing more than a plain pad is not pure markup — the magnet ring itself, and the concentric assembly tolerance between it and the coil, both cost real money. Worth noting: that same teardown shows a Luxshare contract-manufacturing mark, and whether the contract factory is allowed to specify Litz wire usually says more about the cost tier than the brand logo does.

Why do the tall stands and high-power models cost hundreds? Open one and it is obvious: mechanical parts. vivo's 50W Vertical Wireless Charger 2 (CH2351) packs two coils — one for portrait, one for landscape — plus a motor-and-leadscrew reduction assembly with a sliding potentiometer for position feedback, so the coil physically travels up and down to align itself with the phone. There is also an infrared distance sensor to tell whether a phone has been set down, and a Delta NS55B08 fan for cooling. OPPO's AIRVOOC 50W puts a thermistor on each of its two coils, fills the shield can with thermal gel and adds copper foil on top, with a hydraulic-bearing fan at the base. None of this occupies a single line on a spec sheet, yet it is the most tangible gap between a few dozen yuan and a few hundred.

Now the question people ask most: why does a 15W pad feel like 10W? Among the 12 units that passed the safety tests, three were rated 50W, six 15W and three 10W. Bundled originals run proprietary protocols: Huawei, Xiaomi and vivo all hit a full 50W with their own phones, and Huawei took just 64 minutes to go from 0% to 100%. Apple's own 15W pad took about 2.7 hours. Cross brands and the tier collapses: Huawei's 50W unit only managed 11W on an iPhone, about 2.9 hours; Apple's 15W unit gave a Huawei phone 6.8W and took close to five hours. Third-party pads can only use open protocols, mostly landing between 10W and 20W, and the eight third-party units averaged three to five hours for a full charge. The number 15W never holds up on its own — it depends on which device is talking to which.

On charging through a case, the test data is more honest than most product pages. All 12 units charged through a phone case. Using stacked A4 sheets to simulate case thickness, maximum transfer distance ranged from 3.9mm to 7.6mm, averaging 6.0mm, with all four bundled originals above 6.0mm. Translated into daily life: ordinary silicone and standard hard cases are fine; the ones that actually break charging are thick drop-proof cases over 6mm, wallet cases, and anything with a metal ring or magnetic strip. The test also flagged a couple of samples with small gaps around the charging port and a harsh chemical smell — neither will ever appear in an online listing, but you can judge both yourself within three seconds of unboxing.

Three checks I actually use. First, slip a coin between the pad and the phone: a proper product should cut output within a few seconds and the coin should stay cool. If it keeps charging happily, you are holding a cousin of those six failed samples — return it. Second, read the label. If the manufacturer name, maximum power or model number is missing, walk away, and give it a sniff for that harsh plastic smell while you are at it. Third, if it will sit on your nightstand overnight or run all day, pick an aluminium housing with a graphite sheet or a fan; power only stays stable if temperature does. Three-in-one wireless chargers and multi-device pads raise the stakes further — feeding a phone, a watch and earbuds at once means every channel needs its own coil and thermal budget, and reading only the combined wattage is how buyers get burned. For bulk deployments in homes and public venues my advice is blunter: write foreign object detection into your acceptance criteria. People leaving keys, coins and room cards on a charging surface is the norm, not the exception, and for factories doing design and customisation, production and sales, these few components are exactly where the conscience line sits.

This article is originally published by Shanwu. Please credit the source when reposting.

Copyright © 2026 Shanwu. All Rights Reserved.