Adding Qi wireless charging to a product buys you a sealed housing with no connector to fail and a charging experience users already understand. It costs you a receiver coil and IC, a chunk of internal space, a new heat source right next to the battery, and a certification and licensing step if you want to use the Qi name or logo. For a wearable, a medical instrument, or anything that lives in a wet or dirty environment, that trade is usually worth making. For a device the user plugs in once a week, it rarely is.

How Qi works, briefly

Qi is inductive coupling: a transmitter coil in the charging pad drives an alternating field, a receiver coil in your product converts it back to DC. Two aspects matter for design decisions:

  • It is a two-way protocol, not just a field. The receiver communicates with the transmitter to negotiate power, request more or less, and signal completion or a fault. That is why a compliant transmitter does not blast full power into an unknown object.
  • Coupling is geometric. Efficiency depends on coil alignment, coil diameter match, and the separation between coils. Move the receiver a few millimeters off center, or add material between the coils, and delivered power drops sharply while losses rise.

The baseline profile delivers a handful of watts, sufficient for wearables, small sensors, and phone-class devices. Extended profiles reach higher power for larger products. Above that you are into different technologies with different trade-offs.

The electronics side

A wireless charging path has more stages than a USB port, and each one has to be specified:

  • Receiver coil. Characterized by inductance, Q factor, and DC resistance. Larger coils couple better and tolerate misalignment; small products end up trading efficiency for space.
  • Ferrite shield. A thin ferrite sheet behind the coil directs the field and, critically, keeps it out of the battery and the ground plane. Omitting it causes eddy-current heating and erratic behavior. This is not optional.
  • Receiver IC. Handles rectification, protocol communication, and regulation. Many integrate the battery charger; others hand off to a separate charge controller.
  • Charge management. Constant-current then constant-voltage profile, plus temperature-qualified charging so a cold or hot cell is not charged — the same discipline described in battery pack design for a product.
  • Foreign object handling. The transmitter detects metal objects in the field by monitoring power loss; your receiver's reporting accuracy participates in that. Poor accuracy causes nuisance shutdowns.

Expect the whole receiver path to be meaningfully less efficient than a wired input. The energy that does not reach the battery becomes heat inside your enclosure. Many products keep a wired port anyway for factory programming and service — see USB-C in a new product.

The mechanical side: coil, housing, and gap

Wireless charging is as much a mechanical problem as an electrical one:

  • Total gap. Your housing wall plus any air plus the transmitter's own surface all count. Every extra millimeter reduces coupling. Thin the wall locally over the coil if you can.
  • No metal in the field path. A metal back, a metal label, an internal shield can, or a steel screw over the coil will heat up and kill efficiency. This is a real constraint on industrial design, discussed in electronics enclosure design.
  • Alignment features. Users are not precise. A magnetic alignment ring, a recess, or a cradle geometry dramatically improves the real-world experience over a flat pad.
  • Coil mounting. The coil must stay flat and located; adhesive-mounted coils that shift during drop testing cause intermittent charging complaints.
  • Keep sensitive parts away. Magnetometers, hall sensors, NFC antennas, and cards in the field path all misbehave. NFC and inductive charging in the same area needs deliberate coordination — see NFC versus RFID.

Heat is the real limit

Wireless charging concentrates loss in a small volume, immediately adjacent to a lithium cell that is itself warming as it charges. Consequences worth designing for from the start: charge current may need to be reduced when temperature rises, which lengthens charge time; the touch surface has a maximum allowable temperature; and sustained elevated temperature during every charge cycle shortens cell life. Model and then measure this with the real enclosure closed, not on an open bench — the approach is in thermal management in electronic products.

Certification and logo licensing

Two separate obligations, and teams routinely conflate them:

  • Regulatory. A wireless power device is an intentional radiator and must be authorized before sale in the US, alongside the usual electromagnetic compatibility work. See FCC certification for electronics and EMC testing cost.
  • Standard compliance and branding. Using the Qi name or logo requires membership in the standards body, testing at an authorized test lab, and registration of the product. You can build an inductive charging product without that, but you cannot call it Qi, and interoperability with the installed base of pads becomes your problem to prove.

Practical shortcut: using a well-supported reference design and a pre-qualified coil from the same vendor removes a large amount of compliance risk. Custom coil geometry is where interoperability failures come from.

When it is worth it

Strong cases: sealed products that cannot have a connector, devices used with wet or gloved hands, high-cycle-count docking where a connector would wear out, and consumer products where the charging experience is part of the value. Weak cases: products charged infrequently, products where every dollar of bill of materials is contested, and products with a metal exterior that would have to be redesigned around the coil.

How Projects House approaches it

We settle coil size, wall thickness, and heat path together before the housing is styled, because wireless charging retrofitted into a finished enclosure almost always ends in a compromise on either charge time or surface temperature. More on this area is collected on our electronics development page.

Considering wireless charging?

Send us your product details through the contact form and we will assess whether Qi fits your enclosure, power budget, and thermal headroom — before it becomes a redesign.