Sometimes the Deliverable Is a Drawing, Not a Fan

What the OEM actually asked for

A China-based OEM needed a DC cross-flow fan at 3300 RPM on 24 volts. However, the request was for two documents: a spec sheet and a 3D model. In other words, CAD model turnaround was the deliverable.

Evidently that tells you a good deal. The customer is past judging hardware and into detailed design. There, CAD model turnaround is what actually unblocks the work.

• A total length of 330mm at most, since the envelope was fixed.
• Then a 24V DC power architecture throughout the machine.
• A 0-10V control input, so airflow can vary.
• Lastly, papers in Chinese, compliant with GB/T13933-2008.

No airflow or pressure target came with the brief. Even so, the shape supplies the answer. A long, narrow envelope with variable airflow points at a tangential fan and nothing else.

Specifying the DC cross-flow fan

The form factor made the fan type obvious. A long, narrow profile is what a cross-flow wheel is for, since it lays down a wide, even sheet of air rather than a jet.

Why AC was never considered

Here the customer bus is 24V DC, which settles it. An AC motor would need an inverter added, bringing cost, bulk and a failure point into a small assembly. Consequently a brushless DC motor was the only sensible route.

Why the motor sits inside the impeller

So we specified an external rotor brushless motor, which sits inside the impeller hub itself.

That build is what makes the length work. A normal motor mounted beside the impeller adds to the total, and this design had only 330mm to spend. Putting the motor inside the hub buys that space back entirely.

Control without custom work

Our standard SmartEC controller platform met the 0-10V requirement directly. Consequently the fan joins the OEM control system straight away, with no custom firmware to write or debug.

What CAD model turnaround buys the customer

Firstly, the impeller is aluminum. Its low mass allows quick speed changes, and it keeps start-up current down. That matters on a small DC supply.

Meanwhile cold-rolled steel gives the housing rigidity and toughness at a cost suited to commercial kit. The finished model, LWCD-25300MN-07, runs a 25mm impeller 300mm long. It matches the voltage, control and size limits exactly.

Finally we produced and approved a Chinese-language drawing and a 3D STEP model, which closed the project.

Technical Specifications

Note the input power beside the impeller length. Under four watts drives 300mm of airflow, which is what an external rotor motor makes possible in a DC cross-flow fan.

Technical Documentation

The following documents were the final approved deliverables for project LWCD-25300MN-07.

Project Summary: This image shows the key parameters for model LWCD-25300MN-07 as tracked in Longwell’s project management system, confirming the core electrical and dimensional specifications for procurement managers.

Engineering Drawing & Specification Sheet: The official engineering drawing provides all critical dimensions, materials, wiring diagrams, and technical parameters needed by a design engineer for system integration and by quality teams for incoming inspection.
Open LWCD-25300MN-08-00 (PDF)

What fast CAD model turnaround is worth

For an OEM in a competitive market, four things mattered.

• CAD model turnaround, not just components. The heart of this project was speed rather than clever design. Producing a Chinese spec sheet and a STEP model quickly is what kept the customer NPI timeline intact.
• A local supply chain. For a China-based OEM, sourcing from our Ningbo facility removes international freight, import duty and cross-timezone delay. That shortens the path from purchase order to production line noticeably.
• Cost suited to commercial HVAC. Equipment in this market competes hard on price, so the fan is among the first components examined. We keep motor and impeller production in house, which is what makes that examination survivable.
• Test data behind the paperwork. This request was for a DC cross-flow fan datasheet. Nonetheless, every product is backed by testing compliant with AMCA 210/211 and ISO 5801, which supports the design-in work that follows.

Browse our cross-flow fan range, or the DC cross-flow fan series for other lengths. Test methods are defined in ISO 5801.

Questions about customization and data

How fast is CAD model turnaround in practice?

For a standard model, the 3D file and drawing go out the same day the request is logged. For a variant needing a dimension change, allow 3 to 5 working days for the drawing. Tooling, where it is needed at all, is the only step that turns days into weeks.

What is the lead time on 100 to 500 units?

A standard make-to-order HVAC fan runs 15 to 25 days after order confirmation. More complex industrial models, or anything needing ATEX certification, take 30 to 45 days. We also hold stock on some high-volume models for 1 to 5 day shipment.

Can the length or voltage be customized?

Yes. Changing the impeller length or the motor windings of a DC cross-flow fan is normal work under our 90-day NPI process, and we adapt this design for 12V or 48V regularly. Expect an NRE fee between USD 12,000 and 40,000 depending on scope, half of which we credit against your first mass production order.

Are P-Q curves available?

Yes. Full aerodynamic curves, acoustic data and power consumption charts are available on request for every model, generated by internal lab testing following AMCA 210/211 and ISO 5801. For customers with a live project, those test reports can be delivered within one working day.

Why does an external rotor motor suit a compact fan?

Because it takes a separate motor out of the length budget. Normally the motor sits beside the impeller and adds to the total. An external rotor design instead wraps the rotating part around the stator and drives the blades directly. Consequently the motor occupies space the fan already needed.