A standard is a set of tests, not a property of a shape. RoHS & REACH is one of the documents finned ptc air heaters are built to; the sections below say what it fixes, what it does not, and what has to be named on the enquiry for the approval to be usable.
RoHS & REACH — Scope
Restriction of hazardous substances in the materials and the solder, and declaration of substances of very high concern. Required for anything sold into the EU.
What RoHS & REACH Does Not Cover
A compliance declaration, not a safety approval.
This is the division of labour to carry away from any heating standard: safety standards decide whether the part can hurt somebody, and say nothing about whether it holds a temperature, lasts five years or matches the last batch. Performance is a specification you write; safety is one the standard writes.
How a Made-to-Drawing Heater Is Certified
A construction is built and tested to a standard. The insulation system, the creepage and clearance distances, the earthing, the lead anchorage, the temperature under fault and the marking are what the test covers — and all of those are properties of the construction rather than of the outline it is die-cut to.
So a custom outline does not have a certificate of its own, and no supplier can honestly hand you one. What is available is the construction file: the standard the build is tested to, the materials list with their own ratings, and the test reports. That is what an approvals engineer needs, and it is what the end product's own certification is built on.
The practical consequence: name RoHS & REACH on the enquiry, not after approval. A construction chosen for cost and then asked to pass a standard afterwards usually has to be rebuilt, because the insulation thickness, the creepage distances and the lead anchorage are decided at design time and are not adjustable later.
From the capability table: UL 499, IEC/EN 60335, RoHS, REACH, CE, IATF 16949.
What a Finned PTC Air Heaters Is
PTC elements bonded into an aluminium fin stack, for warming air in cabinets, dryers, vehicle cabins and enclosures.
Barium titanate ceramic whose resistance rises steeply above its Curie point, so the power it draws falls as the surface approaches that temperature. The element cannot exceed the Curie point it was made to, whatever the supply or the control does. The elements are clamped into an aluminium fin stack: with air moving through the fins the assembly runs cool and draws its rated power, and with the airflow blocked it simply throttles itself back instead of glowing.
The heat leaves through a clamped joint, and a clamped joint is only as good as the pressure and the flatness behind it. A thermal interface material or a thin film of thermal grease fills the gaps that machining leaves; without one, contact happens at the high spots and the element runs hotter than the plate it is bolted to.
| Element | barium titanate PTC ceramic |
|---|---|
| Insulation system | aluminium carrier with insulating film |
| Total thickness | Element 1.5 mm to 3 mm; assembly to your drawing |
| Maximum size, one piece | 50 x 50 mm to 250 x 150 mm frame |
| Continuous working temperature | 250 °C |
The continuous limit of 250 °C is set by aluminium carrier with insulating film. The element alloy would run far hotter; it is never the element that decides.
The Other Standards This Construction Is Built To
A heater is rarely governed by one document. This construction is also built and tested to:
Safety, materials, substances and quality system are four separate questions with four separate documents behind them. A part can satisfy all four and still be the wrong heater for the duty, which is what the rest of this page is about.
Control and Protection
This is the one construction here that limits its own temperature. Above the Curie point the ceramic's resistance rises steeply, the current falls, and the element settles rather than climbing — so a PTC heater cannot thermally run away even with the control shorted out.
That is a safety property, not an accuracy one. Self-regulation holds a surface somewhere near the Curie point under whatever cooling it happens to have; it does not hold a set point, and the temperature it settles at moves with airflow, with supply voltage and with the load. Where a number has to be held, a sensor and a controller are still required.
Two things still have to be designed for: the inrush, which is several times the running current while the ceramic is cold and which the supply and any switching device must tolerate, and the electrical fault case, which self-regulation does nothing about — a fuse or a current-limited supply is still the protection against a short.
Watt Density: the Two Figures
Watt density, not wattage, is what the construction is limited by. 1 W/cm² unbonded and 6 W/cm² bonded to metal are the limits for this build — so if the wattage is fixed by the duty, the area is what has to move.
Where the required power will not fit into the available area at the free-air figure, the answer is a better thermal path rather than a thinner margin: bond the whole face down, or add a spreader plate. On 150 cm² the difference is roughly 15 W against 9 W, which is usually the whole argument.
A PTC assembly behaves differently at the limit. Deprived of its heat sink it does not run away; it reduces its own power. The consequence of a poor thermal path here is a heater that delivers well under its nameplate power, not one that destroys itself.
Attachment and Thermal Contact
The part is clamped, not bonded. What matters at the joint is flatness, contact pressure and a thermal interface material to fill what machining leaves behind — a dry joint between two nominally flat surfaces touches on perhaps a few percent of its area.
A PTC element clamped without a proper thermal path does not overheat — it throttles itself back and delivers a fraction of the power the assembly was specified for. The symptom of a bad joint here is a heater that seems underpowered rather than one that burns out.
The joint between the heated surface and the load carries every watt the element makes. Fill it: an interface pad, a thin film of thermal grease or a bonded assembly. Two dry surfaces bolted together are a thermal resistance, and that resistance appears as element temperature.
How to Specify One
This is a made-to-drawing part, so there is no catalogue number to quote. A quotation is built from the following, and the more of it that arrives with the enquiry the fewer rounds it takes:
- An outline drawing, or a sketch with dimensions: overall size, holes, cut-outs, radii and the lead exit position.
- The supply voltage, and whether it is AC or DC. The element is wound for one voltage; it is not a switchable range.
- The power required, or — better — the temperature to be reached and the mass or flow it has to be reached in. Given the second, the wattage can be calculated instead of guessed.
- What the heater is attached to, and how. This is what decides which watt density figure applies, and it is the question a quotation cannot proceed without.
- The ambient, and the lowest temperature the assembly must start from. A heater sized for a 20 °C start is undersized for a -30 °C one.
- Duty cycle: continuous, intermittent, or a warm-up to a deadline. Time to temperature is a specification, not a by-product.
- Sensor and protection: which sensor, where it goes, and which limit device is fitted in series with the element.
- The certification the end product is built to, named on the enquiry rather than after approval.
- Quantity and target price, because the construction that is right for fifty pieces is often not the one that is right for fifty thousand.
- The Curie point wanted, and the airflow or thermal path the assembly will have — both decide the power the element will actually deliver.
Lead time: Samples 7-10 days from approved drawing; production 15-20 days.
Finned PTC Air Heaters — Capability Table
These are process limits for the construction, not the specification of one stocked item. Every line is what the factory can hold; what your part holds is fixed on your drawing.
| Parameter | Specification | Limit / note |
|---|---|---|
| Construction | Barium titanate PTC ceramic, electroded on both faces, in an aluminium carrier | Assembly built around the element to suit the load |
| Curie temperature | +80 u00b0C to +250 u00b0C, selected | Selected at order u2014 it is the surface temperature ceiling and cannot be adjusted afterwards |
| Self-regulation | Power falls to a fraction of rated as the surface reaches the Curie point | No thermostat is required to prevent runaway; one may still be wanted for control |
| Element size | 50 x 50 mm to 250 x 150 mm frame | Standard element footprints; assemblies to your drawing |
| Supply voltage | 12 V, 24 V, 110 V, 220 V | The same element works over a voltage band with different output |
| Power output | 1.0 W/cmu00b2 typical in still air, 6.0 W/cmu00b2 with forced air | Output is set by the airflow, not by a setting u2014 this is what self-regulating means |
| Inrush current | 3 to 8 times running current for 1 to 3 seconds | The supply and any relay or MOSFET must tolerate it |
| Dielectric strength | 1800 V AC, 1 minute, element to case | On the assembled unit with its insulation in place |
| Insulation resistance | greater than 100 Mu03a9 at 500 V DC | |
| Terminations | Faston 2.8/4.8 mm, crimp, or flying leads | Chosen for the assembly temperature |
| Life | Over 10,000 hours at rated conditions | Ageing shows as a slow rise in cold resistance, not as sudden failure |
| Certifications available | UL 499, IEC/EN 60335, RoHS, REACH, CE, IATF 16949 | Construction level |
| Airflow | 0.5 to 5 m/s across the fins | Output rises with airflow automatically u2014 the element does the regulating |
| Fan | Axial or blower to your specification, or supplied without | A PTC heater with a failed fan drops its own power instead of burning |
Capability figures are for barium titanate PTC ceramic elements and the aluminium assemblies built around them. The defining property — that power falls steeply as the element approaches its Curie point, so surface temperature cannot run away — is inherent to the ceramic, not a feature of the control.
