Printed Silver and Etched Copper PET Heaters wound for 110-120 V AC. The supply decides the element: 500 W at this voltage is 24.2 Ω, and the same 500 W at a tenth of the voltage would be a hundredth of the resistance in a conductor ten times heavier. This page covers the circuit, the isolation, the switching and what the construction can be built to at this supply.
The Element at 110-120 V AC
Two equations do all the work: P = V²/R and I = P/V. At 110-120 V AC, 500 W is 24.2 Ω and 4.55 A.
| Worked example | 500 W at 110-120 V AC |
|---|---|
| Element resistance, R = V²/P | 24.2 Ω |
| Current, I = P/V | 4.55 A |
The span matters more than the example. At 110-120 V AC a 20 W element is 605 Ω and a 500 W element is 24.2 Ω — a factor of twenty-five in resistance, met by changing the conductor cross-section and the length of the path, both of which are constrained by the outline.
At mains voltage the difficulty is the opposite one. Current is modest — 4.55 A for the worked example — but the element is a long, fine conductor, and a low-wattage heater at 110-120 V AC is the hardest thing in this catalogue to build: 20 W means 605 Ω, which is a very long track to fit inside a small outline without the pitch becoming so tight that adjacent runs interact.
Where the arithmetic will not fit the outline, the usual answers are a lower supply voltage with a small power supply behind it, several circuits in series, or a different construction entirely. What does not work is thinning the conductor further: the track becomes the fuse.
Resistance tolerance is u00b110% standard, u00b15% on request, and power follows resistance inversely: a u00b110% standard, u00b15% on request tolerance band is the same band on the delivered wattage. Where the wattage matters — a warm-up to a deadline, a pack of heaters that must match — say so on the enquiry and the tighter band is selected and tested.
Isolation, Earthing and Safety Class
110-120 V AC is a mains supply, and the construction is built to match: mains-rated insulation, a protective earth connection or a double-insulated build, and creepage and clearance distances held between the element and any accessible surface.
Leakage current is the figure that surprises people. A large heated area behaves as a distributed capacitance to earth, so a big mains heater has a measurable leakage even when it is perfectly sound, and an RCD protecting several of them can trip on the sum. Where several elements share a circuit, allow for the total.
| Dielectric withstand | 1500 V AC, 1 minute |
|---|---|
| Insulation resistance | greater than 100 Mu03a9 |
Every heater is tested to these before it ships, element to any exposed surface. A dielectric test is a pass or a fail, not a measurement — a part that passes at 2500 V is not one that may be run at 2500 V.
What a Printed Silver and Etched Copper PET Heaters Is
Where carbon ink cannot hold the resistance tolerance or the watt density, a silver ink or an etched copper circuit on the same PET film.
Carbon or silver ink screen printed onto PET polyester film, laminated and die cut. It is made on a roll, which makes it the cheapest heater per square metre by a wide margin at volume, and it stops at 120 °C because the film does. Silver ink and etched copper give a much lower sheet resistance than carbon, which is what makes a low-voltage element on a large area practical; the trade is cost and, under a DC bias in damp air, the risk of silver migration between adjacent tracks.
The heat leaves through the bonded face. Everything that is not in contact with the load radiates and convects from the back of the heater instead, which at these thicknesses is a poor path — so an air gap under part of the outline is not a small loss of efficiency, it is a hot spot at that spot.
| Element | screen-printed carbon or silver ink |
|---|---|
| Insulation system | PET polyester film |
| Total thickness | 0.25 mm |
| Maximum size, one piece | 400 x 1000 mm |
| Continuous working temperature | 120 °C |
The continuous limit of 120 °C is set by PET polyester film. The element alloy would run far hotter; it is never the element that decides.
Switching an AC Element
AC switching has a zero crossing to hide behind. A zero-cross solid state relay makes and breaks at the crossing, which all but removes the switching transient and the conducted emissions that go with it — worth having on any installation that also has to pass an EMC test.
Control by burst firing — whole cycles on, whole cycles off, over a period of a second or more — rather than by phase angle. Burst firing generates almost no harmonics; phase angle control chops the waveform and is the reason a heater ends up in the EMC report at all. A heater has enough thermal inertia that a one-second period is invisible at the surface.
Size the relay for the inrush, not the running current, and heatsink it: a triac or SSR drops around one volt per amp of load, and that is real power to be got rid of inside the panel.
Watt Density: the Two Figures
Two watt densities are quoted because there are two thermal situations. With nothing conducting heat away, 0.2 W/cm² is what the insulation survives. Bonded to a heat sink over the full outline, 1 W/cm² is. Anything in between depends on the quality of the joint, and the joint is the customer's to make.
The failure is silent and quick: the element does not know how it is mounted, so at 1 W/cm² in free air the heat simply accumulates in the insulation until it degrades. This is the single most common way these heaters are destroyed, and it happens on the first run rather than after a year.
Leads and Terminations
Lead wire as supplied: Crimped or soldered leads, or a printed silver bus bar with a bonded tail. Length, gauge, exit position and termination are drawing items — the exit position in particular, because it decides where the heater can be routed and it cannot be changed after the tool is cut.
The lead exit is a thermal discontinuity as well as an electrical one. The joint between a fine element and a stranded lead is the hottest point of many heaters, so it is kept out of the highest watt density zone, strain relieved, and — where the exit sits in a hot area — insulated in PTFE rather than in silicone.
Control and Protection
This heater has no way of limiting its own temperature. Resistance heating draws roughly the same power whatever the temperature, so with the load removed, the fluid gone, the fan stopped or the sensor open circuit, the element keeps producing watts until something stops it.
The design must therefore contain a control device and, separately, a protective one: a controller with a sensor to hold the set point, and a bimetal thermostat or a one-shot thermal cutoff wired in series with the element to open the circuit if the loop ever fails. The two are not interchangeable — a controller that has lost its sensor cannot protect anything, which is exactly the fault the cutoff exists for.
PET softens at about 130 °C and loses its dielectric strength as it does, so the cutoff temperature has to sit under that with margin. This is a construction that cannot be allowed to dry out and overshoot.
Sensors can be built into the part: NTC thermistor, PT100 or PT1000 RTD, or a K-type thermocouple, fitted under the same insulation and tested with the heater as one assembly. A sensor laminated into the heater reads the heater; a sensor on the load reads the load. Both are legitimate, and the drawing has to say which is wanted.
Which Constructions Are Wound for 110-120 V AC
110-120 V AC is not unique to this construction. In this catalogue it is also wound into:
The supply voltage is wound in at manufacture. A heater built for one voltage cannot be run on another and rated down by arithmetic — at half the voltage it makes a quarter of the power, and at twice the voltage it makes four times the power and destroys itself.
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.
- Whether adhesive backing is wanted, and what surface it goes onto — a low-energy plastic needs a different adhesive from bare aluminium.
Lead time: Samples 7-10 days from approved drawing; production 15-20 days.
Printed Silver and Etched Copper PET 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 | Silver ink or etched copper circuit on PET film, laminated | Decided at quotation from the outline and the wattage |
| Insulation system | PET polyester film, 0.05 mm to 0.125 mm per face | This is what sets the temperature limit, not the element |
| Total thickness | 0.25 mm | Nominal, before adhesive; add 0.2 mm for PSA backing |
| Minimum size | 20 x 20 mm | Below this the element cannot be routed with a safe edge margin |
| Maximum size, one piece | 400 x 1000 mm | Larger areas are supplied as tiled zones with separate circuits |
| Dimensional tolerance | u00b11 mm on the die-cut outline | On the die-cut outline; hole positions are held tighter |
| Supply voltage | 12 V, 24 V, 48 V, 110 V, 220 V | Wound to the ordered voltage u2014 it is not a switchable range |
| Resistance tolerance | u00b110% standard, u00b15% on request | Measured at 20 u00b0C; hot resistance differs with the element alloy |
| Watt density, free air | 0.2 W/cmu00b2 typical | Nothing conducting heat away u2014 the honest figure for an unbonded heater |
| Watt density, bonded to heat sink | 1.0 W/cmu00b2 maximum | Only valid with full-area contact to metal; specifying at this figure and running in free air destroys the heater |
| Continuous working temperature | -40 u00b0C to +120 u00b0C continuous | Of the heater itself, measured at the element, not the ambient |
| Dielectric strength | 1500 V AC, 1 minute | One minute, element to any exposed surface, no breakdown |
| Insulation resistance | greater than 100 Mu03a9 | At 500 V DC, measured after the dielectric test |
| Lead wire | Crimped or soldered leads, or a printed silver bus bar with a bonded tail | Length, gauge and termination to your drawing |
| Attachment | PSA backing standard; laminated into the end product at high volume | Adhesive-backed heaters need continuous contact pressure while curing |
| Sensor and control options | NTC 10K B3950 bonded to the film, or a printed PTC ink track | Fitted under the same insulation and tested as one assembly |
| Certifications available | IEC/EN 60335, UL 94 V-0, RoHS, REACH, CE, IATF 16949 | Constructions are built to these; the certificate covers the construction, not every outline |
| Resistance tolerance | u00b15% achievable, against u00b115% for carbon ink | The reason to pay for silver or copper on a thin film heater |
Capability figures are for screen-printed carbon or silver ink on PET polyester film. The +120 °C continuous limit is the film's, and it is a hard limit: PET softens and loses dielectric strength above roughly 130 °C, so this construction is only a candidate where the maximum credible temperature is bounded well below it.
