Etched Foil Flexible Heaters
An etched foil heater is built by etching foil tracks that conduct electricity laminated between layers of silicone rubber and nylon for strength and durability. Etched foil as a resistive element is much thinner than wire resistive elements with better heat distribution across the heater's surface.
The silicone rubber provides electrical insulation, flexibility, and durability and is an excellent conductor of heat. Silicone resists water and most chemicals protecting the heating element from damage.
The thin profile of etched foil elements
Wire wound elements are typically thinner than 0.032 inches, while the etched foil is 0.005 inches in thickness. The thinnest etch foil is achieved in the same manner, similar to a circuit board. An image is printed onto metal foil where the non-image areas are chemically removed, leaving tracks at least 0.10 inches wide.
When electricity flows through the tracks, the resistance creates heat in the pattern designed into the heating element. Patterns differ depending on applications. The elements sheet that looks somewhat like a sheet of aluminum foil is laminated or vulcanized between layers of silicone rubber.
The heat from the element is very uniform with superior heat transfer and little lost at the edges compared to wire resistant flexible heaters.
The heating elements provide advantages for applications requiring thin, flexible heat where weight, thickness, and size are essential. These applications can range from medical lab equipment to aerospace applications.
The resistive metal used for etched foil heating elements
As with wire wound heating elements, various metals can be used for the etched foil elements. Some have better mechanical and structural properties than others. While others may be desired due to their thermal, electrical, and conductive properties.
Typical alloys used in etched foil heaters
- Stainless steel
- Nickel chromium
Voltages required for etch foil heaters range from 12 V to 120 V AC/DC
The 12-volt flexible heating element can be battery-powered. Most etched foil heaters have wattages based on DC voltages. Output or wattage is also based on the current flow through the circuit.
Check with the manufacturer for the correct wattage & current rating because the output will be different with the same voltage of AC or DC.
An electric heater resistance that opposes current flow dissipates heat-generated power. The maximum output in the form of heat is based on the amount of current flowing through the circuit and the capacity of the power source.
Each heater will have the voltage and power output printed onto its surface.
If power in watts = E X I then a 12 volt 40 watt heater will draw 3.3 amps.
An 800 watt 120 volt heater will draw 6.6 amps of current.
The silicone rubber offers excellent voltage isolation between the heating element and surrounding surfaces.
The sizes of flexible heating elements
The standard sizes of flexible heating elements are square/rectangular or round.
The square devices are as small as 2” X 2” up to 8” X 8” with rectangular versions 2” X 4”, 4” X 8 “, and 4” X 11”. Round dimensions range from 4 inches to 8 inches.
Wattages vary in size from 40 watts up to 800 watts. Size and wattages spec sheet.
Calculating heat from watts requires calculating the heat produced over time or watt hours. Follow link below for how to calculate the BTU output of this small device.
Resistance to chemicals and other harmful elements
Etched foil heaters using silicone rubber have good resistance to:
Hydrochloric acid - 10%
Sulfuric acid - 10%
Waxes & Plasticizers
Steam up to 266 degrees F or 2.5 bar
Operating temperature range of -76 to 446 degrees F
Installation of heaters
Each heater will come with a set of wire leads for use in industrial electric apparatus. The leads are UL approved and soldered to the etched foil at a joint protected by the silicone rubber layer.
The electrical circuit needs to be protected by a circuit breaker or tied into a thermal control device.
The heaters can be wrapped around a curved surface, sit under, or be attached to the side of a device to be heated. In most cases, a silicone-based or similar adhesive will be used to fix the heater while still providing strong heat conductivity to the surface.
The temperature of the individual heaters are limited by their wattage. Some applications will only require an on/off switch and circuit breaker. Other applications may need a closed loop control system to sense the temperature and maintain it over time.
In this case a variety of thermostat and temperature control devices can be used. Here is a selection of micro sensors designed for DIN rail mounting in cabinets.