Peltier (TEC)
A Peltier module (also TEC, thermoelectric cooler) pumps heat from its 'cold' ceramic face to its 'hot' face when DC current flows; reverse the current and the faces swap roles. Typical modules pump 1–125 W at ΔT up to 70 °C between faces. Examples: Laird CP14, II-VI Marlow RC12-4, TEC1-12706 (12 V 6 A).
A Peltier element is an array of bismuth-telluride pellets alternating n-type and p-type, sandwiched between two thin alumina ceramic plates and connected electrically in series, thermally in parallel. When current flows, electrons in the n-type pellets and holes in the p-type pellets carry heat in the same direction (from cold to hot face), producing a temperature gradient that grows until the conducted heat-back-flow plus Joule heating equals the Peltier pumping. Coefficient of performance (COP) drops from ~0.7 at small ΔT to ~0.1 at maximum ΔT.
In plain terms
A solid-state air-conditioner with no moving parts: like a queue of carriers walking heat across a bridge, switching directions when you reverse the queue.
Why designers use it
- Stabilise laser-diode wavelength by holding the diode at ±0.01 °C with closed-loop TEC control.
- Cool a small CCD or CMOS sensor below ambient to reduce dark-current noise in long-exposure astrophotography.
- Provide compressorless cooling for portable medical sample transport — reagents stay at 4 °C in any orientation.
- Implement spot heating or cooling without refrigerant, in spaces where a vapour-compression system cannot fit.
Best for
- Laser cooling
- Sensor cooling
- Portable refrigeration
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Bulk cooling above ~100 W where COP < 0.3 — vapour-compression is 5–10× more energy efficient at room-sized loads.
- When the hot side heat sink is undersized — a Peltier always rejects heat = Q_pumped + I²R, so the hot side runs much hotter than ambient and ΔT collapses.
Common mistakes
- Stacking modules in series without optimising COP — the second stage must pump the first stage's heat-plus-I²R; naïve stacking actually raises the cold-face minimum temperature.
- Driving with ON/OFF control — thermal cycling of solder inside the module fatigues solder joints and the part fails open within a year; use PWM at > 1 kHz and limit duty.
Where you will find it
- A Coherent OBIS 488 nm laser uses a Marlow RC12-4 Peltier module to hold the laser-diode chip at 25.0 °C ±0.005 °C: a thermistor co-located on the laser submount feeds a PID controller that drives the TEC current; without the TEC the laser wavelength would walk by 0.3 nm/°C as the diode self-heats during a turn-on transient.
- A ZWO ASI294MM-Pro astronomy camera uses a two-stage Peltier to cool its IMX492 CMOS sensor 35 °C below ambient: the cold sensor reduces dark-current shot noise by ~ 4×, allowing 5-minute exposures of dim deep-sky targets that a thermally noisy CMOS camera would render as a uniform grey field of hot-pixel noise.
- An Igloo Iceless 26-quart car cooler uses a 50 W Peltier module backed by a forced-air heat sink: it keeps food 20 °C below ambient (so 5 °C in a 25 °C car) on 12 V power without any compressor or refrigerant, exploiting the Peltier's silent, vibration-free, orientation-insensitive operation that is impossible with vapour-compression in a moving vehicle.
A short history
French physicist Jean Charles Athanase Peltier discovered in 1834 that passing an electric current through a junction of two dissimilar metals either absorbed or released heat, depending on the current direction—the Peltier effect, the inverse of Seebeck's 1821 thermoelectric discovery. This effect remained a scientific curiosity until the 1950s when bismuth telluride (Bi₂Te₃) semiconductor couples were developed, enabling compact thermoelectric modules with meaningful COP values. Melcor (now part of Laird) was an early manufacturer of commercial Peltier coolers in the 1960s. Peltier modules are used today in laser diode temperature stabilisation, portable beverage coolers, and satellite component cooling where compressor-based refrigeration is impractical.