Multistage TECs
Multistage (cascade) TECs can produce a larger Delta T than a single stage Standard TEC. Each additional stage adds greater capability in temperature difference (Delta T) but each successive stage adds less capability than the one before it. This leads to a limit of around 8 to 9 stages, but for most puposes 5 stages is the practical limit due to costs versus useful delta T increase.
The most common multi-stage peltier modules are 2 and 3 stage. A typical 2 stage TEC delta T capability can range between 80°C to 95°C. A 3 stage can reach 95°C to 110°C, a 4 stage can reach 110°C to 120°C, and a 5 stage can achieve around 120°C to 128°C. These limits do depend on temperatures, the specific multi stage TEC, the heat sink, and ambient conditions. Multi-stage thermoelectric modules often have much lower Qcmax capability compared to similarly sized single stage TECs. This is because increasing Delta T capability with multi-stage TE coolers decreases Qc capability. Each stage must move all the heat rejected from the stage above it and additionally lower temperature itself.