I am working on a project where I am using an H-Bridge to control a peltier cooler (60W, 12V, supercool PE-127-14-15-S). I am using an arduino pro mini and have written code where I use serial communication to send the set temperature to arduino, and the mode (heating or cooling) which it then stores in the EEPROM. I have implemented a PI control loop to control the temperature based on an analog input from a thermistor. The software is working fine and when I use LEDs across the h-bridge, I have no problem switching the polarity and it supplies a full 12V. However, when I attach the peltier across the h-bridge (I can still switch the polarity, i.e. heat and cool), but then I only have a voltage drop of 8V for both heating and cooling. I am using a 12V, 12.5A power supply so power is not an issue. I am using 2 N-Channel MOSFETS (BUZ11) to drive my high side P-Channel MOSFETS (FQP27P06) and have 2 N-Channel MOSFETS on the low side of my H-Bridge. I have 1K resistors between the gate and ground for the n-channel MOSFETS, and between the gate and 12V for the P-Channel MOSFETS. From my calculations, the peltier has a resistance of about 2.42 Ohms and the N-channel have a resistance of 0.03 ohms and the P-channel have a resistance of 0.055 Ohm, so I should still have a voltage drop across the peltier of about 11.6 V (which is much more acceptable than 8V).
Any help on why I am seeing such a substantial voltage drop across the peltier would be greatly appreciated.