TM 10-7310-241-12&P Change 1     1-11      1-13.  EQUIPMENT DATA (Continued)              d. Performance Data. Model RAK-15 Model 471012        Heating (water only) Temperature of one gallon of water will be raised by 100 ^oF (56 ^oC) in one hour (max) at an ambient temperature of 70 ^OF (21 ^oC) using HI switch setting. Temperature of one gallon of water will be raised by 100 ^oF (56 ^oC) in one hour (max) at an ambient temperature of 70 ^oF (21 ^oC) using the II switch setting.        Heating (rations + water) Temperature of up to five MRE entrees and 40 fluid ounces of water will be raised to between 150 ^oF (66 ^oC) and 160 ^oF (71 ^oC) at an ambient temperature of 70 ^oF (21 ^oC) using Hl switch setting. Temperature of up to five MRE entrees and 40 ounces of water will be raised to 185°F ± 5°F (85°C ± 2.8°C) at an ambient temperature of 70°F (21°C) using the III switch setting.        Heat retention Better than 45% of the selected heating range at 3 hours after HWR is turned off with the cover closed and latched. More than 45% of the selected heating range at 3 hours after HWR is turned off with the cover closed and latched.        Heating range (low) 150  - 160 ^oF (66-71 ^oC) 150 - 160 ^oF (66-71 ^oC)        Heating range (high) 180 - 190 ^oF (82-88 ^oC) 180 - 190 ^oF (82-88 ^oC)        Automatic Shutdown Power supply voltage less than 22 V dc. Internal temperature greater than 205 ^oF (96 ^oC).  “Boil-dry” condition detected. Power supply voltage less than 20 V dc. Internal temperature greater than 239 ^oF.        Overvoltage Protection Voltage greater than 39 V dc. Voltage greater than 30 V dc.         e.  Environmental Data. Model RAK-15 Model 471012          Temperature (operating) Between -25 and 140 ^oF (-32 and 60 ^oC). Complies with MIL-PRF-44466A.          Temperature (storage)   Between -60 and 160 ^oF (-51 and 71 ^oC). Complies with MIL-PRF-44466A.           Humidity (storage)   Between 10 and 90%. Between 10 and 90%.  It also operates after a 4-hour soak at a temperature of 140^oF and 94% ± 4% humidity. Section III.   PRINCIPLES OF OPERATION 1-14.  HWR FUNCTIONAL DESCRIPTION      a.  PL1.  Electrical connector, which accepts the 22 - 28 V dc, power supply via a suitable power cable (not part of the HWR) from the host vehicle electrical system. b.    Input Circuit.   Electronic network that protects against reverse polarity connection of the power supply   and overvoltage surges in excess 39 V dc (Model RAK-15 only).  For Model 471012, if it does not receive the correct polarity, it will malfunction in a hazardous manner even with the switch in the OFF (0) position. c.  16 V Power Supply.  Provides a stabilized supply of +16 V dc to power the electronic circuits for Model RAK-15.   d. Low Voltage Detector.  Electronic circuit that monitors the power supply and activates the heater off latch   if the voltage level falls below 22 V dc for Model RAK-15.  The undervoltage protection feature for Model 471012 shuts off power to the unit when supply voltage drops below 20 V dc.