Overtemperature protection and thermistors

As a standard, HDD motors are equipped with overtemperature protection. The protection consists of three PTC thermistors in series, one for each phase. The PTC thermistors are manufactured according to norms DIN 44081 and DIN 44082. According to these norms, the resistance for a single thermistor at room temperature is in the range 20 Ohms – 250 Ohms. For three thermistors in series, the total room temperature resistance is typically between 150 Ohms – 300 Ohms (50 Ohms – 100 Ohms per thermistor), but can be as high as 750 Ohm without indicating malfunction.

The PTC thermistors have a switch temperature of 150 C. When T < 145 C, R < 550 Ohm for each thermistor (R < 1650 Ohms for the whole triplet), and when T > 155 C, R > 1330 Ohm for each thermistor (R < 4990 Ohms for the whole triplet). The resistance should be measured with a d.c. voltage no greater than 2.5V. More detailed information about the PTC resistors can be found here.

As an option, HDD motors can be equipped with a temperature measurement device of type KTY84-130. Detailed information about this device can be found here. The resistance of the KTY device depends continuously on temperature, as described in this document.

Available feedback alternatives

Name Type Description Information Data sheet
A Resolver 7 V input, 1 pole pair, 0.5 transf. ratio   Data sheet
D Resolver 9 V input, 1 pole pair, 0.3 transf. ratio   Data sheet
EC Endat 2.1 singleturn 32 lines (19 bits) per rev. ECI 119 Data sheet
ED Endat 2.2 singleturn 32 lines (19 bits) per rev. EBI 135 Data sheet
EE Endat 2.2 singleturn, SIL2 25 bits per rev. ECN 1325 Data sheet
EF Endat 2.2 multiturn, SIL2 25 bits per rev. ECN 1337 Data sheet
EH Endat 2.2 32 lines (19 bits) per rev. ECI 119 Data sheet
EM Endat 2.1 multiturn 512 lines per rev. EQN 1325 Data sheet
EN Endat 2.1 multiturn 2048 lines per rev. EQN 1325 Data sheet
EO Sincos, commutation signal 2048 lines per rev. ERN 1387 Data sheet
EP Endat 2.2 battery buffered multiturn 18 bits per rev. EBI 1135 Data sheet
EQ Endat 2.1 singleturn 18 bits per rev. ECI 1118 Data sheet
ES Endat 2.1 singleturn 512 lines per rev. ECN 1313 Data sheet
ET Endat 2.1 singleturn 2048 lines per rev. ECN 1313 Data sheet
EV Endat 2.2 singleturn 19 bits per rev. ECI 1319 Data sheet
EW Endat 2.2 multiturn 19 bits per rev. EQI 1331 Data sheet
EY Endat 2.2 singleturn 18 bits per rev. ECI 1118 Data sheet
SS Hiperface Sincos singleturn 1024 lines per rev. Electrically equivalent to SRS50 Data sheet
SM Hiperface Sincos multiturn 1024 lines per rev. Electrically equivalent to SRM50 Data sheet
SC Hiperface Sincos singleturn 50mm hollow shaft 64 lines per rev. Electrically equivalent to SEK90 Data sheet