Modular PTC thermistor overload protection system
US4683515A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Nov 20, 1985 |
| Grant date | Jul 28, 1987 |
| Priority date | — |
| Expiry date | Nov 20, 2005 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH02H3/085
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
A motor overload protection system (OL) that has a speed of operation fast enough so that it will always trip before the power switch (MC) has had time to operate if the turn-on control means (ON) is operated under overload conditions. In one version, modules (OL1,OL2) are provided having PTC thermistor sensors (PTC1,PTC2) bonded to resistance heaters (H1,H2) connected in the motor power circuit (L1,L2,L3), these sensors being supplied from a current source (CT) and being effective to shunt current to a protective trip device (TR) upon occurrence of an overload condition, there being an ambient temperature compensating PTC themistor (PTC3) in series in the sensor circuit (OLC). In another version, a thermal mass (TM) is preheated above ambient temperature by an ambient temperature compensating PTC thermistor (ATC) operated above its switching temperature level and a sensor PTC thermistor (ST) and a heater (HT) are also thermally coupled to the thermal mass (TM) with a bias resistor (R1) connected to the sensor thermistor (ST) to provide a step voltage output (OUT) on overload. The heater may be a PTC thermistor (HT) having a higher switching temperature for self-shutoff on higher t…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.