System for protecting electrical devices against overheating

Details System for protecting electrical devices against overheating System for protecting electrical devices against overheating

1999-03-29

2001-04-24

Sherry, Michael J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Circuit interruption by thermal sensing

C361S104000, C338S0220SD, C219S505000

Reexamination Certificate

active

06222715

ABSTRACT:

BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention is directed to an electrical with a device for the protection thereof against overheating.
2. DESCRIPTION OF THE PRIOR ART
Devices for protecting electrical devices against overheating are known in the art. Such devices are disclosed by DE 23 42 015 A1.
For example, in refrigerator cooling units, a so-called motor start-up PTC thermistor can be connected in front of the units' electric motors, such that the drive shafts of the electric motors connect to the units' cooling compressors. In each start-up phase of an electric motor, the current flowing through the PTC thermistor heats it very strongly, as a result of which the resistance of the PTC thermistor increases within a very short time, frequently within seconds, from a few ohms in the cold state to very high resistances.
Since the surroundings of motor start-up thermistors contain oil residues or a generally oily atmosphere, there is a risk that these residues may under unfavorable circumstances be ignited. In the worst case, this may lead to the onset of a smouldering fire in the vicinity of the refrigerator cooling unit to which a motor start-up PTC thermistor is assigned.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a device that protects electrical devices from overheating such that there is no longer even the risk of local smouldering fires being started.
One particular advantage of the present invention is that existing electrical devices need to be altered only slightly so that it is possible to fit a thermal fuse which, according to the present invention, is to be arranged directly next to a critical element. In this way, existing electrical devices can thus be retrofitted according to the present invention with a thermal fuse.
For example, in the case of a motor start-up devices having PTC thermistors, a thermal fuse is arranged directly next to the critical element, in this case directly next to the PTC thermistor. Accordingly, when there is a risk of overheating, immediate response of the thermal fuse is ensured and an electrical device equipped or retrofitted according to the present invention is protected from overheating with absolute reliability.
When the thermal fuse, arranged according the present invention, melts, the electrical supply to the electrical device to be protected is immediately interrupted which reliably avoids the risk of a possible smouldering fire.
Since the thermal fuse is fashioned U-shaped or V-shaped, when a thermal fuse is arranged and fitted according to the present invention inside the housing of an electrical device, for example a motor start-up device having a PTC thermistor, the vertex of the U-shaped or V-shaped fuse is positioned directly next to the critical element, i.e, the PTC thermistor.
When the thermal fuse which is advantageously designed according to the invention, is used and arranged directly next to the element to be made safe, for example a PTC thermistor, then the thermal fuse will melt particularly quickly because of the small distance between the thermal fuse and the critical element to be protected from overheating.
In an embodiment of the present invention, in order to prevent spreading of an incipient smouldering fire, as an additional safety-related provision, the housing enclosing the electrical device consists of self-extinguishing plastic and/or the housing is clad with self-extinguishing plastic.
After (albeit perhaps a short time later) the thermal fuse has melted and the electrical supply has been interrupted, it is no longer possible for the heat source (in the example currently referred to, the PTC resistor of the motor start-up device) to heat up. Further, the incipient smouldering fire is immediately extinguished because the housing enclosing the electrical device, or the entire housing, is clad with self-extinguishing plastic. Spreading of a smouldering fire is thereby prevented with absolute reliability.


REFERENCES:
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patent: 5760676 (1998-06-01), Yamada
patent: 1906101 (1964-12-01), None
patent: 23 42 015 (1975-03-01), None
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patent: WO 95/35577 (1995-12-01), None

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