Use of PTC devices to protect insulated wires in electrical harnesses

• US 6,225,610 B1
• Filed: 07/08/1997
• Issued: 05/01/2001
• Est. Priority Date: 08/23/1993
• Status: Expired due to Fees

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Tyco Electronics Corporation (TE Connectivity Ltd. (United Kingdom))
• Inventors: Walsh, Malcolm R.
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US08/889,664
• Time in Patent Office: 1,393 Days
• Field of Search: 219/483-486, 219/202, 219/203, 219/508, 219/509, 219/504, 219/505, 219/501, 338/20, 338/26, 338/22 R, 338/276, 338/277, 361/27, 361/106
• US Class Current: 219/505
• CPC Class Codes: B60R 16/0207 Wire harnesses
• CPC Class Codes: B60R 16/03 for supply of electrical power to vehicle subsystems or for circuit arrangements for charging batteries H02J7/00
• CPC Class Codes: H02H 9/026 Current limitation using PTC resistors, i.e. resistors with a large positive temperature coefficient

Abstract

Use of PTC circuit protection devices in motor vehicle wiring systems. The devices can replace some or all of the fuses conventionally used. Preferred devices contain PTC conductive polymers. Because the PTC devices can be reset without physical access to them, the wiring system can be arranged more efficiently and more economically. For example, the size of at least some of the wires of the harness can in many case be reduced.

Claims

1. An electrical circuit which has a maximum steady state current under normal operating conditions I_LOAD and which comprises

(1) a source of electrical power;

(2) a PTC protection device having a pass current I_PASS and a trip current I_TRIP and containing a PTC element which is composed of a conductive polymer exhibiting PTC behavior;

(3) an operative electrical device which is spaced apart from the PTC protection device; and

(4) an insulated electrical wire which has a damage current I_DAMAGE and which connects the PTC device to the operative electrical device

and in which

(a) at each temperature within a range T₁ to T₂, where T₁ is 0°

C. and T₂ is 80°

C.,

(i) I_PASS is at least 1.1 times I_LOAD and

(ii) I_DAMAGE is at least 1.1 times I_TRIP;

(b) at at least one temperature within the range T₁ to T₂, I_PASS is at most 1.5 times I_LOAD; and

(c) at at least one temperature within the range T₁ to T₂, I_DAMAGE is at most 1.5 times I_TRIP.

2. A circuit according to claim 1 wherein T₁ is −

40°

C. and T₂ is 85°

C.

3. A circuit according to claim 1 wherein at at least one temperature within the range T₁ to T₂, I_PASS is at most 1.3 times I_LOAD and I_DAMAGE is at most 1.3 times I_TRIP.

4. A circuit according to claim 1 which is part of a battery-powered electrical system of a road vehicle and in which the insulated wire has a gauge of less than 18 AWG.

5. A circuit according to claim 1 which is part of a battery-operated electrical system of a road vehicle and in which the insulated wire has a gauge of 22 AWG or less.

6. A circuit according to claim 1 wherein the PTC device has a resistance at 23°

C. of less than 0.25 ohm.

7. A circuit according to claim 1 wherein the PTC device comprises

(1) two laminar electrodes, and

(2) sandwiched between the electrodes, a laminar PTC element composed of a conductive polymer exhibiting PTC behavior.

8. A harness according to claim 7 wherein substantially all of the insulated wire in said at least one branch circuit has a gauge size of less than 22 AWG.

9. A harness according to claim 1 which includes diagnostic means which indicates when the PTC device is in a tripped condition.