Battery thermal runaway monitor

• US 4,114,083 A
• Filed: 06/15/1977
• Issued: 09/12/1978
• Est. Priority Date: 06/15/1977
• Status: Expired due to Term

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Clark, Steven D., Benham, Harold L., Stovall, Ronald J., Huffman, Hubert L.
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US05/806,799
• Time in Patent Office: 454 Days
• Field of Search: 320/20, 320/21, 320/32, 320/35, 320/36, 320/39, 320/40, 320/48, 340/249, 328/132
• US Class Current: 340/636.13
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: Y10S 320/33 Aircraft or spacecraft application

Abstract

A device for determining a thermal runaway condition in a nickel-cadmium tery. A current sensor develops a DC voltage proportional to battery current and a converter converts the voltage to a pulse train whose frequency is directly proportional to battery current. The pulse train frequency is monitored for fixed periods of time and changes of frequencies are used to determine the slope of the charge current. A maximum allowable slope is specified and fed into a binary up/down counter which also counts the pulse train frequency. When the difference between two pulse train frequency readings is greater than the maximum allowable, a possible thermal runaway condition is indicated and after a predetermined number of consecutive indications, an indicator is energized to provide a warning.

Claims

1. A monitoring device for indicating that a thermal runaway condition exists in a nickel-cadmium battery comprising,

a current sensor connected with said battery for developing a direct current voltage proportional to charge current,

a voltage converter connected with said current sensor providing at an output terminal pulse train frequencies directly proportional to charge current,

binary counter means having input terminals for receiving a predetermined count and having an up counting terminal and a down counting terminal,

first gating means connected between said output of said voltage converter and said up counting terminal for adding for a predetermined time the output of said voltage converter to the predetermined count,

second gating means connected between said output of said voltage converter and said down counting terminal for subtracting for a predetermined time the output of said voltage converter from the two added counts, and

an output terminal on said binary counter means for providing an output signal when the down count in said binary counter means exceeds the sum of the two added counts.

2. A monitoring device for indicating that a thermal runaway condition exists in a nickel-cadmium battery as set forth in claim 1 having counter means connected with said output terminal on said binary counter for counting successive output signals and for providing an output when the count of successive output signals exceeds a predetermined number.

3. A monitoring device for indicating that a thermal runaway condition exists in a nickel-cadmium battery comprising,

a current sensor connected with said battery for developing a direct current voltage proportional to charge current,

a voltage converter connected with said current sensor providing pulse train frequencies directly proportional to charge current,

a plurality of cascade-connected up/down binary counters each having terminals for receiving a predetermined count,

first gating means connected between said output of said voltage converter and said plurality of cascade-connected up/down binary counters for adding for a predetermined time the output of said voltage converter,

second gating means connected between said output of said voltage converter and said plurality of cascade-connected up/down binary counters for subtracting for a predetermined time the output of said voltage converter,

a shift register,

means for entering a count into said shift register when the counter in said cascade-connected up/down counters goes below zero,

alarm means for indicating that a thermal runaway condition exists, and

third gating means connected between said shift register and said alarm means for energizing said alarm means whenever said shift register registers a predetermined number of successive counts.

4. A monitoring device for indicting that a thermal runaway condition exists in a nickel-cadmium battery as set forth in claim 3 having means for clearing said shift register whenever the counts from said plurality of cascade-connected up/down counters are less than a predetermined number of successive counts.

5. A monitoring device for indicating that a thermal runaway condition exists in a nickel-cadmium battery as set forth in claim 3 having second alarm means connected with said plurality of cascade-connected up/down binary counters for indicating a high count in said binary counters which indicates excessive charge current in the battery being monitored.