Battery charging circuit for portable power tool
First Claim
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1. A circuit for recharging battery cells comprising:
- (a) terminals for connecting the circuit to a current source,(b) a fast charge section in circuit between said terminals and said battery cells for charging said cells at a maximum rate, said fast charge section including;
an SCR including a gate electrode completing a circuit path from the source to said battery cells,means for enabling said SCR during a portion of each half cycle of said current source including a capacitor connected to said gate electrode and initiating means for charging said capacitor to a voltage sufficient to produce a current exceeding the gate threshold of said SCR,(c) means for temporarily interrupting the circuit from the current source through said fast charge section when said cells approach full charge, said interrupting means including a normally closed thermostat in thermal relation with said cells, said thermostat opening due to the heat produced by said cells when they approach full charge,(d) means for disabling said fast charge section upon operation of said interrupting means to prevent further charging at said maximum rate.
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Abstract
A battery charging circuit is operable for recharging batteries in both trickle and fast charge modes. The fast charge mode is initiated and maintained by enabling a silicon controlled rectifier in circuit between a current source and the battery. A capacitor maintains the SCR in the operative state until the battery reaches full charge. A thermostatically controlled switch terminates the fast charge mode. The battery is then trickle charged for an indefinite period. Reversion to the fast charge mode is prevented by discharging the capacitor associated with the SCR when the thermostatically controlled switch opens.
25 Citations
11 Claims
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1. A circuit for recharging battery cells comprising:
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(a) terminals for connecting the circuit to a current source, (b) a fast charge section in circuit between said terminals and said battery cells for charging said cells at a maximum rate, said fast charge section including; an SCR including a gate electrode completing a circuit path from the source to said battery cells, means for enabling said SCR during a portion of each half cycle of said current source including a capacitor connected to said gate electrode and initiating means for charging said capacitor to a voltage sufficient to produce a current exceeding the gate threshold of said SCR, (c) means for temporarily interrupting the circuit from the current source through said fast charge section when said cells approach full charge, said interrupting means including a normally closed thermostat in thermal relation with said cells, said thermostat opening due to the heat produced by said cells when they approach full charge, (d) means for disabling said fast charge section upon operation of said interrupting means to prevent further charging at said maximum rate. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A circuit for recharging battery cells comprising:
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(a) terminals for connecting the circuit to a full wave rectified current source, (b) a fast charge section in circuit between said terminals and said battery cells for charging said cells at a maximum rate, said fast charge section including; (i) an SCR including a gate electrode completing a circuit path from the current source to said cells, (ii) a capacitor connected to said gate, (iii) initiating means for charging said capacitor to a first voltage only when said cells are not electrically connected to said recharging circuit, said first voltage being sufficient to produce a current exceeding the gate threshold of said SCR, (c) means for temporarily interrupting the circuit from the current source through said fast charge section when said cells approach full charge, said interrupting means including a normally closed thermostat in thermal relation with said cells, said thermostat opening due to the heat produced by said cells when they approach full charge, (d) means for disabling said fast charge section upon operation of said interrupting means to prevent further charging at said maximum rate. - View Dependent Claims (9, 10, 11)
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Specification