Low-voltage connection with safety circuit and method for determining proper connection polarity
A safety circuit used in low-voltage connecting systems leaves the two low-voltage systems disconnected until it determines that it is safe to make a connection. When the safety circuit determines that no unsafe conditions exist and that it is safe to connect the two low-voltage systems, the safety circuit may connect the two systems by way of a “soft start” that provides a connection between the two systems over a period of time that reduces or prevents inductive voltage spikes on one or more of the low-voltage systems. When one of the low-voltage systems has a completely-discharged battery incorporated into it, a method is used for detection of proper polarity of the connections between the low-voltage systems. The polarity of the discharged battery is determined by passing one or more test currents through it and determining whether a corresponding voltage rise is observed.
1. A safety circuit for use in establishing connections between low-voltage systems to transfer energy from a first low-voltage system to a second low-voltage system, comprising:
a pair of input terminals;
a pair of output terminals;
a detection circuit operatively connected to the input terminals and the output terminals for detecting whether the input terminals and the output terminals are properly connected to first and second low-voltage systems, respectively;
a connection-controlling circuit configured to electrically connect the input terminals to the output terminals only when a proper connection has been detected and using a soft start procedure that reduces inductive voltage spikes; and
a transistor protection s stem for protecting transistors used to electrical connect the input terminals to the output terminals, the transistor protection system comprising a microcontroller that maintains a thermal model of heating of the transistors when power is flowing and a thermal model of cooling of the transistors when power is not flowing, that monitors for over-current conditions that could destroy the transistors, and that monitors for under-voltage conditions on the supply side.
2. A safety circuit as recited in claim 1 , wherein the connection-controlling circuit controls one or more power transistors that are used to electrically connect the input terminals to the output terminals using the soft start procedure.
3. A safety circuit as recited in claim 2 , wherein the soft start procedure connects the first low-voltage system to the second low-voltage system over a period of tens of milliseconds.
4. A safety circuit as recited in claim 1 , wherein the safety circuit is incorporated into a jumper cable.
5. A safety circuit as recited in claim 1 , wherein the safety circuit is incorporated into a battery charger.
6. A safety circuit as recited in claim 1 , wherein the safety circuit is incorporated into a battery boost.
7. A safety circuit as recited in claim 1 , further comprising a discharged battery test circuit configured to supply a test current to the output terminals and measure a resulting voltage to determine a proper polarity of a discharged battery connected to the output terminals.
8. A safety circuit as recited in claim 7 , wherein the discharged battery test circuit is configured to supply test currents of different directions and to compare the voltages caused by the test currents.
9. A safety circuit as recited in claim 1 , wherein the safety circuit is configured to detect whether a battery is connected to one of the pair of input terminals and the pair of output terminals by biasing the desired terminals to a voltage unlikely to occur naturally in one of the low-voltage systems and determining whether the voltage aberrates from the biased voltage by a given amount.
10. A safety circuit as recited in claim 1 , wherein the safety circuit is configured to discriminate between a short circuit and a discharged battery by measuring the rise and fall time of a voltage measured across one of the pair of input terminals and the pair of output terminals as a limited current is allowed to flow.
11. A method of testing a polarity of a discharged battery connected to a first low-voltage system comprising:
connecting a test current source to a first low-voltage system containing a discharged battery;
supplying a first test current to the first low-voltage system;
measuring a first resulting voltage of the first low-voltage system;
supplying a second test current to the first low-voltage system, wherein the second test current is in an opposite direction to the first low-voltage system; and
measuring a second resulting voltage of the first low-voltage system.
12. A method as recited in claim 11 , further comprising making an electrical connection between the first low-voltage system and a second low-voltage system only if the first resulting voltage exceeds a predetermined threshold voltage.
13. A method as recited in claim 11 , further comprising making an electrical connection between the first low-voltage system and a second low-voltage system only if only one of the first resulting voltage and the second resulting voltage exceeds a predetermined threshold voltage and if the electrical connection will be of a proper polarity indicated by the measured first and second resulting voltages.
14. A method as recited in claim 11 , wherein the method is incorporated as a test method upon connection of a battery charger to a system having a discharged battery.
15. A method as recited in claim 14 , wherein the system having a discharged battery is a vehicle.
16. A method as recited in claim 11 , wherein the method is incorporated as a test method upon connection of a battery boost to a system having a discharged battery.
17. A method as recited in claim 11 , wherein the method is incorporated as a test method upon connection of a jumper cable to a vehicle having a discharged battery.
18. A jumper cable for use in establishing connections between low-voltage systems to transfer energy from a first low-voltage system to a second low-voltage system, comprising:
a safety circuit comprising:
a pair of input terminals;
a pair of output terminals;
a detection circuit operatively connected to the input terminals and the output terminals for detecting whether the input terminals and the output terminals are properly connected to first and second low-voltage systems, respectively;
a connection-controlling circuit configured to electrically connect the input terminals to the output terminals only when a proper connection has been detected and using a soft start procedure that reduces inductive voltage spikes; and
a transistor protection system for protecting transistors used to electrically connect the input terminals to the output terminals, the transistor protection system comprising a microcontroller that maintains a thermal model of heating of the transistors when power is flowing and a thermal model of cooling of the transistors when power is not flowing, that monitors for over-current conditions that could destroy the transistors, and that monitors for under-voltage conditions on the supply side;
a first cable connected to the input terminals and comprising first contact clamps for connecting to the first low-voltage system; and
a second cable connected to the output terminals and comprising second contact clamps for connecting to the second low-voltage system.
19. A jumper cable as recited in claim 18 , wherein the safety circuit is contained in a control box proximate one of the first contact clamps and the second contact clamps.
20. A jumper cable as recited in claim 19 , wherein the control box comprises a plurality of light emitting diodes for signaling conditions detected by the safety circuit to a user of the jumper cable.