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EP-3921916-B1 - DUAL BATTERY SYSTEM

EP3921916B1EP 3921916 B1EP3921916 B1EP 3921916B1EP-3921916-B1

Inventors

  • ABRAMOV, IGOR

Dates

Publication Date
20260506
Application Date
20200203

Claims (6)

  1. A dual battery system, including: a primary battery (1) adapted to drive a starter motor (2); an auxiliary battery (3) adapted to drive one or more auxiliary loads (4); an alternator (5) adapted to supply current to recharge the primary battery (1); and a power supply circuit (6) adapted to supply current from the alternator (5) to recharge the auxiliary battery (3) when a surplus condition is detected, the surplus condition indicating that the alternator (5) is generating more electrical power than is required for recharging the primary battery (1), wherein the power supply circuit (6) is adapted to cease to supply current to recharge the auxiliary battery (3) when absence of the surplus condition is detected so that the primary and auxiliary batteries (1, 3) become electrically isolated, thereby ensuring that recharging of the auxiliary battery (3) does not have an adverse effect on the level of charge of the primary battery (1); wherein the surplus condition is determined to exist when voltage measured across the primary battery (1) exceeds a threshold level; wherein the primary battery (1) is a lead flooded battery and the threshold level is between 11.8 volts and 14.0 volts; and wherein the threshold level is adjustable.
  2. A dual battery system according to claim 1 wherein the power supply circuit (6) is able to convert any level of input voltage to the required charging voltage of the auxiliary battery (3).
  3. A dual battery system according to any one of claims 1 to 2 wherein the power supply circuit (6) is configured to dynamically supply or cease supply of current to the auxiliary battery (3) as soon as the surplus condition or absence of the surplus condition is detected.
  4. A dual battery system according to any one of claims 1 to 3 wherein the amount of current supplied by the power supply circuit (6) to the auxiliary battery (3) when the surplus condition is detected is a fixed amount.
  5. A dual battery system according to claim 1 wherein the amount of current supplied by the power supply circuit (6) to the auxiliary battery (3) when the surplus condition is detected is proportional to the amount of voltage by which the voltage measured across the primary battery (1) exceeds the threshold level.
  6. A method of controlling a dual battery system, the method including: driving a starter motor (2) using a primary battery (1); driving one or more auxiliary loads (4) using an auxiliary battery (3); supplying current to recharge the primary battery (1) using an alternator (5); detecting a surplus condition indicating that the alternator (5) is generating more electrical power than is required for recharging the primary battery (1); supplying by means of a power supply circuit (6) current from the alternator (5) to recharge the auxiliary battery (3) when the surplus condition is detected; detecting absence of the surplus condition indicating that the alternator (5) is no longer generating more electrical power than is required for recharging the primary battery (1); and the power supply circuit (6) ceasing to supply current to recharge the auxiliary battery (3) when absence of the surplus condition is detected and electrically isolating the primary and auxiliary batteries (1,3), thereby ensuring that recharging of the auxiliary battery (3) does not have an adverse effect on the level of charge of the primary battery (1); wherein the surplus condition is detected to exist when voltage measured across the primary battery (1) exceeds a threshold level; wherein the primary battery (1) is a lead flooded battery and the threshold level is between 11.8 volts and 14.0 volts; and wherein the threshold level is adjustable.

Description

FIELD OF THE INVENTION This invention relates to a dual battery system and a method of controlling a dual battery system. It relates particularly but not exclusively to a dual battery system for a vehicle where an auxiliary battery for auxiliary loads can be charged with no adverse effects on a primary battery for a starter motor. BACKGROUND TO THE INVENTION A dual battery system is one example of a way of providing for the electrical needs of a vehicle which has a number of electrical accessories or auxiliary loads. The batteries can be connected together, so that together they supply all of the electrical needs of the vehicle. They can also be electrically separated, so that one battery supplies some of the electrical needs of the vehicle while the other battery supplies the rest, or there can be some sort of switching arrangement which allows prioritisation of one of the batteries over the other. The importance of the limiting of amount energy being sourced from starter battery is more apparent now in the time of wider use of smart alternator, start-stop and other car electrical generation limiting technologies. A specific example of a dual battery system includes a starter battery and auxiliary battery is exemplified by US Patent 6,229,279. The system described in that patent includes a power switch arranged between the starter battery and the vehicle auxiliary electrical system battery. The starter or primary battery carries the primary load, which is understood to be the loads essential for starting (starting motor) and safe driving capability, and the auxiliary or secondary battery carries a secondary load which includes vehicle accessories and comfort components. In the system of US Patent 6,229,279, the starter battery and auxiliary battery can be connected together in parallel during operation of the starter. This may be of some assistance if the starter battery has lost some of its charge, but ideally the starter battery should always be charged sufficiently to be able to operate the starter on its own. However, if the level of charge in the auxiliary battery is lower than that in the starter battery, the starter battery will face an additional load if the two batteries are connected during operation of the starter. US Patent 6,229,279 proposes some circuit arrangements to ensure appropriate switching between the starter and auxiliary batteries, but the methods of charging the auxiliary battery in such systems are disadvantageous because of the difficulty of making correct decisions as to the times at which switches needs to be closed or opened. The penalty for the wrong decision is the discharge of the starter battery, leading to an inability to start the vehicle's engine. WO 2014/025069 A1 discloses a power system for a vehicle which includes a generator, first and second batteries connected with the generator, and a connection switch which is provided on a connection line electrically connecting the first and second batteries, and which electrically connects and disconnects the first battery and the generator to/from the second battery. The power system performs regenerative generation by the generator when the vehicle decelerates. A terminal voltage of the first battery is made larger than that of the second battery. The power system further includes a first control means making the connection switch an electrically connected state to apply electrical charge to both the first and second batteries during regenerative generation by the generator, a discharge monitor means monitoring a discharging state of the first battery during regenerative generation, and a second control means disconnecting the connection switch based on the discharging state of the first battery. JP 5762092 B2 discloses a hybrid vehicle that includes: a power generation electric motor connected to an engine; a first power conversion device connected with the power generation electric motor; a second power conversion device 6 connected to the first power conversion device by the high-voltage DC power line, converts the DC power transmitted by the high-voltage DC power line into the AC power, and outputs it to a travel motor, and converts the regenerative electric power of the travel motor to the DC power and outputs it to the high-voltage DC power line; a main battery directly connected with the high-voltage DC power line; and a vehicle control apparatus that determines that charging to the main battery is difficult when the voltage of the high-voltage DC power line exceeds a first threshold value set beforehand, makes the power generation electric motor powering operation to consume the charging surplus of the main battery. SUMMARY OF THE INVENTION The present invention comprises a dual battery system and method of controlling a dual battery system as defined in the claims. Embodiments that do not fall within the scope of the claims are to be interpreted as examples useful for understanding the invention. According to one