The electrical system of the British Chieftain tank
We continue our series of publications of reports on tests and detailed studies of the British tank The Chieftain Mk.5P, which was given to Soviet specialists by the Iraqi military during the Iran-Iraq War.
This time, the document published below describes the electrical supply system of the English car, which includes an auxiliary power unit and heating of the batteries with alternating current.
Power supply system
The Chieftain Mk5P's 28V electrical system is a two-wire system with three channels of generated electrical energy: a DC generator connected to the main engine, a DC generator connected to the auxiliary engine, and an AC generator connected to the auxiliary engine, which is used to heat the hull's batteries.
Four 12-volt batteries, each with a capacity of 100 Ah, connected in series and parallel, are housed in pairs in containers on either side of the driver and are used to start the main and auxiliary engines and power the tank's primary loads. Two similar batteries, connected in series, are located in the turret recess and are primarily used to power the radio when the engines are not running. The capacity of these batteries is sufficient for normal radio operation for eight hours.
Figure 1. Schematic diagram of the power supply system: RN1, RN2 — voltage regulators of the main and auxiliary engines; CT1 and CT2 — starters of the main and auxiliary engines; RK — distribution box; АБI, АБII — hull storage batteries; АБIII — turret storage batteries; E1, E2 — equivalents (see text for designations of other elements); I — to tower consumers; II — protection of power supply and control circuits.
Let's look at the diagram of the tank's electrical supply system (Fig. 1).
Distribution of electric power between consumers is carried out through a housing distribution connection (HDC), a main distribution board (MDB), a rotating contact device (RCD), a tower distribution board (TDSB), and a battery control panel (BCP).
The main generator G1 (table) is a shunt-excited, self-ventilated, commutator-type DC electric machine. Cooling air is drawn into the generator from a dedicated duct through a valve that allows air to be drawn from either the fighting compartment or the engine-transmission compartment, depending on the handle position.
A radio interference filter consisting of an inductor and capacitors is located on the commutator-side bearing shield. A thermal switch, connected in series with the shunt winding, is located in the drive-side generator housing. When the generator housing temperature exceeds 175°C, which can occur during prolonged generator overload or in the event of a voltage regulator failure, the thermal switch interrupts the excitation winding circuit. The thermal switch resets when the temperature drops to 85°C.
The auxiliary engine contains two generators of direct (G2) and alternating (G3) current, mounted on one shaft.
The G2 generator is a shunt-wound DC electric machine with a full complement of auxiliary poles and a compensating winding. It is air-cooled using a centrifugal fan, providing a cooling air flow through the generator of up to 50 m³/s. The generator is a two-wire design.
A box is mounted on the generator housing, containing two power terminals, a connector for the excitation winding, ten 2 μF capacitors rated at 50 V, and a choke for radio interference suppression. A thermal relay, connected in series with the excitation winding, is mounted to the housing on the drive side. The relay functions the same as the main generator.
The following design solutions are of interest in DC generators:
— the armature winding sections are soldered directly to the surface of the collector plates;
— the fan on the collector side is made by injection molding, the thickness of the blades in the middle part does not exceed 1,5 mm;
— the brush holder is made of cast iron.
The G3 AC generator is a single-phase synchronous machine with permanent magnet excitation and an open design. It is air-cooled using an axial fan.
To maintain the voltage of the generators within the specified limits and automatically connect them to the on-board network, as well as disconnect them from the on-board network, the tank uses carbon voltage regulators RN1, RN2.
The main generator voltage regulator (RN1) has two carbon columns: one for regulating the generator excitation, the other for ensuring parallel operation of the generators. The carbon columns are cooled by air supplied from the tank's ventilation system. The voltage regulators are connected to the generator excitation windings via a housing-mounted distribution connection.
The latter distributes electrical energy from generators to consumers and transmits current from batteries to starters when starting the main and auxiliary engines.
In the transmission gear shift control system circuits, in the pump circuits, as well as in the control circuits of the main and auxiliary engines, there are single-pole circuit breakers located on the main distribution board.
There are also two battery heating relays and a relay that controls the fuel injection solenoid.
Electrical power for the tower's consumers is transmitted from the hull through a rotating contact device (RCD) to the tower distribution board (TDB). The batteries located in the tower are connected to the TDB via a two-wire TDB switch (TBS2).
On the rear side of the control panel are circuit breakers and switching devices (relays). A mechanical switch is located on the control panel, the lever of which is connected to a contactor group that disconnects the batteries located in the hull and switches the turret's electrical armor to power from the batteries located in the turret (except for the searchlight circuits).
The batteries, located in the hull, are connected to the on-board electrical system via a two-wire rotary switch located on the battery control panel. This switch has two positions: "on" and "off." In the "off" position, all battery power circuits are disconnected, with the exception of the fire alarm system circuit.
Under normal conditions, with the main engine inoperative, the hull battery switch is in the "off" position, and the turret battery switch is in the "on" position. Under these conditions, the radio is connected to the turret batteries. When the hull batteries are activated, a relay mounted on the turret distribution board is activated, disconnecting the radio from the turret batteries and connecting it to the hull batteries.
The tank is designed to allow the hull and turret batteries to be connected in parallel during combat conditions; the devices can operate without being connected to any generator.
The batteries are charged while moving from the main or auxiliary generator, or from two generators simultaneously.
Charging and discharging modes are monitored using indicator lights with green and red diffusers. These lights work in conjunction with a relay so that the green light comes on when the charging current is 33–42 A and goes out when the current drops to 20–30 A. The red light comes on when the discharge current drops to 5–9 A and goes out when the current is 1–4 A. Both lights are off when the current is too low or there is no current.
The indicator lights are located on the battery control panel. It also houses a connector for an external power source, a battery warmer switch, and a light indicating that the warmer is on. The control panel also includes a battery warmer transformer.
Single-phase alternating current, generated by an alternator designed to warm up the case's batteries at sub-zero temperatures, is fed through a heating relay to a transformer, which reduces the voltage from 200 to 8,5 V. The secondary winding of the transformer has a center tap and is rated for a current of 250 A.
Figure 2. Battery warm-up circuit: I — to the alternator; II — to the switching unit; III — to the battery switch PUB.
The middle terminal of the transformer Tr is connected to the positive terminal of the battery switch, and the two outer terminals are connected to the positive terminal of the battery in each group (Fig. 2). Thus, the batteries are charged through the secondary winding of the transformer, and when the heating is turned on, heating and charging occur simultaneously.
The role of battery temperature sensors is played by E-equivalents, which simultaneously serve as connecting elements for two batteries. The E-equivalents contain "hot" and "cold" thermostats, which are connected to switching units located near the batteries.
When the temperature inside the tank reaches 46°C, the thermostat interrupts the battery heating circuit; it is reactivated once the temperature drops to 31°C. Heating the batteries with alternating current increases the tank's combat readiness at subzero ambient temperatures.
Final World
The Chieftain Mk5P's electrical system, including auxiliary engine generators, provides power to loads while moving and stationary. A key feature of the system is the use of alternating current to warm up the batteries, improving energy balance and increasing the tank's combat readiness at subzero temperatures.
Source:
"Power Supply System". V.D. Konstantinov, A.V. Pavlov, G.I. Uglev. "Problems of Defense Technology". Series VI, Issue 6 (112).
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