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distribution boxes

engine bay - 100V distribution box

The box is physically located on top of (in the drawing it is below) the 12V distribution box. Below a top view of the box, with and without fuse holder covers.

Below, for orientation only, a clipping of the wiring diagram. It will not indicate the peers of all connections, and it may be outdated. Please refer to wiring_diagram for a comprehensive and uptodate view.


The 100V distribution box contains one fuse that protects the output of the traction battery charger, two fuses for the two branches of the coolant heater, and one fuse for the DC/DC converter that supplies the 12V grid.

The ceramic fuses used here are suitable for interrupting high currents at 100V DC (which, by the way, is not the case for 230V AC circuit breakers).

DC/DC converter primary side driver

The circuit board within the 100V distribution box houses the driver that switches the primary side of the DC/DC converter. It is described in detail in chapter DC/DC converter.

engine bay - 12V distribution box

This box is mounted to the “battery box” auxiliary frame, above the gearbox, with the smaller 100V distribution box piggybacked to it.

Below a top view of the box in its current state, and an earlier picture where the larger fuses, the reverse protection diodes and the vacuum sensor (discussed below) are still visible.

Below, for orientation only, a clipping of the wiring diagram. It will not indicate the peers of all connections, and it may be outdated. Please refer to wiring_diagram for a comprehensive and uptodate view.


The 150A main fuse (ANL type) supplies both the additional circuitry and the original 12V grid of the car. The two power diodes between its output and ground are designated to nuke the fuse in case the battery is accidentally reversed. Note that conventional cars usually have “inherent” and very efficient reverse protection by the alternator's main rectifier bridge.

From the output of the main fuse, the other fuses branch out:

  • DC/DC converter output
  • auxiliary heater - currently not installed
  • stereo amp - i.e. the amplifier in the dashboard - the active subwoofer is powered via the rear distribution box
  • vacuum pump
  • blower via GSM - that means only when the air blower is run via the remote control, it is powered via this fuse and a dedicated driver circuit
  • coolant pump - actually the brushless DC model currently installed draws so little input current that I could as well have omitted both this fuse and the coolant pump driver circuit it supplies.
  • The battery computer in the dashboard, that keeps track of the traction battery's SOC (state-of-charge).
  • ignition: The ignition contact of connector “X5” supplies this fuse. It fans out to numerous positions in the diagram.

DC/DC converter output relay

The purpose of this relay (40A, in the drawing it is located at the top right of the box) is described in chapter DC/DC converter.

vacuum pump driver

The driver for the vacuum pump is similar to the primary side driver of the DC/DC converter discussed above. Since the pump is powered from the 12V grid, the driver does however not need electrical isolation between control input and power output. The MOSFET used matches the lower operation voltage but higher current of the pump.

The sensor that controls the vacuum pump (it has a simple on/off contact) is also located in the 12V distribution box.

Note the input diode combiner: Vacuum supply needs to be maintained not only when ignition is on, but also when the air blower in the dashboard is powered via GSM remote control. Reason is that the flap that switches between circulated and fresh air is also “vacuum powered”.

immobilizer relay

The little grey box above the main fuse is a relay that deactivates the motor controller in case the driver's door is opened, the tank lid is open or an isolation fault of the traction circuit against the chassis was detected. These three alarm conditions are collected and relayed by the immobilizer latch that is located in the trunk distribution box.

This immobilizer function is required by ECE R-100 to e.g. avoid that the car is moved while the charger cable is still connected. See also the similar requirement sound indicates state of operation. With the current setup, both conditions will trigger both beeper and immobilizer.

front traction battery box

The front traction battery box contains 7 Lithium cells.

Below, for orientation only, a clipping of the wiring diagram. It will not indicate the peers of all connections, and it may be outdated. Please refer to wiring_diagram for a comprehensive and uptodate view.

Besides the battery management system (BMS) cell modules, the box contains the traction battery computer sender board. This board senses the traction grid current via a hall sensor, and it's voltage. In addition, there is a 100:1 voltage divider that is used by the traction grid idle voltage check circuit in the rear distribution box.

Top view of the front battery box (borrowed from the “battery box” chapter):

trunk distribution box

The trunk (rear) distribution box is located on the passenger side, between backseat and the rear battery box.

Below a top view of the box in its current state (viewed from the backseat side), and an older view (from the rear). On the latter, the 12V fuse holder, the 230V circuit breaker and (already quite hidden in the rear) the GSM module are visible.

Since it is within the car's cabin and thus accessible by the passengers, ECE R-100 requires that it is both “test finger” and “test wire” proof. So. the cover had to get some “test wire traps” (the blue and black bars behind the unavoidable gaps around the top flap) - a fruitful effort that I of course willingly invested.

Rear distribution box with the cover (loosely) fitted, with closed and open lid.

In addition to the circuits shown on above photos, the rear distribution box also hosts the GSM/GPS module (hidden below the brown Pertinax plate), the BMS peripherals board (see respective chapter) and the immobilizer latch (see chapter “immobilizer”).

Below picture shows the rear distribution box fully equipped and describes the various terminals and indicator lights.

Below, for orientation only, a clipping of the wiring diagram. It will not indicate the peers of all connections, and it may be outdated. Please refer to wiring_diagram for a comprehensive and uptodate view.


  • 230V AC 16A circuit breaker: protecting traction battery charger and the auxiliary 230V socket that is located on the trunk distribution box (and that is deactivated for the sake of ECE R-100 and its darn test wire).
  • BMS - management system for the traction battery
  • 230V active indication - a relay contact in the traction battery charger indicates if 230V AC is present. Currently only used for controlling the DC/DC converter (traction circuit to 12V grid). See also above chapter dc_dc_converter_output_relay.
  • isolation check (served from the same fuse as “230V active indication”). See description below.
  • 12V jack 1 / 2 - 12V connectors at the side of the distribution box
  • GSM module - See description below
  • ground tap, battery side - fused tap for circuits that measure voltage (HV voltage check - see below) and current (current-to-RPM converter - see dedicated subchaptercurrent-to-RPM converter) on the traction circuit
  • ground tap, motor side - fused tap required for current measurement by the current-to-RPM converter

buzzer tank lid / door

A magnetic proximity sensor next to the tank lid is triggered when the tank lid is closed. The circuit inverts the sensor's output. In case that ignition is turned on while the tank lid is open, a buzzer will go off and the immobilizer relay in the front 12V distribution box will be engaged.

In parallel to the circuit's MOSFET, the door contact of the driver's door will also trigger both buzzer and immobilizer relay, if the door is opened while ignition is on.

See also above section immobilizer relay.

BMS control board

The central control board of the battery management system surveys the cell modules via a cell loop. Depending on the operational state of the car (i.e. ignition on or off) the cell module interprets an interruption of the cell loop either as “low voltage cutoff” or “high voltage cutoff” condition and triggers it's output relays accordingly. A photo showing the BMS cell modules can be found below in subchapter "front traction battery box".

HV idle voltage check

The circuit checks voltage of the high voltage (traction) battery while the car is idle, i.e. ignition is off. In case the voltage drops below a minimum threshold, the input “IN1” of the GSM module is triggered. The GSM module will then send an SMS notification to alert about the deep discharge of the traction battery.

When ignition is on, the circuit is disabled to avoid false alarm due to intermittent voltage drop at high load. In this state, deep discharge will anyhow be detected and reported by both BMS and traction battery computer.

The input voltage is already pre-scaled by a 100:1 voltage divider located in the front battery box. Since it is referred to the traction grid potential, the input stage and discriminator of the circuit are isolated against the 12V grid by a potential-free DC/DC converter. The output is isolated via a solid state relay. The “HV idle voltage low” alarm is further processed by the HV battery alarm unit on the BMS peripherals board - see wiring - logics.

Below, circuit diagram and pictures of the HV idle voltage check unit.

GSM module

The GSM module (Conrad GX107) with GPS option is used for following tasks:

  • Theft protection via GPS “geofence” function (Probably not needed, a thief would return the car soon or ask for technical assistance).
  • “Voltage low” alarm for the traction battery, via “HV idle voltage check” described above and digital input IN1.
  • “Voltage low” alarm for the 12V grid, via threshold crossing alert for the supply voltage
  • SMS remote query of the (rear) traction battery temperature via a sensor connected to the analog input
  • remote control of DC/DC converter, coolant heater and dashboard blower via switched output (only OUT1 used)

carpe diem!

rear traction battery box

The battery box itself and its cover are described in section battery_boxes.

Below, for orientation only, a clipping of the wiring diagram. It will not indicate the peers of all connections, and it may be outdated. Please refer to wiring_diagram for a comprehensive and uptodate view.

Top view of the rear traction battery box (borrowed from the “battery boxes” chapter):

Besides 23 cells and BMS cell modules, the rear traction battery box contains:

isolation test button

By pushing a test button at the rear of the battery box, a 22kOhms ground fault is simulated. The “isolation check” circuit must detect it and create an audible warning signal.

pre-charge circuit

When the maintenance switch (described below) is closed without preparation, high inrush current peaks to the devices in the traction grid may occur. Furthermore, if there is a defect or shortcut in the traction circuit, a powerful arc may emerge. In case of the motor controller, the fuse is rated 400 amps but might also let pass 1000 amps for a second. So, in the worst case, a power surge near 100kW may emanate, creating a lot of heat, light and ultraviolet radiation, besides unpleasant vapors.

As a precaution, the pre-charge button should be pressed prior to closing the maintenance switch. A yellow LED lamp will indicate whether there is still a voltage between the terminals of the switch. If there is no defect and ignition and remote control are off, the indicator lamp should go dark within a few seconds. Afterwards, the maintenance switch can be closed safely.

The pre-charge circuit (in the circuit diagram, it is shown in the rear traction battery box below the cell chain), consists of a simple voltage divider supported by zener diodes. The LED lamp is rated 12V and has an integrated series resistor.

maintenance switch

The maintenance switch actually is only a connector pair (Anderson 300 Amps, with both contacts connected in parallel) that can be manually separated. ECE R-100 requires that the switch is test finger and test wire proof when it is closed, and it must still be test finger proof when it is opened.

To avoid that the contact apertures of the connectors are exposed to the merciless test finger when separated, one connector is fixed to the battery box, while the other is mounted on a rail. So, they can only be separated by a few centimeters and stay in line.

So as to finally get above assembly test finger proof, a cover is required. The cover will also protect against radiation and metal vapor in case a powerful arc would occur. A short “making-of”:

Maintenance switch with cover, closed vs. open. The strap that is used for pulling the connectors apart can be secured by a pin to hold the connectors separated.

dashboard distribution box

As mentioned above, the dashboard distribution box is actually the former lower glove compartment of the car, with some wires and circuits literally stuffed in. Indeed, it showed that this “chaotic” technique of arranging circuitry works well where little space is available, provided that heat and electromagnetic interference dont pose an issue. Although the available space is fully utilized, you can pull out and access any component within a minute.

The dashboard distribution box is closed with a foam plastic plate covered with synthetic leather.

Below, for orientation only, a clipping of the wiring diagram. It will not indicate the peers of all connections, and it may be outdated. Please refer to wiring_diagram for a comprehensive and uptodate view.


The dashboard distribution box only contains two small fuses between wire coming from the light switch (headlight and position lamps) and the coil terminal of the relay that switches the running light, respectively the 12V gauge in the central console of the dashboard. The first fuse is within the relay box of the running light, the second fuse is directly accessible.

dashboard blower driver

Like the electric coolant heater, the dashboard blower can optionally be enabled via the GSM remote switching output. When the switch “Heizung per GSM”-“Gebläse” is set to “1”, then the blower will run at the speed setting “2” (independent of the position of the original blower speed selector switch in the central dashboard) when GSM OUT1 is “on”.

The driver is switching the positive rail of the blower, so I had to use a P channel power MOSFET as a switch. The transistor is again protected against overheating by a thermo switch. The 1N5401 diode cancels out inductive peaks created by the motor coils.

To avoid interference with resp. reverse current into the speed selector switch, a power diode (see center bottom of the dashboard distribution box diagram) had to be inserted into the wire that connects the common terminal of the speed selector switch to ignition. The diode, mounted on a heat sink, is located behind a plastic cover underneath the glove compartment.

battery computer drivers

The traction battery computer is located in the central dashboard console. It has two outputs that allow to use fuel gauge and battery warning lamp in the driver side dashboard console for reporting the traction battery state-of-charge (SOC). The fuel gauge is a slowly reacting bimetallic instrument, and works fine with 4kHz pulse-width modulated input signal.

The driver “circuits” (in contrast to the circuits proposed in the manual) are simple PNP transistors switched as emitter follower.

running light relay

As already discussed, “running” indication is vital for an electric vehicle! The running lights are small lamps on the car's front, that emit white light and indicate that the car is “active”. They are supposed to go out when other lights are switched on.

Not all brands of running lights are suitable! Some e.g. slyly detect the “running” state by sensing the ripple voltage on the 12V supply. This will only work in conventional cars, as the ripples are only caused by the alternator of a conventional car, when the engine is spinning. The type used here has simple “on/off” terminals and works fine with a conventional relay that also has a “normally closed” contact. When ignition is on, the running lights are powered as long as the relay is idle, and are switched off when the relay is engaged. The relay coil can either be driven by the position light (which is the “legal” option) or by the headlight. In the latter case, the running lights would stay on when the position lights are switched on.

The running light lamps themselves had to undergo a rigid and highly academic test for leak-proofness (see below) and were then mounted into the front guard.

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astra_conv/conversion/distribution_boxes/distribution_boxes.txt · Last modified: 2014/06/20 12:56 by richard