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traction battery charger

The battery charger, which I got via Marco Lorey, had it's characteristics already adapted for a 30 cells Lithium battery. The charger delivers 15 Amps at maximum. Unfortunately, with the given characteristics it would not charge the eight provisional 12V lead-acid batteries you see on below picture. Their charging voltage was too high. It might have worked with only 7 of them, but of course at the risk of a decent explosion in case of inadvertent overcharging.

During the charging process, the charger and the BMS will closely work together: The 15A charging current will be applied up to a certain first threshold voltage, and the device remembers the time to reach the first threshold. The device will then continue charging at a reduced current (around 1A) till either a second threshold voltage is reached, a BMS (HVC) alarm occurs or the time of the second charging phase exceeds half of the first charging phase. This trickle charging phase is utilized by the BMS system in order to balance the state-of-charge of the individually cells, by shunting those cells exceeding a certain voltage (around 3.6V). The charging current is slightly higher than the maximum shunting current, so that in case of imbalance, the voltage of a certain cell may eventually reach 3.7V, where the cell module will create a “HVC” event and interrupt the cell loop.

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 It will not indicate the peers of all connections, and it may be outdated.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.

power connections

On primary side, the charger is connected to the 230V AC grid via a 16 Amp circuit breaker in the trunk distribution box, and the AC connection.

The secondary side is connected to the traction circuit, protected by a 30 Amps fuse in the 100V distribution box

control in- and outputs

The charger has a control input for the BMS control board to signal that at least one cell has reached high voltage cutoff.

Of the output relay contacts, I have used the “mains present” normally_open contact in series with the “end of charge or trickle phase” normally_closed contact to control the DC/DC converter that powers the 12V grid. Using both contacts should avoid that the traction battery is drained if the car is connected to the grid for extended time.

There is also an optional external LED indicator connected to the charger, that I have mounted behind the window next to the tank lid.


The charger is mounted on bolts in the trunk area of the car. One mounting point was not at all accessible from below, so I welded a nut on top of the sheet metal to fix a bolt there.

Originally, the charger was directly bolted to the car chassis. Since it turned out to be quite noisy, I later suspended it in rubber mounts to reduce the noise radiated from the car's floor to the outside.

DIY rubber mount: The mounting hole of the charger is drilled out and the inner tube is inserted. The two rings of outer tube are then placed the inner tube, on top and beneath the charger's mounting plate. A bolt with a large washer is inserted into the inner tube, and presses the whole mount to the chassis.

In order to protect the charger's ventilation holes from the ECE R-100 test wire, I built a cage made of expanded metal mesh.

The cage is fastened by M5 bolts welded into washers and glued onto the trunk floor.

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astra_conv/conversion/battery_charger/battery_charger.txt · Last modified: 2014/05/20 17:59 by richard