The paper describe design of battery powered drive unit intended for tree harvester application. Battery powered hybrid drive unit in working machine is currently quite common (1). The battery capacitance is not sufficient to realize harvester as an only battery powered machine. Nevertheless, the hybrid concept of electric drive is useful to cover short power peaks demands during the harvester standard operation. In harvester application there is typical high ratio between short power peak and average demanded power. The development in batteries increases of significance and possibility of electric drive utilization in three harvesters.

This paper deals with a measurement of alkaline and Li-ion battery impedances in wide-range frequency from about one Hz to a few hundred kHz. Measured battery admittances are used for the construction of battery transfer functions, i.e., the dependences of admittance on frequency. Comparison of transfer functions for different battery types is shown. It is shown that transfer functions for both types have the same form and this transfer function is only the third-order.

This paper deals with the design and operational evaluation of a timber tractor-trailer unit with a hybrid trailer drive. The source of electrical energy for the two induction motors driving the front wheels of the tandem trailer axle is a battery, which is recharged by an induction machine operating as a generator during periods of a lower demand for power from the tractor diesel engine. An electric drive was designed for the defined working cycle of the tractor-trailer unit, and its loading characteristics were tested in the laboratory. The parameters measured on the field tests during timber forwarding were battery voltage and power, and the energy balance. Three adjustment levels of the potentiometer controlling the trailer hybrid drive (50, 75 and 100%) were tested at three different forwarding distances of 100, 500 and 1000 m. Additionally, any slippage of the prime mover wheels and trailer was measured. The maximum peak power taken from the battery was ca. 33 kW during the field tests, whilst the drive was able to deliver a peak output of up to 72 kW for 10 s and permanently up to ca. 50 kW. Even in harsh terrain conditions, the electric drive assisted the combustion engine only when the loaded tractor-trailer unit was travelling uphill. The hybrid drive operation was sustainable for the whole working shift, without the need for recharging when the potentiometer was set to 50%. This appropriate setting of the potentiometer controlling the trailer’s hybrid drive reduced the slipping of the driven wheels of the tractor-trailer unit whilst travelling uphill.

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An electric bike (1kW) with a Li-Ion accumulator 28V/42A was constructed and tested in the Department of power electrical and electronic engineering. Panasonic cells CGR18650C (ca 2Ah) are used in the accumulator. The battery is completed with 7 serialconnected blocks. Each block is a set of 21 parallel-connected cells. The accumulator was tested in the vehicle since 2005 till now. During the tests a distance of approx. 12000km was driven. Some theoretical know-how about the used charging and discharging strategy and about the battery management system is proposed in this contribution. Practical results regarding the lifetime, capacity decreasing, charging problems, temperature dependencies and cell voltage balancing are visible from the long-time experiment described in this contribution too.