3  EP 3 800 012 A1 4  supply into electric energy corresponding to the electric energy supplied by the battery pack, in order to allow operation of the power tool by means of electric energy originating fromthe mains powersupply andtransformed by the powersupplyunit.The battery pack may comprise one ormore batteries,preferably rechargeable batteries, of a Lithium-lon-type or a Lithium-Polymer-type. down therefrom)isverysimilarto the weightofthe battery pack. Therefore, the power tool according to the present invention can be easily used by a user over a longer period of time without signs of fatigue. 5 10 15 [0014] In principle the adapter element is a plug ele- ment having an adapter housing designed such that it can at least partly be inserted into the recess and estab- lishes an electric connection between the first electric cable and electric terminals of the power tool located in- side the recess for electric connection of the power tool toanenergy source(the batterypack orthe mains power supply). Preferably, no electric energy is transformed by the adapterelementbecausethe electricenergy istrans- formed by the powersupply unitand arrives atthe adapt- er element from the power supply unit through the first electric cable. [0010] According to the present invention, the power supplyunitisnotinserted into the recessofthe toolhous- ing but rather located externally. The power supply unit isonlyconnectedto the powertoolby means ofthe adapt- er element inserted into the recess and the first cable. The adapter element creates almost no heat during op- eration of the power tool. This is largely due to the fact thatthe adapterelement comprisesonly passive electric components which create almost no heat during opera- tion.The positioning ofthe powersupplyunitin a distance to the power tool eliminates any risk of overheating of the electric and electronic components of the power tool provided inside the tool housing due to heat from the power supply unit. An efficient heat dissipatio n achieved by the fact that the power supply unit can be freely located in the environment. Furthermore, the heat generated in the power supply unit may easily dissipate to the environmentthroughrespective cooling vents pro- vided in the power supply housing. 20 25 [0015] Any off-the-shelf power supply unit having the desiredelectriccharacteristics may beused as the power supply unit. This is possible because according to the invention the power supply unit is no longer inserted into the recess of the tool housing. Therefore, the design of the power supply housing is not restricted and can have almost any form. For example, conventional high-per- formance switching power supply units may be used which are available of the shelf in large numbers and at reasonable prices. [0011] Thefirstcable may have threemassiforstrand- ed wires, one for the positive pole, one for the negative pole and oneforground. However, itispreferred thatthe first cable has only two massif or stranded wires, one for the positive pole and one for the negative pole. Due to the fact that a reduced voltage (e.g. between 12 V and 48 V) is transmitted across the first cable for operation of the power tool, rather large currents (up to 10 A) will have to be transmitted across the first cable in order to achieve the desired output power at the power t Therefore, wires of the first cable have to be adapted to transmit the relatively large currents and must have a respectively large diameter. [0016] According to a preferred embodiment of the in- vention it is suggested that the electric transformer is adapted to transformavoltage ofbetween 100V and240 V,preferably an alternate voltage between 50 Hz and 60 Hz, of the mains power supply into an operating voltage of 12 V,18 V,24 V, 36 V or48 V, respectively,preferably adirectvoltage,ofthe powertool.The electrictransform- er adapts the voltage of the mains power supply to the voltage the battery pack provides, that is the operating voltage of the power tool. To this end the external power supply may comprise atransformer(analogue ordigital), arectifier,preferably a semi-conductorrectifier(compris- inge.g.semi-conductordiodes,activeelectronic compo- nents,thyristors,and/orMOSFETs),afiltercircuitforbet- ter electromechanic compatibility (EMC). Respective power supply units comprising such transformers are readily available on the market. However, it is the first time that such transformers are used in external power supply unitsinconnection withelectricpowertools,which have originally been designed for battery operation. 35 30 40 45 50 [0012] Furthermore,duetothe factthatthe powersup- ply unit is provided outside of the recess and does not form an integral part of the power tool, no re-approval of the powertoolisnecessaryifthe battery pack isreplaced by the adapter element connected to the external power supplyunit.The approvalofthe powertoolobtainedwhen operated with the battery pack in most cases will also be valid when operated with the mains powersupply through the adapter element inserted into the recess of the tool housing. [0017] It may well be that the external power supply unitisintegrated ina vacuumcleaner,towhich thepower tool may be pneumatically connected in order to aspire and filter dust-laden air generated by the power tooldur- ingitsuse.Tothisend the powersupply unitis contacted with the mains power supply through the vacuum clean- er’s electric and/or electronic components, which are at- tached to the mains power supply by means of a mains powercable.Thevacuumcleanerorits housing,respec- tively, may be provided with a socket to which the power tool may be connected through the first cable and a re- spective plug.The sockethas an outputvoltage (e.g.12V [0013] Finally, due to the fact that only the adapter el- ement is attached to the power tool and that the adapter elementcomprises notmuch more thanan adapterhous- ing, electric terminals and electric cables for connecting the terminals with the first electric cable coming from the power supply unit, the weight of the power tool is evenly distributed along the longitudinal extension of the tool. Preferably, the weight of the adapter element (and part of the first electric cable attached thereto and hanging 55 3