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This work has been executed by request of TRENDSINPTM and appertains to 3 power tool items: drills, angle grinders and electric jig saws in the quantity of 9 samples (3 samples of each type).

The diagnostics implied:
– evaluation of the technical level (by the results of these samples’ analysis listed below)
– examination of tools design particularities
– analysis of main units manufacturing quality
– energetic parameters checkup in the process of no-load working; special attention was paid to the heating of outwards housing parts and vibration at housing and handles
– checkup of motor speed parameters and the brush sparking degree which makes influence upon the functioning of collector/brush assembly.

The checkup and tool analysis results are in the following tables:
1. Measurement of the no-load parameters of tools (at breaking-in stage)
2. Drills diagnostics
3. Angle grinders diagnostics
Finally, it was followed by electric jig saw diagnostics and tests.

Measurement of the no-load parameters of tools
The parameters checkup executed after breaking-in during 5 minutes of each of 9 samples with the rated voltage 230 V. The testing results are shown in table 1. The upper part of it (p. 1–8) contains technical specifications according to the factory shield (in the absence of which they were taken from operations manual), while p. 9-18 contain actual measured parameters.

In consequence of measurements, the correspondence of speed parameters to the ones on the factory shield was certified, the current and no-load power input were defined, the maximum speed of armature shaft achieved at maximum setting of speed control was ascertained, the brush sparking degree was defined.

Contemporaneously with this, the heat of outward housing parts and vibration were evaluated (organoleptically). The results are shown in ‘Diagnostics” tables 2, 3, 4.

The measurements of drills speed parameters have shown that:
– The sample of BATRS doesn’t correspond to the no-load speed parameter (on the factory shield – 2800 rpm max, actually – 3070 rpm).
– The sample of HENDERS is almost identical (on the shield – 2900, actually – 2980 rpm).
– The sample of DWCM is close in this parameter (on the shield – 2800, actually – 2650).

The measurements of angle grinders speed parameters have shown that:
As for BATRS, HENDERS and DWCM angle grinders, all of them have almost identical spindle rotation rate with the one specified on the factory shield.

Whereas in case of drills overspeed doesn’t effect the security and basically effects torque or commutation, for grinders the excess of rotation rate is limited by the ultimate circular velocity of cutting disc up to 80 m/s, otherwise it will result in the broken disc, which is dangerous.

The commutation estimation in the process of no-load testing
As for sparking degree, only one sample of HENDERS drill had insignificant aberration. Annular arc slid periodically in this sample while the permissible sparking rate is 2 grades (stable, even sparking under the whole brush edge). In case of voltage increase to more than the rated 230 V and under working load, this can grow into stable annular arch which is unallowable. According to the standards requirements, the tool must be tested with the higher voltage, equal 1,06 of rated voltage, and when testing on “abnormal working mode” – with even higher voltage equal 1,3 of rated voltage, i.e. 300 V. The tool that reaches the commutation limit at no-load already, can fail these tests.

The maximum rotation rate of the each tool’s armature was defined due to the measurement of no-load parameters. It makes it possible to judge about efficiency of the tool’s cooling and propose optionally (if the data of stator and armature size are available) specific parameters of the tool’s drive.