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Corded Tool Power - a short discussion

What does the word power in power tools actually mean?


Without getting too technical, power tool mechanical power is all about rotational force and speed and power tool electrical power is about voltage and current. It is a mistake to confuse either force or speed for the term power. A good example is a two gear power drill. The slow speed gear setting is not more powerful because it will drill larger holes and the faster gear setting is not less powerful because it can only drill smaller holes. The truth is that both gears produce approximately the same* power output because the motor power input is the same in both cases. However, in gear 1 the output force is high and the output speed is low. In gear 2 the opposite is the case, the speed is high and the force is low. (*Getting technical just for a moment: As with most things in life, this is an approximation and in reality because of the different efficiencies between the gears the power outputs may vary slightly but the principle is still correct).


So, mechanical power is the combination of force and speed and electrical power is voltage and current. On a corded power tool the rating plate will often show a figure for the power. Usually this is measured in Watts or W and normally it does not relate to the mechanical power output from the power tool. Instead it relates to the amount of electrical power the motor draws from the electricity supply under standard controlled conditions. In other words it is a measure of the electrical power input. In many countries it is a regulatory requirement to show this power figure on anything that plugs into the mains electricity supply. It does not indicate how mechanically powerful the output of the power tool is. For example: a high quality corded power tool might have a lower power figure on the rating plate than a lower quality power tool but the higher quality power tool may work much better and produce more mechanical power output. How can this be? The lower quality power tool may be less power efficient and waste more power in the motor or gears or both. You may notice during use that the drill may get hotter. This is because it is wasting mechanical power in the form of heat due to higher electro-mechanical losses, usually as higher friction losses.


With cordless battery power tools things are more complicated and discussed in blog post: Cordless Tool Power


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