S1 S6 motor ratings – what’s the meaning of this ?
S1 S6 motor ratings: here’s a brief explanation of what they mean, how you can understand your CNC machine’s spindle capacity, and how it impacts your machining profits.
In CNC machine catalogs, spindle capacity has traditionally been written as a continuous and short term rating, like this (let’s call this the old spec).
Spindle capacity specs are increasingly written this way (let’s call this the new spec).
What does this mean ?
The old spec example above means that the continuous rating is 5.5 kW and the 15 minute rating is 7.5 kW. You can load the motor at 5.5 kW continuously, or at 7.5 kW for 15 minutes. Specs for larger machines may have 30 minute or 1 hour ratings instead of 15 minutes. The problem with this way of defining the capacity is that CNC machine motors are rarely subjected to a fixed load for a long period of time like 15 minutes. There’s a few seconds or minutes of cutting, then tool change, then again cutting, etc. The old spec. does not mention the duty cycle, the pattern of load that the motor is subjected to.
To fix this problem, the IEC 60034-1 (IEC=International Electrotechnical Commission) standard describes the capability of a motor based on the duty cycle. This is the new spec. Here, S1 is the continuous rating and S6 is the short term rating. S6 is written with a number after it that is the duty cycle for a duty period of 10 minutes.
The new spec. example above means that the continuous rating is 7 kW and the 40 % duty cycle rating is 10.5 kW. You can load the motor at 7 kW continuously (like 24 hours), or at 10.5 kW if the motor gets 6 minutes of rest every 10 minutes. ‘Rest’ means it can be rotating but with zero cutting load. The loaded and idle periods are cumulative, need not be continuous. The duty cycle can be one of these : 15 %, 25 %, 40 %, 60 %.
Text and pics. source: CADEM NCyclopedia multimedia CNC training software.
