how long - often can a servo run near peak output

[AustinT]

Hello,

I am building a laser engraver that will use a servo for high speed rastering. The servo I am looking at produces 220 watts continuous and 660 peak. I ran a few numbers and I need 300 watts during acceleration. I am still under the peak value but It will be under this load a few times a second. Should I use a larger motor? Will it be ok since its under the peak?

Thank you

[Al_The_Man]

If you are exceeding the continuous rating 'a few times a second' it may not take long before the motor overheats.
If you exceed it very occasionally it should be OK.
If in doubt go to a larger motor.
Al.

[mike_Kilroy]

You can tell exactly by calculating the answer:

I prefer to calculate RMS torque required and compare that to rms or continuous torque rating of the motor.

Trms=[(T1^2*t1+T2^2*t2+...+Tn^2*tn)/(t1+t2+...+tn)].5
where T is torque for given time t....

If you want to rms POWER, it is simpler:

Pavg=(P1*t1+P2*t2+...+P3*t3)/(t1+t2+...+tn)

No guessing this way.


PS: The onlyl gottcha to this is if your overload is TOOO LONG for a single one shot time so that it overheats the motor before you get a cooling period or lower toque time.... ie., if you try to output the 300watts for 87 minutes on a motor rated 200watts and thermal time constant of 10 minutes....

[Xerxes]

Typical servo motors specify maximum peak torque to be 3x the continuous rating. Maximum duty cycle at 3x torque is 10% (requiring that 90% of time the load is zero or very light). With >100W motors 3x peak torque can be safely produced for several seconds before overheating.

Many today's servo drives simulate continuously motor temperature based on overload ratio and time constant to prevent motor from overheating. It's usually called I²t protection.