amperage rating

[miljnor]

i have some C23-L55 Poly sci motors and am in the process of putting together the power supply. They are 36v 430 oz-in peek 40.5 oz-in cont. 50.9Watt motors rated at 2.5amps.

do these motors require 2.5amps or is that just at the 40.5 Oz-in rating?

they are rated at 21.6oz-in/amp so does this mean i need 430/21.6 =19.9 (20) amps?

[Evodyne]

Originally Posted by miljnor i have some C23-L55 Poly sci motors and am in the process of putting together the power supply. They are 36v 430 oz-in peek 40.5 oz-in cont. 50.9Watt motors rated at 2.5amps. do these motors require 2.5amps or is that just at the 40.5 Oz-in rating?

Just at the 40.5 oz-in rating.

they are rated at 21.6oz-in/amp so does this mean i need 430/21.6 =19.9 (20) amps?

In a nutshell, yes. But it gets more complicated. That 430 oz-in rating is when running near stall. In that scenario torque is high, but power output to the shaft is low. The bulk of the power delivered from the supply ends up as heat.

For a more in depth discussion (as it relates to sizing your power supply mostly) refer to this thread.

Lance

[snaggletto]

Evodyne is correct.

This is a popular question. Peak torque, and the current needed to achieve it, is basically a measure of what it takes to melt the motor and/or demagnetize the magnets. A servo can and will use more than it's rated current when the motor is under a large load and the current is available from the supply. In this sense it is a good idea to have some extra current available for the motors. However, the rated current, is all that the motor can handle (heat dissipation) for *continuous*, long term operation. However, keep in mind the motor will only use the current that's needed to maintain position.

For example, say you use your 2A servo to drive a really light load and your power supply can supply 20A. If the motor can move the load with only .5A, then that's all it will EVER use. The motor will run cool, and your power supply will be vastly under utilized.

Now say that you use that same setup to drive a really heavy load. Now say the 2A motor requires 4A to even move the load. Your power supply will supply the current that the servo asks for. The servo will run at 4A+ trying it's hardest to move the load. The servo will melt very shortly because it cannot continuosly dissipate that amount of heat.

As seen in the examples given above, the trick is not in the power supply, it's in properly sizing the motors for the application/load. Assuming your motors are sized properly for your application, I've heard that 2/3's of total current is sufficient. So with 3x 2A motors on a mill, that's 6A and 2/3's of that is 4A. This works fine because you won't be fully loading more than one axis at a time.

[miljnor]

so basically what your saying is that the Power supply should be sized with the continous rating in mind. So as not to overheat the motors and since your are multiplying the TOTAL by 2/3 if any one motor needs more than the 2.5amps continious it will be there???

The other threads is quite convoluted and long, I am reading it, but would rather have the answer given directly (don't worry I wont hold anybody liable for MY mistakes! Although that seams to be the "trend" in america these days)

[miljnor]

i have read the other thread and understand thanks all for the info.