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IndustryArena Forum > CNC Electronics > CNC Machine Related Electronics > Is this power supply rating adequate?
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  1. #1
    Join Date
    Sep 2004
    Posts
    31

    Is this power supply rating adequate?

    I bought a new CNC router and I think the power supply is too small. I have 3 PacSci Powermax II P22nrx .... 2.3 amp bipolar, 65 v stepper motors. The motor tag also reads 74 w. Maybe that is watts but I don't know.

    The power supply tag reads 48 volts and 3.2 amp. It is a switching power supply that two sets of 48 volt leads from it. I assume that it is dual channel because of the two sets of leads.

    Is this a proper power supply? Someone told me that I could even use a 24 volt power supply if it had enough amps.

    Any comments appreciated.

    Thanks,

    JR

  2. #2
    Join Date
    Nov 2004
    Posts
    12
    Someone was right. The higher is the voltage, the higher speed your steppers would attain. At a low speed, you need just a few volt to pump 2.3A through the motor. As angular speed grows, so does motor's back EMF, and you start to notice that the drive opens more and more, then stops regulating current and simply opens, then current starts to fall. This is the point where momentum developed by the drive starts to proportionally decrease. If you determine you need a higher speed, then you need a greater voltage PS.

    48V does not look bad - I am more concerned about 3.2A. In a router, both X and Y may pull at the load at the same time - requiring more juice. Also, drives still pump current through a motor that does not move. Most drives, but not all, decrease winding current in a second or so of no stepping, usually two to four times down from the set current. Nevertheless, current protection of a power supply is necessarily faster than that second, so when the router moves the bit down along Z and starts a diagonal cut, all three motors are at full current supply - 7.0A for all three if you run them at full current.

    An attempt to draw more current from a PS causes its output voltage to drop, a condition known as brownout. Most SMPS turn off the output in this case, which likely equals a damaged workpiece. You are not likely to damage anything else, so make a few dry runs of the machine to see if it triggers supply protection, preferrably with different NC programs, involving speedier 3-axis movements. If it does, and assuming you are using constant current drives, decrease set current in the drives until the machine does not blow the PS protection, and then another 20-25%. If you hit this current limit, you are not going to hit the voltage limit, so each of the PS ratings may be a limiting factor.

  3. #3
    Join Date
    Mar 2003
    Posts
    35538
    What type of drives are you using? With Gecko's, you'd want about 5a to run all three motors. Not all drives work the same, though. Some drivers may require up to about 13a.
    Gerry

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  4. #4
    Join Date
    Sep 2004
    Posts
    31
    I am using the Gecko 210 or 201 drives. From reading the past 2 posts it sounds like my Power Supply might be too small if the machine is under max load. Let me add something. There are 2 sets of wires ( 2 black, 2 white) attached to the power supply. The manufactor wires the black one together and the white ones together. I assume the power supply is 2 channel and the manufactor wants to make it a single channel by connecting the channels. The power supply is marked 3.2 amp and I do not know if this is 3.2 per channel or total. Seems like 3.2 total is not enough. 6.4 would probably handle it. But I am not sure.

    My problem is that the z axis fails to lift the router at times and ruins my work. There is no mechanical problem and I want to blame the power supply.

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