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IndustryArena Forum > CNC Electronics > Spindles / VFD > Spindle motors: rpm / voltage / power / current
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  1. #1
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    May 2005
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    10

    Spindle motors: rpm / voltage / power / current

    Hello

    Currently I am running a fanuc asynchronous spindle motor with VFD in v/f mode.

    It is rated to 200V at 17A 1500/8000rpm.

    It's been running fine, I have used 17A at 100% spindle load and 22A as max 150%.
    Motor can operate at 22A load for 30min.
    I need to look at voltage at full frequency, dont remember it out right.

    It still fine motor , but bit too weak to run 50mm tools.
    So I am replacing it with Indramat 2AD100D it is rated 7.5kW at 1500rpm, 173V / 35A.
    Max RPM of motor is 9000rpm.

    First problem is that, if I calculate 3-phase power from 173V and 35A it will be around 10kW.


    I dont know this type of motors well, so I am bit confused what limit I need to respect?

    in case of indramat motor nominal voltage is 173V is this motors max voltage, or voltage at 1500rpm or 9000rpm?


    Can I run full amps regardless of speed?

  2. #2

    Re: Spindle motors: rpm / voltage / power / current

    It's most likely that the main ratings are at the "base speed" which is almost certainly 1500rpm here. Above that, the torque (and current) will tail off, as you won't have enough voltage to maintain the current required for full torque. It will possibly be able to develop the rated 7.5kW up to several times base speed but probably not all the way up to 9000rpm. In general, you will see something approaching constant torque up to base speed and constant power above base speed. The peak and constant power ratings will differ obviously, depending on the duty cycle and cooling. Torque is proportional to current and required voltage is proportional to speed. The v/f characteristic is to maintain constant magnetisation current the machine with varying frequency, thus avoiding the risk of saturating the magnetics. A vector drive scheme is a better solution if you can select that mode in the VFD.

    Bosch / Rexroth / Indramat do very detailed, Germanic datasheets. I suggest you find the one for your particular model. This will show you all the torque / speed / power / duty ratings you require.

  3. #3
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    May 2005
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    10

    Re: Spindle motors: rpm / voltage / power / current

    I have vector drive capable drive, but I have newer managed to setup so that it would not go "over current".

    I have only managed to run these spindle motors in v/f mode.
    If i run normal 3-phase motor I can setup VFD easily to vector mode.

    So this means that I need at leas 3 points to set up v/f mode correctly.
    Voltage at minimum, voltage at rated rpm and same voltage at max rpm.

    Still it is odd that it would have been made only to accept 173V as max.


    Ok, it really seems that I have really beaten hell out of my fanuc spindle motor.
    I have been driving it in constant torque mode, even in 8000rpm,
    I have taken full current out.

    Need to be little bit more careful for now on...

    This will generate new problem for me.
    I have used a spindle load meter, that gets signal from VFD analog output and is proportional to motor current.
    Now I need to figure out if there is even a possibility to get correct analog output to drive load meter.
    now output needs to be a function of frequency and current.

  4. #4

    Re: Spindle motors: rpm / voltage / power / current

    My Hitachi spindle motor is also designed for use with a VFD. The base speed is 1760rpm at 60Hz and 190Vrms but I have set the max speed at 7000rpm (was originally 6000 but hey). It can't produce as much power at max speed but that's not a problem for me. At 6000rpm it would need around 580Vrms, which isn't available. I have around 340Vdc (240Vrms) available, so it's going to start to run out of volts at ~2200rpm. It manages something like constant power up to around 4000rpm from memory, then tails off to perhaps 50% at max speed.

    Once the VFD knows the base speed point, it can scale the rest of the range accordingly. The overcurrent may have been the result of saturation due to incorrect parameters. Unless you give the VFD incorrect parameters, it should be able to cope safely regardless of what you ask of it, if it's in vector mode.

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