Motor stutters at low rpm then vfd throws overload error
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    Default Motor stutters at low rpm then vfd throws overload error

    Hi All,

    Trying to get a new VFD working on a woodworking lathe. Motor is a 2 hp 220v 3 phase. It's a chinese VFD, so I think I've got all the settings set to relate to 60hz. When I turn the motor on, it will stutter/jitter at very low speeds, but as soon as I try turning the speed up, it throws the short circuit/overload error. I bought 2 different brands of chinese VFDs and both do the same thing. Any idea's what could cause this? I've tested the resistance between the 3 pairs and all 3 are dead on 1.4.

    Thanks

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    Quote Originally Posted by jtupnsmoke View Post
    ........... I bought 2 different brands of chinese VFDs and both do the same thing. ........

    Thanks
    The quoted line may explain a lot. The two brands may be much more related than you think. The forbidden brand is sold under a number of other names, OEM'd with variations.

    All I can say is that it sounds as if you do not have the settings correct. We know very little about the details of those, and, I frankly, have a fairly low interest in learning. The quality level has been extremely variable, the manuals poor, and the build quality of those I have seen I would not expect to pass UL 508.

    Teco is Taiwanese, not expensive, not the best available , but they do pretty reliably work. Japanese brands likewise.

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    Quote Originally Posted by JST View Post
    The quoted line may explain a lot. The two brands may be much more related than you think. The forbidden brand is sold under a number of other names, OEM'd with variations.

    All I can say is that it sounds as if you do not have the settings correct. We know very little about the details of those, and, I frankly, have a fairly low interest in learning. The quality level has been extremely variable, the manuals poor, and the build quality of those I have seen I would not expect to pass UL 508.

    Teco is Taiwanese, not expensive, not the best available , but they do pretty reliably work. Japanese brands likewise.
    I have read the same thing about the chinese brands. I got this lathe for free, so really just trying to get it running before dumping more money on a decent vfd. The motor windings don't have any shorts to ground. I'm fairly certain it is a setting also, but i'm not sure which one it is. If anyone cares to have a look at the settings options, i've attached a pic.
    img_20200908_061805.jpg

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    Best guess is either motor rated current, or the acceleration time.

    In general slower accel times reduce current and let you get through the start. I'd try that first. (pic is a little blurry)

    Reducing too far can get into trouble with the maximum time of overload. Good brands will have a 150% current rating for a minute at least. Some have ratings of 200% for a few seconds. What the various chinese brands have, I do not know.

    Usually a 2 to 3 second time is OK, that depends on how much heavy stuff is being accelerated. You may have to experiment.

    Switching VFDs once you have everything working OK is likely a good plan.

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    Quote Originally Posted by jtupnsmoke View Post
    ...When I turn the motor on, it will stutter/jitter at very low speeds,...
    Double check that the motor is wired for 240, and not 480 volts.

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    Well I returned both Chinese VFDs and spent a little more money on a TECO. But now I am pretty sure the motor is not working. The TECO is doing the same thing. I'm looking at replacement motors and this lathe uses a non standard motor frame. It is similar to 56c, except it has a longer shaft at 3.5" and doesn't have the round standoff. Any ideas on a motor that would fit this?

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    As per the above, check the motor is wired right. This is the expected behaviour if one of the windings is connected backwards.

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    If a winding is backwards, the motor will likely not turn, in general. I suppose it could.

    Did you indicate that the motor turns jerkily at low speed, but will not accelerate (that was the impression I got)? Or does it just jump around back and forth and never turn?

    If it will not turn, and/or does not accelerate at all, then yes double check all wiring.

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    Stuttering / jittering at low speed is often a symptom of the drive being in what's called "Sensorless Vector Control" (SVC) mode, but you did not perform what's called an "autotune" or "Motor ID" function first. SVC is a way for the VFD to provide more accurate and steady torque to the load at even very low speeds. But for it to work, the microprocessor inside of the VFD must know what the motor is SUPPOSED to look like mathematically, so that it can crunch the numbers to make it work right. To get that information from the motor, you must perform this "autotune" procedure wherein you let the VFD energize the motor and read what it sees. Most of them allow a "static" autotune, meaning the motor will not have to rotate, that should be good enough for a lathe application.

    With the cheap Chinese drives, their manuals are horrible and they don't provide any tech support, so we ban discussing them here to avoid letting them off the hook for supporting their products as they should. On the Teco drive, it will depend on which model you bought; some do not have SVC so they don't have autotune, but yours likely does. If it is the L510 model, the Auto Tune (they use a space) is parameter 02-07.


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