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  1. #1
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    VFD error. DC bus under voltage

    Is there a way to fix that. Normally happen after a couple hours of work. I have bar puller so lathe is working around 30 minutes per lot of parts.

    I can hear a sound like TUCK and the spindle try to start, couple of turn, a second sound TUCK and the spindle stop with error code UU on the VFD.

    Turn off power on the machine, wait a couple of minutes and turn it on again. Sometime will solve the problem for a couple of parts but alarm come back.

    Thanks for any help.

    Jeff

  2. #2
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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by jeffrey001 View Post
    Is there a way to fix that. Normally happen after a couple hours of work. I have bar puller so lathe is working around 30 minutes per lot of parts.

    I can hear a sound like TUCK and the spindle try to start, couple of turn, a second sound TUCK and the spindle stop with error code UU on the VFD.

    Turn off power on the machine, wait a couple of minutes and turn it on again. Sometime will solve the problem for a couple of parts but alarm come back.

    Thanks for any help.

    Jeff
    First you have to look at the Power supply to the machine, low DC Bus means it has not got enough suppl, so how many amps is the circuit it is on, and what is the cable size
    Mactec54

  3. #3
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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by mactec54 View Post
    First you have to look at the Power supply to the machine, low DC Bus means it has not got enough suppl, so how many amps is the circuit it is on, and what is the cable size
    Hi, thanks for the reply.

    It's on a 20 amp circuit breaker with a 10 awg cable. Power supply does not feed power to the steppers anymore. Replaced them with much more powerful servo stepper with drives on 220v. The fast feed are now 160 ipm. I'm sure I could run the lathe at 200 ipm with no problem

    I think I could have problem with door switches because sometime, when this happen, I just open the door and close the doors a couple of time and the spindle will start, maybe this is not even related to the original problem.

    Thanks again for your help. Jeff

  4. #4
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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by jeffrey001 View Post
    Hi, thanks for the reply.

    It's on a 20 amp circuit breaker with a 10 awg cable. Power supply does not feed power to the steppers anymore. Replaced them with much more powerful servo stepper with drives on 220v. The fast feed are now 160 ipm. I'm sure I could run the lathe at 200 ipm with no problem

    I think I could have problem with door switches because sometime, when this happen, I just open the door and close the doors a couple of time and the spindle will start, maybe this is not even related to the original problem.

    Thanks again for your help. Jeff
    What size is the spindle motor Hp, 20A seems low for a Lathe of this size the 10AWG cable is good for 30A so that is not a problem, the door switches would not cause low Bus voltage
    Mactec54

  5. #5
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    Re: VFD error. DC bus under voltage

    If one leg of a 220v circuit goes out it can trigger that error.
    Andrew Werby
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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by awerby View Post
    If one leg of a 220v circuit goes out it can trigger that error.
    Not at all, the VFD Drive would not power up at all, he is most likely using single phase, and it would be 240v for NA supply not 220v

    A Bus Voltage fault is caused by a low voltage supply and the Bus can't reach the needed 330v /340v
    Mactec54

  7. #7
    Community Moderator Al_The_Man's Avatar
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    Re: VFD error. DC bus under voltage

    A common problem with Electrolytic caps as they age, they lose capacity.
    There is a large bank typically wired on the output of the 3ph bridge.
    May need replacing, Seen it a few times.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by Al_The_Man View Post
    A common problem with Electrolytic caps as they age, they lose capacity.
    There is a large bank typically wired on the output of the 3ph bridge.
    May need replacing, Seen it a few times.
    Yes, I know about the capacitor, I always wanted to buy a spare one, now it's the time. Maybe two

    I don't understand why a 20 amp breaker could cause problem. If the lathe could draw more than 20 amp on a 240 volts, the breaker would just shut off. I could replace it with a 30, 40 or 50 amp breaker and it would not make any difference..

    Thanks a lot for all the replies

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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by jeffrey001 View Post
    Yes, I know about the capacitor, I always wanted to buy a spare one, now it's the time. Maybe two

    I don't understand why a 20 amp breaker could cause problem. If the lathe could draw more than 20 amp on a 240 volts, the breaker would just shut off. I could replace it with a 30, 40 or 50 amp breaker and it would not make any difference..

    Thanks a lot for all the replies
    You did not answer the question, what the spindle motor Hp is this will tell you if your circuit is sized correct, Ok just checked Tormach and they have your machine using a 230v / 20A Breaker for the primary and a 120v 20A for the secondary

    The VFD Drive does not just have a capacitor, it will have a bank of 6 to 8 large capacitor in the Bus, it is not a simple job to just rebuild the Bus, it is easy to check the Bus voltage though which you can do with a regular meter, this will tell you if you have a problem with it or not

    How old is the machine???

    No, the Breaker will only trip, if there is a short circuit it's there to protect the circuit, most will not trip from being undersized, that is not the purpose of a Breaker it is there and will trip if you have a short circuit or a major problem with the wiring

    You can only size a breaker to the circuit cable wire size being used x 125% to 150% larger this is the electrical code requirement
    Mactec54

  10. #10
    Community Moderator Al_The_Man's Avatar
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    Re: VFD error. DC bus under voltage

    jeffrey001 The DC voltage reading across the Capacitors, should be 1.414 x the AC supply, so for 120vac = 170VDC, or so.
    It may show this off load, but if the capacitors have lost value, it will show under load.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  11. #11
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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by Al_The_Man View Post
    jeffrey001 The DC voltage reading across the Capacitors, should be 1.414 x the AC supply, so for 120vac = 170VDC, or so.
    It may show this off load, but if the capacitors have lost value, it will show under load.
    That machine will not be using a 120v VFD Drive it will be 240v so his Bus voltage could be anywhere from 330v to 340v would be normal depending on his voltage supply
    Mactec54

  12. #12
    Community Moderator Al_The_Man's Avatar
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    Re: VFD error. DC bus under voltage

    One other sign of capacity loss , apart from low voltage, is electrolyte leakage on the tops of the caps.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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  13. #13
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    Re: VFD error. DC bus under voltage

    Quote Originally Posted by Al_The_Man View Post
    One other sign of capacity loss , apart from low voltage, is electrolyte leakage on the tops of the caps.
    If he has their big machine 15L, I doubt that he is having any capacitor problem at all, they spec the machine at 20A supply which is too low for a 3Hp VFD Drive driven Ac motor using Single Phase supply, total 20A for the Spindle Motor and the rest of the machine is ridiculous and a total miss calculation by someone
    Mactec54

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