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OT Toshiba vfd trouble shooting help please

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  • OT Toshiba vfd trouble shooting help please

    Well, once again I find myself in over my head (nothing new here!) with volts and electrons and such.

    Bought two Toshiba Tosvert VT 130 G2 frequency drives off fleabay some time ago. Did actually test them both when they arrived, both seemed to work ok.

    In my ignorance, I didn't realize that they used a rather low carrier frequency, thus are annoyingly noisy in operation. So I sold the smaller one and kept the larger one for a pressure washer I wanted to build, where the noise wouldn't be a factor.

    Got motivated the other day to work on this contraption, so went to test this 30 hp rated vfd with the 20 hp, 1160 rpm motor I planned to use. No joy.

    Initially, it seemed that the motor would start to turn, then the vfd would trip out with a fault code indicating over current. I figured it was just because I had the accelerations wrong but I didn't have the time to figure it out right then so I left it for a day or two until I could download the manual again as I sent the first manual with the one I sold.

    Came back to try again, even less go.

    Now the motor won't even try to turn, and at various times get fault codes indicating low dc buss voltage or immediately shows overcurrent fault when increasing frequency from 0 to .1 or .2 hz. One of the recurring fault codes is listed in the manual as "suspect internal drive damage" or something to that effect. Consequently I suspect damaged IGBTs so embark on a campaign of dis-assembly to test same. While we are in there, lets check the 3 diodes. All seem to be copacetic, so back together to obtain the same fault code indicating low dc buss voltage, along with an inoperable dc buss contactor. Try a different motor, same result. Try both motors direct on 3 phase power, both seem to be fine.

    Oh yeah, maybe I should actually measure the buss voltage, what a concept!! That seems to be ok, 340-360 vdc depending on whether or not I have all three input legs hooked to power, instead of trying to make it be a phase converter as well as a vfd.

    After some amount of vocabulary review I came to the realization that the dc buss contactor is not closing. Ok, that would cause the problem, I would think. Not exactly sure if this was the case when I first powered it up but it certainly is the case now.

    More dis-assembly allows me to test the contactor contacts, contactor coil, the coil and contacts for the 24V auxiliary relay that runs the buss contactor, all test good. At one point I can hear the auxiliary relay actuating when I apply power to the unit, and then hear it dropping out at after a suitable delay when disconnecting power, as the dc buss voltage falls. Confirm the 24V signal coming from the control board that operates the auxiliary relay, that part seems to be doing fine. Also should mention that I checked the .75 Ω "soft charge" resistor, was good at that time though I did later let the magic smoke out of that, not exactly sure how. Cobbled together a wad of 2 watt resistors to replace that, pending arrival of replacement parts, and once again back to the "low dc buss voltage" fault code.

    I would also mention that this auxiliary relay seems to control the two fans that are on the unit, as well as the coil on the dc buss contactor coil. Also that I can manually close the dc buss contactor to no effect, except to measure the voltage drop across the contactor (2-3 volts) go away.

    So I then proceed to check for voltages that the auxiliary relay is supposedly switching. Nada, zilch, actually zero on my DMM. Ok, so where is the signal (voltage?) coming from that this auxiliary relay is supposed to be controlling? The traces on the board lead directly to a small full wave bridge rectifier, to the AC inputs of said device. The + - inputs are fed by wiring connected to the large filter caps/dc buss voltage.

    Ok, now I am really floundering in uncharted seas, with a noreaster bearing down. The only thing my limited electronic skills can conceive is that this is some scheme to monitor the ripple voltage on the dc buss? As mentioned, the dc buss voltage seems to be ok, a Yaskawa manual mentions a low buss voltage trip point of 190 vdc. I can measure an ac voltage of 2-4 volts across the dc buss with no load, but am not smart enough to know is this is significant or relevant?

    So I hereby throw myself on the mercy of this distinguished body, does anyone here have any insight into the protection schemes employed in this unit? That would fit in less than 10 paragraphs and be comprehendable by a neophyte such as I?

    Or should I ask if anyone wants a big box of parts with some good IGBTs and bad memories??


  • #2
    If genuinely bad, repairs are often not worth it/possible with reasonable expense. Without a service manual and parts, it is often not possible to guess what the design is doing unless you are very familiar with VFDs.

    1) does the unit power up and operate in V/Hz mode with no motor attached and no fault codes?

    2) What is your input type with the low bus report? single or 3 phase? Almost certainly will not be happy with single phase.....

    3) Does sound as if the precharge relay is not closing, which means a possible problem with the internal housekeeping power supply, OR a problem with the bus capacitor being bad. or the voltage measurement circuit is bad.........

    The contactor should close AFTER the drive decides that enough DC is present. That is to prevent a huge surge that charges the capacitor. if it never decides the voltage is good, never closes.
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    • #3
      Originally posted by becksmachine View Post
      Bought two Toshiba Tosvert VT 130 G2 frequency drives off fleabay some time ago.
      In my ignorance, I didn't realize that they used a rather low carrier frequency, thus are annoyingly noisy in operation. So I sold the smaller one and kept the larger one for a pressure washer I wanted to build, where the noise wouldn't be a factor.

      BTW, Toshiba are usually configurable for carrier frequency, .5 khz to 15khz.
      If these are used units, someone may have dropped the frequency on them? it may be worth resetting to factory default settings before attempting to use them?