VFD to Power Supply Trouble
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  1. #1
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    Default VFD to Power Supply Trouble

    Hi All,

    Might be knocking on the wrong door here but this is my situation:
    I have [email protected] to an AB Powerflex 755 drive in voltage adjust mode, outputting [email protected] The 400VAC is unusual, but is required. All components in the panel and on the machine are rated for this power.

    My drive is having no problem powering a programming port (European style 200V plug for computers) and a couple of fan motors. But it refuses to power up a 24VDC power supply. Power supply part number is DN4033, it is 380-480VAC 50/60Hz input, 24VDC 10Amp output. Whenever I enable the drive with the power supply connected, the drive immediately quits displaying a hardware overcurrent fault. The drive is rated for 11 amps continuous, 26 Amps peak...the power supply is rated for peak inrush current of 4 Amps. There's no way it is actually drawing more current than the VFD can handle. Power supply is verified as still good/not smoked by hooking it directly to mains voltage (480VAC @60Hz).

    No wiring problems, no obvious gotcha's in drive parameters....

    Any ideas are welcomed and appreciated.

    -Justin

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    Your problem is probably pulse -related. been there seen it done that, threw out the t-shirt.

    The current at 50 Hz input is 4A, but the VFD puts out pulses at a considerably higher frequency than 50 Hz, which are causing an overcurrent due to the capacitive input of the power supply. Long term, the rectifiers probably would not like the pules either.

    I have done that, sort-of, by running the VFD into a step-down transformer and rectifier, to do a quick and dirty regulated supply (we had lots of VFDs and not any power supplies, and needed it "right now". What the transformer did was to add series inductance, which limited the higher frequency pulse current, while not having much effect on the 50 Hz.

    You could, if you really need to do this, add an inductor in series with the power supply input. That would limit pulse currents and keep the VFD happy. I assume the VFD is being used to get 3 phase, and the power supply in the machine is 3 phase input?

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    JST, the power supply is 3 phase input. The VFD isn't used exclusively to get three phase, I have that on the wall, but it's 480/60Hz*. The VFD is used to get 400VAC at 50Hz.

    We only need [email protected] for this one little project, and will never need it again (hopefully). We don't want to rent an expensive generator, because of cost and because my customer is very bad at sticking to timelines, so we may end up renting the thing three times before we run our machine off with said customer.

    I was thinking the same as you this morning, and looking at three phase transformers. VFD intor transformer, transformer into power supply/machine. That gets us 50Hz from the VFD, cleaned up and stepped down to 400VAC by the transformer. I'm having a hard time finding a trans that would work, and since I can't promise my boss it will work, he's not going to want to do that.

    I do have an AB RFI Filter here, number 2090-XXLF-X330B, maybe the caps/inductors in there would be enough to save me? If I put it between the VFD output and the power supply?

    When you mention putting an inductor on the power supply input lines, I don't assume you mean something as simple as a ferrite ring...sadly.

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    Quote Originally Posted by I'llFixIt View Post
    J
    When you mention putting an inductor on the power supply input lines, I don't assume you mean something as simple as a ferrite ring...sadly.
    That might actually work. Don't configure it as a comon mode choke, you would need two ferrite rings with two separate windings. I suspect the issue is that
    the 24 volt supply is a switcher and does not play well with the pulse modulated VFD output.

    I'm sure there's a reason you don't run the supply off the mains, that it has to be off the VFD output.

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    Jim, yes the power supply is a switching power supply, and I have to assume you are correct, though I don't understand why. I know capacitors are bad on vfd outputs, but that's about it.

    I might have 3 or 4 ferrite rings around, I also have the RFI Filter.

    I have to supply the machine with [email protected] at the machine isolating disconnect, as a contractual agreement with my customer, who will run the equipment in Europe at that voltage.

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    Another option would be to try some other kind of non-switcher supply for the 24 volts dc. Needs to be regulated? Could be just a transformer
    and a diode bridge, capacitor filter after that.

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    I explained in my post on the other thread before i saw this one.

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    I do not know if "a ferrite core inductor" would work. Depends on the inductor.

    Inductors have a "saturation point", an amount of current at which the core cannot carry any further magnetic field. At that point the core "disappears" as a component, and the inductor becomes an air-core inductor, of far less inductance. So at a certain current the "inductor" stops being one.

    You probably do not want to get involved in inductor design, you have product to test. So a commercial solution is likely to be best.

    My suggestion was for something on the order of a standard 3 phase inductor of perhaps "3% impedance", and rated for the available current. They are a stock item and should be available on short notice. Not terribly expensive.

    The inductor will put very little impedance in series at 50 Hz, but much more at the switching frequency. That will cut the pulse current, and should allow the drive to easily handle your machine's power supply. ( a 3% inductor has 100x the impedance at 5 kHz that it does at 50 Hz).

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    Johansen, thanks for the reply there.

    Moderators, delete this thread maybe? I can't figure out how to do that.

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    JST,

    I doubt the AC FLA load is 5 amps, but you're probably right that I'll spend more time finding info to verify that wouldn't saturate whatever I tried, compared to ordering something and giving it a go.

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    Quote Originally Posted by JST View Post
    I do not know if "a ferrite core inductor" would work. Depends on the inductor.

    Inductors have a "saturation point", an amount of current at which the core cannot carry any further magnetic field. At that point the core "disappears" as a component, and the inductor becomes an air-core inductor, of far less inductance. So at a certain current the "inductor" stops being one.

    You probably do not want to get involved in inductor design, you have product to test. So a commercial solution is likely to be best.

    My suggestion was for something on the order of a standard 3 phase inductor of perhaps "3% impedance", and rated for the available current. They are a stock item and should be available on short notice. Not terribly expensive.

    The inductor will put very little impedance in series at 50 Hz, but much more at the switching frequency. That will cut the pulse current, and should allow the drive to easily handle your machine's power supply. ( a 3% inductor has 100x the impedance at 5 kHz that it does at 50 Hz).
    First to all, I'm sorry I am continuing to reply in both threads, but I don't want to inconvenience anyone by asking them to go to another thread, which I created by mistake in the first place.

    JST, another user here had suggested using spools of wire as individual inductors. While I'm game to try that, I also would like to find something I can quantify/rationalize why it would work.

    Here's my calculation for determining desired inductance of a line/load reactor I might buy:
    L(inductance) = (percent impedance x voltage) / (Frequency Factor x Full Load Amps)
    L = (.03 x 400) / (314 x 11)
    L=.0035
    L= 3.5mH
    So I need a 3 phase line/load reactor with a total of 3.5mH inductance, or individual inductors of 1.2mH each, approximately.

    Barking up the right tree here?

    I only have a bit more time I can spend on this before it just makes more sense to spend thousands on a [email protected] generator. Really trying not to have to do that.

    BTW, other thread, again very sorry for having created 2, that was an accident: 400VAC 50Hz Cost Effectively

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    https://www.automationdirect.com/adc...ctors/lr2-47p5

    model # LR2-47P5

    Cost yah under a hundred bucks US. Percent will be a little different at 400V.

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    Thanks JST.

    For $116 I can get a similar one from MTE via Galco, I'm going to go that route. For $100, worth a go.

    I have 2 machines that this VFD needs to feed. Should I get one load reactor, or would it be better to mount 2 close to the machine electrical disconnects?

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    Can you hook up a motor into the circuit?

    a "rotary inductor"?

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    Quote Originally Posted by CalG View Post
    Can you hook up a motor into the circuit?

    a "rotary inductor"?
    you could use a 9 wire motor as a 3 phase line reactor. lock the rotor so it doesn't spin up. the y connected coils would be disconnected and the other 3 coils used.

    the impedance will be on the order of 14% corresponding to a 7:1 locked rotor amps. (though you're only using half the windings so it would be more)


    the losses would be really high though because the rotor is a shorted turn. worth an experiment for sure.


    if you are thinking of using a large 3 phase motor as a capacitor to filter the square waves out.. (line/load reactor upstream of the motor) yes it will also work but not well.. perhaps good enough to get things working though, if for some reasons you couldn't just use some capacitors.

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    Coil location is not a big deal, coil does not need to be right up at the machine. This is waveform shaping, and not RFI filtering.

    Ideally would be a sine filter on the output of the VFD, but that may not be needed. You just need to cut the high frequencies so as to keep the current under control.

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    Thanks guys. Unfortunately we had some slow times at our shop recently and mass cleaning was in effect, some dummies threw away every motor we had, including one that is a head to a bridgeport mill (With a shiv still on it)!

    JST, I haven't found a sinewave filter that is really any cheaper than a generator. Since I can't be sure even the filter would work, the cost would be sunk and I'd still need to buy a generator if it didn't work = money wasted.

    Ordered a load reactor from MTE, RLW-001403. Will give that a go. If that doesn't work, the idea will be scrapped altogether in the interest of time vs. cost.

    Will report back.

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    Update, load reactor allows the power supply to power up instead of overloading the VFD as before, so the reactor must be filtering. However, the power supply squealed like a pig and sounded like it might blow up. So I guess this idea is dead at this point.

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    Quote Originally Posted by I'llFixIt View Post
    Update, load reactor allows the power supply to power up instead of overloading the VFD as before, so the reactor must be filtering. However, the power supply squealed like a pig and sounded like it might blow up. So I guess this idea is dead at this point.
    Did you add delta caps after the load reactor?


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