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  • #16
    ABB (huge) says 1 year of inactivity - reform. They give a couple of methods one of which is "switch on and wait a while (1-3 years of inactivity, model dependent) before run. When I talked to ABB tech support they just shrugged... Literally "do it if it makes you feel better". Here's a link to the ABB doc. https://library.e.abb.com/public/43b...tions_G_A4.pdf

    Here's another article from KEB. Yep... use a variac. https://kebblog.com/vfd-storage-and-...tor-reforming/


    Hitachi says nothing about their vfds (at least what I could find). Last Saturday I installed two capacitor banks in Hitachi 15hp vfds. The replacements were dated 2008! I looked at the schematics... nothing to perform a long "reform" - just the usual inrush (very common) limit on power-on. I let them settle for an hour before I flipped the run switch and developed full power.

    So... if you REALLY want to read up on this stuff... enjoy : https://www.dfrsolutions.com/hubfs/R...Capacitors.pdf

    Not sure what I'm going to do with my drawers full of cherished decades old electrolytics after reading the later
    Last edited by lakeside53; 01-14-2020, 02:38 AM.

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    • #17
      Originally posted by Paul Alciatore View Post
      I can't imagine a VFD manufacturer recommending that you purchase a somewhat expensive auto transformer to properly form the capacitors in their units. That would almost be a kiss of death to their sales effort. "Whadda you mean, it can blow up? Well, I sure ain't gonna buy that PoS."
      I Imagine car and truck makers would lose sales if they said maintenance was required "Whadda you mean, change the oil and filter, it can blow up? Well, I sure ain't gonna buy that PoS"...

      Originally posted by Paul Alciatore View Post
      I suspect if any of them actually think that far ahead as to imagine what should be done to preserve a unit that is sitting unused for long periods, then they would add a bit of resistance in that input circuit to protect those capacitors. Something like your lamp. Or another element that has a high initial resistance and then drops down to a lower value after a few seconds. That is, IF they actually think that far ahead: I really wonder if it would actually happen. Perhaps some of the older and better players in that market..
      Like mentioned, at about 70% of line voltage there's a click as the soft-start relay closes and shorts the resistor that limits inrush... On quality VFDs, not too sure about rock-bottom priced barrel-bottom scrapings.

      Originally posted by Paul Alciatore View Post
      Anyway, I still would recommend a shorter period for the preservative treatments.
      It's called preventative maintenance, Quite a Good Idea and saves time in the long run.

      Dave H. (the other one)

      Rules are for the obedience of fools, and the guidance of wise men.

      Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

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      • #18
        I have a Hitachi 2.2KW VFD that has been unplugged for a while - I think 2 years, maybe less but I'm not certain when it was unplugged. It runs on single phase 220. What's the best way to safely bring that up? What I read above mirrors my searches - no guidance from Hitachi. Can I use a 120 volt variable transformer to reform that? I'll need to borrow one from a friend. Thanks!

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        • #19
          At 1-2 years 'd just turn it on and wait and 30 min to an hour before you push the run button.

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          • #20
            Wouldn't it be a lot easier to just run the machine for a couple of minutes once a month or so? It's just like owning an infrequently-used boat or motorhome—run the engine once a month, and at more than a mere idle.
            As for powering a VFD down, well, every mains power outlet in my shops is switched—and before I lock up I check that every switch is off. Simple enough.

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            • #21
              Also interesting I have read is that many recommend a contactor between line power and the VFD so that cuts off all power to it and also protection from electrical spikes. So that is just like unplugging it. It gets used once or twice a month so it doesn't go long between use. I am more worried about the display burning out than anything else but that seems unlikely.

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              • #22
                My former employer used VFDs up to 30 hp. The line in was 480, 3-ph. The VFDs are used only to change speeds, nothing else. They are hard-wired to the breaker panels and left on continuously. In the last 5 years only two have failed out of dozens in service. They are some high end Japanese brand, but I forgot the name.

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                • #23
                  So when crossing your fingers and powering up a stored VFD, or other capacitor based power supply, is it best to have the device colder or warmer?

                  I mean, which temp is most favorable to keeping the smoke in - 30F or 80F?

                  I realize most electronic devices are out of spec at the extreme of 30F, but the optimal temp for this is probably worth knowing.

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                  • #24
                    Originally posted by Paul Alciatore View Post
                    You have a point with the capacitors, but I would be fearful of putting a VFD on a Variac. There are many designs out there and there is no telling just how the rest of the circuitry will react to the lower Voltage levels. It may be perfectly OK. But, on the other hand, bad things could happen.

                    .....
                    So..... here is a question for you: What happens when you turn the VFD off?

                    Yep, it drops through all those same voltages.

                    What happens when you turn it ON? Yep it goes, more or less quickly, through all those voltages. Slower with a resistor inrush preventer, faster with an NTC.

                    The power for the controls will not come on until the little SMPS that supplies it on any modern VFD decides the voltage is high enough, and turns on. That will be high enough to supply cntrol voltages.

                    Older VFDs with transformer power supplies are a different matter, no telling what will happen, but the odds are strongly in favor of them having a well-controlled turn-on point. Might be in the PS, might be a voltage detector on the control voltages that does not allow the controller to boot until there is enough voltage. There are small ICs that do that, holding the reset line in reset until the voltage comes up to a defined point, made for exactly that problem..

                    Now, if you have a Huanyang, or some other cheap asian VFD (I understand there are even cheap copies of the Huanyang), then there is no telling.

                    But any reasonable brand should have some defined way to handle low voltages, turn-on, brown-out, or turn-off. That sort of testing is part of the design process for any company wishing to make a reliable product.
                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #25
                      I have a couple of 10hp VFDs that I have had in storage for almost 10 years.
                      You bet your booty that I will be slowly bringing those capacitors up with a
                      variac and a current limiting resistor.

                      Posts above about re-forming not being a good idea and under-voltage not
                      being a good idea is just ignorance based fear.
                      Everyone loves to opine.
                      No one like to actually research things.

                      -Doozer
                      DZER

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                      • #26
                        Would like to add, out of the two that failed while on continuously, one had spent 12 hrs trying to turn a locked rotor (everything was smoked in that case) and the other failure was from swallowing a voltage spike that blacked out the entire East side of town for several hours. The electrician said it punched holes thru the mosfets. Both units were around 5 hp, I had to change the motors and etc.

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                        • #27
                          Cooper turbo compressor used to test their multi-hundred horsepower compressors at 2:00 am
                          because they would brown out the city of Tonawanda. I had a classmate in college that worked
                          there. He was in the room during the run in test and was not supposed to be in there.
                          He got his arm sucked into the compressor intake. It was not the turbine fins that killed him,
                          it was that the suction was so great that he could not pull his arm out and it sucked all his
                          blood out. The professor in my class that I had with the guy told us about it, and thus why he
                          would not be re-joining us back in class. Poor guy.

                          -Doozer
                          DZER

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                          • #28
                            Originally posted by Doozer View Post
                            I have a couple of 10hp VFDs that I have had in storage for almost 10 years.
                            You bet your booty that I will be slowly bringing those capacitors up with a
                            variac and a current limiting resistor.

                            Posts above about re-forming not being a good idea and under-voltage not
                            being a good idea is just ignorance based fear.
                            Everyone loves to opine.
                            No one like to actually research things.

                            -Doozer
                            Doozer, From what I have read its no problem to use a higher HP VFD on a lower HP motor, would that be your opinion? Lathe coming is 7.5HP and I am planning on buying a 10HP VFD with my thinking being more robust given the higher rating. What says you please?

                            Cheers!

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                            • #29
                              Larger VFD on smaller motor is very Ok.
                              Just make sure to program the amps draw to get the proper motor protection from the VFD.
                              If you are trying to run a VFD off single phase and it is not rated for it (some are)
                              you need to go like double the size, or add 4x the capacitance to the DC bus.

                              -D
                              DZER

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                              • #30
                                It depends on how big a mismatch there is.

                                If enough difference, the current limit protection sensors may not be very accurate, especially trying to set them at the low end of the current scale, and it may be hard to get proper protection. A 2:1 difference is OK, a 10:1 gets to be a bit iffy, and beyond that is just not a good plan.

                                However, if you were to, for instance, use one large VFD to supply 60 (or 50) Hz 3 phase to a number of motors, you could just put motor controllers on each, and run as if the big VFD were an RPC. You just need enough capacity to start the biggest motor.
                                1601

                                Keep eye on ball.
                                Hashim Khan

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