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Thread: Choosing a VFD

  1. #1
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    Default Choosing a VFD

    With the new lathe expected to arrive sometime next week I'd like to figure out a plan for the VFD conversion to run off single phase.

    I'm expecting to find it has a mid-60s era 4HP two speed motor (1500/3000 RPM).

    What VFD brands are recommended? Seems like all of the cheap imports work. Lot of good comments on Powtran, particularly from BobL so I'd tend to swing that way because at least if I get stuck I can post a question on here and get a coherent response. But I'm open to opinions.

    What size, noting Powtran have a gap in their range at 3kW?

    The Powtran thread is getting a bit old. Has anyone purchased direct lately and can confirm it all still works the same?

    Any tips on what the messing around with the motor is likely to involve? Obviously the VFD takes over the speed control but should I set it up as 2p or 4p to start with? I have motor rewinder options here if I get stuck.

    Thanks, Tim

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    The first thing to establish i whether the motor is a delta (∆) or a star (Y)

    If the motor is a straight 415V ∆ then, short of a a complete rewind, the motor cannot be used at full power running from a 240V 3P VFD.
    If its a two speed (Wound) motor then these can be converted but will require a specialist to do this.

    However in both cases you could avoid touching the motor using something like an Ecogoo VFD which converts 240V to 415V + 3P.

    I haven't purchased a Powtran for about 2 years but I still get emails from them so I know they are in business.

    A 3kW Powtran should do. I would get a PI91XX series VFD - they cost more but they have many useful features.

    The VFD should be set up just like the motor (ie relevant number of poles). I recommend removing all switch gear between the VFD and the motor so if its a Dahlander motor and you want to retain the two speeds (somewhat unnecessary if you have a VFD) then you MUST make sure the motor has come to a dead stop before switching or you may damage the VFD/motor.

  3. #3
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    If it’s a 4HP motor why would you nobble it trying to run it on a 3HP supply?

    If you find the motor needs rewinding, it’ll likely just be cheaper to buy a package deal from Connons, or get an Ecogoo.

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by racingtadpole View Post
    If it’s a 4HP motor why would you nobble it trying to run it on a 3HP supply?
    Where does the "3HP" come from?

  5. #5
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    Tim, when you get your lathe, take a photo of the motor name plate and post it here.

    Thanks,
    Paul

  6. #6
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    Yep, as soon as it turns up I'll post the nameplate.

    As far as I can gather the standard factory motor was probably 380V 1500/3000 rpm dahlander. But that may not necessarily be the spec for an export to Aus

  7. #7
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    Apologies, my bad, I misread 3kW as 3HP. I’m going to blame the industrial strength painkillers I’m currently on (at least that’s my excuse, and I’m sticking to it).

    Carry on

  8. #8
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    Having used a few now, I'd just go straight for one of the EcoGoo 220-380v 4kw units:
    https://www.aliexpress.com/item/4001249189042.html

    I've bought all mine from the Ecogoo Store on Aliexpress and not had an issue. Generally arrive pretty quickly too - current environment considered.

    Without knowing how your lathe is wired, my general approach would be to run the motor in its low speed configuration, and run at a higher frequency (up to 100hz) to get the higher speeds.
    The control side for the existing contactors is likely run off 240v or 110v, and probably off a transformer. The machines I've done had transformers that were multi-tapped on the input side and 110v output. So it was a simple case of supplying 240v to the appropriate input tap and everything downstream of that worked as original.
    I usually get the motor running straight from the VFD via the VFD control panel first as its just simpler for my brain, then I know its working and just have to get the remote start via the VFD inputs sorted.
    Typically I disconnect the 380v wiring from the motor contactors first up - both the supply to the contactors and the outputs to the motor windings.
    With a 2-speed motor you may find that the speed change is handled by one contactor and it defaults to low speed when energised.
    In that case you could leave the motor side of that contactor alone (just disable the control side so it can't go to high speed mode) and it would save you having to mess around re-terminating those connections.

    After getting the motor running from the VFD I then set up a couple of simple toggle switches to the VFD inputs for testing so I can get the remote start/stop/direction working.
    Once that is done, I then use the switched contacts on the start/stop and fwd/rev contactors to replace the toggle switches.

    Using that approach has a few advantages compared to other ways I've tried:
    • minimal wiring change overall, so easy to convert back to original if required
    • control wiring stays completely original, and any safety devices or features stay as they were eg brake microswitches/clutches, e-stops etc
    • VFD output is permanently connected to the motor so no chance of accidentally breaking that circuit and causing damage.
    • nice easy steps that can be validated as you go, rather than getting to the end and hoping it works - and having to start troubleshooting from scratch when it doesn't.

    What it doesn't give you though is:
    • the ability to distinguish between a normal stop (up to a few secs) and an emergency (ASAP) stop.
    • along similar line - if you have a manual spindle brake (eg foot brake) then jumping on the brake hard could end up fighting the normal programmed motor deceleration.


    Finally, all the VFD's I've played with have the default accel/deccel time set to 10secs. Leave that setting as-is until you get things working, then bring it down to whatever works best. Generally I find 3-4secs accel is nice and easy on your power supply, but you can get away with a quicker stop of 1-2secs as long as you haven't got a lot of inertia (in which case you may need to increase that time to prevent VFD errors - its an over-voltage of some sort from memory).

    Steve

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    This should help.
    Attached Images Attached Images

  10. #10
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by OxxAndBert View Post


    What it doesn't give you though is:
    • the ability to distinguish between a normal stop (up to a few secs) and an emergency (ASAP) stop.
    • along similar line - if you have a manual spindle brake (eg foot brake) then jumping on the brake hard could end up fighting the normal programmed motor deceleration.
    On my WW bandsaw with a VFD and foot brake, I set the VFD to "coast to stop" and incorporated a microswitch triggered by the brake that turns stops the VFD. Then you can stomp on the brake as hard as you like without affecting the VFD. More so for a fat-wide blade, and less so for the 6mm wide blade.

    If you want to use a switch attached to the VFD switch to stop the lathe and only want to use the brake in an emergency then any switch attached to the brake should be a proper contactor based switch on the power input side to the VFD. The emergency switch thus cuts the power to the VFD. This is also an electrically safer option in that it completely separates the VFD/motor from the mains. It's not appropriate that this be done on a regular basis especially under load but I'm assuming that this is for an emergency.

  11. #11
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    Re wiring diagram - looks like its all just simple mechanical switching apart from the low voltage contactor on the input (which will be redundant anyway with the VFD setup).

    Speed selector - nice and easy, just set it to low speed for a start and don't forget about for now.
    Leave the thermal breakers in place for a start - won't hurt but likely not necessary as you should be able to cover that with settings on on the VFD side if you really wanted to remove them. I personally wouldn't bother.

    on/off/fwd/rev switch:
    Remove 9/10/11 from the switch and connect them to the output side of the VFD.
    I'd disconnect the supply to the switch (6/7/8) and just make them safe with insulating terminals even though they should never get any voltage on them when running the VFD.
    Now that the switch is completely disconnected you need to find some contacts to signal the VFD to stop/run and in which direction. Probably a common contact and one for each direction but depends on which method you use on the VFD side

    Your single phase supply goes direct to the VFD.

    You won't have:
    - power on light (you could wire this up on the input side before the VFD if you really want, but generally the big flashing red numbers on the VFD are suitable replacement).
    - coolant pump. They are always a hassle. Without getting too creative the options include: separate VFD to run it (overkill), or swap for single phase motor.
    One I haven't tried but AFAIK will work fine is to just hook it up in parallel with the main motor and either have it run permanently when the main one is running, or only switch it on/off when the main motor is running.
    Before anyone jumps in and says that you can't switch anything downstream of a VFD, my understanding is that as long as the main motor is running and the coolant pump is relatively small in comparison, the main motor provides an electro-magnetic buffer that prevents any of the normal reverse EMF (or whatever it is that upsets the VFD's if you downstream switch) from causing issues.

    Steve

  12. #12
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by OxxAndBert View Post
    - coolant pump. They are always a hassle. Without getting too creative the options include: separate VFD to run it (overkill), or swap for single phase motor.
    One I haven't tried but AFAIK will work fine is to just hook it up in parallel with the main motor and either have it run permanently when the main one is running, or only switch it on/off when the main motor is running.
    Before anyone jumps in and says that you can't switch anything downstream of a VFD, my understanding is that as long as the main motor is running and the coolant pump is relatively small in comparison, the main motor provides an electro-magnetic buffer that prevents any of the normal reverse EMF (or whatever it is that upsets the VFD's if you downstream switch) from causing issues.
    You can readily switch on/off a parallel motor with certainty provided the other motor is permanent connected to the VFD and not running under load. A smaller motor switched on/of while a larger one is under load is less of a problem than the other way around.

    However The main problem with this is the coolant pump and flow will then run at the speed of the main motor
    Thus at high speeds you will have to adjust the flow to the speed, while at low speeds the impeller may not even work.
    On my mill @42Hz the impeller did not have enough grunt to even lift the lube/coolant from the floor level tank, while at 60Hz it was squirting the fluid half way across the shed.
    I ended up putting a 0.4HP VFD on the pump but I hardly ever use it as I now run a misting system.

  13. #13
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    The VFDs that step the voltage up sound like the way to go. My searching only turned up a few older threads on this style and it was hard to judge if they were a thing or not. It seems they now are.

    I'd like to make it work as near as possible to original. The safety contactor might require some further investigation. I suspect it is involved in preventing it from automatically running when the power is switched on

    I haven't spent any time thinking about coolant.

  14. #14
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    Interesting to see that Ecogoo have the same gap in their range at 3kW. Next size up is 4kW. Seems unbelievably cheap.

    I should really be using a Siemens drive.

  15. #15
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by browny View Post
    I'd like to make it work as near as possible to original. The safety contactor might require some further investigation. I suspect it is involved in preventing it from automatically running when the power is switched on
    Correct but the VFD will do that automatically (unless you program it to do otherwise).

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