Which VFD for my surface grinder?
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    Default Which VFD for my surface grinder?

    Hey guys, picking this up Monday and wondering what VFD to get for it... I am considering CFW300 (ip20) or a KBAC 24D (ip65). basically it will need to convert single phase 110v to the 3 phase 230v for the motor.

    Is there any issues with the CFW300 being rated for a 1.5hp motor? I don't wanna over power it and blow the motor out. I have used a larger version of the KBAC on my other grinders and have high respect for their product, top notch quality so I may just go that route. I'm just not sure what to get and then will probably need a little help setting it up.



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    Quote Originally Posted by razoredgeknives View Post
    Hey guys, picking this up Monday and wondering what VFD to get for it... I am considering CFW300 (ip20) or a KBAC 24D (ip65). basically it will need to convert single phase 110v to the 3 phase 230v for the motor.

    Is there any issues with the CFW300 being rated for a 1.5hp motor? I don't wanna over power it and blow the motor out. I have used a larger version of the KBAC on my other grinders and have high respect for their product, top notch quality so I may just go that route. I'm just not sure what to get and then will probably need a little help setting it up.


    You can't "over power" an electric motor with any VFD.

    The motor will only draw the amps it requires to satisfy Ohm's law with induction in the mix.

    Over VOLTAGE is a different thing, Ask your electrician.....

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    Your motor is 1HP, so 1.5HP VFD will work fine. I, personally, would, probably, choose a 2HP one. The price difference won't be great, but you'll have a good safety margin.

    P.S. As stated above, a VFD rated for higher power won't damage any lower power motor. It's like your electric circuits at home: it work for a small LED night light as well as it works for a washing machine. As long as the voltage is correct and the consumed power or amperage are not exceeding the supply capacity, everything will be just fine. So you can use a 5HP VFD if you have one available, but it's just not needed.

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    You cannot use a conventional VFD on this surface grinder and maintain all the controls/functions, you would only be able to use it if directly connected to the motor but you still would need to power the other functions such as feeds/pumps, etc. Better off with an RPC winch would maintain all the functionality and could power the unit without modifications. Also check the input voltage is set to 240VAC.

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    Very good point. One RPC will serve your whole shop without any machine modifications. VFDs may be desirable for a limited number of needs/types of machines, IMHO. Otherwise, it just brings extra expenses, extra work and extra headaches.

    But if the grinder is the only 3-phase machine you'll ever have (which is hard to imagine), then using a VFD is justified.

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    The CW300 drive is fine in my opinion. I know the guys that developed that drive pretty well.

    A couple of points - historically the limiting factor on how big a drive you would want to use on a motor was based on the having enough resolution to measure motor current. If the drive was too big, the current sensors were sized for bigger motors and had difficulty with supplying the proper current feedback at low levels. General rule of thumb was to limit the drive to 10 times the motor horsepower. Don't know if this has changed any with the newest generation drives.

    One advantage to oversizing the drive compared to the spindle motor is that you can start the coolant/hydraulic pump motors against the running drive. Coolant pump is usually no issue, but a hydraulic pump motor can get a little bit big for starting into a running drive - hydraulic motor can be as big or bigger than the spindle motor - you would need to size the drive accordingly. On my Reid, the hydraulic motor is the same size as the spindle motor.

    On mine, I changed the hydraulic motor to single phase (needed a new motor anyway) and I start the coolant pump against the running drive. And my drive rated amps are not much more than my spindle motor.

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    Are you aware that for the 115V input version, an easily overlooked aspect of the larger 1-1/2HP drive is that it requires a 40A circuit breaker to feed it on the 115V side. Not easy to find and if you do, that means running #8 wire to it and probably hard wiring it, then using a 60A rated local disconnect. Going down to a 1HP rated drive means you can use a 20A fuse in a 30A fused disconnect and run regular 12ga wire, even use a 20A receptacle to power it. That’s the reason you don’t see a lot of other VFD mfrs offer higher than 1HP for the 115V input versions, it becomes impractical to install it.

    Everyone is allowed their opinion, so here’s mine. A company I worked for a decade+ ago was offered the chance to assemble the WEG drives in the US when they began exporting them from Brazil. One look at the internals and our EEs told the owner he would be crazy to be in any way associated with that drive product line.

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    Other than the Phase Perfect VFDs I am not aware of standard VFDs being able to drive the internal electronics of machines and/or drive different motors not running in unison. Looking briefly at the Harig schematic/manual the stepping function is electronically controlled and there are also motors for the coolant and lubrication, the specs which varies by model. It may be possible to use a VFD for the grinder drive motor and tap the transformers for single phase 240VAC, but it is not a plug and play procedure. A RPC would be a much easier option and practical for this application. If one is literally looking for a plug and play RPC then maybe look at the American Rotary AMP RPCs, very quiet and compact, otherwise look at the used market or make your own.
    AMP American Rotary
    Harig 618 Control Board
    harig-control-board.jpg

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    Quote Originally Posted by Jraef View Post
    Everyone is allowed their opinion, so here’s mine. A company I worked for a decade+ ago was offered the chance to assemble the WEG drives in the US when they began exporting them from Brazil. One look at the internals and our EEs told the owner he would be crazy to be in any way associated with that drive product line.
    I missed the 115 volt input but the rest of my comments hold.

    As far as WEG, they have come a LONG LONG way in the last decade in their products. Motors and drives. Motors in particular can compete with any vendor out there today, depending on what you are buying.

    The drives are ok - there are better drives but for this type of use I would not be afraid to use them. I have several CFW drives running in my shop.

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    Quote Originally Posted by mksj View Post
    You cannot use a conventional VFD on this surface grinder and maintain all the controls/functions, you would only be able to use it if directly connected to the motor but you still would need to power the other functions such as feeds/pumps, etc. Better off with an RPC winch would maintain all the functionality and could power the unit without modifications. Also check the input voltage is set to 240VAC.
    I would do an RPC but I've heard that can throw off things in the motors on a surface grinder and give an inconsistent finish... one other guy I read on this form stated that he was having issues w/ finishes using an RPC until he switched to a VFD and the problem went away. Harig tech seemed to think a VFD would work fine as long as I set it to 60hz? What do you think?

    For instance, found this in another thread here...

    Quote Originally Posted by Lakeside53 View Post
    I would not run a surface grinder spindle on a static converter. You will see the vibration in the surface finish. Single phase can be problematic also. A VFD would be my choice. If you have very fine finishes, even a vfd may require an output reactor (cheap) to smooth the waveform to almost sinusoidal.

    Static converters do implicitly not limit the hp; hp is developed by the motor against the load applied. If you demand (by load) more than 50-70% of the original hp, the motor will overheat.
    Quote Originally Posted by MichaelP View Post
    Very good point. One RPC will serve your whole shop without any machine modifications. VFDs may be desirable for a limited number of needs/types of machines, IMHO. Otherwise, it just brings extra expenses, extra work and extra headaches.

    But if the grinder is the only 3-phase machine you'll ever have (which is hard to imagine), then using a VFD is justified.
    Yeah it will be the only machine, at least for a long time.

    Quote Originally Posted by mksj View Post
    Other than the Phase Perfect VFDs I am not aware of standard VFDs being able to drive the internal electronics of machines and/or drive different motors not running in unison. Looking briefly at the Harig schematic/manual the stepping function is electronically controlled and there are also motors for the coolant and lubrication, the specs which varies by model. It may be possible to use a VFD for the grinder drive motor and tap the transformers for single phase 240VAC, but it is not a plug and play procedure. A RPC would be a much easier option and practical for this application. If one is literally looking for a plug and play RPC then maybe look at the American Rotary AMP RPCs, very quiet and compact, otherwise look at the used market or make your own.
    AMP American Rotary
    Harig 618 Control Board
    harig-control-board.jpg
    Yeah the Harig tech I spoke with (Jim Seyllars) stated that I can use a VFD and pointed me to Automation Direct but wasn't sure exactly how many I would need since there are 3 motors on this thing... (pics below). The main power input comes in and follow the red lines in the top of the pic below, and what's interesting is there is a regular 110v plug on the back of the machine for the lamp and stuff so it must have a built in RPC at some point in the schematic I would imagine?

    So do you think an RPC would be fine?





    Spindle motor



    Stepper motor



    Hydraulic motor

    Last edited by razoredgeknives; 09-11-2019 at 04:38 PM.

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    After looking at it more I guess a good question instead of the OP title would be...

    Which RPC should I get? I would ideally like to get a good brand that's used on ebay or something, otherwise I'm looking at North America Phase Converters, really impressed with their stuff.

    any suggestions?

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    You have a mix of AC and DC motors, the surface issue problems are with a static converter and not an RPC. I would expect more surface finish issues with a static converter, but I do not use them. A VFD could be used to drive just the surface grinder motor if you really needed it, but I am very doubtful that it will be plug and play driving the whole machine, but whatever if the company say it can be done, go for it. The 110V outlet is from the transformer step down, which is common. You need to see what the voltage input is set on the machine, 230/460 and if the latter it would need to be rewired for 230VAC.

    Lots of decent RPCs, size depends on if you are running one machine or plan to have other 3 phase equipment.Had a few people use the American Rotary RPC,s and they seem to like them, but lots of decent brands new/used. You want a lower speed RPC like 1750 RPM.

    Phase Converters | Power Transformers | Power Accessories | American Rotary

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    I bought a 15HP 1200rpm monster motor from a local motor repair shop. Then I ordered a panel for rotary phase converter from WNY. You need to tell them what idler you have, esp., if it's a low rpm motor (they adjust capacitors to suit it better). I've never had any problem with this setup. In the beginning, I was going to build the panel myself, but the cost of the components+shipping would be close if not higher than what they charged me for a very well built one.

    And do yourself a favor and get a low rpm motor. They are a WAY less noisy. I couldn't stand RPCs with 6500 rpm motors: they were screaming like pigs being slaughtered. I can hardly hear my 1200 rpm one working.

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    Alright compared American Rotary RPC's to North America RPC's and ended up going with the latter... was very impressed w/ customer service and apparently the guy I spoke with used to be a manager or something at American and wasn't too happy w/ some ethics about the types of motors they used and stuff. Anyway, ordered the PL-5hope it does what I need!

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    RPC with 5hp 6500rpm(?) idler? Hmm...

    Not something I'd do with my money, but it will certainly work with your grinder.

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    I was informed that it's 1750 rpm...

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    Please note I am not an electrical engineer, or a grinding expert.
    I would just like to say that for me, on my old B&S Micromaster using a VFD where the spindle and starter coil are the only electrical load I really love the VFD for being able to vary spindle rpm. Lets me fine tune the finish.

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