[austinatxr]

Hi Guys,
I have done quite a few searches on the forums trying to see if there is any specific advice regarding the merits of a transformer vs vfd with voltage doubler, and I haven't really seen specific advice, so here goes:

I am assembling a cnc router for a high school robotics team to use. We cut wood prototype parts, and polycarb/6061/6063 "production" parts.

The gantry is a shapeoko xxl (belt driven xy, ballscrew "hdz" z axis). Not ideal, but the "price was right".

In reading posts here, it seems that one should steer clear of the 120v spindles. So, I have purchased one of these: https://www.amazon.com/gp/product/B077BY1L86 which seemed to be a good combination of: not too much power from mains, 240v instead of 120v, and not too heavy (9lbs instead of the typical 12lbs). Assuming that these specs are in the right ballpark (always questionable, which is why i ordered through amazon), I now need to figure out how to drive the spindle.

Realistic/Ideal situation is that I will have access to 240v single phase mains, when the robotics team moves to a new build space (we are currently shopping for warehouse space and hope to have a new manufacturing space in the next couple of months). In the mean time, I need to run this spindle from a 120v 15a supply (certainly NOT ideal).

Further complicating things is that I would like to, occasionally, take the machine on "field trips" in a trailer to other schools to demonstrate cnc machinery, where likely I will have access to 120v 15a mains. The machine itself is being built into a table/enclosure with casters to facilitate easy movement and the abuse of being trailered around.

With all of that setup, here is my question:
Does it make more sense for me to:
1) buy a VFD with a voltage doubler, such as a https://www.amazon.com/Huanyang-Vari.../dp/B07GD628D7
OR
2) should i use a step up/step down transformer, and get a straight 220v to 220v vfd, such as this guy: https://www.amazon.com/HY-HUANYANG-V...p/B0775S7KFW/?
of note: I happen to already own an older version of this guy: https://www.powerbright.com/product/vc2000w that is not being used for anything else, and so it is "free" to me.
OR
3) is there another option that I haven't considered?

My research so far seems to indicate that transformers should be 95% efficient or better, but I dont know about the efficiency of voltage doublers, or if there are any other considerations other than just efficiency.

And then as a follow up question: What other considerations should I be thinking about? Should I be setting the current in the vfd for each phase to a lower number when running off of a 110v/15a mains, in order to not overload the 110v mains? Should I be worried about supply fitering, or mains contactors for the table/enclosure that the machine will be in? Other considerations I should be thinking about when running the machine in the student environment?

Thank you so much for taking the time to help out a noob.

Austin
Robotics mentor

[mactec54]

Hi Guys,
I have done quite a few searches on the forums trying to see if there is any specific advice regarding the merits of a transformer vs vfd with voltage doubler, and I haven't really seen specific advice, so here goes:

I am assembling a cnc router for a high school robotics team to use. We cut wood prototype parts, and polycarb/6061/6063 "production" parts.

The gantry is a shapeoko xxl (belt driven xy, ballscrew "hdz" z axis). Not ideal, but the "price was right".

In reading posts here, it seems that one should steer clear of the 120v spindles. So, I have purchased one of these: https://www.amazon.com/gp/product/B077BY1L86 which seemed to be a good combination of: not too much power from mains, 240v instead of 120v, and not too heavy (9lbs instead of the typical 12lbs). Assuming that these specs are in the right ballpark (always questionable, which is why i ordered through amazon), I now need to figure out how to drive the spindle.

Realistic/Ideal situation is that I will have access to 240v single phase mains, when the robotics team moves to a new build space (we are currently shopping for warehouse space and hope to have a new manufacturing space in the next couple of months). In the mean time, I need to run this spindle from a 120v 15a supply (certainly NOT ideal).

Further complicating things is that I would like to, occasionally, take the machine on "field trips" in a trailer to other schools to demonstrate cnc machinery, where likely I will have access to 120v 15a mains. The machine itself is being built into a table/enclosure with casters to facilitate easy movement and the abuse of being trailered around.

With all of that setup, here is my question:
Does it make more sense for me to:
1) buy a VFD with a voltage doubler, such as a https://www.amazon.com/Huanyang-Vari.../dp/B07GD628D7
OR
2) should i use a step up/step down transformer, and get a straight 220v to 220v vfd, such as this guy: https://www.amazon.com/HY-HUANYANG-V...p/B0775S7KFW/?
of note: I happen to already own an older version of this guy: https://www.powerbright.com/product/vc2000w that is not being used for anything else, and so it is "free" to me.
OR
3) is there another option that I haven't considered?

My research so far seems to indicate that transformers should be 95% efficient or better, but I dont know about the efficiency of voltage doublers, or if there are any other considerations other than just efficiency.

And then as a follow up question: What other considerations should I be thinking about? Should I be setting the current in the vfd for each phase to a lower number when running off of a 110v/15a mains, in order to not overload the 110v mains? Should I be worried about supply fitering, or mains contactors for the table/enclosure that the machine will be in? Other considerations I should be thinking about when running the machine in the student environment?

Thank you so much for taking the time to help out a noob.

Austin
Robotics mentor

It is hard to say which is best 120V to 220V VFD would normally be better But a suitable Transformer like what you already have but 3000w would also be a good choice and buy a 2Kw 220v/240v VFD Drive to suit the spindle, which can then be run and have a better performance when used it with 240v single phase so you can have the best of both worlds by having a 120v/240v Transformer

You could try it with the Transformer you already have make sure the Transformer has a Ground on the output

The spindle Ground also needs to be checked 4th pin to make sure it has continuity to the spindle body most don't and this has to be corrected

One thing to remember when doing a setup like this never Plug or Unplug the Power to the VFD Drive you must have a disconnect which the circuit Breaker can be used for this, if you don't have a Disconnect switch at the cabinet

A EMI Filter is a must which should be mounted close to the VFD Drive input Power here is what I recommend Lambada RSEN-2030L this is 30A rated you could use a little lower amperage same spec filter but this size will still work very well and cost will be much the same

15A is a push to run a 1.5Kw spindle it will trip the breaker if the cut gets to heavy or the spindle loads up 20A would normally be a minimum for 120v supply

[austinatxr]

It is hard to say which is best 120V to 220V VFD would normally be better But a suitable Transformer like what you already have but 3000w would also be a good choice and buy a 2Kw 220v/240v VFD Drive to suit the spindle, which can then be run and have a better performance when used it with 240v single phase so you can have the best of both worlds by having a 120v/240v Transformer

You could try it with the Transformer you already have make sure the Transformer has a Ground on the output

The spindle Ground also needs to be checked 4th pin to make sure it has continuity to the spindle body most don't and this has to be corrected

One thing to remember when doing a setup like this never Plug or Unplug the Power to the VFD Drive you must have a disconnect which the circuit Breaker can be used for this, if you don't have a Disconnect switch at the cabinet

A EMI Filter is a must which should be mounted close to the VFD Drive input Power here is what I recommend Lambada RSEN-2030L this is 30A rated you could use a little lower amperage same spec filter but this size will still work very well and cost will be much the same

15A is a push to run a 1.5Kw spindle it will trip the breaker if the cut gets to heavy or the spindle loads up 20A would normally be a minimum for 120v supply

First: Thank you thank you thank you! I really appreciate the advice, and I'm glad I'm not going down a completely bad path with all this.

3kw transformer: makes sense, I'll do that.

Spindle ground: yep, good reminder, I'm already planning on switching the plug out for a cable gland, and while I have it open, I'll be sure to ground out to the frame of the unit.

Transformer ground: this detail slipped past me in my planning, good catch! I'll be sure the transformer is doing proper grounding.

Spindle: power making/breaking: can you recommend a good switch or breaker? Eventually I want to implement a proper cabinet for this, and get a proper estop wired in, but I have been waiting until I can put the proper dedicated time in to think about it. I also want to run the machine a little bit so that I have a better understanding of where the most critical safety concerns are, and how the enclosure it's working with the typical workflow, etc. Safety systems are always tricky, and require more thought. So, I guess I'm looking for something to do the making and breaking, that can eventually be mounted in a metal box.

Filter: perfect! Thanks so much, I'll be sure to put this one in.


20a 120v seems to be "commercial standard" in my area, so I'll definitely have to keep that in mind for the demos. I am hoping I can turn down the current going to the spindle when doing demos, so that I'm not tripping breakers.

Again, I cannot thank you enough for your advice, I really appreciate it!

[Al_The_Man]

In order to set up a re-refernced GND on an isolation transformer, you have to connect (any) one side of the secondary to the service earth GND and this conductor then becomes a 'Neutral'.
If this is on a 230v/240v secondary, this would mirror the European 230v standard.
There is an example in NFPA79 of which there is a old version via Google, or I could post the relevant page.
Al.

[mactec54]

First: Thank you thank you thank you! I really appreciate the advice, and I'm glad I'm not going down a completely bad path with all this.

3kw transformer: makes sense, I'll do that.

Spindle ground: yep, good reminder, I'm already planning on switching the plug out for a cable gland, and while I have it open, I'll be sure to ground out to the frame of the unit.

Transformer ground: this detail slipped past me in my planning, good catch! I'll be sure the transformer is doing proper grounding.

Spindle: power making/breaking: can you recommend a good switch or breaker? Eventually I want to implement a proper cabinet for this, and get a proper estop wired in, but I have been waiting until I can put the proper dedicated time in to think about it. I also want to run the machine a little bit so that I have a better understanding of where the most critical safety concerns are, and how the enclosure it's working with the typical workflow, etc. Safety systems are always tricky, and require more thought. So, I guess I'm looking for something to do the making and breaking, that can eventually be mounted in a metal box.

Filter: perfect! Thanks so much, I'll be sure to put this one in.


20a 120v seems to be "commercial standard" in my area, so I'll definitely have to keep that in mind for the demos. I am hoping I can turn down the current going to the spindle when doing demos, so that I'm not tripping breakers.

Again, I cannot thank you enough for your advice, I really appreciate it!

For simplicity sake for testing you could use the Breaker on the Transformer, but when you do the cabinet then you will need a different setup, it is going to get a little tricky when you use it with the Transformer this only requires a single pole Breaker, as what is on the Transformer, when you wire your cabinet for 240v single phase NA then you will need a 2Pole Breaker

A disconnect is like attached, these come in many different styles, if you need to be total safety compliant then a Safety Relay may be required all of these parts come in many different styles

[mactec54]

In order to set up a re-refernced GND on an isolation transformer, you have to connect (any) one side of the secondary to the service earth GND and this conductor then becomes a 'Neutral'.
If this is on a 230v/240v secondary, this would mirror the European 230v standard.
There is an example in NFPA79 of which there is a old version via Google, or I could post the relevant page.
Al.

Here is a video of all that is needed, it is not a Building Transformer so can have a single Ground /Earth wire from the input supply Ground / Earth star point mounted, which it may already have

[Al_The_Man]

That video is for a UK worksite transformer where the secondary centre tap is earth grounded.
Although that is an OK practice It is not a requirement for a N.A. control transformer used in industrial equipment.
Whether the secondary is 120 or 240, one side of the secondary can and should be connected to earth GND in order to restore to a grounded neutral system.
This has been the practice for many decades now and conforms to NEC/CEC.
Al.

See Transformer 1T in the NFPA diagram.
A fuse/disconnect is not required in the N.

[mactec54]

That video is for a UK worksite transformer where the secondary centre tap is earth grounded.
Although that is an OK practice It is not a requirement for a N.A. control transformer used in industrial equipment.
Whether the secondary is 120 or 240, one side of the secondary can and should be connected to earth GND in order to restore to a grounded neutral system.
This has been the practice for many decades now and conforms to NEC/CEC.
Al.

See Transformer 1T in the NFPA diagram.
A fuse/disconnect is not required in the N.

The Video shows all configurations he just has to look at how the Transformer he has is wired to see if it complies

Your 1T would not be suitable to Ground a VFD Drive too

[Al_The_Man]

Your 1T would not be suitable to Ground a VFD Drive too

You would have to explain that one to Me !!
Done all the time.
Max.

[mactec54]

You would have to explain that one to Me !!
Done all the time.
Max.

You run one of these step/up Transformers 120v to 240v driving a VFD Drive and spindle, I find that to be a tall one there are very few people that do this, most of those that do, I have helped with there setup

[Al_The_Man]

You run one of these step/up Transformers 120v to 240v driving a VFD Drive and spindle, I find that to be a tall one there are very few people that do this, most of those that do, I have helped with there setup

So if you are using a 120v/240v transformer, how are you handling a re-reference of the earth ground?
You don't require a C.T. secondary.

[mactec54]

So if you are using a 120v/240v transformer, how are you handling a re-reference of the earth ground?
You don't require a C.T. secondary.

I don't think any of this is very productive as the Transformers we are talking about are CE certified and without looking inside one we are only guessing as to how they have been wired, there are a lot of users here that have had no trouble with using normal wiring practice's to use these Transformers and have not seen anyone have a problem as far as Grounding goes

I'm not saying it can't be Grounded as you say, as it can as there is a code that referrers to transformer Grounding this way the VFD Drive is normally Grounded to a star point so it does not matter at all how they have the secondary of the Transformer wired I only mentioned to check to see how they have made the connections in the Transformer

[Al_The_Man]

Unless you reference the supply to earth ground (set up a grounded Neutral) the VFD and more importantly, personnel are NOT protected.
Basic electrical theory!
I checked the current regs, that cover grounding and basically nothing has changed, the non grounded supply option applies mainly to simple control circuitry.!

[austinatxr]

So, from what I understand, most of the transformers that come in the "black box" on amazon are not isolating transformers. They are autotransformers.

[austinatxr]

I think for testing, I will use the 2kw black box that I have (after i confirm that the case is grounded to earth on the input side at least, John Ward I think did a teardown of one of these in another video, and showed that it probably wouldn't hurt to do so). Since it is an autotransformer (non isolating, single winding), and I don't really know what I am doing yet, I am not planning on messing with it, other than the case grounding.

In the short term, when I go to use this, if i am on 120, ill use the transformer for the spindle, and hopefully a separate wall circuit for the rest of the machine, after I confirm that I am not causing a grounding issue by doing so.

If i am on 220-240v, I will not use the transformer, and instead put the vfd on the 220v, and the rest of the devices on a separate circuit for 110v, again, after I confirm that I am not causing a ground loop problem by doing so.

In the future, when I have a proper cabinet, I think I will get a proper isolating transformer, that can handle 220 or 110 input, and output 220 and 110. Ive seen several that are 3kw, full-isolating transformers that indicate that they can do this per their documentation. I will find a non-standard plug for the input of the cabinet, and make 2 pigtails that can use the non-standard plug, and can plug into either 220 or 110, depending on which pigtail you use. This way you dont end up with live connectors anywhere. The one downside of doing it this way, is if you are doing a demo, and you are on 110, then when the vacuum (2-3a 110v), the air pump for chip clearing (2-3a 110v), the steppers and gantry control (1a-2a 110v) and a few other accessories (im guessing 2-3a 110v) are all running, you probably only have about 7 or 8 amps of 110v left for the spindle, assuming you are on a 15a supply, and that all the stars in the sky align. So, this system will not be very user friendly one for demos. Fortunately, most of the places I will be giving demos at will be commercial spaces, which around here typically run 20a 110v circuits, so it gets a little better.

Ill have to do some more thinking about the demos, and how to handle the grounding if multiple circuits are being used. My spidey sense tells me that I am probably causing a ground loop scenario though when using multiple circuits.

[mactec54]

I think for testing, I will use the 2kw black box that I have (after i confirm that the case is grounded to earth on the input side at least, John Ward I think did a teardown of one of these in another video, and showed that it probably wouldn't hurt to do so). Since it is an autotransformer (non isolating, single winding), and I don't really know what I am doing yet, I am not planning on messing with it, other than the case grounding.

In the short term, when I go to use this, if i am on 120, ill use the transformer for the spindle, and hopefully a separate wall circuit for the rest of the machine, after I confirm that I am not causing a grounding issue by doing so.

If i am on 220-240v, I will not use the transformer, and instead put the vfd on the 220v, and the rest of the devices on a separate circuit for 110v, again, after I confirm that I am not causing a ground loop problem by doing so.

In the future, when I have a proper cabinet, I think I will get a proper isolating transformer, that can handle 220 or 110 input, and output 220 and 110. Ive seen several that are 3kw, full-isolating transformers that indicate that they can do this per their documentation. I will find a non-standard plug for the input of the cabinet, and make 2 pigtails that can use the non-standard plug, and can plug into either 220 or 110, depending on which pigtail you use. This way you dont end up with live connectors anywhere. The one downside of doing it this way, is if you are doing a demo, and you are on 110, then when the vacuum (2-3a 110v), the air pump for chip clearing (2-3a 110v), the steppers and gantry control (1a-2a 110v) and a few other accessories (im guessing 2-3a 110v) are all running, you probably only have about 7 or 8 amps of 110v left for the spindle, assuming you are on a 15a supply, and that all the stars in the sky align. So, this system will not be very user friendly one for demos. Fortunately, most of the places I will be giving demos at will be commercial spaces, which around here typically run 20a 110v circuits, so it gets a little better.

Ill have to do some more thinking about the demos, and how to handle the grounding if multiple circuits are being used. My spidey sense tells me that I am probably causing a ground loop scenario though when using multiple circuits.

Sounds like a plan, take a look at what the new single Phase welders are using this may help you as far as plugs go they have one plug on the machine and 2 separate cords that plug into it, one for 120v the other for 240v so only one main plug would be needed

I would not use that type of plug look for and use Twistlock plugs

[Al_The_Man]

how to handle the grounding if multiple circuits are being used. My spidey sense tells me that I am probably causing a ground loop scenario though when using multiple circuits.

Not if you use a recommended method of equi-potential bonding to earth ground.
Also if using a isolation transformer, Do you intend implementing an earth ground on the secondary, or use the secondary with no ground reference, (galvanic isolation)?
Al.

[austinatxr]

Sounds like a plan, take a look at what the new single Phase welders are using this may help you as far as plugs go they have one plug on the machine and 2 separate cords that plug into it, one for 120v the other for 240v so only one main plug would be needed

I would not use that type of plug look for and use Twistlock plugs

ohh cool! that makes sense, I was thinking i could just wire up 2 plugs, but then i started trying to figure out how to not have "live prongs" on the unused side, and decided that 2 separate pigtails with 1 connector that hits all of the conductors made sense. that way all the conductors get covered whenever you plug a pigtail in, avoiding live conductors that are exposed. I am very happy to go and borrow connectors that are already in use for this purpose though.

That kinda has me thinking, if the welders already have a power supply doing that, I wonder if there is more to what they are doing that I can borrow for this purpose? ill have to do some more investigation.

[austinatxr]

Not if you use a recommended method of equi-potential bonding to earth ground.

I will have to look into this, this sounds like something i need to research.

Also if using a isolation transformer, Do you intend implementing an earth ground on the secondary, or use the secondary with no ground reference, (galvanic isolation)?
Al.

So, first, I have not done nearly enough research to answer this in any kind of reasonable way. My initial gut feeling though is that it is probably more sensible to do "typical" case-grounding everywhere, and re-reference the secondary to ground, so that the downstream's equipment assumptions of "referenced earth ground neutral" are maintained, rather than try to build a completely floating cart. I think this keeps things closer to "standard".

I like the idea that a fault causes a breaker to pop, rather than a fault is just "intrinsically safe" as long as you dont touch two wires.

The real reason I am thinking of going with the full isolation transformer is because they have more copper, which means more thermal mass, and hopefully a longer and more stable life. I also like the idea of being able to disconnect the ground reference if I have to troubleshoot anything, but this would only be for me or someone I trust to do very specific and well-planned troubleshooting. For typical use I think I want the ground referenced, and maybe even enforced somehow by the system. More thought is required for me.

Correct me if I am wrong, but, I think the ground reference also opens up the possibility of adding in gfci and other safety devices, but, that will be for the cabinet design when I get to doing that "properly".

I am trying to break this into step-wise chunks, so I definitely have a "progression" I am trying to follow, rather than trying to naively "one shot" all they way to the end. It will also allow me to learn about each of the components before I try to implement them poorly. Especially the safety related ones.

[austinatxr]

Also, i just had to share this little gem. Many people have talked about the spindles not being case-grounded. Well, it looks like I won the lottery! Is that, is that a ground wire attached I see? Awesome!

but wait, is it screwed into plastic?!?!? Could they possibly have run a wire, and then somehow NOT gotten it to actually contact the case?

VERDICT: The fluke says that the two are electrically connected. Continuity to the case is there.

It does mean that the "ground" conductor is the screw itself, and not contact between the ring crimp and the case itself, since the plastic that the ring is sitting on is definitely NOT conductive. I feel that while valid, this is getting closer to nit-picking rather than more serious safety concerns. It is a definite attempt to move in a better direction. Someone will probably argue that a "bad" ground is worse than no ground at all, because it makes you think you are safe when you really aren't, but I think that this wire shows time, money and effort on the part of the manufacturer to try to do it better, and I think it is better to encourage safety efforts in the long run.

Also, this model seems to feature o-rings for the water channels that go through to the rest of the motor, instead of just a tight fit and some sort of compound. Nice!

It still has an "aviation connector" on the top though, I switched that out for a gland-end as recommended elsewhere on the forums. The gland end I got from mcmaster was a VERY nice fit. clearance fit for sure, but only about .010"-0.015" clearance or so, depending on where I measured.