# RPC and Mill Pictures



## Hacker (Jan 12, 2021)

Hello,
After trolling this site for awhile I thought I would show what I have been up to. Last summer I toke a chance and purchased a basket case Fritz Werner mill. Over the last six months a machinist friend and I have gone over it and checked it out and cleaned it. When we could not find any major mechanical issues with it other then the rapid traverse motor  was missing (and still is) I decided to build a rotary phase converter (RPC) and a 240 to 440V transformer to get it running. Once I had the crude RPC running to supply power to the motor I found that the previous owner have made some changes to the wiring and bypassed the brake, reversing switch and the start switch. Decided that it was easier to tear it all out and rewire it and add stop and start switches closer to the operating controls. I then finished the RPC and fine tuned it. Everything now works on the mill but there are a few issues to resolve and whether to put the rapid traverse motor in. I want to use the mill for awhile and then decide if the machine is worth putting more money and time into it.  Doubt that I will give this a full restoration  just try and get that awful paint job off it and leave it at that. I have attached a few pictures of the milling and the RPC .


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## kevin.decelles (Jan 12, 2021)

what is in the grey box on the floor to the right of the file cabinet?


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## Hacker (Jan 12, 2021)

That is the 240/440V setup transformer


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## Tom Kitta (Jan 12, 2021)

Neat power readers I have to add these from Aliexpress to my setup.


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## Hacker (Jan 12, 2021)

They are actually very accurate, which was a bit of a surprise. Hopefully they last.


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## Proxule (Aug 16, 2022)

Nice balanced leg voltages, I went down the RPC route too many years ago, But found VFDs cheaper faster and more practical.
Thanks for sharing!


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## Hacker (Aug 17, 2022)

Thanks,

I would have gone the VFD route if I didn't need 440V in the shop. 

I have actually fine tuned the voltage on RPC and it is less then 5% when the mill is running.


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## Tom Kitta (Aug 17, 2022)

I went VFD route, realized its a mistake, got RPC and I am very happy. Once you have multiple machines RPC works soooo much better then VFD. I would still use VFD but not for 3ph but just speed control i.e. with 3ph input. 

RPC IMHO is much more practical choice then VFD with multiple machines. Also you can run machines with multiple motors, you can run welders, you can change voltages etc.


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## Susquatch (Aug 17, 2022)

I am up to 3 VFDs now and still happy. Planning another one for my lathe when I find the right motor. Love the variable speed. Love having everything plug and play. No regrets.


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## Proxule (Aug 17, 2022)

Tom Kitta said:


> I went VFD route, realized its a mistake, got RPC and I am very happy. Once you have multiple machines RPC works soooo much better then VFD. I would still use VFD but not for 3ph but just speed control i.e. with 3ph input.
> 
> RPC IMHO is much more practical choice then VFD with multiple machines. Also you can run machines with multiple motors, you can run welders, you can change voltages etc.


To some degree yes I agree, But there is a reason the industrial and commerical factories run VFD's 
Biggest reasons is that you can adjust output speed on the fly, Adjust Tq curves and program the VFD to a specific motor to provide low end Tq and other misc goodies a RPC cannot.
Not to mention you have to balance an RPC to a specific load on each leg to be with in X % of amperage / voltage.
I am sure commercial RPCs can compensate on the fly, By a semi fancy vector VFD from good old china will run you 300$ shipped. Not so much for a commercial RPC

Just my 2 cents.


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## Proxule (Aug 17, 2022)

Hacker said:


> Thanks,
> 
> I would have gone the VFD route if I didn't need 440V in the shop.
> 
> I have actually fine tuned the voltage on RPC and it is less then 5% when the mill is running.


Surprised you are unable to run that 440v motor on 220v. Most but not all 3 phase 440s I been near were able to run on 220. 
What a shame.


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## Tom Kitta (Aug 17, 2022)

Proxule said:


> To some degree yes I agree, But there is a reason the industrial and commerical factories run VFD's
> Biggest reasons is that you can adjust output speed on the fly, Adjust Tq curves and program the VFD to a specific motor to provide low end Tq and other misc goodies a RPC cannot.
> Not to mention you have to balance an RPC to a specific load on each leg to be with in X % of amperage / voltage.
> I am sure commercial RPCs can compensate on the fly, By a semi fancy vector VFD from good old china will run you 300$ shipped. Not so much for a commercial RPC
> ...



Also most factories have normal 3ph input and do not need to change from 1ph to 3ph.  I would not mind using a VFD in the same way - i.e. 3ph to 3ph. I have no problems connecting VFD to RPC. 

You do not need to balance RPC at all - being within 10% is good enough. This is for voltage, not sure about what do you mean by amps. You can build in a circuit that would automatically add or remove capacitance to adjust for voltage. 

I guess you could also add VFD to fix some output issues. 

Bottom line is RPC is so much easier to use then VFD. Its not even close. With RPC, you get new 3ph machine. You bring it home. You plug it into the wall and just like that it works. With VFD you have to, buy an VFD (300 adds up quick) then you have to connect the VFD to the machine, then you have to figure out how to make the VFD be nicely enclosed, then you have to deal with what do I do with resistive loads & what do I do with multiple motors. And finally, with VFD you have to wait for the machine to spin up to speed - vs. RPC, its full speed after fraction of a second. 

With 15 motors in the shop a 300 VFD would add up to a whopping $4500 not to mention wiring issues I discussed above. And an RPC will run you like $500. 

Finally there is the freedom of being able to change voltages, run resistive loads. Its like if you had native 3ph in the wall. 

I strongly suggest anyone serious about this hobby should use RPC. If you want VFDs - you can just add them after RPC output for speed control.


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## Tom Kitta (Aug 17, 2022)

Proxule said:


> Surprised you are unable to run that 440v motor on 220v. Most but not all 3 phase 440s I been near were able to run on 220.
> What a shame.



I run into multiple motors that were 460v only (or 440v or 480v) I have my surface grinder running on 460v as motors are re-wired 600v motors and only support single voltage.


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## DPittman (Aug 17, 2022)

Isn't there supposed to be some sort of energy saving with the start up of motors using a vfd? I thought I read something about that somewhere but I could be out to lunch also.


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## Tom Kitta (Aug 17, 2022)

DPittman said:


> Isn't there supposed to be some sort of energy saving with the start up of motors using a vfd? I thought I read something about that somewhere but I could be out to lunch also.



There is a soft start switch or you can use a VFD to use as soft start - but this is beyond most hobby shop motor sizes. 

You can also use Delta - Y switch. 

Its not to hit power company with a huge spike load. No savings in energy. 

RPC will waste energy continuously but so do VFDs. I guess you need many VFDs on to equal an RPC. But under heavy load RPC will be getting more efficient while VFD less...


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## Hacker (Aug 18, 2022)

Proxule said:


> Surprised you are unable to run that 440v motor on 220v. Most but not all 3 phase 440s I been near were able to run on 220.
> What a shame.


It is actually 380V that I am running, I just used the 440V as that is what most people recognize. The motor housing on the mill is fitted to the mill and I would have had to get it rewound to work on 220.


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## Hacker (Aug 18, 2022)

Tom Kitta said:


> Also most factories have normal 3ph input and do not need to change from 1ph to 3ph.  I would not mind using a VFD in the same way - i.e. 3ph to 3ph. I have no problems connecting VFD to RPC.
> 
> You do not need to balance RPC at all - being within 10% is good enough. This is for voltage, not sure about what do you mean by amps. You can build in a circuit that would automatically add or remove capacitance to adjust for voltage.
> 
> ...


Agreed that for 5 HP motors and larger as well as where multiple voltages the RPC is probably the cheapest way to go. Also if you built the RPC yourself then it is also going to be cheaper and easier to repair when something fails. 

If you are running smaller machines where the motors can be easily changed to a common voltage go with the VFD and and run it on a designated circuit. Most small home shops you will be running one machine at a time. If your size the VFD correctly you can get away with running two motors at a time. I did this on my lathe where the tracer motor and coolant pump are connected to one VFD and I can run them at the same time.


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## Susquatch (Aug 18, 2022)

Hacker said:


> If your size the VFD correctly you can get away with running two motors at a time. I did this on my lathe where the tracer motor and coolant pump are connected to one VFD and I can run them at the same time.



This is new info to me. Normally, the VFD senses the current flow in the motor winding and uses that as feedback to provide better output control. Two motors would confuse the bejezzus out of it. 

Was there a VFD setting you used (ie something like ignore feedback and brute force the output) to make that work?


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## Degen (Aug 18, 2022)

Susquatch said:


> This is new info to me. Normally, the VFD senses the current flow in the motor winding and uses that as feedback to provide better output control. Two motors would confuse the bejezzus out of it.
> 
> Was there a VFD setting you used (ie something like ignore feedback and brute force the output) to make that work?


I am with you on that one, I wouldn't do that or recommend it, it's just asking for serious trouble.

With the cost of VFD's (good quality budget ones that some of our members use) you are far better off as each can duty sized for the motors in question, along with optimizing performance for each machine.


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## Tom Kitta (Aug 18, 2022)

Hacker said:


> Agreed that for 5 HP motors and larger as well as where multiple voltages the RPC is probably the cheapest way to go. Also if you built the RPC yourself then it is also going to be cheaper and easier to repair when something fails.
> 
> If you are running smaller machines where the motors can be easily changed to a common voltage go with the VFD and and run it on a designated circuit. Most small home shops you will be running one machine at a time. If your size the VFD correctly you can get away with running two motors at a time. I did this on my lathe where the tracer motor and coolant pump are connected to one VFD and I can run them at the same time.



When I said more then one motor I did not mean a coolant motor but similar sized 2nd motor. Say my surface grinder has 2hp for grinder and 1hp for the table. Or my drill press has 2hp for the drill and 1hp for the arm. 

If you are using single VFD you would need to size it to the largest motor you are starting in your setup. Some pp have VFD on a little cart, plug one end into 240v 1ph, the other end to a machine they are running. Maybe some vfds have quick "memory" option for a different motor setup. 

Using more then one machine is quite common. I use up to 3, mill, lathe and saw. But usually just two. This is why one has "power feed". 

Switching motors, even when smaller, say 2hp to common voltage may not be "cheap" or may not be easy.


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## Tom Kitta (Aug 18, 2022)

Susquatch said:


> This is new info to me. Normally, the VFD senses the current flow in the motor winding and uses that as feedback to provide better output control. Two motors would confuse the bejezzus out of it.
> 
> Was there a VFD setting you used (ie something like ignore feedback and brute force the output) to make that work?



You can get away with small side currents, say your main motor is 5hp, and you also have a light using say 50w, and a control transformer that uses few watts, and coolant pump using 50w motor. I would  assume power feed motors should be fine as well - maybe you run into issues with the Z on a mill where power feed motor may be large on old mills.


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## Susquatch (Aug 18, 2022)

Tom Kitta said:


> You can get away with small side currents, say your main motor is 5hp, and you also have a light using say 50w, and a control transformer that uses few watts, and coolant pump using 50w motor. I would  assume power feed motors should be fine as well - maybe you run into issues with the Z on a mill where power feed motor may be large on old mills.



The following is just musing on my part. I'm not pretending to know more than I know....LOL!

I think a light would have zero impact on the performance as long as the light can handle the high frequency characteristics of the VFDs output. In other words, I would not expect all lights to work, but incandescent might be fine. To the VFD, I think they would disappear masquerading as a lower impedance motor with zero shifting around of the feedback signal. Similarly, a very small motor might get masked out by the big motor's dominance of the signals.

It's the two large motors (say 3hp and 1hp) that surprises me. I would not have guessed that would work very well and I would have instinctively stayed away from even trying it.

But obviously, it works for a few others on here so there must be more going on than I would have guessed.

A question for you guys - are you using the variable frequency output of the VFD when you do this or are you just running 60Hz in and out for everything on the output circuit?


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## Tom Kitta (Aug 18, 2022)

Susquatch said:


> The following is just musing on my part. I'm not pretending to know more than I know....LOL!
> 
> I think a light would have zero impact on the performance as long as the light can handle the high frequency characteristics of the VFDs output. In other words, I would not expect all lights to work, but incandescent might be fine. To the VFD, I think they would disappear masquerading as a lower impedance motor with zero shifting around of the feedback signal. Similarly, a very small motor might get masked out by the big motor's dominance of the signals.
> 
> ...



With 3hp and 1hp you probably can get away with starting them both at once. But if you do not I am like 90% sure most VFDs sized for say 3hp would throw a code if you run 3hp motor and then started 1hp or vice versa. Maybe you could get away with this with a large VFD, say sized for 7.5hp, flipping the 1hp motor on and off.


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## Degen (Aug 19, 2022)

Tom Kitta said:


> With 3hp and 1hp you probably can get away with starting them both at once. But if you do not I am like 90% sure most VFDs sized for say 3hp would throw a code if you run 3hp motor and then started 1hp or vice versa. Maybe you could get away with this with a large VFD, say sized for 7.5hp, flipping the 1hp motor on and off.


No this is a bad idea.

Transferring from one machine to another, yes, but not ideal as you can't tweak the VFD to maximum performance to a motor.


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## Tom Kitta (Aug 19, 2022)

Degen said:


> No this is a bad idea.
> 
> Transferring from one machine to another, yes, but not ideal as you can't tweak the VFD to maximum performance to a motor.



Certainly not a good idea - never tried it. But Susquatch was wondering what one can get away with - or I think he was.


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## Hacker (Aug 19, 2022)

Susquatch said:


> This is new info to me. Normally, the VFD senses the current flow in the motor winding and uses that as feedback to provide better output control. Two motors would confuse the bejezzus out of it.
> 
> Was there a VFD setting you used (ie something like ignore feedback and brute force the output) to make that work?


I guess I should have been clearer on this. The tracer is a 2HP motor and the coolant motor is a small fractional HP motor. I start the tracer first and the coolant afterwards so the VFD never really notices that there are two motors there.  I checked with the supplier about what I was planning before purchasing the VFD and they said it would be fine. I don't use it a lot but it has worked fine.
I would not do this on a setup with a 3 and 1 HP motor either as it has been mentioned that you have to set the operating parameters to the motor size.


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## Susquatch (Aug 19, 2022)

Tom Kitta said:


> Certainly not a good idea - never tried it. But Susquatch was wondering what one can get away with - or I think he was.



That's a very good way to put it Peter.

To be clear, it's not something I would advocate as it's clearly outside the envelope of how VFDs are supposed to be used.

But I'm always curious about other ways to do things that are unconventional or outside the box.

So I do wonder if it would work, what the limits are, what the issues are, what trouble you could get into, etc.

Thinking about how a VFD works, it's easy to conclude that it's not a good idea to run two or more large motors simultaneously off the same VFD.

When you move those considerations to a large and small motor, it gets a little harder to conclude anything. It might work quite well or it might not. It's possible that the VFD would accommodate the small motor or that it could trick the VFD into thinking something was happening with the big motor that could lead to very bad control outputs. It might work, but without an analysis and/or full diagnostic testing, I'm instinctively against doing it. Ya just because they are both turning one might think it's all running ok, but then again you might be slowly destroying one or both motors or the VFD. I just don't know. I can only speculate. A VFD is a very sophisticated device - much more so than we tend to think.

On the other hand, I think that a purely resistive load like an incandescent light would probably become a constant factor to the VFD that it can easily handle. Again, just speculation.

The best advice I can give is to use them as they are designed to work - with a single motor. In most cases, that is single phase 220 in and 3 phase 220 out. If the input has a neutral, you can run any peripheral devices on either 120 or 220 single phase power out of the main power box (before the VFD) and still have only one power cord and not have any concerns about the VFD or the primary motor.

I suppose there are peripherals that require 3 phase, but single phase is MUCH more common and many of the 3 phase devices are not really 3 phase because internally they only use one leg of the power input. All I'm saying here is that it's silly to convert 1ph to 3ph and then only use 1 of the 3 phases. Better to just go direct.

My own mill is a good case in point. I am currently running two power lines (115 & 230) because my 230 has no neutral. Basically, the guy who built my shop didn't run a neutral for the 230 circuit. My plan is to rewire that circuit with a neutral, bring one cable into a master on/off switch on the back or side of my mill base, run that to a VFD in a main control box beside it (with speed and direction controls up near the motor), and tap into half the 230 after the main power switch to get 115 for my DRO, power feeds, & light.

Same goes for every other 3phase machine in my shop.

Unlike many others, I don't want 440 or 550 in my shop at all. If I did, I'd probably go with an RPC and transformer. But even then I'd probably still want a VFD to get variable speed, braking, and soft start.


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