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VFD (Variable Frequency Driver) for 3-phase motors.

Minder

Apr 24, 2015
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The one I built a couple of decades ago had a P.B. start circuit using a capacitor, no pony motor.
M.
 

Robo_Pi

Oct 5, 2015
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The one I built a couple of decades ago had a P.B. start circuit using a capacitor, no pony motor.
M.

Well, I confess that I'm not up on exactly how any of this works. I mean, I know the difference between simulating phases using semiconductors like a VFD works, and providing three actual phases like a rotary phase converter does. But I'm not clear one exactly how the pony motor works in the rotary phase converter.

I'm not even clear on exactly how "single-phase" 220 house service works. I know that it's two 110 lines, But are they out of phase? Is so then wouldn't that be 2-phase 220v?

It seems that on the rotary 3-phase converter they create the 3rd phase called the "Ghost Phase", and this is somehow being created by the pony motor?

Even though I don't understand the details of exactly how it's done I think I get the idea that 3 phases are needed apparently 120 degrees out of phase from each other? Or something like that.

Apparently the VFD adds the additional PWM to the mix. So it's not just creating 3-phase, but it's also providing good speed control using pulse width modulation. I use PWM all the time on small DC PM motors. So I understand how PWM works. So a VFD is both a phase converter and a PWM.

I probably don't need the PWM. All I need is to create a 3 phase 220volt source.

Do you recall how you did it without using a pony motor? Did you do it just with capacitors, or did you also use semiconductor switching too?

When you use a pony motor there's no semiconductor switches required. The pony motor apparently replaces the need for switching.

I'd need to read up on this and find out what size pony motor I would need, etc.

It's interesting stuff. I'd like to gain some experience with this. Like I say, I have a 1.5hp 3 phase motor to play with. Could that be used as a pony motor to create the 3-phase to drive other motors? Does the pony motor need to be as large as the motor you're driving?

In other words, if I want to drive a 2 hp 3-phase motor would I need to have a 2 hp pony motor to do that? I'm guessing that the pony motor will probably need to be at least as large as the motor it's driving, or possibly even larger.

But then you need two motors. The motor you want to drive, plus the pony motor.

You say you did it with just a capacitor alone? If that's possible then why are people messing around with pony motors?
 

Y2KEDDIE

Sep 23, 2012
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Not strictly true, All the VFD's I have installed since the 80's have been on regular 3ph motors, two were on a machine I retro-fitted with motors from the 50's!
If concerned, a 3ph choke/inductor can be fitted between VFD and motor.
This helps both motor and VFD.
M.

You are correct.

In all the "New" installations I used an Inverter rated motor, as "Good Engineering Practice".
Yes , filters can help, provided you know you need them before you destroy the motor.. It was easier to just use the correct Inverter rated motor.

I've used line filters with the large VFD's, but largely due to reduce back fed noise affecting other equipment in my MCC.

Like you I have had good luck with older motors. Worst case you can destroy the motor and VFD if the insulation breaks down. Older motors may or may not have good insulation properties, but may still work.

-----------------------------------------------------------------------------------------------------------------------------------------

I like the Rotary Phase Converter in the Video. The only issue is that the pony motor needs to be running before you can start the motor on your equipment.

I thought about installing one large pony motor and connecting multiple motors around the shop, but tuning may become an issue.with changes in load. I think multiple converters are the best approach.

The Capacitor Phase converter I referred to , does not need a pony motor, and can be connected to the line continuously.

I guess the main point is: there are lot's of options out there. You just need to do a little research.
 
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Robo_Pi

Oct 5, 2015
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The Capacitor Phase converter I referred to , does not need a pony motor, and can be connected to the line continuously.

I guess the main point is: there are lot's of options out there. You just need to do a little research.

Well, doing the research is going to take me some time simply because I'm not familiar with what all the options are.

Thus far I appear to have basically four options:

1. Convert all my machines over to single phase 110v or 220v motors.

This seems like the simplest solution actually. I had a large South Bend lathe and a J-head Bridgeport mill at one time. They both ran on regular 110v just plugged into a normal house outlet. I don't recall what size motors they had in term of hp. Physically the motors were well under a foot in diameter. And only about a foot or so in length. So they weren't very large motors. I'm guessing they were probably either 1/2 or 3/4 hp. Whatever they were they were plenty powerful enough for me. I didn't have any lack of power problems. And it is nice to just plug into standard 110v. I didn't even need to do any special house wiring for the. I never blew a fuse. And I think that old house only had 20 amp fuses. And yes they were fuses and not circuit breakers. It was an old house. So I never had a problem in the past running 110 motors. This solution does seem to be the easiest for me. The only cost would be to replace the motors on the machines when I rebuild them. In fact, this was my original plan actually.

2. As I say, the machinists on the machine forum said that I really need to use 3 phase motors with VFD's. But with all due respect to them I'm starting to think that they are all just a bunch of spoiled brats who are too lazy to change belts and just want to dial in an exact speed they want. While I agree that is nice, it's simply not necessary for me. I had no problem in the past running 110v motors and changing belt position to set up for a specific speed. That's just fine with me.

3, Now a third option appears to be the pony motor converter to run non-speed-controlled 3 phase motors. Now PWM just raw 3-phase. That would certainly work for me just to be able to use the original 3 phase motors without having to replace them. It also appears to be a much simpler build. No expensive semiconductor switching. Just a few capacitors, a pony motor, and you're off to run you machines. Sounds much simpler than a VFD PWM.

4. And now you are suggesting a possible fourth method of somehow just using capacitors alone without a pony motor? That sounds even simpler. But I haven't seen any information on how to build one of those yet. No semiconductor switches involved there?

I thought about installing one large pony motor and connecting multiple motors around the shop, but tuning may become an issue.with changes in load. I think multiple converters are the best approach.

Well, that kind of important to me. I don't want to need to build a 3 phase converter for every machine. I'm looking for one phase converter to rule them all. I would only be using one machine at a time. It's just a personal hobby machine shop. I won't be having employees runing multiple machines at once.

I'm hoping to eventually accumulate the following machines:

1. Large lathe,
2. A large milling machine similar to a Bridgeport J-head.
3. A Surface Grinder
4. Possibly a Shaper eventually. Only if I find a really good deal on one.

All of these will most likely be antique machines. So questions of good motor wire insulation may come up. Probably best not to go with PWM since that sends pulses that are more likely to break down weak wire insulation.

In fact, simply because these machine will most likely be several decades old solution #1 might actually be the best solution. Just put a fresh 110/220 motor in each of them and be done with it.

Just as a reference to show that I'm not the only one doing this madness check out this old antique 3-phase motor restoration. I think he runs this off a rotary phase converter that also has a pony motor.

But look at how grungy this motor was. He just cleaned it up and it's been serving him well ever since.

This motor was 70 years old. You don't need to watch the whole video, you can see how grungy the motor was in the first 5 minutes of the video. He actually got this thing all back together and it runs like a Swiss Watch. No rewiring. Just basic clean-up.

This just shows what's possible. But as I say, I think he's running this from a pony motor converter, so he's not using a VFD PWM. I'll need to contact him and see if I can find more details on his 3-phase power source.

 

Robo_Pi

Oct 5, 2015
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Here's a video of the man above running his rebuilt motor.

Check the video at about the 15:00 mark. Notice he first turns on his 3-phase converter. It sounds to me like a pony motor starts up when he does this. Also, he had been driving his Shaper using that same converter. This motor he just rebuilt belongs to a milling machine. So he's using the same converter to run both of these machines. One at a time of course.


I'm basically doing the same things this fellow is doing. He's just a hobbyist who restores old machines and makes himself a nice little machine shop with all antique machines.

I want to basically do the same thing.

It sure sounds like he's using a pony motor converter. So that might be the way to go for me too.
 

Minder

Apr 24, 2015
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.

I'm not even clear on exactly how "single-phase" 220 house service works. I know that it's two 110 lines, But are they out of phase? Is so then wouldn't that be 2-phase 220v?

It seems that on the rotary 3-phase converter they create the 3rd phase called the "Ghost Phase", and this is somehow being created by the pony motor?

The way a RPC works is it uses the standard 1ph 240v and uses a bank of capacitors to provide a phase shift to produce a 3rd conductor (3ph)
If viewing it from a virtual neutral point of view, now you have 3 conductors that are 120deg out of phase with each other (WRT the virtual neutral).
The pony motor is only used to start the motor rotation, once it is up to speed the motor is switch off.
The method for the one I built uses a large start capacitor to operate the initial start function in place of the pony motor.
N.A. 1ph service is a secondary of a centre tapped 1ph transformer providing 120v - 0 - 120v single phase.
As I mentioned, if concerned using an older motor on a VFD, use the choke on the output.
The 1950's motors I used the VFD on are still running, 20yrs later.
M.
 

Y2KEDDIE

Sep 23, 2012
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If it's just a hobby , and for your self, I wouldn't worry too much about the insulation factor. Like I responded to the other fellows post. I only use Inverter rated motors on new installations as good practice. Some of these older motors probably are more rugged than new. Hopefully you won't be pushing the load limits of the machine.

Most hobbyists are using VFD 's just so they can get 3 phase power. Speed control is just one side benefit. It is far better to run your machine at slower, geared down speed with full motor speed, than to reduce speed with the VFD, while in high gear. Think of it like using the transmission in your automobile.

The choices are also tied to efficiency,
You will derate the motors with Capacitor Phase Converter....least
Rotory Phase Converter....... better
VFD........................................better
 

Robo_Pi

Oct 5, 2015
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The pony motor is only used to start the motor rotation, once it is up to speed the motor is switch off.

Are you sure about that? From what I'm seeing the pony motor runs continuously the whole time the converter is on.

In fact, I just found a video where the fellow I mentioned above fixed his pony motor from squealing because it was annoying to have to listen to it squeal the whole time he was running a machine.


Apparently he bought his pony motor phase converter and paid quite a bit for it. I'd definitely build my own like in the 3-part video I posted earlier. I might go with the pony motor converter. Especially now that I know this is what Steve Summers is using. His apparently runs his shaper, lathe, milling machine and surface grinder. One converter for the whole shop.

The greatest expense for me would most likely be the pony motor itself. I wonder if I can use a 3 phase motor off an old machine for use as the pony motor?

If I can do without a pony motor and without semiconductor switching I'll look into that as well. But I haven't seen any information on a 3-phase converter that uses only capacitors. Can you point to a video or article that explains how to build one?
 

Robo_Pi

Oct 5, 2015
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If it's just a hobby , and for your self, I wouldn't worry too much about the insulation factor. Like I responded to the other fellows post. I only use Inverter rated motors on new installations as good practice. Some of these older motors probably are more rugged than new. Hopefully you won't be pushing the load limits of the machine.

Most hobbyists are using VFD 's just so they can get 3 phase power. Speed control is just one side benefit. It is far better to run your machine at slower, geared down speed with full motor speed, than to reduce speed with the VFD, while in high gear. Think of it like using the transmission in your automobile.

The choices are also tied to efficiency,
You will derate the motors with Capacitor Phase Converter....least
Rotory Phase Converter....... better
VFD........................................better

I won't be pushing these machines. I typically take pretty light cuts.

From what I'm learning thus far the Rotary Phase Converter appears to be the best choice for my application. It might be the lowest cost for me to build from scratch. And the most versatile in terms of running all my equipment. I really don't need the VFD PWM speed control. For me that just represents expensive semiconductor switching that can go bad just when you don't need it to.

The Rotary Phase Converter seems a bit more dependable and rugged. And apparently it might provide a bit more power than a Capacitor Phase Converter. Using just capacitors is tempting because of simplicity, but if derates the motors I might be better off going with the full Rotary Phase Converter.

So I'm learning slowly. Thanks for all the help.

Right now I'm leaning toward either a Rotary Phase Converter, or possibly my original idea of just converting everything over to single phase motors.

I'll have to wait and see which route I'll eventually take.

But I think I'm going to pass on the VFD PWM. That seems like overkill for my purposes.

Although this inexpensive one from Banggood doesn't look too bad. It will supposedly drive up to 2HP 3-phase motors. It's only $125. But if I had to buy one for each machine I might be better off with the Rotary Phase Converter for the whole shop.

VFD Inverter

The problem with a VFD is that if it blows out I'd have to buy a new one. If I build my own Rotary Phase Converter, if something goes wrong I can just repair it. I like to have things I can repair myself.
 

Minder

Apr 24, 2015
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See this Utube for example of a Pony motor.



The motor runs with the main motor but only under power at switch on to get the main motor up to speed.
After this it can just free-wheel.
The pony is a 1ph motor.
I will see if I still have my DWG's.
M.
 

Robo_Pi

Oct 5, 2015
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See this Utube for example of a Pony motor.

The motor runs with the main motor but only under power at switch on to get the main motor up to speed.
After this it can just free-wheel.
The pony is a 1ph motor.
I will see if I still have my DWG's.
M.

There appears to be different people using the term "pony motor" to mean different things.

This man has a 10 HP rotary converter motor that he calls the "idler motor". Other people appear to be calling their "Idler motor" a "pony motor". In this case he's just using a small single-phase motor to get his 10HP 3-phase idler motor up to speed to avoid having a rush of current to get it started.
 

Robo_Pi

Oct 5, 2015
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Here is a link to the one I used, in there there is a link to PDF that shows the design and tuning from one of the originators of the RPC, Fitch Willams.
https://somanyhobbies.wordpress.com/2016/01/20/rotary-phase-converter/
M.

It looks like that motor runs continuously too. What drops out is the starter capacitor that gets it started. But the motor itself continues to run the whole time the converter is in operation. At least that's what I'm getting from a quick overview.

In any case, I'm learning a lot. I think I will experiment with building a Rotary Phase Converter and see how that goes.
 

Minder

Apr 24, 2015
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The one I show has only one, the 3ph motor, and yes, started by capacitor, the one with the 1ph pony motor does this start duty in place of the cap, but runs in a free wheel fashion after the start.
M.
 

Robo_Pi

Oct 5, 2015
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I think I'm finally understanding this circuit thanks to the last schematic you linked to.

rpc1.jpg


This schematic makes things greatly simplified to understand. All this rotary circuit does is generate the Ghost Phase and makes it available at terminal T3-C. The other two terminals are just the standard legs of the normal 220 volt house service, terminals L1-A and L2-B.

So once I build the above Rotary Phase Converter, I would actually plug my lathe (or other machine) into terminals L1-A, L2-B, and T3-C.

In other words, the lathe would then be basically running directly from the 220 line with the additional Ghost Phase provided by terminal T3-C. So obviously the idler motor would need to be running continuously when running the lathe (or other 3-phase machine).

This design certainly looks simple enough. And of course, I could add any additional circuit breakers anywhere I want. I would obviously have a circuit breaker on the original 220 input lines. Then I would have additional circuit breakers between this unit and the lathe itself on all three phases. I might even add an additional circuit breaker inside the unit just to the right of the terminal block. Just to have an overkill safety feature.

It looks good to me. I think I'm ready to go for trying to build one. I'll use that 3-part video I posted earlier and follow his steps. I'll also download and study the document he referenced.

About the only thing I'm not currently clear on is what size 3-phase idler motor I will need? I'm guessing that it will need to be at least as large as the largest 3-phase motor I'll be driving? So if I plan on driving 2HP motors I'll need to have at least a 2HP idler motor. I would guess this would be the case. I also imagine that I could probably use a larger idler motor with no problem.

In other words, it probably wouldn't hurt to have a 3hp idler motor to drive 2 hp machines?

I'll need to obtain a 3 phase motor to use as the idler motor. So that will be the part I'll need to look for first. Once I have that motor, I can order some capacitors and see if I can hook it up to drive the 1-1/2 HP 3-phase motor I showed earlier in this thread. That would be my first experiment. If I can get that 3-phase motor up and running I'll feel confident that I can improve from there.

Based on the schematic above this circuit looks really simple. I'll of course make it more complex with additional circuit breakers, on/off switches, and indicator lights, but other than that it's a pretty simple circuit.

~~~~~~~

Just as an added note, I just now noticed that he's using a 5hp idler motor and says that he won't be using it to drive anything over 3hp. So this indicates to me that the idler motor needs to be larger than the motors the unit is driving. I'd probably do best to keep an eye out for a good 5hp 3-phase motor to use as the idler motor. I don't expect to be driving any motors larger than 3hp.
 

Minder

Apr 24, 2015
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It helps to be larger than the motor it is feeding.
BTW, this is a similar way that the electronic versions work, PhasePerfect etc, they take the 1ph and pass it directly through as two phases and produce the 3rd 120deg phase from the 240 1ph pair but electronically.
M..
 

Robo_Pi

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It helps to be larger than the motor it is feeding.
BTW, this is a similar way that the electronic versions work, PhasePerfect etc, they take the 1ph and pass it directly through as two phases and produce the 3rd 120deg phase from the 240 1ph pair but electronically.
M..

Except for the case where they are using PWM speed control. Then they would need to modulate all three lines.

I recall looking at the oscilloscope waves of the output of a VFD PWM and all three phases were being pulse width modulated. So that would require a separate semiconductor switch for each phase. But yeah, if they are just converting to 3-phase without PWM they would only need to use electronics to produce the third phase.

I don't know which is more desirable for me. Probably using an actual rotary motor. Using semiconductor switching gets into more complex electronics and expensive semiconductor switches. And when they blow it's not pretty. The physical rotary motor is probably a more rugged and durable method if no PWM is needed.

In any case, I've learned quite a bit about this phase conversion. It's really pretty simple once you understand what's going on. I really like the simplicity of the mechanical rotary idler motor. So that's what I'm currently most attracted to. Especially now that I have a really good understanding of the circuit. I hate working on things when I'm not perfectly clear on what they are actually doing. But this circuit is truly simple now that I see what it's actually doing.

In fact, you could actually add PWM speed control on the output of a rotary phase converter if you wanted to. That way the PWM unit would be totally separate from the actual phase converter. All you'd be doing is modulating the three legs. You could do that between the rotary phase converter and the machine you're driving if you wanted to. I really have no need for PWM so I'm not going to bother with that. I'm happy with mechanical speed changes. I have no problem changing belts and gears. I'm used to doing things that way. As Y2KEDDIE mentioned, using gear changes often results in better torque anyway. So I'll stick with using the mechanical transmissions for speed changes.
 

Robo_Pi

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By the way. Thanks for all the links and comments in this thread. It's all been very useful indeed. I'm really glad I posted here. Good forum you guys have.
 

Minder

Apr 24, 2015
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Except for the case where they are using PWM speed control. Then they would need to modulate all three lines.

I recall looking at the oscilloscope waves of the output of a VFD PWM and all three phases were being pulse width modulated. So that would require a separate semiconductor switch for each phase. But yeah, if they are just converting to 3-phase without PWM they would only need to use electronics to produce the third phase.
.

My post was using the fixed freq 3ph versions, the VFD typically produces a variable frequency 3ph sine wave with PWM modulation of each cycle.
The VFD linked to is one of the Huanyang Chinese versions and they typically lack any kind of decent support or manuals.
Fortunately there are many that have already gone through the headaches and a few hundred posts can be found on such as the CNCzone re set up etc..
M.
 

Robo_Pi

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Yeah, this is why the Rotary Phase Converter is appealing to me. Buying a cheap VFD is probably asking for trouble. And an expensive one is simply beyond my budget. Especially if I would need to buy one for each machine.

A simple homemade Rotary Phase Converter that I understand and can repair myself if needed is far more attractive.

One phase converter to rule them all. That's appealing to me. No fancy speed controllers required. That's just unnecessary complexity for my purposes. Someone who wants the PWM would do well to pay for a good one. It's just not important to me.

So yeah, I'll stay away from the Banggood VFD. Although I have seen videos of people who seem to be pleased with theirs. From what I understand if you take the time to set it up properly and don't abuse it they can work pretty well. But yeah, have problems with it, and about all you can do is buy a whole new one. I'm not going down that road.
 
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