Phase Converter Question

[Robert Feingold]

Hi,
I just bought a hardly used 2004, ACM LT 20 bandsaw for $850 from a friend. I believe the brand is now being sold under the name of Laguna. I will be cutting turning blanks of various sizes up to the maximum 15" high with all different types of wood. It will be used maybe an hour or 2 a week.
Attached are the motor specs and Bandsaw spec plate. I will need a 3 phase converter as I will be running it on single phase 220.
After researching phase converters from suppliers I am now a bit confused.

1-Although inexpensive (about $150) I'm being told not to consider static converters as after startup, the motor will only run on 2 phase giving me only 2/3 power. Besides the obvious issue should i consider this?

2-Rotary converters are more expensive, $450-North American Phase converter, $1,200-Kay industries, for a 5 HP, but will supply 3 phase power to the bandsaw motor. Since my lathe motor is 5 HP I'm told I should use a 7.5 HP or higher rated converter.
Can the $450 5 HP converter be adequate for my purpose? I have no interest in spending $1,200.

3-Does anyone know a source for used converters?

4-Should i sell it and buy a comparable bandsaw for about $2,500

Thanks,
Rob

 

[Robert Feingold]

The bandsaw HP is 5.
The specs are in one of the photos.

 

[Bill Boehme]

I agree that a static phase converter would not be the best way to go. In actually, the static converter only generates a two phase output during the initial startup and after the motor gets up to speed the converter drops out and the motor continues to run on single phase power. This means that the motor mechanical output power would only be 2/3 of rated horsepower .... at best .... and actually could be as low as 1/2 of rated power.

You could consider a rotary phase converter which would give you clean three phase power. I don't if the cost is reasonable.

Another possible option is to use a VFD, but just set it to 60 Hz and leave it there. The VFD uses pulse width modulation (PWM) to synthesize three phase power over a wide range of frequencies. I don't know if there are five horsepower VFD's that run on single phase, but it might be worth checking out.

You could also consider getting a single phase 5 HP motor. Occasionally a good deal shows up on eBay.

Finally, you might think about getting a smaller single phase 3 HP motor which would sill be more than adequate. The 5 HP motor is mainly the result of the horsepower war between Laguna and MiniMax in the early 2000's.

 

[Bob Sheppard]

Hi,
I just bought a hardly used 2004, ACM LT 20 bandsaw for $850 from a friend. I believe the brand is now being sold under the name of Laguna. I will be cutting turning blanks of various sizes up to the maximum 15" high with all different types of wood. It will be used maybe an hour or 2 a week.
Attached are the motor specs and Bandsaw spec plate. I will need a 3 phase converter as I will be running it on single phase 220.
After researching phase converters from suppliers I am now a bit confused.

1-Although inexpensive (about $150) I'm being told not to consider static converters as after startup, the motor will only run on 2 phase giving me only 2/3 power. Besides the obvious issue should i consider this?

2-Rotary converters are more expensive, $450-North American Phase converter, $1,200-Kay industries, for a 5 HP, but will supply 3 phase power to the bandsaw motor. Since my lathe motor is 5 HP I'm told I should use a 7.5 HP or higher rated converter.
Can the $450 5 HP converter be adequate for my purpose? I have no interest in spending $1,200.

3-Does anyone know a source for used converters?

4-Should i sell it and buy a comparable bandsaw for about $2,500

Thanks,
Rob

I'll second Bill on getting a VFD. I just bought an old Powermatic 66 table saw, with a 3 HP 3 phase motor. I'm planning on getting a VFD to convert to single phase, without losing any power.

 

[Larry Copas]

In my shop I have a static phase converter, a rotary phase converter, and three VFD's. The VFD is the only way to fly with a bandsaw. The advantages are it gives you variable speed which may or may not be used, braking which is great, they are quiet, and cheap compared to a rotary phase converter.

The down side in your application is VFD's for a motor bigger than 3 HP get expensive. There is a solution with risk. Many 3 HP VFD's are rated for 150% current for 1 minute. Pedal to the metal you might trip the VFD but with normal cutting I don't think you would have a problem. I know, not a good answer but with my experience using VFD's I would give it a try.

 

[john lucas]

Yes I think VFD is the way to go. The downside is finding someone who can match the drive to your motor. I tried my best to install one for a friend and we never could get it going. I didn't have any problem with the 2 I purchased and installed on other equipment. We finally found a motor repair shop in town that knew what he was doing with VFD and was able to get the thing to run with a motor.

 

[Bryan Lisowski]

I second the VFD. Reach out to the following person. Jack Forsberg is 1 of the most knowledgeable people about this topic and builds VFDs. He is in Canada, but sells and ships to America. You won't regret reaching out, even if you don't buy you will get an education.

http://jforsberg.ca/connect-with-jack/

 

[john lucas]

I purchased mine from this company along with a matching motor. A friend sent them the specs to his motor and got a VFD. I don't know if they still do that, it was over 10 years ago.
https://dealerselectric.com/

 

[Robert Feingold]

I second the VFD. Reach out to the following person. Jack Forsberg is 1 of the most knowledgeable people about this topic and builds VFDs. He is in Canada, but sells and ships to America. You won't regret reaching out, even if you don't buy you will get an education.

http://jforsberg.ca/connect-with-jack/

Bryan,
I reached out to Jack and found him to very knowledgeable and speaks in a non technical language that most people would understand. He priced a VFD including shipping and a remote control panel for $378. Expect it will arrive in about 2 weeks, Ill report back. Jack told me that he will walk me through the install process.
He has many YouTube videos on a variety of subjects including woodworking & turning under the name of Jack English machines.
Bryan-thanks for the referral and thanks for all of the other valuable reply's.
The AAW Forum is a valuable resource that has helped me many times where I would otherwise be out in the cold.

 

[Bryan Lisowski]

Robert, glad I could help in a small way, and looks like you will have the saw up and running soon.

 

[Don Wattenhofer]

I agree that a static phase converter would not be the best way to go. In actually, the static converter only generates a two phase output during the initial startup and after the motor gets up to speed the converter drops out and the motor continues to run on single phase power. This means that the motor mechanical output power would only be 2/3 of rated horsepower .... at best .... and actually could be as low as 1/2 of rated power.

You could consider a rotary phase converter which would give you clean three phase power. I don't if the cost is reasonable.

Another possible option is to use a VFD, but just set it to 60 Hz and leave it there. The VFD uses pulse width modulation (PWM) to synthesize three phase power over a wide range of frequencies. I don't know if there are five horsepower VFD's that run on single phase, but it might be worth checking out.

You could also consider getting a single phase 5 HP motor. Occasionally a good deal shows up on eBay.

Finally, you might think about getting a smaller single phase 3 HP motor which would sill be more than adequate. The 5 HP motor is mainly the result of the horsepower war between Laguna and MiniMax in the early 2000's.

The rotary phase converters do not provide clean 3 phase power the odd phase runs at a lower voltage then the phases connected directly to the single phase lines such that you will not get the full 5 HP not that it matters much. The VFD is by far the best option since besides giving a very clean 3 phase output it also will control the acceleration, overload protection and will also provide the start stop functions. If he stays with the 5 HP motor he will probably need to get a VFD sized to operate on single phase since most advertised units larger than 3HP don't list the 1 phase input.

 

[Bill Boehme]

The rotary phase converters do not provide clean 3 phase power the odd phase runs at a lower voltage then the phases connected directly to the single phase lines such that you will not get the full 5 HP not that it matters much......

Thanks for the correction. I suppose that I was thinking about a three phase generator directly coupled to a single phase motor.

 

[Bryan Lisowski]

@Bill Boehme

I know this is off topic, but how do you quote a previous post in your response? I tried clicking the quote in the blue banner under the post but didn't work. As a new member could you or anybody help?

Thanks.

 

[Richard Coers]

The rotary phase converters do not provide clean 3 phase power the odd phase runs at a lower voltage then the phases connected directly to the single phase lines such that you will not get the full 5 HP not that it matters much. The VFD is by far the best option since besides giving a very clean 3 phase output it also will control the acceleration, overload protection and will also provide the start stop functions. If he stays with the 5 HP motor he will probably need to get a VFD sized to operate on single phase since most advertised units larger than 3HP don't list the 1 phase input.

Not sure where you got your information Don. From American Rotary; With our Patented VIT Generator producing a true three-phase sine wave and our patented Microsmart controller monitoring and controlling your voltages, your equipment is receiving very clean balanced power. To give an example, typical utility three-phase power is balanced around 10%. With a Digital Series phase converter, you will get roughly 2-5% balance. This means with a Digital Series phase converter, you are providing your equipment with cleaner power than utility three-phase.
https://www.americanrotary.com/blog/common-questions-answered-comes-three-phase-power/

Maybe you were referring to homemade rotary phase convertors?

 

[Dean Center]

@Bill Boehme
I know this is off topic, but how do you quote a previous post in your response? I tried clicking the quote in the blue banner under the post but didn't work. As a new member could you or anybody help?Thanks.

Look at the message you want to quote, and at the far right edge of the pale blue stripe across the bottom of the message will be "Quote" and "Reply". You want to toggle "Quote" to "+", and then click on "Reply". A new message box will open up with the quoted message at the top and the cursor just below. Or at least that's the way it looks and works for me.

 

[Bryan Lisowski]

Look at the message you want to quote, and at the far right edge of the pale blue stripe across the bottom of the message will be "Quote" and "Reply". You want to toggle "Quote" to "+", and then click on "Reply". A new message box will open up with the quoted message at the top and the cursor just below. Or at least that's the way it looks and works for me.

Dean thanks for the help.

 

[Bill Boehme]

A slightly quicker way (one less click) is click on "Reply". It is only necessary to click on "Quote" if you want to quote several other posts.

 

[Dean Center]

It is possible to toggle the quote off. Somebody new might not recognize that it's "-" and get very frustrated. I like my comments to help people and move the discussion forward.

 

[olaf Vogel]

Bryan,
I reached out to Jack and found him to very knowledgeable and speaks in a non technical language that most people would understand. He priced a VFD including shipping and a remote control panel for $378.

So will this VFD convert single phase to 3P?
Because in that case, you got a great deal.

Between Soft Start and braking, VFDs are a great solution.
I also use 5 hp VFD (Delta brand) but use 3P in from the RPC.

 

[Don Wattenhofer]

Not sure where you got your information Don. From American Rotary; With our Patented VIT Generator producing a true three-phase sine wave and our patented Microsmart controller monitoring and controlling your voltages, your equipment is receiving very clean balanced power. To give an example, typical utility three-phase power is balanced around 10%. With a Digital Series phase converter, you will get roughly 2-5% balance. This means with a Digital Series phase converter, you are providing your equipment with cleaner power than utility three-phase.
https://www.americanrotary.com/blog/common-questions-answered-comes-three-phase-power/

Maybe you were referring to homemade rotary phase convertors?

I am not referring to home made phase converters and I don't know what VIT stands for. I admit that my experience may be a little dated but I would be interested to know if your VIT can compete with a VFD in price and ease of use.

 

[Don Wattenhofer]

Amazon has a 4KW drive listed (746 watts per HP = 3730 watts) for about $160.00 with free shipping and it can be supplied with 240 volt single or 3 phase power.

 

[Robert Feingold]

So will this VFD convert single phase to 3P?
Because in that case, you got a great deal.

Between Soft Start and braking, VFDs are a great solution.
I also use 5 hp VFD (Delta brand) but use 3P in from the RPC.

So will this VFD convert single phase to 3P?
Because in that case, you got a great deal.

Between Soft Start and braking, VFDs are a great solution.
I also use 5 hp VFD (Delta brand) but use 3P in from the RPC.

Yes, that’s what its supposed to do. I’m happy that I solved the problem and will now have a more than adequate band saw at a great price for my purpose. That is assuming it works as expected.

 

[Richard Coers]

I am not referring to home made phase converters and I don't know what VIT stands for. I admit that my experience may be a little dated but I would be interested to know if your VIT can compete with a VFD in price and ease of use.

variable impedance technology (VIT)
No idea about the brand of VFD being quoted here, so can't compare price. If you shop for price only on a VFD, then a Chinese brand VFD is obviously going to be cheaper than a high quality rotary phase convertor made in Wisconsin. The big advantage of the rotary phase convertor is that you can wire into a 3 phase breaker box and with the push of a single button, you have 3 phase power for the entire shop. That's pretty easy to use.

 

[Bill Boehme]

Some miscellaneous thoughts about the difference between a rotary phase converter and a VFD:

• Rotary phase converter
  • The output is true sine wave
  • The frequency is fixed at the same frequency as the single phase input power
  • The cost is relatively low
• Variable frequency drive
  • The output is three phase, but not sine wave. A scheme known as pulse width modulation is used. It consists of a string of pulses that all have the same amplitude, but the time duration (width) of the pulses vary. The pulses occur at 5000 (or greater) pulses per second. The effect on the motor is basically the same as sine wave power*.
  • The main advantage of a VFD is that the frequency can be varied over a wide range resulting in variable speed output from the motor.
  • The cost is higher and depends on what capabilities it has.

* Not all three phase motors are equal when it comes to working with a VFD.

 

[olaf Vogel]

Some miscellaneous thoughts about the difference between a rotary phase converter and a VFD:

• Rotary phase converter
  • The output is true sine wave
  • The frequency is fixed at the same frequency as the single phase input power
  • The cost is relatively low
• Variable frequency drive
  • The output is three phase, but not sine wave. A scheme known as pulse width modulation is used. It consists of a string of pulses that all have the same amplitude, but the time duration (width) of the pulses vary. The pulses occur at 5000 (or greater) pulses per second. The effect on the motor is basically the same as sine wave power*.
  • The main advantage of a VFD is that the frequency can be varied over a wide range resulting in variable speed output from the motor.
  • The cost is higher and depends on what capabilities it has.

* Not all three phase motors are equal when it comes to working with a VFD.

Hi Bill and thanks for your feedback. But I have a few questions:

1 - why is it important that the motor "sees" a sine wave - as opposed to the "chunked up" wave created from VFD?
2 - What characteristics should a motor have when working with a VFD? I've been pretty indiscriminately mixing and matching. No issues yet.

My RPC's output voltage is not equal across the manufactured leg - which I'm told is common.
(207 volts vs. 228v for the two native legs. That differential was large enough to be a problem for the VFD's. I found a Balancing Transformer, with various taps on the coils. And was able to balance it out to 221v, where everything is fine).

As mentioned up-thread, having an PRC allows me to plug in tools without a VFD (like a table saw, radial arm saw, drill presses, grinders etc), all with cheap used 3P motors. For applications where speed control is required (lathe, dust control) or soft start is required (big ol' bandsaw, camelback drill press) then a VFD is really handy. I can feed in 3P and not worry about derating the VFD.

So far I've been using Delta brand, shipped from China. From what I gather, any electronics under $1000 are all from China anyway, just with a local distributor / badging. Cheap and the Delta instruction manuals are excellent.

 

[Bill Boehme]

1 - why is it important that the motor "sees" a sine wave - as opposed to the "chunked up" wave created from VFD?
2 - What characteristics should a motor have when working with a VFD? I've been pretty indiscriminately mixing and matching. No issues yet.

First of all, it isn't accurate to characterize the VFD pulse width modulation (PWM) output as "chunked up". Several decades ago before today's VFD technology existed various schemes for motor speed control were developed. One frequently used, but crude implementation produced a binary output like the figure below.





By contrast a PWM implementation has a hundred or more pulses per output cycle making it a reasonably good approximation of a sine wave. The reason that a sine wave is needed Is that the rotor is chasing a rotating magnetic field created by the three phase input. In order to have smooth rotation sinusoidal input signals to the motor windings are needed.

There are several major issues with the crude scheme depicted in the figure above. The magnetic field rotates in large discrete jumps so the rotation of the motor shaft will also be rough and noisy. This will also result in the motor running very hot.

There are some caveats with VFD control. The most significant is the same issue that exists with the power switch for an electric motor. When the switch is turned off the rapidly collapsing magnetic field induces a voltage in the windings that tries to maintain the flow of current as the switch contacts are opening. The voltage spike is great enough that it it is able to arc across the the gap resulting in pitted contacts.

In a VFD the switching is done instantaneously by semiconductors so the energy in the magnetic field can result in very large voltage spikes that are basically noise riding on the sinusoidal voltage. Older motors with class A or B insulaton on the motor windings may not be able to withstand these voltage spikes resulting in insulaton breakdown and arcing to adjacent windings. Insulaton breakdown usually occurs at sharp bends in the winding. The effect on motor performance is a very gradual decrease in output power over months or even years. The decrease in power is so gradual that it may not be noticed until performance gets really poor.

 

[Don Wattenhofer]

First of all, it isn't accurate to characterize the VFD pulse width modulation (PWM) output as "chunked up". Several decades ago before today's VFD technology existed various schemes for motor speed control were developed. One frequently used, but crude implementation produced a binary output like the figure below.

View attachment 27851



By contrast a PWM implementation has a hundred or more pulses per output cycle making it a reasonably good approximation of a sine wave. The reason that a sine wave is needed Is that the rotor is chasing a rotating magnetic field created by the three phase input. In order to have smooth rotation sinusoidal input signals to the motor windings are needed.

There are several major issues with the crude scheme depicted in the figure above. The magnetic field rotates in large discrete jumps so the rotation of the motor shaft will also be rough and noisy. This will also resul in the motor running very hot.

There are some caveats with VFD control. The most significant is the same issue that exists with the power switch for an electric motor. When the switch is turned off the rapidly collapsing magnetic field induces a voltage in the windings that tries to maintain the flow of current as the switch contacts are opening. The voltage spike is great enough that it it is able to arc across the the gap resulting in pitted contacts.

In a VFD the switching is done instantaneously by semiconductors so the energy in the magnetic field can result in very large voltage spikes that are basically noise riding on the sinusoidal voltage. Older motors with class A or B insulaton on the motor windings may not be able to withstand these voltage spikes resulting in insulaton breakdown and arcing to adjacent windings. Insulaton breakdown usually occurs at sharp bends in the winding. The effect on motor performance is a very gradual decrease in output power over months or even years. The decrease in power is so gradual that it may not be noticed until performance gets really poor.

Excellent explanation - I might add that before the switching depicted in your attachment the first exposure that I had to VFDs was about 1979 when a company named Parametrics was selling their new speed control that put out a completely square wave form.

 

[olaf Vogel]

Hi Bill and thanks for the great explanation! And in understandable english!

First of all, it isn't accurate to characterize the VFD pulse width modulation (PWM) output as "chunked up".

"chunked up was my poor terminology" sorry.

There are some caveats with VFD control. The most significant is the same issue that exists with the power switch for an electric motor. When the switch is turned off the rapidly collapsing magnetic field induces a voltage in the windings that tries to maintain the flow of current as the switch contacts are opening. The voltage spike is great enough that it it is able to arc across the the gap resulting in pitted contacts.

Do mean when power to the VFD is switched off?
My practice has been to hit stop on the VFD and when all motors have stopped, to switch off the PRC, then the master power on the fuse panel.

Older motors with class A or B insulaton on the motor windings may not be able to withstand these voltage spikes resulting in insulaton breakdown and arcing to adjacent windings.

Unfortunately, I've never seen any such markings on a motor. What "tags" or terminology should I look for to ensure proper insulation types?
(as far as I know all my motors are from about 1980 or newer - its just the machines that are older.

Thanks again for this great info!

 

[Bill Boehme]

?... Do mean when power to the VFD is switched off? .....

No, that's not what I was trying to say at all. I was wanting to describe why high voltage spikes occur when a motor connected directly to the power mains through an ON/OFF switch (no VFD) is turned off. I wanted to avoid getting too technical, but I'll make another slightly more technical attempt. There is a lot of energy stored in the motor's magnetic field (the motor is basically a large electromagnet with a lot of stored energy in its magnetic field). When the power is shut off all of that stored energy has to go somewhere. What happens is that the rapidly collapsing magnetic field induces a high voltage in the motors windings. Compared to the speed of the high voltage build up, the speed of the mechanical switch contacts opening is really slow. This means that most of the stored energy is dissipated externally. The main point is that a a high voltage spike is generated by a rapidly collapsing magnetic field. The amplitude of the spike is proportional to the speed of the collapsing magnetic field.

The pulse width modulation scheme is analogous to the mechanical switch opening except that the pulses happen 5,000 to 10,000 times per second and the switching speed is less than a microsecond so the amplitude of the voltage transient is much greater than the mechanical switch example.

...... Unfortunately, I've never seen any such markings on a motor. What "tags" or terminology should I look for to ensure proper insulation types? (as far as I know all my motors are from about 1980 or newer - its just the machines that are older. ....

Here is a great link to a Baldor presentation describing NEMA motor nameplate requirements.

 

[olaf Vogel]

Awesome:

Here is a great link to a Baldor presentation describing NEMA motor nameplate requirements.

Thats an excellent doc - thanks for the link.
There are so many docs in industry that are close to unintelligible for someone without an engineering degree.

And it explains the question well - and a few other items on the motor tags that I didn't understand.
(it also raises more questions,.....that may lead to brain overload.

I'll have to check my various motors on the weekend.

 

[Bill Boehme]

The description was simplified for general audience consumption, but the rest of the story is that the difference between insulation classes is the thickness of the insulation which increases the dielectric strength. In a nutshell, dielectric strength is how high the voltage can go before the insulation breaks down when the insulated wire is in direct contact with a bare metal surface. Insulation breakdown means arcing occurs through the insulation. Motors designed specifically for inverter duty might not ever see the thermal environment of class H windings, but for dielectric strength needed in inverter operation class H windings would be essential.

NOTE: I don't want to leave the impression that you must have a motor with class H windings if it is used with an inverter. The specs for many motors with class B insulation allow inverter operation within certain limitations such as min and max speed, temperature, and duty cycle. There is usually a trade-off in service life when used in inverter duty. For hobbyist woodturners the effect on service life isn't likely to become an issue. Also, not all inverters are created equal when it comes to high voltage suppression. I'm not sure how one would go about finding the answer to that question. Line reactors might help.