Need recommendation on phase converter

[Greg Hairston]

I am purchasing a 9HP Slider with scoring. Need a converter that can handle this and possibly the addition of a widebelt sander. What would you recommend

Greg H

[Dan Oelke]

I don't have much experience with any .... at least not yet. But I have been looking on and off and over on Woodweb you wil see postings by Jay from American Rotary on a semi-regular basis for converters. Seem to be well made and relativly reasonable prices.

[Steven Wilson]

Try a rotary phase converter from Kay Industries; very popular with the Felder and MiniMax folk's

[Rob Russell]

Try a rotary phase converter from Kay Industries; very popular with the Felder and MiniMax folk's

Ditto.

Don't forget to factor in dust collection if your DC ends up being 3-phase also.

[Ian Barley]

Greg

My recommendation - make sure that "native" 3 phase is out of the question before you buy any converter. I know it is not always possible and sometimes can be stupidly expensive - then a converter makes sense - but I have found real three phase runs my machines better than any converter ever has.

[Greg Hairston]

Ian,
Native is definitely out. The 3 phase on the pole ends about a mile up from my house. It would cost about 20K to run it. I talked to the folks at the power company today. I have an electrician check into it also. I am in a rural residential area. 3phase is scattered all about but not near my house/shop.
I am looking the the Kay based on reputation. They seem to be more honest about their ratings. They list a 10Hp converter at 10 HP however other companies state they have a 30Hp (at the same price point) but when you talk to them they say you should go 2-3 times the HP of the machine. Seems a bit fishy to me. Especially when you start comparing overall size and weight of the machine. I may step up to the Kay 15HP just in case I add a machine of higher HP in the future.

Greg

[tod evans]

greg, the good thing about kay converters is when (not if) you get more 3-phase equipment and need to upgrade you`ll be able to recoup most of your outlay.....02 tod

[Bill Randall]

New to the game: Can someone give me a short, plain English lesson on 3-phase. What is it, what's it mean to me and my equipment, how do I get it, etc. Thanks!

[Charlie Plesums]

Single phase motors pull at opposite sides of the shaft, so trickery is required to get starting torque (the starting capacitor, etc.).

Three phase power pulls at three different points around the shaft, 120 degrees apart, in sequence, so there is starting torque naturally, and the power is applied more evenly... like the difference between a 3 cylinder engine and a 1 cylinder. Virtually all large motors (over 5 hp) are three phase. All power-plant generators are three phase, but one of the three phases can be "sent" to a residential neighborhood with fewer wires and transformers, and with only small motors, the power company declares that sufficient.

If you have single phase and need three phase, you can run a single phase motor to turn a three phase generator, but to handle the starting load, the generator has to be pretty hefty (or have a big flywheel). There are some tricks that combine the motor and generator in a single "rotary converter." You can power one of the three phases of a three phase motor, with just enough trickery into the other phases to get things started, and get 70% of the 3 phase power with a low cost static converter.

[Mike Henderson]

Three phase is a bit difficult to explain but let me take a shot.

When you have two wires, you can put a voltage across those two wires. If you hook a load up to the end of those two wires, current will flow from the source to the load and back again.

When our electrical engineering ancestors were designing our power transmission system, they were looking for a technique that would allow them to transmit more power. One way to do that is to add a third wire.

If you were looking head on into two wires, you'd see two points. If you were looking head on into three wires, and they were arranged in the right design, you'd see three points in the shape of a triangle.

Just as you could apply a voltage across the first two wires, you can now apply a voltage across each of the two points of the triangle. Since you have three sides, you can apply three voltages.

You can do this with direct current or with alternating current, but it is with alternating current that we get some gains. It's a bit difficult to explain "phase" in alternating current but here's one way. Although the voltage across two wires is a sinusoid, another way we can look at it mathematically is as a rotating phasor (just an arrow spinning around).

We could apply the voltage across the three wires so that all the phasors lined up (were "in phase"), or we can do something else. It turns out that if you apply the voltage so that the phasors are 120* apart, you get the best situation for efficiency in transmission. Additionally, this works very well for motors. By the right design, we can use this 3 phase power to create a rotating magnetic field that will spin the rotor of a motor.

One problem for residential power users is that 3 phase power is not brought to the home, only single phase power is. Incidentally, single phase is just power that is taken from any two wires of the three phase transmission line.

Most woodworkers would like to have three phase power but, if they're not in an industrial park, it's probably not available to them.

This may not be a good explanation - maybe too theoretical.

Mike

[Bill Randall]

Good info. I gather, then, that I cannot construct 3-phase out of my electrical panel, only with a separate feed from the power company. That and the understanding were exactly what I was looking for. :)

[Dev Emch]

WHAT THE HECK DID YOU JUST SAY?

O.K. So your buying a 9 hp slider with scoring. Great saw choice and you will love the beast. But a table saw is an EASY start machine. Not all machines are EASY start. For example, an oliver planer with a direct drive motor and an 80 pound cutter head is a HARD start machine. Not all phase converters can start such a beast.

Kay has been making converters since the 1940s and that is what I am using now. My first converter was a home brew and was not large enough to run what I needed to run. In the Kay world, a Kay idler motor is TWO TIMES the converter rating. So if I buy a 10 HP Kay, then I know it has a 20 HP idler motor.

A 10 HP KAY would be the choice for starting up your new table saw. But since its an easy start, almost any 10 hp rated converter will do the job.

Here is where your comment diverges. A widebelt sander is a POWER P-I-G. For example, the nice Timesaver that Lou has is a 37 inch sander with about a 20 hp drive motor. Nevermind the feedmotor for now. In order to run this beast, you may have to go to as much as a Kay 20 HP converter which means your running a 40 HP idler motor. Now I dont know off hand if a wide belt sander constitutes an EASY start or a HARD start. If its an easy start, you may be able to get away with a 15 HP Kay converter. If its a hard start, you may need more than a 20 HP converter.

What many folks in such a dilema often do is to slave converters. For example, you may have a 5 HP, a 10 HP and a 20 HP converter. These all feed the wildleg back plane on your three phase service panel. So when its time to run the little three phase jointer, you would use the 5 HP converter only. When you wish to run your table saw, you use the 10 converter only. When you need to run the widebelt sander, you may wish to use both the 10 hp and 20 hp converters at the same time.

Now here is the WARNING caveat with such a system. The use of to much balancing capacitance can drive the wildleg voltage on a 230 volt system close to 400 volts. Thus, each of the slave converters must be isolated from the main wildleg bus bar with contactors. If not, even though your not using any one converter, the system can look back into the bus bar network and see the idle balancing capacitance for each of the unused converters. This problem can be identified by an excessively high wildleg to main leg voltage.

Also, ideally you should have a converter sized for the load your running in order to try to achieve wildleg voltage balance. For the most part, this is a pretty loose suggestion. I use a 15 hp converter to run a 2 hp metal cutting lathe all the time. But to run a 2 hp woodlathe or jointer on a 20 or 30 hp converter is not necessarily a good idea.

So I would advise you start by using a 10 converter (purchased or home made) and take it from there when you bring the sander home. You will have lots of electrical work in front you when this day arrives.

[Philip Glover]

Has anyone out there used digital phase converters, such as Phase Perfect? http://www.phaseperfect.com/
On the surface, these seem to have some advantages over rotary.

PCG

[Dev Emch]

Whats up with this three phase jazz anyway?....

1). The reason power companies hate you is that three phase power needs a tap into each of your three main transmission lines. Normally, three phase lines are broken down into THREE unique 7200 volt feeders on which several homes can be attached EACH. You show up with your three phase hobby shop, you effectively throw their cute little world out of wack.:D

2). AC power is generated by an alternator. Since a circle has 360 degrees, if I divide that circle into three segments, I get 360/3 or 120 degrees. The outer ring of the alternator is divided into three independent windings. But these windings SHARE a common rotor which is a huge rotating DC magnet. A small DC generator is mechanically coupled to the rotor shaft and this how the rotor gets its DC exciting voltage. Power is created by slicing a magnetic field. Now that is relative. I can either slice through a stationary magnetic field or a moving magnetic field can slice through a stationary bar. Either way works. The stator windings are that stationary bar. So as I rotate the huge electrical magnet, I create voltage in the stator windings.

3). Three phase power is about relationships and team work amoung the three main supply conductors. This relationship is based on the 120 degree phase shift which if you remember your high school math class can only occur with a sine function. Two sine waves can move apart and the distance on the zero horizontal axis that the two intersects move apart is called the phase shift. If I shift enough, a sine wave turns into a cosine wave and then back into a sine wave. For this reason, there can be no DC three phase systems. The 60 cycle frequency is driven by the alternators rotor RPM. Granted pole count enters into this but for this discussion its not material. If I shut down an alternator, I wll see the frequency coast from 60 cycles down to zero cycles as the machine comes to a stationary halt.

4). The most relavent difference between a true three phase system and a phase converter system has to do with the neutral. A phase to neutral connection will have the same voltage regardless of which phase your one. A - B - or - C to neutral. (Of course real world systems may see a minor variation in phase voltages but its very minor). In a phase converter system, DO NOT MAKE THE MISTAKE of hooking up a wildleg to neutral connection as this voltage IS NOT (REPEAT! IS NOT) the same as say an A or B leg to neutral value. Also, your wildleg will be higher than the other two legs and this value will fluctuate as a function of loading.

Hope this background helps a bit...

[Dev Emch]

Has anyone out there used digital phase converters, such as Phase Perfect? http://www.phaseperfect.com/
On the surface, thses seem to have some advantages over rotory.

PCG
They are marginally better but they have their issues. They use DSP microprocessors to control a pulse width modulation scheme with final output capacitance filtering to remove high frequency transients (harmeful to older motors). What I dont like about them is their dependence on current computer technology and the inability for use to repair or modify them as needed in the field. A rotary is a very crude device in comparision and its easy to replace parts and bearings, etc. to keep these humping along for years to come.

Edit Note: I have worked on and am restoring an older francis turbine alternator. Some of the units in our high country using pelton wheels and francis horizontal turbines coupled to westinghouse, GE and Fairbanks-Morse alternators were built during the 1920s and are still humming along today. The onsite controls are gone in favor of wireless central automated control systems using microwaves and RF technology but the old alternators are still running. What does that tell you?

[Cliff Rohrabacher]

If $$ is an issue you might consider building one. The largest expense in building one is the 3 phase motor you'd need to drive.
You can get them from a junkyard for cheap and 99 times out of 100 they are junked only because of bearings that you'll replace for less than $ 20.

[Cliff Rohrabacher]

Adding:

On a phase converter the wildleg is most often found by measuring the three voltages to ground (neutral) rather than line-to-line.

[tod evans]

4). The most relavent difference between a true three phase system and a phase converter system has to do with the neutral. A phase to neutral connection will have the same voltage regardless of which phase your one. A - B - or - C to neutral. (Of course real world systems may see a minor variation in phase voltages but its very minor). In a phase converter system, DO NOT MAKE THE MISTAKE of hooking up a wildleg to neutral connection as this voltage IS NOT (REPEAT! IS NOT) the same as say an A or B leg to neutral value. Also, your wildleg will be higher than the other two legs and this value will fluctuate as a function of loading.

Hope this background helps a bit...


dev, i`m used to three phase "pot" power and find this confusing?? are you saying that folks running a third leg generator can check voltage from the wild leg to ground and get 120 (on a 220-3ph system)?

the power that i get from pots on the pole when checked to ground is 120-120-240, not 120-120-120.

checking voltage between any two legs on "pot-power" will read 240 regardless if you include the wild leg .

please make this clear to this ol` hillbilly....tod

[Rob Russell]

Tod,

I think you're both saying the same thing.

On a rotary phase convertor that's being run off of 240v single phase power, the wild/generated leg will start at 208 volts to ground. It's 208 because that's the (square root of 3)*120 = 1.732*120=208. Based on other factors, like loading or capacitance that gets added to the system to better balance the 3 legs, that voltage on that wild leg can definitely increase.

The voltage between legs will be nominally 240v for all 3 combinations A-B, A-C and B-C.

[Steven Evans]

FYI for non electricians, most would consider that homes run on 2 phase power(no such thing) and that it is kind of mis leading to call it single phase. But 1 phase is the standard name.

3 phase has 3 hot legs and neutral/ground They come from generators with a delta or wye windings.

1 phase has 2 hot legs. Run one leg to neutral/ground gives you 1 phase 120 volts. Run Leg1 to Leg 2 and that will give you 240 volts.

So a single phase motor would have a hot leg every 180 degrees
A 3 phase motor would have a hot leg every 120 degrees.

[Rob Russell]

Steven,

There actually is 2-phase power, where the phases are 90 degrees out from each other. It was used long ago when power systems were sprouting up all over the place.

"Single-phase" power is what's supplied to our homes and is the appropriate term for it. The fact that the utility company transformers may have multiple taps so we can get both 120v and 240v is how they distribute the power, but it's still all "single-phase".

Rob

[Charlie Plesums]

...What many folks in such a dilema often do is to slave converters. For example, you may have a 5 HP, a 10 HP and a 20 HP converter. These all feed the wildleg back plane on your three phase service panel. So when its time to run the little three phase jointer, you would use the 5 HP converter only. When you wish to run your table saw, you use the 10 converter only. When you need to run the widebelt sander, you may wish to use both the 10 hp and 20 hp converters at the same time....
40+ years ago as an EE student, we did an exercise of hooking multiple three phase generators together (actually we fed 3 phase power we were generating into the Northeast power grid... before the great Northeast blackout, but unrelated...). We had to go through quite an exercise to be sure we had the same phase rotation (simple) and were in synch (exact same speed and rotational angle of our generator as the power grid, not simple). Won't you have the same issue if you hook two rotary phase converters together? Or does the bigger converter simply jerk the smaller converter into compliance?

[Dev Emch]

40+ years ago as an EE student, we did an exercise of hooking multiple three phase generators together (actually we fed 3 phase power we were generating into the Northeast power grid... before the great Northeast blackout, but unrelated...). We had to go through quite an exercise to be sure we had the same phase rotation (simple) and were in synch (exact same speed and rotational angle of our generator as the power grid, not simple). Won't you have the same issue if you hook two rotary phase converters together? Or does the bigger converter simply jerk the smaller converter into compliance?

Been there and done that. We used hunkin copper knife switches mounted to marble control panels along with the three phase lights. On the pelton wheels, we also had feedback loop controlled needle jets to adjust the turbine shaft speed by throttling the two main jets. On the francis turbine (made by worthington) we have a more complex mechanical set of vanes controlled by a hydraulic/electric governnor and a mechanical linkage. Stability and lack of rotational transients is controlled by huge flywheels located between the turbine and the alternator.

The grid is massive and a poly phase machine driven mechanically has momentum. When the two diverge, you can get a multi ton machine to try to bounce around like a out of balance washing machine. This would be very bad!

An induction motor can function as a generator however with one serious drawback or caveat. Induction rotors are cammillions in the sense that they can change pole counts etc. depending on the particular stator used. If I run an induction motor as a generator (alternator), because of its slip, it has no regulated means of maintaining 60 cycles. You also have to run faster than 60 cycles (i.e. faster than sycnro speed) to get it to function as a generator. How much faster? That varies depending on the applied load. So when this is done to provide small aux back up power to field stations, stock tank water pumps, etc., the system is usually wired up to the grid. It does not take much of a hook up and your not back feeding power onto the grid either. But the grid connection uses the 60 cycles of the grid to sync up your induction generator. What a pain and that is why they are not used much and when used, for only small aux or backup applications.

In the case of a phase converter, a converter is not an alternator. It is a converter. The idler functions as a rotating transformer using the two secondary unused windings of the stator. The first winding is used to drive the idler. This is called single phasing and you can run a three phase motor on single phase albeit you cannot start it nor can you get much power out of it. In the case of an idler, you often have a start up scheme such as a phase shifting start capacitor and cutout switch or even a secondary pony motor. Because the idler stator is built like an alternator, you pick up the mechanical 120 degree phase separation.

But the sycnronous nature of the grid drives and locks the idler to speed and provides the AC coupling frequency for your fields. So converters are very much driven by and sycned up to the grid inputs.

The only time one is really concerned about sycnc frequency is when your doing something on your own with say a freq or your own alternator in which case you have manage the frequency yourself. Either way, I dont want this stuff back feeding onto the grid. This is esp. true of a freq which is used to drive older direct drive shapers and moulders to 7200 RPM and they do this by changing the 60 cycle input to a 120 cycle output.

There are two types of converters used in woodworking shops. The phase converter and the frequency converter. One converts single phase to three phase and the other converts 60 cycles to 120 cycles.

[Dev Emch]

FYI for non electricians, most would consider that homes run on 2 phase power(no such thing) and that it is kind of mis leading to call it single phase. But 1 phase is the standard name.

3 phase has 3 hot legs and neutral/ground They come from generators with a delta or wye windings.

1 phase has 2 hot legs. Run one leg to neutral/ground gives you 1 phase 120 volts. Run Leg1 to Leg 2 and that will give you 240 volts.

So a single phase motor would have a hot leg every 180 degrees
A 3 phase motor would have a hot leg every 120 degrees.

This IS NOT TWO PHASE POWER! This is playing tricks with the pole pig. Many older turn of the century woodworking machines had true two phase motors and the OWWM guys are always checking to make sure their not hooking up three phase to a two phase motor. This would be very bad!

In a two phase system, your alternator has two independent winding sets in place of the standard three. You have two power supply conductors on the pole instead of three and your phase shift if solid at 180 degrees instead of 120 degrees.

Transformers are special versions of inductors/coils. Inductors/coils and capacitors both shift phase by 90 degrees but in opposite directions. But phase shift can be modified at run time by haveing inductance and capacitance partially cancel out any effective shifts. Mechanical shift cannot be cancelled out the same way.

So in a standard pole pig, you have a single primary rated at about 7200 volts and dual center tap secondaries rated at 120 volts each. The secondary tap is at ground level so you have two discrete systems at work here if you will. That is why you want your service center breakers balanced out. One half is being fed by one secondary and the other half is being fed by the other secondary.

But because one secondary is effectively polarity reversed, you have 240 volts accross both hot leads of your secondaries. This is called differential potential as opposed to single ended potential (black and white). Now if I switch polarity on a sine wave, what was positive is now negative, etc. This is exactly what happens if I phase shift a sine wave 180 degrees which is where the notion of a two pole system came from.

Hope this clears a few things up....

[Mike Henderson]

Dev, maybe I'm misunderstanding your comments on two phase power. I think two phase power is offset 90*, as mentioned by Rob in an earlier post. The two legs of single phase power in a residential installation are 180* offset (when referenced to ground).

Mike