Going 3-Phase: General Discussion

[Jeff Raymond]

OK. Ya'll have convinced me that I'm going to go to a wide jointer and Big Boy planer. Since both will require 3-phase power, the next consideration is the 'rotophase' which I am using here in the generic context.

Since this is going to be a one-person shop (that would be me) it isn't likely that I would have more than one machine starting up at a time, which is the largest current draw; and more than 2 running at any given time.

What this writer knows about electricity is simply dangerous, does anyone know how to actually figure out how big of a 3-phase generator is the right size? I am told that any electrical motor over 5 hp is basically useless, looking at 3 hp models, which should be enough tear up a bunch of otherwise good lumber.

Any thoughts or commentary are more than welcome.

Thanks in advance.

[Jim Becker]

A little bigger is better than too small...at least that's what I'm told...when it comes to rotary phase converters. I'm sure some good advise will arrive here from experienced folks...I've stuck to single phase. And with 3-phase, you'll be able to take good advantages of motors over 5hp...something not true of single phase. Many current (Euro) 3 phase machines are over 5hp and you know that's true of a lot of old iron.

[Rob Russell]

Jeff,

For a rotary phase convertor (RPC), the general rule of thumb is that you need a RPC with an idler motor at least as large as the largest motor you want to start. The alternative is to have 2 smaller RPCs which allows you to run small loads with 1 running and start loads with 2 running. The voltage balance is something you want to look at. With a honkin' big RPC if you want to run a 1 HP 3-phase drill press, the voltages will be sort of out of whack.

I went with 7.5 HP motors on my 3-phase equipment (saw/shaper, jointer/planer).

Rob

[Rick Christopherson]

I am told that any electrical motor over 5 hp is basically useless, looking at 3 hp models, which should be enough tear up a bunch of otherwise good lumber.

If you are below 5 hp, then you are still in the single-phase motor range. Who has told you that you need to use 3-phase motors, and more importantly, why did they tell you this?

Buying a new 3-phase motor with the intention of putting it on a phase converter defeats the purpose of the 3-phase motor. The only time you want to do this is when you cannot buy the specific tool without a 3-phase motor.

I don't recall which one of my articles discusses the choices of using 3-phase tools, but to learn more, you can read either Electricity in the Woodshop or Building a Phase Converter.

[Cliff Rohrabacher]

I know a lot of guys running 15 HP motors on PhasePerfect digital converters,.

[Jeff Raymond]

If you are below 5 hp, then you are still in the single-phase motor range. Who has told you that you need to use 3-phase motors, and more importantly, why did they tell you this?

Buying a new 3-phase motor with the intention of putting it on a phase converter defeats the purpose of the 3-phase motor. The only time you want to do this is when you cannot buy the specific tool without a 3-phase motor.

I don't recall which one of my articles discusses the choices of using 3-phase tools, but to learn more, you can read either Electricity in the Woodshop or Building a Phase Converter.

Thanks for your quick response.

I am going to buy vintage ex-Big Boy shop equipment which is 3-phase stuff. From what I have been able to determine, you get better big tools for the same or less dough in 3-phase than in single phase. The industrial strength previously-operated tools seem only to come in 3-phase.

Does this make more sense?

[Jerry O'Brien]

I can tell you that the landscape has changed a lot since I last used one of these. I am sure you know that there are two types of converters. One uses a rotating machine and one is a static devices that generally operates with some additional capacitors.

Here are some things to consider when you look into one of these. Find out what the power factor will be at the out put. Power factor is the watts divided by the volt-amps. Another way to define this is that it is the cosine of the angel between true power and the apparant power.

Also find out about what is called the "K" factor. That is something that is relatively new. It has to do with any DC loads on an electrical network. It is caused by anything witha DC component. Things like computers. Digital phone systems. Laser printers. If you end up needing a transformer you might consider using a "K" rated transformer.

Those are just a couple of things to consider. You might also ask the power company what they would charge to drop a three phase line to your shop. In some areas it is very reasonable, in others not so.

This might be a good time to suggest that you not be well grounded.

Jerry O'Brien-----------Electrical Sales, over thirty years

[Christof Grohs]

I picked up a 10HP Kay Phasemaster RPC about a year ago at an estate auction. I attend auctions on a fairly regular basis and I was sick of turning down great deals on equipment because I did not have 3Ph power, like the nearly new Felder KF700 combo machine that sold for $1200 a mile from my woodshop It's now been a year since I bought that darn RPC and I've yet to use it or run across another piece of 3PH equipment, so it sits gathering dust. It goes without saying that the day I sell it I will run into another Felder machine

[Jeff Raymond]

It's true that I am not 'well grounded,' in many ways, but got the OK to get this thing done anyway. The trick, I am beginning to learn, is to find what you want at the right price not too far away from the intended location (your shop). This way, I can go look at a piece of arn and check it out prior to purchase.

Christof: How about it? Wanna move that Phasemaster?

Here's a pic of a typical for-sale Tannewitz TS:

[Ryan Kolarik]

I am in a similar situation, where I would like to invest in some nice old iron, much of which seems to be 3 phase. I have been looking over Phase-a-Matic's website which looks pretty helpful in determining the proper phase conversion needs for your application. You can send them the exact model numbers of the machines you will be using, and they will help you choose the appropriate converter.

Though I haven't researched it much yet, from the looks of their website, they seem to consider most woodworking machinery to be in the light to moderate load catagory, for which you might be able to get by with a static converter which are much cheaper than the rotarys. They will however only run machines at 2/3 of their horsepower. I'd get in direct contact with these guys or a similar dealer with the specifics of your power needs for the big equipment you end up purchasing.

[Mark Hubler]

You might also consider using variable frequency drives inside of a rotary phase converter, depending on the horsepower and the $$$. The VFD gives you a lot of options that are not available with other devices; like soft start, low voltage On/Off switching, and adjustable motor speed. I bought mine from www.dealerselectric.com , but there are other places too. My favorite is Teco-Westinghouse.

[Bill Brady]

The frequency drive option would be a lot simpler. You would just have to wire the individual tools, not the entire shop. You should be able to pickup a 5 HP drive for $300 to $400.

[M Toupin]

Jeff,
The general rule for RPCs is 1.5X the largest motor you want to run. If you're looking at a 5hp 3ph, then you'll need a 7.5hp if you go by the general rule. Check out the practical Machinist site, they have a whole section on RPCs and VFDs. Good place to get an education.

VFDs are an option if you're staying under 3hp which can be fed by single phase 220v. Anything over that will require 3 phase which kinda defeats the purpose...

You can build a RPC cheaply, though you need to take a serious look at your power situation. a 7.5hp RPC is going to need somewhere around 60 amps to run IIRC.

Mike

[Rob Russell]

Mike's correct about VFDs.

Anyway, you can program a lot of VFDs to run off of single phase input by telling the VFD to ignore low bus voltage. The problem is you need to derate the VFD - double the size of the motor you want to run to do that. If you're trying to run a 5 HP motor, you'd need a 10 HP VFD and would need to verify that you can program the low bus voltage ignore setting.

As a brief summary, there are 5 ways to get 3-phase power:

• Street power (easiest, expensive if not already there)
• Electronic phase convertor like the Phase Perfect. Provides true 3-phase, balanced power. Pricey.
• Rotary Phase Convertor (RPC). Cheaper, can build your own out of spare parts. Voltage is not as well balanced. Will get 70-90% of power out of the load motor depending on voltage balancing. Can be noisy.
• VFD - motors above 3 HP can get expensive to run off of VFDs if all you have is single-phase power. Typically better power than an RPC, but VFDs can cause problems for machines with CNC controls.
• Static phase convertor. Cheap. All they do is get a 3-phase motor running. Some have a capacitor to help balance the running voltage, but you generally only get 50% power out of the motor.

[Brian Boru]

I run a rotary converter for my joiner and band saw. It provides current in all 3 phases and although not perfect, will allow a motor to provide all or nearly all its rated horsepower.

http://www.kayind.com/

Sizing and Selection Work Sheet

http://www.kayind.com/tech_center/sizing_worksheet.htm