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Table Saw Upgrade #4: Powering a 5HP Monster with Single Phase Power

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Blog entry by MikeGCNY posted 02-19-2011 04:34 AM 2693 reads 1 time favorited 6 comments Add to Favorites Watch
« Part 3: On the Fence and Need Some Help Part 4 of Table Saw Upgrade series Part 5: Putting it Back Together »

So, just as I suspected, the 66 came with a fairly new 5 horse 3 phase Baldor motor. (Yeah Me!) I was able to figure this out by calling Baldor’s customer service and reading them through the different numbers on the motor plate. As it turns out, the motor is only 2 years old. The saw is 22.

As many of you know from reading other posting on Lumberjocks, there are several options to consider when your shop simply has single phase power and your machinery requires 3 phase power. The first of these options is to replace your motor all together with a new (or used) single phase motor. Because the motor in my Powermatic was so new, and because it was 5 horsepower, I could not bring myself to replace it with a 3 horse motor. I could have replaced it with a single phase 5 horsepower motor, but because the cost is so high I would be better off buying a brand new saw. This being said, I opted to keep the saw and its motor and to figure out a way to power it with single phase current.

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Many of you will ask: “Mike, why do you need a 5 horsepower table saw?” My answer: “I don’t! It is just the principle of it.”

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Now before I begin here, I must admit that I am a Computer Scientist, not an Electrical Engineer, so forgive me if I don’t have all of the facts straight or 100% correct. I did my best over the past week to evaluate the options and to come to a decision that was right for me. What follows are some of my findings that led me to my decision.

If you would like to power a three phase motor off of a single phase power source, you have the following options:

  1. Static Phase Converter
  2. Rotary Phase Converter
  3. Variable Frequency Drive (or AC Drive)

Static Phase Converter

A static phase converter is a low cost method to power a 3 phase motor on a single phase power source. A static converter is essentially a “battery” that stores up electricity that is used to power the 3rd phase of the motor. Because it stores electrical energy, it can only deliver power for a short period of time, and thus is only used to get the electric motor turning. Once spinning, the “battery” is drained of its power and stops supplying power to the third phase. For this reason, if you choose to employ a static phase converter you will only be leveraging 2/3rds of the power of your motor.

A good way to view a static phase converter is to think of a human propelled merry-go-round in a park. Picture three adults standing around the merry go round while it is stationary; each adult represents a phase, where the third adult represents the phase supplied by the static converter. Now picture all three adults grabbing the bars of the ride and then spinning in. Once they get it going the third adult runs away to take care of something else and only two adults are left spinning the ride. This is essentially what happens when you use a static phase converter to “spin” your motor.

With this disadvantage you might wonder why someone would ever use a static converter. Price. A static phase converter is the most economical way to power a piece of equipment that requires three phase power where the operator is not concerned with horsepower loss. (Note: In recent years, Variable Frequency Drives have come down in price, making it less economically attractive to run static phase converters. We will learn about this more later.)

Rotary Phase Converter

A rotary phase converter (RPC) is essentially a 3 phase electric motor that is used to generate a third phase of electricity. You can think of it as an “electric powered electric generator”. Rotary phase converters are great because when sized correctly, they allow you to power your equipment on 3 phase power with no horsepower loss.

So what is the down-side? Price. Because rotary phase converters often require a larger horsepower motor than the motor you are powering, they can get expensive. Additionally, rotary phase converters are very heavy (I almost bought a used 7.5 horsepower unit that weighed 270 pounds) they present a bit of a shipping challenge when you are buying them from a remotely located vendor (although I must admit, I found a couple of vendors who offered free shipping).

If you plan on purchasing or already have more than one machine that requires 3 phase power, a rotary phase converter might be a good option for you because, if sized correctly, you can run multiple machines off of a single RPC. You might not be able to start all of the machines simultaneously, but if that is your requirement you are most likely not a hobbyist.

Variable Frequency Drive

A variable frequency drive (VFD), or AC Drive, utilizes electronics to convert single phase power into three phase power and deliver this power to your motor with no power loss. VFDs control the frequency of the electricity that is being delivered to your motor, thus allowing you to soft start your motor and to precisely control the speed of your motor’s rotation. With this also comes the ability to electrically stop your motor. Although you would probably not want your TS to stop spinning on a dime, you may choose to have the VFD stop the blade from spinning within 2 seconds of hitting the “Stop” control.

So what is the down-side? VFDs require a bit more skill to setup and program for your particular need. In addition, VFDs with single phase input can get pricey – especially when you are powering motors with horsepower ratings greater than 3.

VFDs also require that they are wired to the motor directly, so you will need to implement some sort of “On/Off” switch. Most VFDs have switches, but they are tiny buttons similar to the ones that are on a electronic thermostat. Now I don’t know about you, but when I am balancing a sheet of ply and need to start my saw the last thing I want is a tiny “on” button. When the ply goes through the blade the last thing I want to do is to have to look for an “off” button.

My Choice Was…

After a dozen or so hours of searching online and calling vendors for both RPCs and VFDs, I decided to go with a VFD. I did find a 7.5 hp RPC in Manhattan on Craigslist that I talked the guy down to $500.00 for, but it was very large and I don’t imagine that I will be buying much more 3 phase equipment.

I was able to get a VFD for $200.00 from an online retailer. I simply called them and explained my situation and told them what I was looking for. The salesman that I talked with was a great guy and gave me a great price on the unit.

My decision to use a VFD was based off of the following:

  1. Price: For me, a $200.00 VFD seemed very reasonable. (One alternative was to replace the motor with a single phase Leeson that I found new for $300.00 w/o shipping.)
  2. My Dad is an Electrician: Because my dad and a close family friend are electricians, my labor costs are basically nothing (well, maybe a Pizza). Because they are both master electricians (and my dad is also an Electrical Engineer), I can be sure that they will hookup the VFD correctly.
  3. I wanted to keep the existing motor. My dad keeps telling me “You want 3 phase for machines that big, trust me!”

So I hope whoever reads this finds it helpful. Again I am not an Electrical Engineer or an electrician so for those that are, please don’t beat me up as to the validity of my comments (I know there are some exceptions to what I said above). Before you purchase any equipment, be sure you consult with whatever vendor for whatever solution you decide and make sure that your particular piece of machinery will work with their product. As a tip, have a picture of your motor plate handy to read to them over the phone, or as I did, to email to them.

And remember, if you are uncomfortable with electricity hire a professional.



6 comments so far

View cabmaker's profile

cabmaker

1311 posts in 1553 days


#1 posted 02-19-2011 04:51 AM

Nice saw, hope it works out for you.

View mcase's profile

mcase

438 posts in 1874 days


#2 posted 02-19-2011 05:04 AM

Mike,

Thanks for the logical and detailed explanation. Looks like a great machine you got there.

View Beginningwoodworker's profile

Beginningwoodworker

13347 posts in 2417 days


#3 posted 02-19-2011 05:33 AM

Mike thats a nice saw.

-- CJIII Future cabinetmaker

View sawdustphill's profile

sawdustphill

53 posts in 1435 days


#4 posted 02-19-2011 04:02 PM

Mike thanks for the info on the the 3 phase converters
and a nice saw hope it works out for you

Phillip

View Tyrone D's profile

Tyrone D

314 posts in 1077 days


#5 posted 01-31-2012 11:19 AM

Hello, where did you get the VFD from?
I am restoring a vintage Wadkin Bursgreen AGS10 table saw(I have a blog about it) and the motor is three phase.
I know a couple of websites, I’d just like to add a couple more fish to the pond.
Thanks.

Your saw is beautiful.

-- --Tyrone - BC, Canada "Nothing is ever perfect, we just run out of time."

View boiler13's profile

boiler13

1 post in 1018 days


#6 posted 03-05-2012 11:44 PM

Very helpful article. I bought an old Clausing (Kalamazoo/Atlas) 3110 at auction for $200. The scrap is worth more :-) I went with a static converter and it’s sorry. I’ve never cut on something so true and stable but when I need to rip maple into long strips (make custom alphabet blocks w/ a cnc) it bogs down and stops. I end up with about 8 1/4” cuts over and over to get one stick cut.

Follow Mikes advice and spend another 150 to get the VFD and not a static converter. I’m still weighing this vs a new single phase motor.

Jim

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