I am building an above the garage shop (near Chicago). I am a guy that makes furniture for myself, family and friends. In the past I had a key to the woodshop at school…now I live FAR from school. 1. What are the benifits of 3 phase? 2. Should I afford it? 3. Is there a reason for me to buy a 3 phase 5hp table saw (Sawstop)?
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Replies
If you have 3 phase available then by all means take advantage of it. By nature, 3 ph motors develop the same horsepower in a smaller package and there are thousands of 3 ph used machines on the market for CHEAP!
As for the SawStop, I own one and you won't be dissappointed whether it's a 5hp 1ph or a 3ph. It's simply the best cabinet saw under 1000lbs on the market regardless of of the unique safety features.
Jeff,
Three phase has definite advantages, especially for heavily used machinery, but the advantages are considerably less clear in a small part time shop. The biggest advantage for a home shop is that you can use relatively inexpensive surplus industrial woodworking equipment, machines that typically came in three phase only. Unfortunately most of this old machinery weighs a half ton or more and usually needs some restoration.
Another drawback is that you can't get three phase power in most residential areas, and even if you could get it, the cost for the service would overwhelm the small savings in efficiency and lower maintenance costs.
Home shops that run three phase machinery do so with converters based on various technologies. The converters start with the available single phase and create fair to excellent simulations of three phase. The converters can be shop built if you are so inclined, but, if you are going to purchase one, you will spend several hundred to a thousand dollars or more based on the size you need to handle the load.
My basic advice would be that unless you are seriously into buying and restoring "old iron", you would probably be better off sticking with single phase. Also used single phase machines are easier to sell and command a higher price.
John White, Shop Manager, Fine Woodworking Magazine
Edited 8/21/2006 10:31 am ET by JohnWW
Thanks to both of you. I believe I will end up sticking with single phase. I would rather build with wood than restore iron. I am excited about getting the sawstop saw, 5hp for a few extra bucks seems to make sense.
5 horsepower will need an electrical circuit with greater capacity to supply it, so you should look at your wiring before going to the larger motor.
John White
Hey John,While I agree with nearly everything you wrote, I'll take an exception to the part about the cost. I run a hobby shop in the middle of Seattle and I pay the same price per KWh for the 3Ø at the shop as I do for my power at home. In addition, since the 3Ø was available at the pole outside my shop, the city only charged me $700 for the installation of the second transformer.I would also add that 3Ø motors last much longer than single phase, under the same conditions, and that a 3Ø panel in your shop can be a great convenience. For instance speed and directional control over motors is now a snap.A 3Ø motor also cost a fraction of what a comparable single phase costs, so if you have 3Ø available, you can re power a weak single phase machine into a more powerful and useful one very economically.The cost of my 3Ø service was paid for with the acquisition of my first salvaged machine.My 2¢
Tom
I have 3 phase in my shop and it is generated by a Rotary Phase converter. I purchased it from Gentec Phase Converters located in Port Washington, Wi. Mine is a 20hp unit. It will start and operate any motor up to 20 hp and will operate up to 60 HP as long as you don't start them all at once. It operates on a single phase 60 amp circuit. The important thing to keep in mind is that a rotary phase converter is the most efficent. There are other types but apparently they are not as efficient. My biggest problem was in convincing my electrician friend that they do work. He had bad experiences in the past but now is a big believer. The after sales support from Gentec was fantastic. It was them who convinced my electrician friend that they do work and he did not have to increase the wire guage inside the control box. I paid about $1100 dollars 2 years ago and became aware of them through Woodweb. I picked it up at the factory at 1030 on a Sat nite as I was passing through. I paid $300 for a Kraemer, 1900 Cfm dust collector, 3 ph. The cats now walk on the other side of the road when they pass my shop. I also bought a Crescent mortiser(floor model, 3 ph) for $531 through an industrial on-line auction. I had tried to buy a Wadkin at a local auction and it went for $2100. It was single phase and every man and his dog was bidding on it. Some of the older equipment may require some work but that has not been the case with my purchases. The Crescent was made in the 40's. My only regret is that I did not know about phase converters and Gentec years ago. I have no affiliation with Gentec other than a very happy customer. I have a friend that has 2 ,100 hp rotary phase converters in his shop. One runs a 9 motor older Wadkin moulding machine and the other is for the rest of his shop. Both are on a 200 amp . single phase circuit
I have a 5 hp three phase motor on my Powermatic 66 in my basement shop. I use a frequency drive to convert the single phase to three phase for this one machine. I really like the soft start provided by the freq driveI have it set for 5 seconds to ramp up to full speed. I also have a 5 second coast down so the saw blade is fully stopped in 5 seconds. All that is required is a freq. drive rated for 208-230 and it can be used on your single phase power.
I had thought of that route but by the time I bought a drive for each machine it was not cost effective. I think it is the way to go if you just have one or two motors.
I'm no expert electrician, but I think you are missing a decimal or something. I don't think it is possible to produce sixty horsepower from sixty amp 220 line. If it had the same efficiency as my 4.8 hp motor, it would need 275 amps. Compared to my 3 hp motor it would be 300 amps. I realize there could be differences in efficiencies etc. but I believe there would be that much difference. A 3 hp motor can take up to 60 amps to start the motor.
Somewhere between your math and my install lies the truth. It was GenTec that provided the info on the size of circuit. They did say that 60 amp would be the minimum. They did say that should I attempt to run closer to the 60 Hp I would have to have a bigger amp breaker My table saw has a 10 hp main mtr and a 1 Hp scoring motor. I have a 5 hp DC . It powers them like no tomorrow and the voltage does not Fluctuate when all 3 are running at once.
Edited 8/27/2006 8:46 pm ET by 2x4
Dear 2x4,
I am not an electrician but I have studied electricity some. That being said, let me run some figures before you:
1 horsepower = 746 watts
60 HP = (60 x 746) = 44760 watts
I = P/E = 44760/220 = 203.45 amps
safety factor = 80 percent
203.45/.8 = 254.32 amps
What I have shown you here is that for a sixty horsepower motor to run at 100 percent efficiency on 220 volts, it should be on at least a 254 ampere circuit breaker. Since you are only running sixteen hp you should have a
16/60 = 0.26667 or 0.26667 x 254.32 = 67.8186 ampere breaker ie. it would be necessary to have a 68 amp breaker to drive your equipment if it were all delivering the maximum power simultaneously. Of course breakers don't come in such odd sizes so you would have to go to the next available size. Another thing is that 100 percent efficiency is never attained, so that would require more power. The reason you are getting by is probably that those motors are not delivering maximum power simultaneously. It would be interesting to hear the comment from a real electrician.
2x4
Unless I am missing something here, you are wasting a HUGE amount of electricity for no reason. In your list of tools, I didn't see anything that stood out as requiring a 20 hp converter. Did you know that any time that converter is running (just at idle) you are burning 50-amps at 240 volts? That's 10 to 12 KiloWatts just to drive the Idler motor, even if the tool motor only draws a couple of amps, or isn't even running at all.The savings that you think you made with buying 3-phase tools is lost on a daily basis from your converter.It sounds as though you have gone out of your way to purchase 3-phase tools over single phase, thinking they were more efficient, but you have lost that efficiency by running a converter. It is one thing to take advantage of buying a 3-phase tool for a bargin and run it on a converter, but you should not be doing this on a default basis.And yes, the other poster was on-track when he was pointing out the fact that you can't run a 60 hp motor. Actually, it is much worse than he stated. Because your idler motor is already consuming 50-amps from your single-phase supply, you only have enough capacity to run a total combined tool load of 10 more amps, which equates to less than 3 hp before you begin to overload your circuit.The Law of Conservation of Energy dictates that your 60-amp, 240-volt, single-phase circuit can only deliver a total of 12-horsepower. Your idler motor consumes 10-hp (1/2 of its full-load rating) which leaves you with 2-3 hp for a tool (or the sum of all tools).Even if you have a tool large enough to justify the 20-horsepower converter, I strongly recommend that you get a smaller converter to power your smaller tools.Rick Christopherson
Rick. I appreciate your concern for my energy costs but it has not risen signifcantly now that I am using the 3 phase.As I have previously stated I am not an electrician. Your statement that my system has only enough power left to run a 2-3 hp motor leads me to believe that your knowledge of electricity and or phase converters is also lacking. I am operating a SCM slider with a 9 HP main motor and a 1 HP scoring motor. At the same time I have a Kraemer 5 HP Dust collector running. All are running on 3 phase power. I do let each motor reach its operating speed before I start the next one. As I operate a one man shop this poses no problem. The literature I have read on phase converters suggests that they all will operate a total of 3 times their rated HP . This does not mean they will operate a single 60 hp motor. My understanding is that they will only start a motor to what ever HP your rotary phase converter is rated but will operate a number of these motors up to 3 times the phase converter rating.
I appreciate your concern and hope you are enjoying the long weekend.
Brian
Actually I do know a thing or two about electricity and phase converters. My statement wasn't that your converter couldn't handle the motor loads; it was that your 60-amp circuit couldn't handle the loads. Somewhere or another there is a missing piece of information. Either your circuit is larger than 60 amps, or your converter is not what you think it is.An induction motor running without a load will draw about 1/2 of its rated nameplate current. A dust collector is always under load, so it will draw closer to its rated horsepower. This means your 9 hp saw will draw at least 22 amps at idle, plus another 3 amps for the scoring blade, and your dust collector will draw about 20-24 amps. Add these up and you get 45-49 amps for a no-load tool load. When the saw is cutting, it will probably draw about 75%, so this puts it up at 36 amps. So your moderately loaded tools will then be drawing the full 60 amps from the circuit, and this is not counting any energy draw from the converter itself.So given this information, there are three possible scenarios: 1) Your circuit is much larger than 60-amps, or 2) Your converter is a static converter, or 3) The 20hp rating is the maximum rating, but the idler motor is much smaller.What's the model number of your converter? If they have a website, I'll look up the specifications.
Edited 9/4/2006 2:08 pm ET by RickChristopherson
Rick.. not sure where you are getting your load ratings for you motors. The metal label on my dust collector Weg 5 hp 3 phase motor shows an Amp rating of 4.67 amps. I am not prepared to crawl under my saw to find out the other ratings.but I do recall they were similiarly low The circuit breaker is 60 amp, It is a rotary phase converter and having been around tools and electric motor for all of my working life I do know the approx size of electic motors and the Leeson motor that makes up the phase converter is definitely in the 20 hp range. One thing I did not mention is that I am running an isolation transformer to boost the 220 3 phase to 575 3 phase.
In my earlier post I made mention of my Industrial Electrician friend who connected this up told me what I was trying to do would not work and it was only after talking to Gen Tec that he was convinced it would work. It appears you and him may be on the same page although he was converted into a believer. I am not sure you will be , lol. Prior to buying the rotary phase converter I had spoken with several suppliers in an attempt to determine if it was feasible and they all had the same info as Gen Tec. If you go to the Gen Tec web site you will see that the Maximum single amp fused circuit you would require is a 108 amp single phase circuit. This was explained to me by Gentec as the requirement if I was running at maximum capacity of my phase converter. Under the present load conditions I was told a 60 Amp breaker would be sufficient and it has yet to be tripped and the system does operate admirably.
Sorry I can not give you a better explanation but it does work and that is the best I can do. Have a good one.
Brian
Something is askew. Law of physics -
P = IE where P is in Watts, I is in Amperes, and E is in volts. P = IE = (60amps)(220volts) = 13,200 watts. Since 1 horsepower is 746 watts it holds that 13,200/220 is 17.69 HP. If your circuit is putting out a maximum of sixty amperes, it cannot by the law conservation of energy produce more that 17.
69 horsepower at 100% efficiency. The fact is that nothing is 100% efficient and proper operation requires that you should not exceed 80% of the rated amperage rating. Eighty percent of 17.69 HP is 14.15 HP. You should expect to get somewhat less than 14.15 HP from 60 amps It is impossible to attain as much as 17.69 HP.
As per my last post I am running the 220 three phase through an isolation transformer and boosting the 220 to 575 volts and my motors are 575 volt motors .
Brian
As per the other posters your numbers still don't add up. You said your WEG 5 horse motor draws 4.69 amps, at 575V thats about 3.5 horse if it was 100 percent efficient which it is not.
Since the house is on fire let us warm ourselves. ~Italian Proverb
"As per the other posters your numbers still don't add up. You said your WEG 5 horse motor draws 4.69 amps, at 575V thats about 3.5 horse if it was 100 percent efficient which it is not."
It's three-phase, so multiply 4.69A the square root of 3 to get 8.1A at 575V. That's 4.67kW, or 6.26 hp. With a 5 hp rated output, that's an efficiency and power factor combined of about .80, which is pretty typical of a 5 hp three-phase motor.
Look at this 575V Baldor. 4.8A full-load, full-load efficiency of .875, full-load power factor of .92. Very similar numbers.
http://www.baldor.com/products/perfdata.asp?1=1&catalog=M3613T-5&product=AC+Motors&family=General+Purpose%7Cvw%5FACMotors%5FGeneralPurpose&winding=36WGX882&rating=40C+AMB%2DCONTBe seeing you...
Thanks for the comparison. I was beginning to believe that my system would go bang and all the smoke would escape from the wires. I would be suspect it it was manufactured off shore but I had been to the plant and the size of the unit required was determined by the people at Gen Tec. I would have bought what ever they recommended. It works flawlessly and you can't beat their prices.The components inside the control box are all brand name.
Brian
Remember "You had me at 'hello'?"
You lost me at "square root". :)
(PS this is not an appeal for a dumbed-down explanation, probably the people who need the information actually understand what you wrote and why)My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
You are quite right on the motor, Do your figures agree with mine on the supply side single phase current draw being about 19-20 amps running just the 5hp WEG?
Since the house is on fire let us warm ourselves. ~Italian Proverb
Brian,
It doesn't matter whether you run power through a transformer or a converter or both, the amount of usable power on the output must equal the same on the input. The amperage figures I gave were based on the single-phase equivelent, not the 3-phase nameplate. These numbers represent how much current is required from the 240-volt, single-phase circuit.However, I looked at the website for your converter. I'm amazed at their stated power consumption at idle. As I stated previously, a 20 hp motor will normally draw 10 hp at idle, but your converter's idler motor only draws 2 hp at idle. I suddenly recalled someone else emailing me about this converter several months ago, asking about the ratings because the ratings are hardly believeable.I still have a hard time believing that they can get a 20 hp motor spinning with so little power, but in light of your situation, I stand corrected.
Edited 9/5/2006 12:35 pm ET by RickChristopherson
This is a good one going on right now. I haven't popped in here for quite a while.
Maybe a way to help settle this thing is to have him use a meter that clamps(induction meter) around one of the single phase wires and see what his loads are with the conveter running by itself and when his machines are turned on. Not a bad tool to invest in, especially if dealing with machinery/electrial
I have a 15HP rotary Phase A Matic and I believe that they recommend a 100 amp single phase breaker and #4 wire for suppling power to the converter and 3phase panel. After that, the wire size can be dropped to the appropriate machinery needs.
As a matter of fact since I'm moving, again, I need to look this up before hooking up the system at the new place.
And as a reminder to all... Never use the "generated leg" to supply power to the magnetic controls on your 3 phase machinery. Only use the same legs that were origionally single phase.
Actually, using the ammeter is what will confuse this issue more than what I started some time ago. The manufacturer's specifications are listing the amount of non-reactive power the converter draws through a non-comercial utility meter, but does not reflect the actual current drawn in the wires (like an ammeter would show).The distinction is watts versus volt-amperes. In my original postings on this topic I hadn't noticed that they were specifying watts. On the other hand, a commercial facility will likely have a utility meter that registers volt-amperes instead of the residential watts, so at a commercial facility, the converter would impact the utility bill. The American Rotary idler motor does draw slightly less than half of its nameplate current when it is idling, but because the phase-shift (aka powerfactor) is down near 0.1 at idle, the amount of power shown on a residential utility meter socket will be very low.Unfortuantely, this might make people think that very little current is flowing through the converter, and mistakenly size the feeder circuit too low. If you put an ammeter on the converter supply wires, it would show that the converter is drawing somewhere between 30 and 50 amps at idle.
Here's is a excerp from phase-a-matics website for their rotary converters
View Image
230V MODELS ( R Series) & Electrical Specifications230V single-phase in and 230V 3-phase out
View Image
Model
Largest Motor HP See #1. Below
Multiple Motors Lightly Loaded .See #2 Below
Approx. Idle Current
Disconnect Switch Fuse (Time Delay Fuses)
NEMA Starter Size
Starter Heater Amps
Minimum Single Phase SupplySee #3 Below.
R-1
1 HP
3 HP
1.5 AMPS
10 AMPS
00
4.8 A
15 AMPS
R-2
2 HP
6 HP
2 AMPS
10 AMPS
0
7.7 A
15 AMPS
R-3
3 HP
9 HP
2.5 AMPS
15 AMPS
0
10.4 A
20 AMPS
R-5
5 HP
15 HP
3 AMPS
30 AMPS
1
15.9 A
30 AMPS
R-7
7 1/2 HP
22 HP
5 AMPS
40 AMPS
1
26 A
40 AMPS
R-10
10 HP
30 HP
7 AMPS
45 AMPS
2
35 A
60 AMPS
R-15
15 HP
45 HP
8 AMPS
60 AMPS
3
48 A
100 AMPS
R-20
20 HP
60 HP
10 AMPS
80 AMPS
3
63 A
125 AMPS
R-25
25 HP
75 HP
11 AMPS
100 AMPS
3
80 A
160 AMPS
R-30
30 HP
90 HP
12 AMPS
125 AMPS
3
94 A
200 AMPS
R-40
40 HP
120 HP
13 AMPS
150 AMPS
4
117 A
250 AMPS
R-50
50 HP
150 HP
15 AMPS
200 AMPS
5
145 A
300 AMPS
.1. Largest Motor HP: Almost all machines require sizing the converter 50% larger or more than the largest HP motor of your machine. See paragraph #4 above. Also refer to Sizing For Load Types.
Tom,
You are lucky that your shop had 3 phase readily available and that it only cost $700.00, though you didn't say what the total cost of bringing in the service, panels, and wiring cost. In areas where three phase isn't already at the pole, which is true in most residential settings, the cost would be much higher.
In addition, in many places, the cost of the three phase service is over and above the cost of the existing single phase service, with a basic service fee that gets charged every month even if no 3 phase power is used. The fee structure is different with every utility so you may have a better deal than most places.
While 3 phase motors do hold up better than single phase, the advantage is only significant when the machinery is used a lot, at least several hundred hours a year. The question I answered was for a home shop, and I doubt that the additional cost of installing three phase power would ever be made up in reduced maintenance in that setting. I have a number of machines with single phase motors that are going on 60 years old and the motors are still fine.
Speed and directional control, along with a soft start and braking, can be added to any machine with a 3 phase motor by using a VFD control which only needs a single phase input, there is no need to wire the whole shop with 3 phase for just one or two machines that can profit from VFD.
Used 3 phase motors can often be found very cheaply, but new motors in 3 phase are typically only 10% to 15% cheaper than the equivalent 3 phase. Also many older machines can not be remotored easily since many of them had machine specific motors that can't be replaced with a stock motor because of the special mounts, frame, and shaft design.
From my point of view, three phase is only justified for heavily used machinery or for someone who really wants to play with large old industrial weight machines.
John W.
"The cost of my 3Ø service was paid for with the acquisition of my first salvaged machine." Yep and that compressor rocks!!! ROFL. I think you had an advantage, though, because your shop is in a commercial area. Isn't that probably why the 3Ø was there? Don't know if it relates to this discussion, but the Great NW has some of the cheapest electric rates around, no?forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Hey John,Yeah, I was lucky that the pole in front of my shop had 3Ø. The cost of installing the service was not significantly more than for a new single phase service. A new service panel was needed anyway, as the building was a vintage 1913 Vaudeville theater with an antiquated 100A service. My reasoning was, if I needed a new service, and 3Ø was available just outside my door, why not take advantage of it? I'm very glad I did.Jamie,Yeah, the 3Ø runs down my street. If I was off the main line, It wouldn't have been cost effective. It's true, in the Great Pacific Northwest we do enjoy cheaper power, but that's changing. Ever since the power rate scandals that rocked Enron and others, our rates have been slowing approaching the national average.Tom
You have been given geat information. If you ask around one of the first myths you will hear is that 3 phase is cheeper to run. It is not. At my shop (in a comercial buisness park) 3 phase is the same price as single phase and it is charged by the KWHr in the same manner as well. 3 phase motors dont use less electricity they use less amperage over more wires. The net wattage is the same. I had easy access to 3 phase, all I needed was a 200 amp service disconect and a 3 phase breaker panel. New that will cost about $1600! Used on Ebay around $1,000. that dosent count the buss lines to connect the single phase panel, the single phase panel, or the meter base. Although a single phase panel isnt necessary it would be cheeper for me than getting a three phase panel large enough to handle all the shops needs. All the componets related to three phase electrical supply are 3 to 4 times more expensive. Breakers can easily cost $45 bucks, and Home Depot dosent have them. So even though I have a couple of three phase machines I chose to not get the service. THe prospect of getting a 24" planer or an 18 CFM compressor for half the going rate was tempting, but I couldn't justify it. Also I know that in most residential areas 3 phase actually costs more per KWHr because they consider is a comercial service.
Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
Thank you. I figured as much. At some point I may end up with a phase converter...but since the 3 phase saw that I am thinking about (Sawstop) has not been purchased to go into the shop in the house that I will be moving into next month, I am going to buy the 1 phase saw and see what comes up at auctions etc after I have the shop up and running.
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