Single Phase vs. Three Phase for new tools

[Michael Koons]

I've been active on the forum lately as I'm in the process of buying a new J/P and bandsaw and due to unforeseen circumstances, I continue to have more questions.

I have the option of getting a single phase 4HP J/P or the 3 phase 6HP version. I've researched RPC's and it looks like I can get a 10HP RPC for around $1000 and it looks like installation is pretty straight forward. Do you guys agree that adding a phase converter is no big deal?

The reason I need to know is because if I go 3 phase, I get some options opened up to me. For example, I can get an electric lift on the planer table on the 3 HP version. Hand crank on the 1 HP version. For those of you with experience with the 3ph and 1ph options, do you have thoughts on which is the better direction to go? I imagine that 1ph 4HP is more than enough power for my needs but is the added HP in 3ph worth going that way? I'm interested in anyone's thoughts who may have gone through the same decision process.

As always, thanks!

[Mike Henderson]

If you have 3 phase electrical service to your location, then definitely go 3 phase. If you have to generate 3 phase, I would probably choose to have single phase motors rather than go through the space, cost, and electrical loss of generating it from single phase.

But I was going to generate 3 phase, I would do it with a VFD.

Mike

[Matt Day]

But I was going to generate 3 phase, I would do it with a VFD.

Mike

This.

If he had three phase already, it would be a no brainer.

$1000 sound high for an RPC. A quick look at factorymation and it looks like a 7.5hp VFD is under $500.

[Howard Acheson]

Do you have 3 phase power to a pole close to you and/or is you shop already wired for 3 phase?

What do you perceive to be the benefits to 3 phase?

[John Lanciani]

If I had the money to spend I'd be looking at a Phase Perfect digital converter. http://phaseperfect.com lots of upside, only real negative is cost.

[fRED mCnEILL]

I have a 3 ph table saw with 5HP motor and have a RPC. I bought the saw at an auction and didn't realize it was 3 ph.So I was able to find a cheap rpc. This was 15 years ago and the rcp has worked well although I did have a couple of problems with switches.
While it works fine it is a pain in the butt as to saw I need to turn on the rcp and then the saw. Same with turning it off. I could leave the rcp running all the time but that is wasting electricity and creating some additional noise.
My understanding is the only reason for 3 ph. is cheaper power although when you get into bigger motors 3 ph may be the only kind you can get. Using a RCP just adds another level of complexity.
I recently bought a used compressor that had a 3 ph. motor. I couldn't figure out how to connect the 3 ph wiring so tried a single phase motor.Worked perfectly.

If I had a choice I would not go 3 ph.

[David Kumm]

once you go three phase you will never go back. Opens up more choices, better machines especially on the used market, larger motors, fewer problems. VFD's are great for a few machines, but if you have a shop full, and RPC or better yet, a Phase Perfect, is the way to go. Dave

[Jesse Busenitz]

once you go three phase you will never go back. Opens up more choices, better machines especially on the used market, larger motors, fewer problems. VFD's are great for a few machines, but if you have a shop full, and RPC or better yet, a Phase Perfect, is the way to go. Dave

+1 I just moved shop and upgrade to some 3 phase machines, and I found a like new 15 hp RPC for 350$ and installed a 3phs load center. It was very simple to wire once I read the instructions:D Having 3 phs opens up the doors for some real deals on machines that nobody wants to touch.

[Peter Quinn]

I went RPC, cost was around $1K from American rotary, simple to install and use. If you want to power a single machine a VFD may be the way to go, I have several different machines that run 3 phase, I run a feeder and shaper together, etc, so the VFD was not my preferred option. Seems maybe the VFD's have dropped in price lately? Used to be over 5HP got pretty expensive quick. Even so buy three machines and put a VFD on each, suddenly the RPC looks cost effective. Phase perfect is perfect except the cost, great if cost is no object, or you really need power that good such as for CNC operation. If its a machine you start and stop frequently like a drill press the VFD seems a better option than a RPC due to noise, cost of generating unused power (though they don't draw a tremendous amount at idle), just easier than starting and stopping the RPC. But for a planer, shaper, etc that in my case I generally run a batch of something, so start it, use it, turn it off for extended periods, the RPC works well.

As far as the convenience, nothing beats a power drive table on a planer, would sure make a combo more attractive than cranking all the way up and all the way down as required to change over on some models.

[Larry Copas]

Sooner or later you will want/need 3 phase so you might as well do it up front and save a lot of jockeying around along with money. I have a RPC and use it all the time. The only drawback is the noise and to a lesser extent turning it on/off. I should have located it some place where I couldn't hear it.

I also have 3 VFD's. I use them only on machines that will benefit from variable speed. In my case its a Bridgeport milling machine, bandsaw, and lathe. I would guess the life span might be similar to TV's or any other solid state device. Above 3 horsepower they are cost prohibitive for me to use.

[Keith Hankins]

I've been active on the forum lately as I'm in the process of buying a new J/P and bandsaw and due to unforeseen circumstances, I continue to have more questions.

I have the option of getting a single phase 4HP J/P or the 3 phase 6HP version. I've researched RPC's and it looks like I can get a 10HP RPC for around $1000 and it looks like installation is pretty straight forward. Do you guys agree that adding a phase converter is no big deal?

The reason I need to know is because if I go 3 phase, I get some options opened up to me. For example, I can get an electric lift on the planer table on the 3 HP version. Hand crank on the 1 HP version. For those of you with experience with the 3ph and 1ph options, do you have thoughts on which is the better direction to go? I imagine that 1ph 4HP is more than enough power for my needs but is the added HP in 3ph worth going that way? I'm interested in anyone's thoughts who may have gone through the same decision process.

As always, thanks!

I've been using 3 phase for a while. If you only will have one tool then a vfd can be a cheaper option but I wanted to be able to handle multiple tools. I went with a 10hp RPC from American Rotary. Great group to work with and made in America if thats important to you at all. I like the older tools and they are cheaper and made 10 better than new(IMO).

if it wer me, I'd def go the 6hp route and install the RPC. There are plans out there to build them but I decided I wanted a supported unit so Amer rotary was a good choice. Mine came with a baldor idler motor to generate the 3rd leg. It's quiet and works like a charm. Knowing what I know now, only thing it would do diff is maybe buy a cheaper idler motor instead of a new one to save a little money. you will be surprised how cheap you can pick up 3 phase motors up on CL or ebay. I picked up a 2hp baldor for 70 bucks because someone bought it not know it was 3 phase.

Good luck if you have any questions let me know. BTW AR puts on sales all the time.

[Mike Schuch]

I love my 3 phase tools! By far their biggest advantage is that I paid about 1/3 what the comparable 1 phase tools would have cost. Not everyone knows about phase converters or VFD's and fewer yet want to mess with them. 3 phase tools are great when it comes to resale... if you are buying the used equipment!

[Michael Koons]

Thank you for all the replies. In all my reading, it seems not all RPC's are alike. I've read that on most RPC's, the 3rd leg will fall off under full load. It seems like only the Kay Industries RPC's maintain balanced power and that their RPC is rated for the HP of the actual 3ph tool you're running. Is this everyone else's experience? I'm guessing the way to get around this is to get a higher rated RPC from one of the "other" suppliers.

[David Kumm]

Kay and Arco rate their converters by the size motor they will start. Most others need to be uprated 1.5-2X depending on how hard starting the motor is. All will provide a fairly balanced voltage once under load and you can buy most all with additional balancing if you need that for the electronics. Quality of the motor is a primary difference. Some use a Baldor, some are Asian, some are steel frame, some are cast iron. Some will run a larger frame motor than others. Do some reading and talking to a few companies. You will find similarities but also some differences. Ask about the motor quality and the quality of the caps and components. There are different price levels of the internals as well. Dave

[Mike Schuch]

Thank you for all the replies. In all my reading, it seems not all RPC's are alike. I've read that on most RPC's, the 3rd leg will fall off under full load. It seems like only the Kay Industries RPC's maintain balanced power and that their RPC is rated for the HP of the actual 3ph tool you're running. Is this everyone else's experience? I'm guessing the way to get around this is to get a higher rated RPC from one of the "other" suppliers.

From what I can tell when I built my 10hp RPC about 20 years ago there are 3 basic implementations of RPC's.

1) Big idler motor started by a smaller pony motor. The pony motor mechanically disengages once the idler motor is up to speed. The generated leg isn't balanced to the other 2 live legs.

2) Big idler motor started with capacitors. The generated leg isn't balanced to the other 2 live legs.

3) Big idler motor started with capacitors and run capacitors used to balance the 3rd generated leg. This is the design I used and the current on the third leg stays balanced with the other 2 legs when I am starting my big 7.5hp radial arm saw.

I think you will find all 3 designs to be effective for running 3 ph machinery and your worry about the third leg fall out under full load is more marketing hype than anything you really need to worry about.

[Peter Kelly]

The one downside I've found with 3ph machinery is re-sale. Can be considerably more difficult or time-consuming to sell used three phase as opposed to single-phase machines as you rule out the hobbiests, anyone not willing to mess with VFDs, phase converters, etc.

One thing I'm very jealous of with Europe is the availability of 3ph resedential service. Pretty common in Germany, Scandinavia, etc.

[Mike Schuch]

The one downside I've found with 3ph machinery is re-sale. Can be considerably more difficult or time-consuming to sell used three phase as opposed to single-phase machines as you rule out the hobbiests, anyone not willing to mess with VFDs, phase converters, etc.

One thing I'm very jealous of with Europe is the availability of 3ph resedential service. Pretty common in Germany, Scandinavia, etc.

I completely agree! I would never buy new 3 phase tools for a shop without 3 phase service. But I never buy new stationary tools anyway. I buy cheap used 3 ph tools for bottom feeder prices because no one wants to mess with running 3ph tools on 1ph.

[Mike Heidrick]

What service do you have coming in to your shop and what size motors do you want to run? Can you do your own electrical? All factors that would determine if 3ph was right for you. I have RPCs and VFDs. Some make more sense to use than others depending on the tool. Even with a big RPC I will continue to use both.

[Chris Padilla]

This is probably too simplistic but:

Pro: 3-phase
Hobbyist: 1-phase (more appropriately called split-phase)

I would never ever mess with 3-phase...there is no need to IMO...unless you can get the local utility to wire you up for a reasonable rate and that doesn't happen. One can do just about everything with good old 240V/30 A and a nice 200 A panel.

[Ian Moone]

swings and roundabouts!

What extra you spend on 3 phase supply run in & wiring of the shed - you save being able to buy used 3 phase machines that businesses have depreciated to $zero value on their tax books over time & often quit for next to nothing & most hobbyists aren't interested.

My 3 phase Mig welder with traveler 330 amps for $500 for e.g.

To buy one used for my eldest lad (who has no 3 phase power) best I could get used was 250 amps with traveler and $2K & had to literally fight others off to get it!.

Opposite if you wish to sell tools - only those with 3 phase power can buy so you won't get the same re-sale values and demand as single phase.

Cost to wire 3 phase thru the shed is horrendous..compared to single phase. My small 21 ft x 24 ft shed - with 4 x 3 phase outlets that run a 3 phase Robland X31 combination wood work machine, the 3 Phase welder, 3 phase compressor and 3 phase twin bag dust extractor... wiring & switching / sub mains box etc, was around $4K.... and I did a lot of it myself (dug trenches, ran conduits and ran the wires & just paid a sparky to hook it all up, to be "legal").

So what you lose wiring up, you CAN save buying good used 3 phase gear cheap.

In terms of the capability - there's no comparison with 3 and single phase... over load a machine on single phase and you trip circuit breakers etc - but with 3 phase they will do 3 times the work.

Mind you our 3 Phase is 415 volts versus your 220?.

A 4 HP x 3 phase machine & your dealing with 4 Clydesdale horses - not 4 Shetland pony's of single phase.

There's horses and theirs horses.

Which brings me to the 3 "ranchers" all drinking at a bar in Singapore One from USA and One from the UK and one from Downunder!.

First Rancher from the UK - says (about his land holding which in the UK is measured in acres) - "Why I can ride my best thoroughbred Arabian horse hard all day and I am still on my own land!"
Second Rancher from Texas - says (about his land holding which in the USA is measured in thousands of acres) "Why heck I can ride my best quarter horse hard all week and I am still on my own land!".
Third Rancher from the Kimberly region of Downunder - says (about his land holding which is Oz is typically measured in the thousands of square miles & where they ride the rough bush brumbies), leans back after swigging most of his cold beer in one go, and says laconically "yep, yep, yep, I had me a lazy horse like that once - had to shoot it!" :D

Horses ain't all Horses Sol!

Go with the 3 phase Clydesdales from the outset if you can - they all eat a lotta of hay, and all crap pretty much the same amount of mess to clean up - but the former will outwork the latter every time!.

If you going to have a "workshop" you might as well equip it with the ability to "work".

A water wheel mill on a dry crick ain't going to grind no grain unless you want to stand and urinate on the wheel all day. ;)

[David L Morse]

swings and roundabouts!

Nice analogy.


A water wheel mill on a dry crick ain't going to grind no grain unless you want to stand and urinate on the wheel all day. ;)

Thanks, I finally understand Australian beer.:D

[Mike Henderson]

In terms of the capability - there's no comparison with 3 and single phase... over load a machine on single phase and you trip circuit breakers etc - but with 3 phase they will do 3 times the work.

Mind you our 3 Phase is 415 volts versus your 220?.

A 4 HP x 3 phase machine & your dealing with 4 Clydesdale horses - not 4 Shetland pony's of single phase.


Nope, a 4 HP motor is a 4 HP motor, whether it's powered by single phase or 3-phase. There is no difference in the power or the ability to do work, especially for small motors like 4 HP.

Mike

[If there was a difference, the 3 phase motor would not be rated at 4 HP, it would be rated higher. And a 3 phase motor is not more efficient. If you look at the physical size, a 3 phase motor is approximately the same size as a single phase motor with the starting cap removed.]

[To put it another way, HP is the measure of the ability to do work and motors are designed and tested to produce a certain amount of work (HP). If the 3 phase motor referenced above could do 3 times the work of a 4 HP single phase motor, it would be rated at 12 HP, not 4 HP.]

[The BIG advantage of a 3 phase motor over a single phase motor is reliability - no starting cap and centrifugal switch. A 3 phase motor consists of just the absolute minimum - a set of field coils that provides a rotating magnetic field, and a rotor. The only real failure part is the bearings and modern bearings are pretty good.]

[Malcolm McLeod]

It's true that not all horses are created equal, but by definition and common convention, all 'horsepower' are equal. It doesn't matter how that horsepower is generated: water-wheel, 6 Shetland ponies, 1 Clydesdale, or via P=iV. So, assuming a manufacturer's motor and specifications are as advertised - - any 1Hp motor will generate the same power as another.

This doesn't mean there are no differences. Look at physical size, purchase cost, efficiency, life expectancy, or how it operates in the intended application or loading. This applies even to motors in same voltage/phase classes.

As for 1-phase vs. 3-phase, the most significant differences as they related to the OP's dilemma are costs, and basically reduce to 3: purchase; operating; and maintenance.

1.Purchase costs and considerations are fairly well covered here (at least for me). Used 3ph tools are cheaper to buy, but this is offset by installation cost for 3ph electrical supply (whether from grid, RPC, or VFD); particularly for 1st time 3ph install. That first step is a significant one. But for a plant full of tools, 3ph is a no brainer because of reduced cost of the feeder circuits (less copper, smaller electrical gear).

2.Operating costs are also pretty much a wash for a small scale operation. Any cost difference for 1ph vs 3ph for the average small shop are, in my experience, negligible. This holds true until your shop's electrical power demand gets to the point that premium efficiency motors, power factor, harmonics, and facilities engineering enter your daily world.

3.Maintenance costs include down-time, replacements/parts, availability, and trouble-shooting. These (and opinions about them) are probably all over the map, especially if you regularly abuse a tool (You wouldn't do that!? ...Would you?) 1ph probably has slightly higher average maintenance & replacement costs just because of the start capacitor and related centrifugal switch in a 1ph motor. Availability of 3ph is probably better.

Do you want to consider performance issues? 3ph motors are typically touted as having better locked-rotor (start-up) torque compared to 1ph motors of equal horsepower. One standard I can remember, cites typical 3ph locked-rotor torque as 400% of full-load torque (developed while at-speed). Compare this to 350% for capacitor-start 1ph motors. Not a huge difference and, unless you start your tools under load, this start-up condition is largely irrelevant. Full-load torque is typically nearly identical for a given Hp motor (subject to manufacturing quality, etc...).

I could argue that all the above makes the decision a wash.

So how about convenience issues? I am not faced with this decision, but the discussion leads me to believe I'd not look at 3ph power until I had multiple 5hp to run simultaneously (or single 10hp). Running 3ph would just not be mentally convenient IMO.

My $0.02. I tried to skip the theory and myth, and just focus on the practical. Hope it was worth the read.

[Martin Wasner]

This is probably too simplistic but:

Pro: 3-phase
Hobbyist: 1-phase (more appropriately called split-phase)

I would never ever mess with 3-phase...there is no need to IMO...unless you can get the local utility to wire you up for a reasonable rate and that doesn't happen. One can do just about everything with good old 240V/30 A and a nice 200 A panel.


Tough to get a motor over 7½ horsepower in single phase.

[Mike Henderson]

Tough to get a motor over 7½ horsepower in single phase.

I didn't try to see what the largest motor was that is offered in single phase, but there's a bunch of 10 HP motors offered in single phase. Here's (http://www.amazon.com/1725RPM-215TZ-Leeson-Electric-140311/dp/B000A7POWM/ref=sr_1_6?s=hi&ie=UTF8&qid=1444515023&sr=1-6&keywords=10+HP+motor)one.

If you search amazon for 10 HP motors you'll get a lot of hits on single phase motors. Also eBay.

I found a bunch more here (http://stuccu.com/s/10+Hp+Single+Phase+Motor-MbSLsTI-Buy-Exclusive-Deals-70-OFF-Save-Big-Lowest-Price-On-10-Hp-Single-Phase-Motor-Best-In-Stock-Fast-Free-Shipping?mt=e&keyword=10%20hp%20single%20phase%20motor&ap=1s2&cid=71295930378&caid=555a4b85b1b1c62814ca698c&netid=1&network=g&aaid=555a4b85b1b1c62814ca698e&gclid=CjwKEAjw7uKwBRDUlJvRo-z6rgMSJACbmSBhmmTtJkr1HbXE7IzdeGB-QHQdtAyeIofhtmVwz37orBoCk9Hw_wcB).

Mike

[I also found a Baldor 13HP and 15HP offered in single phase. The 15 HP is 230V and draws 245 amps at startup! (according to the data sheet)]

[Martin Wasner]

43 amps, holy crap. I don't think I've ever seen anything over 7.5hp in a piece of woodworking equipment.

[Martin Wasner]

My sander is a bit less than 50hp total, it draws something like 155 amps.

[Martin Wasner]

43 amps, holy crap. I don't think I've ever seen anything over 7.5hp in a piece of woodworking equipment.

Over 7.5hp single phase that is.

[Malcolm McLeod]

I believe amp draw for 10Hp at 240V/1phase is typically 40 amps. That's #8 AWG wire.

15Hp at 240V/1phase is typically 60 amps. That's #6 AWG wire.

...And both assume you're not running it to the back-40 (I think sizes are for 50ft or less??). If you need it, I hope you own a copper mine!

[David Kumm]

I've read many who give good reasons for staying with single phase but I don't recall ever reading of someone who went three phase ever regretting it. Yes, large machines can be made to run single phase but not very practical. Not just the wiring cost, but the size 2 and 3 starters get expensive and while the resale of three phase is somewhat more difficult, unless you run desirable machines, trying to unload a 10-15 hp single phase machine will be way more difficult. Dave

[Mike Henderson]

I believe amp draw for 10Hp at 240V/1phase is typically 40 amps. That's #8 AWG wire.

15Hp at 240V/1phase is typically 60 amps. That's #6 AWG wire.

...And both assume you're not running it to the back-40 (I think sizes are for 50ft or less??). If you need it, I hope you own a copper mine!

Whether the motor is running at single phase or 3 phase, it will require the same power to produce the same HP. So assuming the same input voltage, the total current will be the same for either single phase or 3 phase. But with the 3 phase, the current will be divided over three wires, instead of two as in single phase. So you could use smaller wire for the 3 phase, but you have to run an additional wire.

I would guess that the total amount of copper is about the same for either.

Mike

[Ross Canant]

once you go three phase you will never go back. Opens up more choices, better machines especially on the used market, larger motors, fewer problems. VFD's are great for a few machines, but if you have a shop full, and RPC or better yet, a Phase Perfect, is the way to go. Dave

+2. RPCs are easy to wire. Once you have 3 phase the whole world of cheaper industrial machinery opens up. I have a ton of 3 phase machinery now. It goes cheap at auction because most people can't power it.