Member
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.
Member
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.Originally Posted by Peter Kelly
Member
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.
Glad its my shop I am responsible for - I only have to make me happy.
Moderator
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.
Guest
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!"
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.
Last edited by Chris Padilla; 10-10-2015 at 11:35 AM.
Member
Nice analogy.
Thanks, I finally understand Australian beer.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.
Beranek's Law:
It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.
Contributor
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.]
Last edited by Mike Henderson; 10-10-2015 at 2:00 PM.
Go into the world and do well. But more importantly, go into the world and do good.
Member
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.
Guest
Tough to get a motor over 7½ horsepower in single phase.
Contributor
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 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.
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)]
Last edited by Mike Henderson; 10-10-2015 at 6:29 PM.
Go into the world and do well. But more importantly, go into the world and do good.
Guest
43 amps, holy crap. I don't think I've ever seen anything over 7.5hp in a piece of woodworking equipment.
Guest
My sander is a bit less than 50hp total, it draws something like 155 amps.
Guest
Over 7.5hp single phase that is.
Member
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!
Contributor
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
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