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Thread: Single vs Three Phase Saws
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13th July 2019, 11:21 AM #1Senior Member
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Single vs Three Phase Saws
When I get a proper shed in the future I’ll be looking to get a good panel saw (like a 2.5m slider) and a new jointer/planer (410mm) so I spend some time browsing used machines and getting an idea of options and the market.
I’d like to understand more about power options, my first impression is that for those two machines it would be roughly the same price, perhaps cheaper to install Three Phase or a phase converter and buy the machines in good second hand condition with all the options rather than buy single phase new (those types of machines seem like hens teeth in single phase secondhand)? I presume a phase converter is better if you move house and three phase is better if you are pretty settled? For only two machines the phase converter seems like a simpler option...but then you get a good dust extractor secondhand and see a secondhand welder you really like and then someone is selling a spindle moulder for cheap...and then you spend all your time plugging and unplugging machines.
Secondly, is there a performance difference running a 4kw single phase planer or saw compared to a 4kw three phase machine? I think you don’t need a big start capacitor? But once running is the machine going to practically cut timber the same way for the same power rating? If there are differences, does the performance with a phase converter match three phase or single phase?
I just see really good discounts from new price on machines with plenty of life left in them from businesses upgrading or going bust and think, why would I buy new when I’m not running a business with them!
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13th July 2019, 07:47 PM #2GOLD MEMBER
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I see no performance difference but re-sale could be affected, single phase being easier to sell. If buying new I would buy single phase, used it would be three phase because as a rule three phase machines are cheaper or so the internet keeps telling me. I bought a three phase slider new then worked out that it most probably was not the best decision so my machines since then have been single phase for the reasons outlined. Rotary phase converters don't seem to be a big thing in Oz whereas they are in the US.
CHRIS
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13th July 2019, 10:27 PM #3Senior Member
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I’ve always thought three phase is smoother with more torque because each phase is offset from each other, the motors are smaller for the same output, they are more reliable because they don’t have a starter winding etc. But at the same (small) 4kw motor size I’m not surprised if these things really don’t make much difference in use.
Buying new I would tend to get single phase for flexibility and resale for most tools like you Chris. You can get single phase of every type of tool you would need at home unless you have a farm or business.
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14th July 2019, 07:11 PM #4
Once you start talking 4KW single phase, you are dealing with a potential requirement for close to 20A continuous and 80 to 100A start currents. This puts quite a strain on your mains feeder. I have recently come across reports of consumers pole fuses being reduced from 100A to 80A when smart meters are installed because the particular smart meters being used by the utility company are 80A limited.
If that situation applied, and the house and shop were being supplied from a common feeder and meter, just running the machine would be taking 25% of your available supply, and motor starting could be compromised if anything in the shop or house is using a significant amount of power at the same time, eg, water heater, oven, AC, decent sized dusty etc..
On the other hand, if you used a 3phase unit and VFD, and the motor could be configured for 240V 3 phase, you could set the VFD to slowly ramp up to operating speed and reduce your starting current significantly. You would still draw a similar current when running, but it could make a difference in that it would be guaranteed to start, even with other things operating.
I am just finishing building a new house 210m from the mains service, and will shortly be building the workshop to go with it. The meter box is at the street boundary and about 2m from the mains connection pit. Three phase is then undergrounded to the house and shed. Cost was $8,200 for single phase, or double that for 3 phase (2 cable runs for single, 4 for 3phase). The house could just make do with a single phase service (32A induction hotplate, oven, 2KW range hood etc), without leaving anything much for the shop. Plus plans for decent size lathe and mill, some decent WW machinery and an existing industrial grade 3ph 4KW carhoist to go into the shop as well.
I understand that not everyone has the funds to go native 3ph, or are building from scratch so already have the trenching and conduit factored in, but once you start talking a few multiple KW machines it is definitely a good move if you can afford it.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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14th July 2019, 08:09 PM #5.
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Nope on the torque.
HP = torque x rotational speed .
A SP motor producing 1HP at a nominal RPM MUST be producing the same torque as a 3P motor producing 1HP at the same RPM.
The issue of smoothness is difficult to determine.
In principle 3P operation should be smoother and I routinely measure vibe in motors and indeed 3P motors are on average smoother than SP motors
However, most 3P motors are also better made than single phase motor eg the rotor is better balanced and they usually use better quality bearings so these contribute as much or more that the 3P operation itself.
Buying new I would tend to get single phase for flexibility and resale for most tools like you Chris. You can get single phase of every type of tool you would need at home unless you have a farm or business.
I have a relative it Italy who designed and builds small/medium electrical motors and 90% of what he makes is now 3Phase with a built in cut down VFD. Because of the high degree of control a VFD affords to motor operation expect to see many more such motors in the future. In fact many are already appearing in top of, and even mid range, washing machines.
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14th July 2019, 09:34 PM #6GOLD MEMBER
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The only machine I would absolutely buy three phase would be an arc welder or a MIG as they do not have any null period in the electrical supply. The difference is astounding and very noticeable but I have never used one of the inverter type welders now sold so can't comment on those. Even three phase can be different in welders, the welders at our local tech were Lincolns IIRC a known very good brand but my three phase ESAB is very noticeably better with a way smoother arc and feed.
The only three phase that can be supplied from 240 is 240 and no one supplies native 240V three phase motors in Oz. I am lucky in always having had three phase to our house as it was done many years ago for no charge but sadly that is not the case these days.CHRIS
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14th July 2019, 10:19 PM #7Senior Member
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Thanks Malb. Makes sense, with a couple of 20a circuits in the garage plus airconditioners etc I think I’m getting close to the limit of my switch so can appreciate that it might get expensive to keep running more of those points. By the way you are right about the 4kw motor, turns out the machines I was looking at tend to be 4kw standard 3ph, 1ph option is only 3kw.
Thanks Bob, you always remind me I should re-read stuff I learnt in uni...its embarrassing for an engineer to forget the basics Also I presume the VFD would help run a bigger 230v 3ph on a smaller circuit just because it softens the startup power draw? Power draw will be basically the same under load, but that isn’t why you need an oversized circuit? But a VFD can’t help you run a 400v three phase motor, you have to get proper three phase supply?
Chris, I agree on the three phase lincoln, they beat the snot out of a cheap little stick welder that I grew up with. I like the idea of an inverter tig/stick machine when I eventually get one.
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15th July 2019, 12:02 AM #8Senior Member
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Ok, so you mean you have 230v three phase, not 400v? That would rule out a lot of 400v secondhand machines right? I thought three phase supply is 415v?
Felder for example seem to have the standard option 400v 3ph 4kw (needs true 3ph supply?), no cost 230v 3ph 4kw (can run on 1ph supply with a vfd?), option 230v 1ph 3kw (needs a 20a circuit). I’m confused about voltages now, can these motors simply be configured for 415 or 230v or are they a different motor?
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15th July 2019, 01:16 AM #9GOLD MEMBER
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No & perhaps badly written, we have 400V three phase. There are dual voltage motors for three phase available by changing the configuration of the connection on the motor, Clearvue Cyclones have always have always used this style of motor. The Felder motor has a braking function in it and needs a special approach when changing it to a 230V three phase connection from a VFD.
CHRIS
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15th July 2019, 09:01 AM #10.
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Nominal 3P 400V machines will run on a supply anywhere from 380 to 440.
European machines are nominally 220-230V SP and 380V 3P, North American machinery is 120 SP / 240V 3P.
AS Chris says Because of this many machines are made with motors that can be converted to run on either 240V 3P or 415V 3P. The conversion relies on the motor coils being configured (usually in the mains/motor junction box) as a star (Y) connection when used on 415V 3P and as a Delta (∆) when used on 240 3P. This enables machines to be used in either North America or Europe without changing the motor.
Sometimes the motor cannot be converted easily in the mains/motor junction box and need to be opened up - a task recommended for a motor rewinder. Sometimes the 415V motor is configured as a 415V ∆ - these cannot be converted to 240V 3P ∆ and the motor has to be replaced or rewound.
My 30+ year old Italian belt sander sander is one example. I got it free because the previous owner did not have 3 phase. I switched the motor from Y to ∆ and a 240V VFD in the mains/motor junction box and I was in business. My MW lathe, DP, DC and Band saw were running SP motor machines and are now running 3P used 415V 3P motors converted to 240 V3P motors so I can access the very useful functions of VFDs. The most I paid for any of these motors was $70 and 2 were purchased for $30.
I also have 2 415V 3P (Y) grinders and an exhaust fan 415V 3P (Y) that could not be converted in the mains/motor junction box so I had to open up the motors and do the conversion internally.
A few years ago I purchased a 5HP 3P 415V ∆ motor from a big TS for $35 to have a play with on my HP test rig. It ran fine on 240V 3P but only generated about half the power.
There's a longish thread on these forums on use of VFDs, called "VFD install summaries", that will give you an idea of what can be done.
VFD install summaries
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15th July 2019, 11:21 AM #11Senior Member
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Thanks Bob, and on a motor plate I presume it is always a star configuration unless it says 400v Delta (with the symbol).
Alright, I think I’ve got a decent understanding now, three phase for a decent shed is a good investment.
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15th July 2019, 12:20 PM #12SENIOR MEMBER
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not sure about OZ rules/regulations but if you have access to 3 phase power, buy second hand 3 phase machines.
I prefer 3 phase machines, they are built for industrial environment, they are built to take some beating, they are overkill for average hobbyist.
if you dont have 3 phase then just buy single phase machine.
resale or not, shouldnt really matter your decision? we live to enjoy life, appreciate quality tools, thinking about resaling value is not top of "what I enjoy doing" list.. maybe some of you do...
I took a leap to 3 phase maybe 5 years ago? and never looked back or regretted. I dont think same can be said about staying single phase.SCM L'Invincibile si X, SCM L'Invincibile S7, SCM TI 145EP, SCM Sandya Win 630, Masterwood OMB1V, Meber 600, Delta RJ42, Nederman S750, Chicago Pneumatics CPRS10500, Ceccato CDX12
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15th July 2019, 12:42 PM #13.
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I've found out it's best not assume anything.
Some 3P machines without anything written on the motor plate like TSs and DCs are connected as 415V 3P ∆ (remember these cannot be used on 240V 3P and expect to deliver full power)
I've seen some even say they are convertible on the motor plate but on open up the mains/motor junction box there are only 3 wires coming from the motor and you cannot tell whether they are Y or ∆ without opening the motor.
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15th July 2019, 12:50 PM #14Senior Member
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And here is me naively thinking that machine electrical plates would have to denote something like the wiring configuration as a standard
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15th July 2019, 01:19 PM #15SENIOR MEMBER
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some machines have basic wiring configuration but you probably need someone to check it fully, who know what modification the previous owner has done to the machine's electrical aspect.
to give you an example,
when I received my 18.5kw sander, its a direct start motor, I didnt just plug it in my power point and turn it on, I only have 63amp in my shed, the starting current will probably take out the street transformer fuse.... as a result I bought a VSD and hired an industrial electrician to re-wire the sander completely. if one day I want to sell my sander, I will take out the VSD and sell the sander as is.SCM L'Invincibile si X, SCM L'Invincibile S7, SCM TI 145EP, SCM Sandya Win 630, Masterwood OMB1V, Meber 600, Delta RJ42, Nederman S750, Chicago Pneumatics CPRS10500, Ceccato CDX12
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