Considering a 3 phase CNC small lathe - - - have 240V single phase

[ajoeiam]

In Canada having 3 phase wiring is strictly a commercial or industrial option.
While the 2 phase wiring is standard for residential. This allows 110 volt single phase and 220 volt two phase appliances.
Having used single phase, two phase and three phase wiring there are advantages to each.

Three phase being what it is is strictly a management decision.
Really doesn't need to be that way but getting the management to understand the advantages of being 'like the rest of the world' is a very very difficult position!!

I'd like to hear what the advantages of each as you see them.

(I'm seeing not a lot of advantages to our present system except that its legacy and that makes it 'cheap' but its sure not helping our competitiveness!!!)

TIA

 

[L98fiero]

(I'm seeing not a lot of advantages to our present system except that its legacy and that makes it 'cheap' but its sure not helping our competitiveness!!!)

The only thing that makes it 'cheap' is that it is legacy, 110v uses more copper which is quickly becoming a problem but removing and replacing with smaller wire for 220/240v is more expensive than it's worth and just like Imperial size tooling, it's harder and more expensive to buy internationally.

 

[dazz]

Hmmmmmmmmm - - - - I've seen VFDs even past 2k HP - - - - - but I would bet that they're NOT cheap.
The fact that one needs to oversize the VFD (the rating that I've found was to use 58% when using the vfd to produce the third leg) that gets to be the expensive part!
I'm thinking that when you calculate the costs of up-rating 3 or 4 larger VFDs it might be cheaper to get an electronic inverter and then size the vfds for just rated but I haven't calculated that as of yet!

Hi
My largest VFD is rated to 3.8kW (5HP). It is designed for 230VAC single phase input. VFD derating is only required if a 3 phase unit is driven from a single phase supply.

Old tech, or low quality modern VFDs produced switching voltage spikes that required motors with better insulation. Not so much of a problem with modern high quality VFDs.

The biggest rotary converters (motor-generators) I have worked with were rated to 1MW power. The motors were supplied with 11kV. The generators produced 6.6kV. Those were expensive. Cost is relative.

I would not touch cheap no-name Chinese VFDs. I have 3x VFDs. All are recognised industrial brands. They cost more but are better value for money.

 

[EMF]

well, I can give you my thoughts on this since I ran a motor, generator, alternator shop and built several Phase converters.

If you use a phase converter, you have to wire in 3 phase power, that means additional wiring and all that expense. If the whole shop will be wired and all stuff is 3 phase, great. If not, add money for the wiring and box and breakers for 3 phase and they ain't the cheapest things you can buy.

3 phase motors are cheap, single phase are not cheap. If the windings in 3 phase are bad, new motor. Bearings are cheap. Single phase motors have capacitors and centrifugal switches and as a rule, the caps go bad first, then the cent. switch which then burns the motor up. I have repaired a few centrifugal switches but it was lucky that the motor used a switch I had. Usually single phase motors are made somewhere on earth and nothing is standard.

And remember, with a VFD and 3 phase motor, you get variable speed, simple switch reversing, and, If you order now, motor deceleration which means an electrical brake to slow the motor quickly instead of waiting for it to run down.

3 phase motors are easy to reverse while each time you start and stop a single phase motor, the caps. and the centrifugal switch cycle, and they only have so many cycles in their life. Wiring a single phase, reversable motor with a switch or relays is a pain. VFD reverses for you. I don't like lathes with single phase motors that cycle a lot because of the failure of both the caps. and the centrifugal switch causes motor changes more often than I like. All the lathes I worked on were either 3 phase or converted to 3 phase with a VFD. My current lathe is single phase and the 3 phase motor and VFD are on the shelve ready to change out but then, I'm only a hobby machinist and don't use it like we did in the shop. When I got my lathe, I spent 9 hours fixing the control circuits and wiring so it worked right.

On the negative side, you don't fix VFD's unless you got the skills and equipment. I tried several times and found it easier to just get a new one. If you pay someone, do a cost benefit for sure. Also, wiring one up for your application takes a bit of electrical skill which you may or may not have. Your decision.

Boils down to what you have. If you have a spare 3 phase motor around, use it to make a phase converter. They are not complicated in their primitive state and the wiring diagrams are out there on the net. I have done most conversions using 220 single phase to a VFD. Rarely does it pay, if you already are wired for single phase, to run a rotary phase converter for 1 or 2 machines unless the wiring between them is close. I used rotary phase converters where I had really big motors or lots of them and then the phase converter usually is cheaper than a VFD, especially to run a 30-50 horse motor or to power a whole machine shop.

 

[Ken I]

Just my 10c worth.....
Most VFD's are intolerant of out of balance phase loads - like a single phase coolant pump on a 3 phase lathe - so check out the ratings of any VFD for phase imbalance limits.
I would think a single phase butt welder (blade welder) on a 3 phase bandsaw would not work.
Regards, Ken

 

[hanermo3]

3 phase is inherently cheap in motors and wiring and infrastructure.
So most/all new(ish)buildings in spain/eu deliver 3 phase to the panel and or to the user.

200 amps service is unheard of.
200 x 240 x 1.4 == 56 kW capacity.
- 380 V is about double == 112 kW.
Big industrial workshops with 2-5 HAAS machines might have that 56 kW, mostly half or less.
We ran 5 HAAS machines at once off a 50 kW genset .. in the best demo room in the EU.
Had to turn the accelerations down.

One can run anything off a VFD if the draw is less than 2/3 peak, 1/2 capacity.
Anything will run happily off a 10 kW vfd if the peak load is 5 kW or less.

 

[stragenmitsuko]

I have three fase 380V in my shop .
Even then , I 'm still a big fan of vfd's .
Most my machines have one 380V in - 380V out .

The soft start , the rpm control , the easy reverse , the brake ....
can't be beaten . I love it . Especially the soft start .

 

[Steamchick]

Not that I am much bothered, as the VFD from single phase to the DC PM Motor is a practical solution for my lathe... but what would a single phase to 3 phase solid state converter cost compared to a rotary converter?
Assuming that you are not running 3-phase VFD, I would have guessed that instead of the cost of a single phase motor, 3-phase motor (as generator) + 3-phase motor (in the machine) - That's 3 similarly sized motors! - The cost of a modern solid state pack to give you 3-phase VFD output for the machine's motor would be a more practical solution. Unless you live in a field of free spare motors and haven't got the bucks for the VFD?
K2

 

[mrehmus]

Not that I am much bothered, as the VFD from single phase to the DC PM Motor is a practical solution for my lathe... but what would a single phase to 3 phase solid state converter cost compared to a rotary converter?
Assuming that you are not running 3-phase VFD, I would have guessed that instead of the cost of a single phase motor, 3-phase motor (as generator) + 3-phase motor (in the machine) - That's 3 similarly sized motors! - The cost of a modern solid state pack to give you 3-phase VFD output for the machine's motor would be a more practical solution. Unless you live in a field of free spare motors and haven't got the bucks for the VFD?
K2

Rotary converters, in my experience, cost much more than a VFD. A rotary converter, IIRC, does not have full power on two of the three legs since is it just an induced current. VFDs give full power on each leg. Another small issue is that rotary converters, at least all that I've been around, are noisy whereas a VFD just has a small fan noise.

 

[awake]

Unless you live in a field of free spare motors and haven't got the bucks for the VFD?

That was the key for me in going with an RPC - I picked up a 3hp 3ph motor for free due to a broken end-bell. For use as an RPC, it was more than good enough to TIG-braze the bell back together. I also had access to a near-infinite supply of contactors and capacitors, since a neighbor had an HVAC business and was happy for me to go through his scrap yard any time I wanted.

Moral of the story: It pays to make friends with those who collect junk under-appreciated treasures.

 

[Bentwings]

I have three fase 380V in my shop .
Even then , I 'm still a big fan of vfd's .
Most my machines have one 380V in - 380V out .

The soft start , the rpm control , the easy reverse , the brake ....
can't be beaten . I love it . Especially the soft start .

we have a grizzly 10x22 with the 120 motor that has a three phase converter. It got huge power for small lathe. The biggest draw back is there is no reverse or left hand threading unless do awkward tool position there is variable speed and digital read outs that are ok it’s basically the 602 base model with up grades I was taught to cut threads a most cutting away from the chuck or left to right. There is a cool lead screw reverser for the standard grizzly 602 lathe but ours has a completely different gear train and this rework didn’t work so we just live with it . We like the power the three phase apparently gives about half again the standard motor power plus variable speed. There are a number of companies that have lathes like the 602 with their own modifications . The issue I have withbthem is their on line documentation is light grizzly has all the manuals and operating instructions plus parts catalogs right on line ther customer service is pretty good if you get the right person some know the product well some are not so good . The thing was easyvtonsetbup, it’s heavier than you think wevgotvthevoptional stand which was a good choice the lathe dropped right on it we leveled it and plugged it in and tested the same day we got it . Grizzly doesn’t give me anyting
Byron