Author Topic: Single or 3-phase ?  (Read 205 times)

jpigg55

Single or 3-phase ?
« on: October 26, 2020, 11:40:32 PM »
I have a question about motor power choice. Some of the new lathes I've been looking at offer a choice of either single or 3-phase motors.
Single phase would be plug and play, but 3-phase motor with VFD gives ability of finer speed control, to a degree.
Given the choice, what is your opinion on which is the better option ?
SB 9A, Clausing 8520, Sanford MG 612

ddickey

Re: Single or 3-phase ?
« Reply #1 on: October 27, 2020, 05:21:10 AM »
3 phase motor w/vfd. No comparison.

Carpenter84

Re: Single or 3-phase ?
« Reply #2 on: October 27, 2020, 05:44:13 AM »
100% VFD 3 phase.
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

4GSR

Re: Single or 3-phase ?
« Reply #3 on: October 27, 2020, 06:37:46 AM »
100% VFD's, too.

The thing I like, if your taking a heavy cut and power is lagging, down shift your gear selector to a lower gear, crank up the VFD and keep cutting.  People talk about the lack of power in the lower herz range.  That's because they don't want to adjust for it by shifting the headstock gearing to speed up and or get the herz up in the 60-75 range or higher.  I don't like to over speed a motor, especially of it is a older motor.  Maybe go up to 70 herz max. And try not to run any motor below 40-45 herz.
Ken

Carpenter84

Re: Single or 3-phase ?
« Reply #4 on: October 27, 2020, 07:03:45 AM »
My vfd is set to max 85hz.

I accidentally set it to 400 the first time I set one up, AND had the pot wired backwards, so slow was fast.. yikes!!  Ya, donít do that...

But yes, there is absolutely a honey zone. One thing I really like about having the vfd (aside from a dial for speed control, and push buttons) is having the vfd set on the amperage display as standard. so I can monitor how the lathe is running and cutting, and adjust the pulleys accordingly to keep about the 2-3 amp range with the motor running in a 1000-1300 rpm range for efficiency and cooling. Too slow and the fan doesnít spin fast enough to cool.


Note: 2-3amps with a 1.5hp motor..
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

4GSR

Re: Single or 3-phase ?
« Reply #5 on: October 27, 2020, 08:12:57 AM »
Yeah, I like the amp reading when using the face mill on the mill.  When the amps start getting upward toward 4.2-4.3, it's time to index the inserts.  Normal amps, no load or little load, is around 2.4-2.6 on my 1hp motor.  And it's a 1960's made motor.
Ken

jpigg55

Re: Single or 3-phase ?
« Reply #6 on: October 27, 2020, 08:29:55 AM »
Sounds like 3-phase with VFD is thee winner.
I was watching ZMOTORSPORTS video review of the PM 1340GT lathe (https://www.youtube.com/watch?v=KNbbEoJf1TI) and he was talking about how and why he went with a VFD set-up, got me curious.
He also talked about some installing additional motor cooling. I'm assuming additional cooling is another fan set up to move more air thru the motor.
SB 9A, Clausing 8520, Sanford MG 612

f350ca

Re: Single or 3-phase ?
« Reply #7 on: October 27, 2020, 08:49:10 AM »
I avoided 3 phase motors for years, mind you that was the pre VFD period. Changed out a couple of 3 phase motors to single phase. Then needed a larger lathe, swapping out a 10 hp motor wasn't an option, actually don't think a 10 hp single phase would fit, so bought an electronic phase converter. Same basic idea as a vfd without the variable, but functions like a rotary phase converter as in switch loads, run multiple motors etc. It now runs the big lathe the Hardinge and a surface grinder.
None of these need electronic speed changes.
A few years ago picked up a small radial arm drill with a two speed 3 phase motor that is gear driven, not easy to change out motors. Rather than run 3 phase power to it I bought a VFD that always sits at 60 hertz, with 2 speeds and 4 gears there's no need to run the motor off its design frequency.
If you can get away with single phase why bother with extra electronics that can fail.
My whole cabinet shop runs on single phase

Greg

Greg

4GSR

Re: Single or 3-phase ?
« Reply #8 on: October 27, 2020, 09:49:09 AM »
My oldest VFD is going on 14 years old.  The brand name is Delta, Asian made.  It powers my 1HP mill motor.  Believe it is a 1.5kw unit a little over kill.  So far it has held up good.  When the mill, as well as all of other my machines are not being used, I disconnect the power the the machine by either a breaker or knife switch at the machine. Doing this keeps stray currents from getting into the works and frying a VFD.  I also have surge suppressors installed on most of my VFD devices to help too, as well as the incoming current in the house has one too.

jpigg55

Re: Single or 3-phase ?
« Reply #9 on: October 27, 2020, 12:38:37 PM »
Going single phase would be the easiest and cheapest. A quick look showed a VFD capable of running a 3 HP motor adds an extra $345+ to the price tag.
I could see this as an option to reduce spindle speed for the models I've looked at with minimum spindle speed of 70 to 90 RPM.
Beyond finer speed control, I couldn't find any other benefit of going 3-phase with VFD other than increasing the number of possible options.
SB 9A, Clausing 8520, Sanford MG 612

PJB

Re: Single or 3-phase ?
« Reply #10 on: October 27, 2020, 12:56:52 PM »
Instant reversing.   
1991 Bridgeport Series I 2J-VS  9"x48"
1979 Clausing Colchester Bantam Mk2 11"x30"
1972 Harig Super 612
2015 Tormach PCNC-1100 Mill

"I wants what you gots!"

Carpenter84

Re: Single or 3-phase ?
« Reply #11 on: October 27, 2020, 01:44:59 PM »
Instant reversing, lower current requirements, more efficient operation, control wiring does not have to be line voltage/amperage.
The Chinese VFD's, I think, are perfectly fine, and affordable.
Given the option, I would go VFD. I'm not sure the extra cost makes a heck of a difference on-top the multi thousand dollar bill. But if you're splitting hairs on cost, then go single phase. But if there's financial wiggle room, I'd go 3 phase for the benefits.
Shawn

First 9x42 column mill,
Enterprise 10x28 lathe,
Ko Lee 6x12 surface grinder,
Airco dip/stick 160 welder,
Fully stocked wood shop.

Terrywerm

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Re: Single or 3-phase ?
« Reply #12 on: October 31, 2020, 05:04:27 PM »
If I were buying new I would definitely go with the VFD and 3 phase motor setup. I've been considering doing that for my old Logan lathe and for my Clausing 8520 for the greater flexibility in speed control. Soft starts and stops on the lathe would be a plus too, though not necessary on the mill. Reverse would be nice on the lathe for doing metric threads, and due to the threaded spindle, the soft start and stop feature would be a necessity to keep the chuck from spinning off the spindle.


I do understand the desire to reduce cost, also. However, purchasing the machine with a 3 phase motor would be cheaper than converting over later, especially if they offer a 3 phase / VFD package deal right from PM. I don't know if they do or not, but many times respectable savings can be had with package deals when they are available.


 :coffee2:
Terry

Making chips with old machines!

4GSR

Re: Single or 3-phase ?
« Reply #13 on: October 31, 2020, 07:18:51 PM »
Long before VFD's became common, I used to build my own phase converters.  The first one dad and I ever built was around 1973-74 for a 3HP motor.  I built countless number of them since then. I've even built a couple for starting up 10HP motors, those were scary at the time I did them.  You never know what to expect when starting one.  I try to balance the capacitors across the three phases.  Without a oscilloscope it's really hard to tell if you have them balanced or not. Volt meter helps if you know what you're doing, I don't most of the time.  I still have a portable one that can be run as a static converter or as a RPC with a pony motor, I call it.  It's good for 5HP start with or without using a 5HP pony motor.