Author Topic: vintage lathe restoration - 3 phase supply.  (Read 24868 times)

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Offline capnahab

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vintage lathe restoration - 3 phase supply.
« on: August 30, 2016, 05:45:20 pm »
Dear Guys,
I am a surgeon in the UK so you may have to bear with me on technical matters (on both counts.) I was directed here after seeing Robrenz's fantastic videos on youtube.
I am restoring a 1957 lathe. It has a 2 speed 3 phase motor, - 3.75HP and 7.5HP. I have a 15HP rotary converter to power it , - professionally installed to the garage with a 10mm 60amp supply. The electrician however didn't know much about connecting it to the lathe. It works great at low speed.  When I try to start the motor in fast speed it seems to overload the converter. Phoned the converter manufacturer. I tested the voltage drop on start up - drops from the UK 240 supply to about 230 for a second, then back up to 240, - so pretty negligible.
I think the three wires of the converter output could be worked into the switch in the wrong order but I don't know how to explore the circuitry to determine how to fix the problem. I have a  multimeter and know the basics of how to use it. I enclose some photos of the switch, electrical panel and front control.
Any tips would be great.
ps proper 3 phase will cost me about $20,000, so I have discounted that...
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #1 on: August 30, 2016, 05:48:01 pm »
Sorry , and heres the lathe.
 

Offline eKretz

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Re: vintage lathe restoration - 3 phase supply.
« Reply #2 on: August 30, 2016, 06:07:16 pm »
Changing the order of the wires will do nothing but reverse the motor direction. Wondering why you didn't go with a variable frequency drive, was it too expensive? They can easily convert single phase to 3 phase, and also give you infinitely variable speed within their range of frequency.

BTW, beautiful old Dean Smith & Grace.
« Last Edit: August 30, 2016, 06:10:08 pm by eKretz »
 

Offline douardda

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Re: vintage lathe restoration - 3 phase supply.
« Reply #3 on: August 30, 2016, 06:25:44 pm »
By all means, please, install a VFD. This wonderful lathe deserves it.

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Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #4 on: August 30, 2016, 06:31:12 pm »
Thanks eKretz,
The most powerful VFD available in the UK is about 2.5-3 Kilowatt. Not sure exactly why.
 

Offline HighVoltage

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Re: vintage lathe restoration - 3 phase supply.
« Reply #5 on: August 30, 2016, 06:41:02 pm »
I have a lathe that came with a single phase motor and speed was controlled through gear and belt changes.
Well that sucked big time.

Then I installed a 3 phase motor and frequency controlled drive system, based on a LENZE 3 phase 400V, 7.5 KW VFD
You can get them sometimes cheap on ebay.

After this mod, the lathe is a hundred times more useful and I never have to change gears again.

There are 3 kinds of people in this world, those who can count and those who can not.
 

Online IanB

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Re: vintage lathe restoration - 3 phase supply.
« Reply #6 on: August 30, 2016, 06:41:59 pm »
I'm absolutely not an expert on rotary converters, but I wonder if the rotary converter does not have enough system (mechanical) inertia to cope with the startup load of the lathe motor. Does the converter "bog down" when you try to start the motor? If so, I wonder if fitting some kind of flywheel to the converter might help? (If it is at all possible to do so.)
I'm not an EE--what am I doing here?
 

Online Ian.M

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Re: vintage lathe restoration - 3 phase supply.
« Reply #7 on: August 30, 2016, 07:11:04 pm »
The other possibility would be if the control system contactor coils are being powered from the generated phase.  Control systems should always be powered from the original supply.  Its complicated by the tendency for control system manufacturers to attempt to balance single phase loads evenly over all three phases so some control box rewiring may be required
 

Online IanB

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Re: vintage lathe restoration - 3 phase supply.
« Reply #8 on: August 30, 2016, 07:23:40 pm »
The other possibility would be if the control system contactor coils are being powered from the generated phase.  Control systems should always be powered from the original supply.  Its complicated by the tendency for control system manufacturers to attempt to balance single phase loads evenly over all three phases so some control box rewiring may be required

Perhaps this could be tested by simply rotating the order of the three phases connected from the converter to the lathe? There are three possibilities (1-2-3, 3-1-2, 2-3-1) and maybe one of these works better than the others?
I'm not an EE--what am I doing here?
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #9 on: August 30, 2016, 07:53:19 pm »
That's essentially what they guy at the rotary phase converter ?RPC manufacturer said. The generated phase being the likely problem. Obviously they aren't going to be able to give specific advice about every machine.
It's very common to use RPCs for heavy machines - this guy illustrates. - https://youtu.be/IZny57ddM8k . No one describes much in the way of machine rewiring. I just wondered if there was any EE logic to help me.
 

Online edpalmer42

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Re: vintage lathe restoration - 3 phase supply.
« Reply #10 on: August 30, 2016, 07:56:52 pm »
You mentioned that the input power is only dropping from 240 to 230, but what about the output voltages?  Do you have a clamp-on ammeter to measure the current in the output lines?  Maybe there's a fault in the motor.

Ed
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #11 on: August 30, 2016, 08:05:54 pm »
Ed - good point , I will do that before I start switching the wires into the lathe.
 

Offline Andy Watson

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Re: vintage lathe restoration - 3 phase supply.
« Reply #12 on: August 30, 2016, 08:45:58 pm »
Are you trying to take this motor from a standing start to full speed in one step?
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #13 on: August 30, 2016, 08:57:00 pm »
Well, that could be the problem. I have no instruction manual that describes normal use. One of the pictures shows the front panel , two buttons, one for slow one for fast. When I push fast with the motor already running in slow absolutely nothing happens. No noises or change in either lathe or converter.in normal use with a true 3 phase supply  I suspect mechanically to change speed you put it in neutral then hit fast with the motor already running. The machine gear settings are the same.  Then re- engage the clutch.
If I hit fast from stopped it overloads the converter. One possibly problem could be the control panel not sending the fast signal through ?. Though why should it be any different than true 3 phase
 

Online IanB

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Re: vintage lathe restoration - 3 phase supply.
« Reply #14 on: August 30, 2016, 08:58:58 pm »
I think you have not told us exactly what you mean by "overload the converter"? What does it do, exactly?
I'm not an EE--what am I doing here?
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #15 on: August 30, 2016, 09:13:11 pm »
This video shows startup in slow, then press fast. Then stop and try starting from stopped to fast. Essentially the boost light continually flashes and the converter chatters .
https://youtu.be/Aryl-0iWgiQ
 

Offline KJDS

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Re: vintage lathe restoration - 3 phase supply.
« Reply #16 on: August 30, 2016, 09:30:06 pm »
I suspect that there is an issue with either the brushes or the windings on the fast coils of the motor.

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #17 on: August 30, 2016, 09:40:22 pm »
I think it's unlikely to be the motor, despite being from 1957 the lathe has lived in a tech College until I bought it. It runs perfectly in the slower speed. Can I text the motor somehow ?.
 

Online IanB

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Re: vintage lathe restoration - 3 phase supply.
« Reply #18 on: August 30, 2016, 09:49:36 pm »
Hmm. I wonder how the motor changes from slow to fast? I wonder if it could be something like changing from a star to delta connection on the windings or something like that? (Bearing in mind I don't know about three phase motors and we need someone in this thread who does.)

I short, I am wondering if there is a wiring/connection problem of some sort between the converter and the lathe...?
I'm not an EE--what am I doing here?
 
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Offline Andy Watson

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Re: vintage lathe restoration - 3 phase supply.
« Reply #19 on: August 30, 2016, 09:54:26 pm »
I'm not convinced that it is overloading the convertor. I think it sounds like there is a contactor in the DSG that is dropping out (for some reason?) and the convertor is reacting to this.
May be time to sketch-out the circuit and work-out what it should be doing.
 
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Online tautech

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Re: vintage lathe restoration - 3 phase supply.
« Reply #20 on: August 30, 2016, 10:25:49 pm »
OP
On a lathe group I'm a member on there is often discussion about power problems when 3 phase lathes are used in other than industrial environments where the mains supply is generally strong. Sometimes the lathes are tripping VFD's especially when cold and a often discovered fix for this is to change the viscosity of the headstock lubricant. It's just not quite that simple, one must match the particular properties of the recommended lubricant with a lower viscosity one. As these old lathes were designed to run for long day shifts the headstock temperature rise had to be catered for when the lathe got hot with a higher viscosity lubricant but today lubricant technology is vastly better and the additives make it so that much lower viscosity oils can now be used.
Benefits are much lower power requirements when the lathe is cold and surprisingly headstocks will often run cooler with modern lubricants.
Avid Rabid Hobbyist
 
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Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #21 on: August 30, 2016, 10:33:13 pm »
I think a circuit diagram would definitely help. I will phone DSG tomorrow. Not holding out a lot of hope, -they have been through many changes of owner.
 

Online edpalmer42

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Re: vintage lathe restoration - 3 phase supply.
« Reply #22 on: August 30, 2016, 10:39:56 pm »
Start at slow - okay - push the fast button - nothing happens
Start at fast - converter freaks out

The difference in behaviour is because in the first case, the motor is already spinning.  Do these motors have a centrifugal switch?

Regarding the wiring diagram, any chance it's bolted on the lathe or the motor itself?

Ed

P.S.  Yes Ian, we desperately need someone who knows 3 phase motors.   :-DD
 
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Online tautech

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Re: vintage lathe restoration - 3 phase supply.
« Reply #23 on: August 30, 2016, 11:00:45 pm »
1440 and 720 RPM translates to 4 and 8 pole motor. The poles (windings) will be switched into another configuration to enable the high RPM mode.
Get a sparky or your local motor rewinder to check this motor is behaving properly, if it is suspect the switch over HW as not doing its job.
Avid Rabid Hobbyist
 

Offline rch

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Re: vintage lathe restoration - 3 phase supply.
« Reply #24 on: August 30, 2016, 11:15:30 pm »
My only experience of using a three phase motor is using one with a variable frequency inverter drive, and I strongly recommend getting a suitably rated one on Ebay or somewhere. 

But my only other observation is that the incoming neutral wire does not go anywhere, and it is just possible it may be needed for the higher speed.   Of course, there would have to be somewhere to connect it!
 


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