Author Topic: vintage lathe restoration - 3 phase supply.  (Read 24919 times)

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Online tautech

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Re: vintage lathe restoration - 3 phase supply.
« Reply #50 on: August 31, 2016, 08:10:48 pm »
If you want three Avo8 meters they are here for the taking, just off to the scrappy. I have three of the equivalent GEC Selectest meters, no real difference other than they don't explode if you drop them.

Last comment, don't even think about fitting a VFD. The static/rotary converter will quite happily run this sort of machine.
Yep moving coil meters will be better to "see" what is happening than DMM's.
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Online edpalmer42

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Re: vintage lathe restoration - 3 phase supply.
« Reply #51 on: August 31, 2016, 08:29:07 pm »
Actually, if I'm interpreting the specs correctly, it looks like the converter is running at full capacity.  Although it's rated for 11 KW, that's when more than one motor is involved.  It's only rated to start a 7.5 KW (10.0 HP) motor, which is what you've got.  So it should be able to do the job, but not much more.

Ed
Look again, it's only 7.5 HP

Doh!  Got confused between KW and HP.  Sorry!  :-[

Ed

P. S.  Double Doh!  Sorry for double posting earlier.  I looked in the thread and didn't my message so I thought I'd hit the wrong button. 
« Last Edit: August 31, 2016, 08:31:47 pm by edpalmer42 »
 
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Offline woodchips

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Re: vintage lathe restoration - 3 phase supply.
« Reply #52 on: August 31, 2016, 08:38:41 pm »
Does the box have a large auto transformer in it? Need to step the 230V up to 400V and at 11kW will be about 8 or 9" cube sort of size.

Caps look a bit anaemic too.
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #53 on: August 31, 2016, 09:04:08 pm »
Ok gentlemen (and ladies). I have at last found time from my chauffeuring duties.
Voltages across the three wires. measured singly , haven't got enough clip on test leads at the mo.

Lathe at rest
A-B 438 volts
A-C 450 volts
C-B 437 volts

Motor on low speed, no chuck turning,
A-B 433
A-C 430
C-B 414

Motor on low speed, chuck turning at fastest possible in low speed, 380 rpm (max mechanical load)
A-B 428
A-C 415
C-B 413

Motor attempted start in high speed, but motor never starts.
A-B drop to 370
A-C drop to 320
C-B drop to 360

Looks to my uneducated eye that  ? wire B is the weakling (? generated circuit) and perhaps I should swap B and C ?. ( see Jeroen's post above.).
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #54 on: August 31, 2016, 09:13:28 pm »
Sorry scratch that last sentence, don't know what I am talking about.
 

Online tautech

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Re: vintage lathe restoration - 3 phase supply.
« Reply #55 on: August 31, 2016, 09:14:46 pm »
Ok gentlemen (and ladies). I have at last found time from my chauffeuring duties.
Voltages across the three wires. measured singly , haven't got enough clip on test leads at the mo.

Lathe at rest
A-B 438 volts
A-C 450 volts
C-B 437 volts

Motor on low speed, no chuck turning,
A-B 433
A-C 430
C-B 414

Motor on low speed, chuck turning at fastest possible in low speed, 380 rpm (max mechanical load)
A-B 428
A-C 415
C-B 413

Motor attempted start in high speed, but motor never starts.
A-B drop to 370
A-C drop to 320
C-B drop to 360

Looks to my uneducated eye that  ? wire B is the weakling (? generated circuit) and perhaps I should swap B and C ?. ( see Jeroen's post above.).
Of course it's worth a try but the motor rotation will change should it run.
Is your lathes rotation reversed using the motor control or a gearset in the headstock?
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Online Ian.M

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Re: vintage lathe restoration - 3 phase supply.
« Reply #56 on: August 31, 2016, 09:16:13 pm »
If you swap any two wires, it will reverse the motor.   To keep it running the same way you have to rotate the wire sequence. 
e.g. Labeling the wires in lower case and the terminals in upper case, either a=>B
b=>C
c=>A

or
a=>C
b=>A
c=>B
 
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Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #57 on: August 31, 2016, 09:27:35 pm »
The lathe chuck rotation is reversed mechanically by gears in the headstock. Thanks for the tip about reversing the motor and not just swapping.
 

Online edpalmer42

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Re: vintage lathe restoration - 3 phase supply.
« Reply #58 on: August 31, 2016, 09:29:47 pm »
When I look at the picture of the switchgear, I see 4?, 6? relays/contactors.  When you push the slow button, I'd expect one or more of the relays to operate.  What about when you push the fast button?  Any change in the relays?

Any one of the relay or switch contacts could be dirty or have a broken or loose wire.

Ed
 

Online tautech

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Re: vintage lathe restoration - 3 phase supply.
« Reply #59 on: August 31, 2016, 09:31:20 pm »
The lathe chuck rotation is reversed mechanically by gears in the headstock. Thanks for the tip about reversing the motor and not just swapping.
Swap a phase by all means and if it runs you can use the headstock gear set in reverse to run the lathe as normal.
Might be an ugly fix but a fix nonetheless.
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Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #60 on: August 31, 2016, 09:50:20 pm »
Tautech, - I wasn't suggesting Imwas going to swap a pair of phases, it would only give me a limited range of forward speeds, and yes an ugly fix, - just saying thanks as I had forgotten that swapping a pair of wires would reverse the chuck.
Ed- there is no audible action in any switchgear when I hit fast. I have phoned the lathe manufacturer ( Dean Smith and Grace) for the circuit diagram.
 

Offline woodchips

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Re: vintage lathe restoration - 3 phase supply.
« Reply #61 on: August 31, 2016, 09:53:39 pm »
The direction of rotation is an irrelevance at the moment, particularly as it doesn't seem to rotate at all.

Which phase is the one straight from the output of the autotransformer? Looks like AB or BC, but the voltage shouldn't drop that much considering you have the other motor running all the time, it does run all the time?
 

Offline stj

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Re: vintage lathe restoration - 3 phase supply.
« Reply #62 on: September 01, 2016, 01:51:49 am »
thoughts.

why does the motor plate say "BRUSH", does it use brushes?

and this worked at some point, so a wiring fault is unlikely - probably a burned contact or open coil on one of the contactors.
 

Online tautech

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Re: vintage lathe restoration - 3 phase supply.
« Reply #63 on: September 01, 2016, 02:03:47 am »
why does the motor plate say "BRUSH", does it use brushes?
It's a generic motor plate used for most Crompton Houston motors, notice there are NO specs for any brush listed. Some single phase high torque motors used brushes for starting torque the switched to plain induction for run mode.
« Last Edit: September 01, 2016, 02:05:58 am by tautech »
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Online edpalmer42

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Re: vintage lathe restoration - 3 phase supply.
« Reply #64 on: September 01, 2016, 03:01:47 am »
In case you haven't found it, here's a 41 page message thread on DS&G lathes: http://www.practicalmachinist.com/vb/general/dean-smith-grace-lathe-owners-164418/

Ed
 

Online edpalmer42

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Re: vintage lathe restoration - 3 phase supply.
« Reply #65 on: September 01, 2016, 03:07:18 am »
Ed- there is no audible action in any switchgear when I hit fast. I have phoned the lathe manufacturer ( Dean Smith and Grace) for the circuit diagram.

But when the unit isn't running and you hit the fast button there's a *very* audible action.  I'm really suspicious of that switchgear.

Ed
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #66 on: September 01, 2016, 06:10:44 am »
All that very audible action is from the chattering of the rotary converter.
 

Offline eKretz

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Re: vintage lathe restoration - 3 phase supply.
« Reply #67 on: September 01, 2016, 07:22:02 am »
A good installation with a VFD would entail rewiring the lathe.  They're not real happy when you use the machine controls to stop or reverse.  I use a VFD on a shear with good results, but when I use it on a drill press it always faults when using the drillpress on/off controls.

I use a rotary converter on a similar sized lathe and it works fine except for the highest speeds.   It's a 7.5hp converter with a 30A 220 breaker and it will always trip at the top end.  Current draw can get excessive when trying to spin up that much iron.

I'd put a clamp on ammeter and see what the draw is and if that looks reasonable I'd suspect a contactor  or internal wiring problem.

Yes, a machine's original switch gear should never be used to switch the motor when a VFD is installed - all switching should be managed by the VFD. If desiring to use the original switch gear it can be used to control the VFD remotely using low voltage signals. To avoid faults when accelerating or decelerating heavy inertial loads, set the accel/decel ramps so that accel/decel takes a little longer, this gives a soft start/stop effect and removes some of the spike in current. If you need rapid braking you'll have to install a DC load resistor to take the brunt of the load off of the VFD.

In this case, a VFD would be fine. Using one to convert single to 3 phase but not utilizing the frequency adjustment is pretty safe as far as "old motors with poor insulation" go - most of the older motors were built a hell of a lot better than their modern counterparts - especially those from suppliers of reputable companies like DSG. I've seen VFDs installed on hundreds of old machine tools with their original motors (using the frequency adjustment) and nary a problem if the motors are in good shape to begin with.
« Last Edit: September 01, 2016, 04:15:25 pm by eKretz »
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #68 on: September 01, 2016, 02:19:24 pm »
Dean Smith and Grace true to their reputation have come up with the goods. It helps that I live next door  ;) I have attached the circuit diag that is likely the one.
The service manager is in the field but says
- dual wound motor
- Burdon resistors on the high range that could be at fault (don't know how to test the motor or resistors...)
He suggests checking the resistance of each winding and the resistors in the panel.
he also mentioned checking the contacts on the 2R contactor (whats that ?)
Cheers
Nick
 

Offline Andy Watson

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Re: vintage lathe restoration - 3 phase supply.
« Reply #69 on: September 01, 2016, 03:41:47 pm »
Wow! I am amazed that DSG are still alive.

The diagrams shows that all the auxiliary electrics (contactors and lighting etc.) are fed from L1 and L3 - as has already been mentioned, these need to correspond to the phases given in the convertor instructions (L1 and L2 - I think).

What's that pneumatic/hydraulic looking contraption in the bottom right of the control box - is it a mechanical damper operating on the contactor?


he also mentioned checking the contacts on the 2R contactor (whats that ?)
Contactors are multi-way arrangments of contacts that are closed (or opened) simultaneously. In this case the contactors are operated electriccally by a solenoid. There are four lablled LS, HS, m2 and 2R - Low speed, High speed, Motor 2 (coolant motor) and one that removes the resistors from circuit. I am guessing that the last is time delayed such that the motor starts in high speed with the resistors in circuit. Then after a short delay the resistors are shorted-out.
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #70 on: September 01, 2016, 03:59:34 pm »
between the switch and the motor there is another box (see below) that I could possibly measure the resistance of each phase in ?.

 

Online edpalmer42

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Re: vintage lathe restoration - 3 phase supply.
« Reply #71 on: September 01, 2016, 04:12:17 pm »
I just noticed what could be a disconnected wire in the switchgear.  See attached detail from the top left corner of the switchgear photo.
 

Offline Andy Watson

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Re: vintage lathe restoration - 3 phase supply.
« Reply #72 on: September 01, 2016, 04:17:21 pm »
I just noticed what could be a disconnected wire in the switchgear.  See attached detail from the top left corner of the switchgear photo.
I think that is a connection to the bottom of the contactor solenoid - all the other contactors have a similar connection.
 

Offline capnahab

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Re: vintage lathe restoration - 3 phase supply.
« Reply #73 on: September 01, 2016, 05:00:33 pm »
I have rotated the phases
A>B, B>C, C>A and here's the video. Early days but looks successful, the RPC hardly noticed and takes about 10 seconds to get up to 700rpm which isn't bad for a 14 inch chuck weighing about 80 pounds. Its nice to have the circuit diagram. I may need to replace the whole panel eventually. Having said that everything on the lathe is built to last a very long time.

Thanks very much guys for all your interest and help. Really appreciate it as it gave me the confidence to fiddle with the wiring.

https://youtu.be/are3efuZQZk
 

Offline Andy Watson

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Re: vintage lathe restoration - 3 phase supply.
« Reply #74 on: September 01, 2016, 05:08:56 pm »
Great news.

Having said that everything on the lathe is built to last a very long time.

Yes. I am extremely jealous ;)
 


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