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Lathe Wiring

Tom Kitta said:
I have actually few few machines that run 240 -> 120v transformer - I even use two such transformers to power a lamp.
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This is atypical. Most people wire 4 wires for 240.120V - transformers large enough (in history 200VA or better) normally aren't part of a normal installation, in my experience...
PaulL said:
Don't put a 3HP motor on a cheap 3HP VFD.
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This.
YotaBota said:
For my lathe I went the TECO route as well, 2hp VFD on a 1.5hp motor, luv it.
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I installed a TECO 2HP for 2HP mill and Surface grinder - both are low load machines, even on startup. On higher load machines, such as a lathe, I'd be careful using a 2HP on a 2HP machine. It isn't much more money, even on a TECO, to get some extra capacity.
 
Dabbler said:
This is atypical. Most people wire 4 wires for 240.120V - transformers large enough (in history 200VA or better) normally aren't part of a normal installation, in my experience...
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I actually have almost no 1ph machines, certainly no large machines other then the compressor - all are 3ph so 3 wires + 1 ground. Almost all these machines have transformers for control voltage, either 120v or 24v. Usually the transformer is large - 100Va or bigger. Most transformers have more then one tap, some have three - 240, 480, 600.
It feels smaller 3ph machines try to avoid transformers - like say pedestal grinders or two small drill presses I now have.
 
Blue Wall said:
It has a 1.5 hp...what would be a big enough motor....
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2Hp or even 2.5Hp is plenty on a lathe that originally had a 1.5 HP motor. Just make sure you set a suitable spin up time on your VFD so the bigger motor spins up slower than it could if left to its own. This will make sure the gears and bearings in your lathe are not overly stressed.

I plan to measure my existing spinup time and then set my VFD to spin up a wee bit slower than that.
 
Tom Kitta said:
I actually have almost no 1ph machines, certainly no large machines other then the compressor - all are 3ph so 3 wires + 1 ground. Almost all these machines have transformers for control voltage, either 120v or 24v. Usually the transformer is large - 100Va or bigger. Most transformers have more then one tap, some have three - 240, 480, 600.
It feels smaller 3ph machines try to avoid transformers - like say pedestal grinders or two small drill presses I now have.
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It should be noted that there are two different standard wiring layouts for 3 phase - Y and delta. Y has 4 conductors plus a ground. Delta has 3 conductors plus a ground. In the Y configuration, in theory, the central neutral carries no current. In practice it has to be double sized because it carries transient currents causes by imbalanced loading in the phase circuits. Delta wiring is more common especially for longer distances
 
mbond said:
It should be noted that there are two different standard wiring layouts for 3 phase - Y and delta. Y has 4 conductors plus a ground. Delta has 3 conductors plus a ground. In the Y configuration, in theory, the central neutral carries no current. In practice it has to be double sized because it carries transient currents causes by imbalanced loading in the phase circuits. Delta wiring is more common especially for longer distances
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I'd like to add that the vast majority of motors you will see* are delta wound.

My first 3PH wiring job (45+ years ago) was to fix a rotary phase converter installation. The licensed, bonded, 'master' electrician had wired it up so when the lathe was turned on 2 of the 3 power capacitors blew up, or rather burst, and the third was overheated. Knowing the difference between delta and Y configurations was the key to fixing it.

* except for 208V 3PH - I've seen a few in my time...
 
Dabbler said:
I'd like to add that the vast majority of motors you will see* are delta wound.

My first 3PH wiring job (45+ years ago) was to fix a rotary phase converter installation. The licensed, bonded, 'master' electrician had wired it up so when the lathe was turned on 2 of the 3 power capacitors blew up, or rather burst, and the third was overheated. Knowing the difference between delta and Y configurations was the key to fixing it.

* except for 208V 3PH - I've seen a few in my time...
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I have not seen a 3ph Y wound motor in over 50 years.

To be fair, I guess I should say that if I did see one, I didn't know it..... LOL!
 
The primary advantage of the Y connection scheme is if your primary load is on the 'side' voltage phases. If all three phases work together on the same machine, then delta is the obvious choice.

So in a 120/208 system, if the load is all 120, then Y wiring makes sense. Same in a 347/600 system and higher voltages. But other than a 120/208, the phase to ground loads all fall away in significance i think
 
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