Trying to figure out wiring for my DIY CNC - toroidal transformer to 2 phase 240V

[rickjohnston]

Hello all,

This is my first post here, so please bear with me if I don't know all the lingo yet. I have been a hobbyist machinist for quite some time, and have an old geared bench mill and a lathe that was made in the early 1900's (Seneca Falls) that have both served me well, but I have wanted to build a CNC mill for quite some time now and I finally pulled the trigger.

My current hang-up is trying to find a way to build the basic power structure for my machine. I will be using a 240V 2.2KW spindle, so I am trying to stay with using a single power plug for the machine if possible. That is what has lead to my current dillema. After scouring the web for a week now trying to get a handle on how to wire this up, I have discovered that I really understand less than I need to to get this rolling.

I think the crux of my issue is trying to wire a dual primary toroidal transformer to a 2 phase (US not European) 240VAC supply. I "THINK" I have everything else mostly squared away, but I don't have confidence that I have the primary side hookup right?

I have attached my wiring schematic in PDF format for review if anyone is willing to take a look?

The transformer is a Hammond 1182T60P. The specifications can be found here:
http://www.farnell.com/datasheets/22...902.1508184824

page 3 about 1/2 way down:
dual primaries 240/120
dual secondaries 120/60 @ 25A

Thank you all for the help, and I look forward to more questions to come

Rick johnston
Cedar Ridge, CA

Edit: do not use the attached diagram, it has been updated...see later posts

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[ger21]

The white wire from the outlet is not ground, it's neutral, and is not used for 240V. Ground is the bare copper wire.

I **think** that you just tie the white and brown on the transformer together so they are in series, but get confirmation from someone more knowledgeable than me. But that's how my Antek supply is wired.

[rickjohnston]

Gerry, thanks for the reply!

That's what I thought at first as well. This may be a case of over thinking things on my end, but after pouring over forums and wiring schematics trying to get to the bottom of this, I "THINK" that the 240V wiring diagrams are for our European cousins (and other places that use 240V)? As I understand it, they have a dedicated 240VAC lead, a Neutral and a Ground. So that works as show in most dual primary wiring diagrams.

I am using a US standard 240V dual pole breaker (20A) that provides 2 120VAC lines, a Neutral (as you pointed out) and a ground (bare copper). If I hook each positive line to the input side (in series) as the common wiring diagrams show, there is no ground for any electrons to flow to? I'm not sure how this could work?

Thanks again,
Rick

[ger21]

Power never flows through the ground, unless there's a short.
I'm not qualified to explain it, but for 240V in the US, it's just the two hot wires. The ground is for safety. It's should be connected to your cabinet, but I don't think that there's any ground connection to the transformer.

[Jim Dawson]

Just wire it with 240 volts (220 is European voltage, and has a neutral as one leg). In the U.S.A think of the 2 hot wires as L(ine)1 and L(ine)2, many times colored red and black. In the U.S.A, Canada, and Mexico the Neutral is defined as a grounded current carrying conductor, is normally white, and derived from the center tap on the pole transformer, and is normally grounded at the pole. Not used in a 240 volt circuit. Ground is just that, a conductor that goes to an Earth ground and is a safety conductor.

If the diagram shows 220 and a NUT or something like that, then read that as L1 and L2 for use in the U.S.A.

2 Phase power only exists in some limited areas on the east coast, around Pittsburg, Pa, and is a 4 wire system. What you are calling 2 phase is actually single phase.

It can all be a bit confusing when first getting started.

[rickjohnston]

Gerry,
Thanks again for the reply!

I have revised and re-attached the diagram. I think I have it wired now as you suggested? Unless I hear otherwise I will use this wiring scheme.

Rick

Edit: do not use the attached diagram, it has been updated...see later posts

[rickjohnston]

Thank you for explaining that Jim! It makes much more sense to me now. I have revised the diagram in the post below.

Thanks again,

Rick

[Jim Dawson]

In the last diagram above, remove the neutral completely and connect the ground wire to the GND terminal and you should be good to go. And don't forget the ground to the spindle motor.

[rickjohnston]

Jim, in the case of the spindle motor, I believe the neutral is needed? I base that on this video on wiring the spindle and driver I intend to use. It could explain part of my confusion as well

You can skip ahead to about 4:40


It shows connecting the 240VAC neutral(wht) to the driver, and the ground(copper) to the chassis. And the spindle motor has no ground. I just want to make SURE I have this right, smoke is bad...



Thanks,
Rick

[Jim Dawson]

The guy in the video is incorrect. The neutral should not be connected to the GND or E terminal. The ground wire should be connected there. The neutral should not be used at all in the VFD circuit. Having said that, the Neutral and the Ground wires do connect together somewhere back up the line. In older systems it could be at the breaker panel, or in newer systems may be at the power pole or service entrance depending on local codes.

Bring all grounds back to a single point in your panel to help prevent ground loops. If your spindle connector is a 3 pin connector, run a 4 wire cable to the spindle and connect the green wire to a screw or something. The spindle must be grounded. If the spindle connector is a 4 pin, confirm which pin is the ground by checking the resistance to the motor case. The ohms to case should be near 0

[rickjohnston]

Jim, thanks again. I can confirm that the neutral and ground are tied together at the panel.

I have finished rev 3.0 (third times a charm right?) Please see attached.

So grateful for the help!

Rick

[Jim Dawson]

That looks much better.

I'm happy to help out where I can. I'm an old retired guy that has been doing this stuff for about 50 years. Time to pass on knowledge where I can.

[ericks]

In some cases you would connect the neutral to the vsd....

......in your case Jim gave you the correct advise

[ger21]

You never use the neutral in the US for a 240V application.

[ericks]

You never use the neutral in the US for a 240V application.

I know that, i did not refer to the US....thought i'd mention it cause there are guys from all over the world here

[Al_The_Man]

Yes the confusion usually arises when Off shore in particular equipment mark some equipment L & N for 240v as places like Australia and UK etc, use one phase (230v) of a 400v 3ph star secondary transformer with a star point (grounded) neutral.
In N.A. as stated, the 240v is derived from a centre tapped 1ph transformer with the centre tap being the grounded neutral (120-0-120).
Can get a little confusing.
Al.

[rickjohnston]

I figured I should see this through to the end so that future builders might find use in this post.

Attached is the final wiring diagram. I added a DC power supply to the circuit to power the breakout board, sensors, etc...
You may need to source a different 240VAC to DC power supply to suit your specific needs.

If anyone sees any mistakes please let me know and I will update this file.

Thanks again to everyone for your help.

Rick

[ericks]

Thanks for sharing...

[Al_The_Man]

I would indicate the Earth GND's connected in the star point method.
Also just as a point of interest, if 120v is derived by way of a 240v/120v transformer for other N.A. based equipment used in the system, it is permitted to connect one secondary to the main service GND and declare this a neutral to re-establish a grounded neutral.
Al.