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Monarch 120/240 transformer

rimcanyon

Diamond
Joined
Sep 28, 2002
Location
Salinas, CA USA
I need 120v to power the machine light and the DRO on the 49 10EE. The LED machine light is rated 14W and the DRO is not rated, but the small power supply says .5A max. I have a Monarch 120/240 control transformer from a 57 10EE (the one that is normally mounted inside the motor compartment, not the one that is in the compartment with the main contactor.

So I assume the Monarch transformer is adequate. It is rated .15KVA, which is 120W capacity. Any opinions?

I also plan to run the wiring through the same hole under the headstock that is used for the wires that go from the contactor to the reversing switch and on/off switch. Is there room for another pair of wires through there?
 

matt_isserstedt

Diamond
Joined
Dec 15, 2003
Location
suburbs of Ann Arbor, MI, USA
I think completely reasonable/comfortable to use a 150va transformer for that purpose.

I can speak to the wiring but there's always room for "one more" :) The THHN is pretty tough stuff if you can fish it, although the bigger concern might be contact or friction with wires that are on the order of ~70yo...
 

Cal Haines

Diamond
Joined
Sep 19, 2002
Location
Tucson, AZ
How many wires you can put into a conduit isn't a simple function of what will physically fit. You also need to take into account how much current is being carried by the wires and if they have enough space to dissipate heat. There are tables in the National Electric Code and elsewhere that list the percentage of the conduit that can be safely filled.

Cal
 

rimcanyon

Diamond
Joined
Sep 28, 2002
Location
Salinas, CA USA
The wires from the rotary switch compartment on the back of the headstock go to the main contactor compartment via a channel on the bottom of the headstock. It turns out there was plenty of room to run both the cord from the light and the low voltage wire for the DRO. Tomorrow I will mount the DRO power supply on the back of the contactor compartment, so all the wiring will be hidden except a few inches where it comes out and goes into the light and DRO. Will post photos once it is finished.

Matt, thanks for the affirmation. I installed the transformer in the motor compartment, and there was an unused opening on the bottom side of the contactor compartment into the main motor compartment, with ½ npt threads, so the conduit connected right up.
 

rimcanyon

Diamond
Joined
Sep 28, 2002
Location
Salinas, CA USA
I added the transformer and it is powering the machine light and dro just fine. However, the DRO has a lot of instability in the display. The transformer secondary is floating currently, should I strap one secondary leg down, make it common with one of the 220V primary legs?
 

thermite

Diamond
I added the transformer and it is powering the machine light and dro just fine. However, the DRO has a lot of instability in the display. The transformer secondary is floating currently, should I strap one secondary leg down, make it common with one of the 220V primary legs?

I would not.

But I have "Corcom style" EMI/RFI filters in the Hell box I might add.

NB: A(ny) DRO SHOULD have.. a VERY well-armoured PSU and all-else anyway.

Industrial environments are legendary hostile to sensitive 'tronics goods.

I used to wave a stout corded variable-speed drill motor all around the stuff I built, running the primitive SCR trigger through the range as a poor-boy test of the goods. And those were for white-collar office machines, not shop floor atall.

Have an O'scope? What's it finding, and where?

And if it is not NEW, you might have a look at the DRO, I/O, bonding and grounding as well as power?

It shouldn't do this .... even if the power is downright nasty.
 

rabler

Cast Iron
Joined
May 25, 2020
Location
Rural S.W. Indiana
I added the transformer and it is powering the machine light and dro just fine. However, the DRO has a lot of instability in the display. The transformer secondary is floating currently, should I strap one secondary leg down, make it common with one of the 220V primary legs?

I’d try shielding the wires from the transformer output to the light and dro. Ground the shield at one point only. A common mode choke may be another thing to try.

The only real hazard I see of strapping one leg is getting the wrong leg could put your 120V at 220V relative to ground. Not sure the dro would like that? You could temporarily pull a neutral off something and safely strap one leg to that as a test. Pick the leg that goes to the conventional neutral on your dro.
 

rimcanyon

Diamond
Joined
Sep 28, 2002
Location
Salinas, CA USA
I’d try shielding the wires from the transformer output to the light and dro. Ground the shield at one point only. A common mode choke may be another thing to try.

The only real hazard I see of strapping one leg is getting the wrong leg could put your 120V at 220V relative to ground. Not sure the dro would like that? You could temporarily pull a neutral off something and safely strap one leg to that as a test. Pick the leg that goes to the conventional neutral on your dro.

There is no neutral on the machine. It has 3-phase and ground. The transformer is connected between the two leads from the utility company, not the generated leg.

The instructions for the DRO say “It is recommended that the unit’s case is grounded to the machine. Use a wire … from the cabinet equipotential terminal (refer to manual) to a suitable point on the machine body.

Damn Brits, wish they would speak English. Worse than Thermite.

So before I hook ground to the machine, I thought that it might be necessary to tie primary and secondary circuits, so that the ground actually has a relationship to the secondary circuit.
 

thermite

Diamond
There is no neutral on the machine. It has 3-phase and ground. The transformer is connected between the two leads from the utility company, not the generated leg.

The instructions for the DRO say “It is recommended that the unit’s case is grounded to the machine. Use a wire … from the cabinet equipotential terminal (refer to manual) to a suitable point on the machine body.

Damn Brits, wish they would speak English. Worse than Thermite.

So before I hook ground to the machine, I thought that it might be necessary to tie primary and secondary circuits, so that the ground actually has a relationship to the secondary circuit.

Minds me.. my UK Passport needs renewed.

:)

Floating secondaries INSIDE a system are more often a beneficial feature than a detrimental bug. We call that "isolation" transformer configuration with good reason.

"Ordinarily" there should be no need to do more than give the DEVICE the ground it asked for..

The circuitry THEY have already built into should put it to good use for the needs OF said device. "DRO" in this case.

Try it.

"PE" AKA "Protective Earth" is also a good "Signal" ground for this where used as "Frame" ground.
 

rabler

Cast Iron
Joined
May 25, 2020
Location
Rural S.W. Indiana
There is no neutral on the machine. It has 3-phase and ground. The transformer is connected between the two leads from the utility company, not the generated leg.

The instructions for the DRO say “It is recommended that the unit’s case is grounded to the machine. Use a wire … from the cabinet equipotential terminal (refer to manual) to a suitable point on the machine body.

Damn Brits, wish they would speak English. Worse than Thermite.

So before I hook ground to the machine, I thought that it might be necessary to tie primary and secondary circuits, so that the ground actually has a relationship to the secondary circuit.

Definitely try grounding it.

Beyond that, you are dealing with electrical noise. Electrical noise is a bit of a black art. Even amongst electrical engineers. But basic principles aren't too complicated. The general approach is 1) find the source of the noise, 2) find the path of the noise to the problematic location (DRO). 3) Mitigate either 1) or 2).

DROs use a high gain amp on the wires to the scales. This is the noise sensitive part of the DRO that will result in a flickering display, if everything else is behaving.

Noise can get into the DRO via any wire, as any wire acts as an antenna to some extent. Or it can come in through other things connected to the power source. Power supply wires, or scale wires. Scale wires are normally inside a metallic sheath of some sort, which acts as a shield to keep noise out of those wires. And there is no other electronics connected to the scale wires, so nothing else there to create noise. So in your case the power line wires are suspect. The fact that the transformer output floats does increase the noise sensitivity, as there is not a low impedance high frequency path to ground through the transformer. In other words, floating makes it a better antenna. But it does not cause the noise.

I understand that the lathe is powered via 3-phase w/o 120V. I would assume you have 120V somewhere in the building. I'd connect the DRO to 120V with the lathe otherwise powered off first, to be sure that the problem goes away. Hack up and extension cord or whatever. Just to confirm assumptions that electrical noise from the lathe's internal guts is the issue, diagnostic only.

Then with the same extension cord/hack in use, turn the lathe on and see if the problem occurs or doesn't occur. If it does occur, you rule out the transformer as the path of noise. If it doesn't, then the transformer is part of the noise path, although very unlikely the source.

You could even go as far as disconnecting the wires from the transformer output and splicing that to the extension cord as a 2nd step to test the noise source and path.

That's the systematic way to proceed. The shotgun approach is to put some ferrite beads/choke on the power supply line going into the DRO to try to reduce suspect noise.
 








 
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