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What's all involved in switching machine's input voltage from 480 to 240?

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
I've got a new (to me) surface grinder that was wired for 480V 3 phase at the shop it was in, and I have 208 3 phase (25HP VFD) where I'm at. So I know I have to switch any 3 phase motor's wiring to the proper windings. Also change heaters. Also change transformer taps so low voltage is correct. Anything else? Want to make sure I don't miss anything.
 
For any auxiliary motors, pumps and the like, they may or may not be set up to switch voltages. Seems as if they were "cheap" and in some cases might have been supplied to fit whatever voltage configuration the machine was shipped as.
 
So since you are very vague about what you really have, converting a Kikinda, Elb, Okamoto or similar with hydraulics, integrated position control or magnet control is going to be waaay more complex than a 6X12 Boyer Schultz with a simple switch for on and off.


Bill
 
Yeah it's definitely on the complex end of the spectrum. I figured the low voltage stuff would all be handled by that particular transformer. There is one that looks like it's specifically for the controls, 120 in and taps for 10 and 30 out.

The grinder is a Brown & Sharpe 818 Micromaster with the Dial-a-Size option. You enter parameters for rapid approach height, coarse grind downfeed rate (.0001" - .0099" range), point that the grinder switches to fine feed and fine downfeed rate (.0001" - .0009" range). Then how many spark out passes you want. When it's done it will retract the head and park the table for loading/unloading. Table is hydraulic, head is controlled by a stepper.

I've only looked at the main spindle motor so far but it has windings for both high and low voltage. I think the hydraulic pump motor will too.

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I can't add anything on your wiring dilemma, but that is one heck of a nice grinder...does it make espresso too?

PS. Don't forget to verify hydraulic motor/pump proper rotation.

Stuart
 
So my advice to you is:
If you are really using a Variable Frequency Drive (VFD) to generate the 3 phase.
Power only the 3 phase motors from the VFD.
Split off ALL single phase loads and power from real power company single phase.
Faithfully follow each 3 phase wire from disconnect to the motors and unhook any noise filters, spark killers etc.
These devices will be overloaded and burn up (think smoke and fire here) when connected to VFD power.

Otherwise if you really mean Rotary Phase Converter (RPC).
All single phase loads must be powered from the power company phases.


Don't forget the coolant pump motor.

Hope this helps,
Bill
 
Yes, a 25 HP rated VFD. It is running from single phase though so it's derated to about 13 HP. I was thinking a bit about going that route with the single phase anyway. When you say noise filters are you referring to ferrite beads? And I'm not familiar with "spark killers," can you elaborate?

Edit: looks like capacitors to prevent arcing when switches are activated. I will have to check into that. Can you explain why there would be a problem with these running from a VFD? Something to do with the carrier frequency perhaps?

I'm thinking of running the spindle itself from a separate 3 HP VFD for RPM control and soft start.
 
The picture of the enclosure shows all kinds of mags and transformers and what have you. Sticking a frequency drive on will require some fairly extensive modifications in there. It would almost seem a RPC would be a much better choice as the only thing to be changed might be heaters, coils and xformer primary connections..maybe a tad easier but maybe not.

There is a lot of stuff crammed into that enclosure.

Stuart
 
Yes, it is absolutely crammed. I was going through search looking for a basic ops manual for this grinder and found someone asking why the electrical box was so big...and empty on a regular version Micromaster. Apparently the Dial-a-Size option is why!

I think much or all of the control stuff is run from that one transformer that takes 115 in and spits out 10 and 30, so running that from the utility single phase instead of a leg from the VFD should take care of most of the circuit board stuff.
 
The 3 phase spark killer is one of these: (click to enlarge)

3 phase spark killer.jpg

The RC network is not made to handle high wattage noise.
The output of the VFD is a PWM of the carrier frequency to simulate a sine wave of current.
Thus the high voltage transitions of the PWM appear as noise to snub, and will overload the resistors in the device, resulting in smoke and or fire.

Bill
 
I have run a VFD into a transformer before . . . i.e. 480V 3-phase VFD output into a 480:4160 V transformer to get the conductor size down and get power to ground and then back through a 4160:480 transformer to get back to 480V. (crazy application where we had an aerial wind turbine in a helium tube with 3 light weight tethers to ground each at 4160) . . . Airborne wind turbines: Meet the BAT - CNN

At any rate this got to us experimenting with running odd voltage generators from different VFD power sources with a transformer between them to get the current levels under control. Wound up trying this with a low voltage high pole count generator in a sub sea tidal turbine and it worked great to current match the inverter.

Soooo you might try just leaving your grinder at 480V and then getting a 208V:480V transformer and connect the VFD to the 208V leads and the grinder to the 480V leads. A sine filter on the VFD output might be nice but your cables would be so short you probable wouldn't need it. We were running cables as long as 5000 ft and the sine wave filter was a requirement for those cable lengths.
 
...

Soooo you might try just leaving your grinder at 480V and then getting a 208V:480V transformer and................

Really.are you serous???? This is an easy peasy rewire and could do such in my sleep.
Resizing the heaters and fuses is the biggest pain.
The machine was designed to run off of both voltages.
If you do not have a schematic or wiring digram, draw one.
Bob
 
Really.are you serous???? This is an easy peasy rewire and could do such in my sleep.
Resizing the heaters and fuses is the biggest pain.
The machine was designed to run off of both voltages.
If you do not have a schematic or wiring digram, draw one.
Bob

If the starter contactors are rated for the current, yes, likely all you have to do is change taps in the motor, upsize fuses and heaters and go.

We have lots of transformers in our test inventory . . . so we don't think this is really out of the question. And transformers like this are not uncommon - here is one for $200 Used Eaglerise Transformer | HGR Industrial Surplus
 
Yeah the motors are no problem. Reconfiguring the wires and changing heaters/fuses is pretty simple. I've now checked all three motors (spindle motor, hydraulic and coolant pumps) and they are all configurable for lower voltage. The starters should be good to go, they are rated for 5 HP at 460, 3 HP at 230. My biggest motor is the spindle at 2 HP. As far as running the low voltage stuff, consensus seems to be that it would be best to just disconnect the input to the transformers and run the 120V into them from the wall, correct?
 
..., consensus seems to be that it would be best to just disconnect the input to the transformers and run the 120V into them from the wall, correct?

The transformer input is not configurable for both 220 and 440 where the 120 is made? That would be weird for a B&S machine.
I would not pull 120 from the wall unless a very last recourse. Here I would put in a new control transformer if needed.
Never good to have multiple power input lines let alone 3-phase and normal wall plugs. Sometimes they don't agree on what ground is.
Old controls of this age will not like ground loops at all it takes is that one green wire buried somewhere to change from isolated to linked.
Plus you really do want one big red disconnect to hit if things go wrong for lord knows why.

I have never seen this machine. It that a Slo-Syn (Superior Electric) stepper card rack? What year is it?

At the price for used the X-former shown by motion makes a lot of sense rather than rewiring.
Will this do 240/480 as a 208? Others in stock at the Huge Giant Rat seem a bit higher price tag?
Put a disconnect in front of it also unless you need a good coffee warmer.
Bob
 
Well it has been mentioned that running the controls from 120 made from a VFD would be bad ju-ju and that is my only option at the moment. That's why I was asking if that's a real big concern and thinking about running low voltage from the wall. No 3-phase where it's at. And yes, was planning on a disconnect.

I'm not sure what year it is, is there a serial lookup somewhere? I am not sure what the card rack is, will check it next time I'm in front of the machine.
 
As far as running the low voltage stuff, consensus seems to be that it would be best to just disconnect the input to the transformers and run the 120V into them from the wall, correct?
That would not be my consensus. I'm with the Bob on this one, separate feeds to a machine are not good.

Seems like (I sound like PeteM now) the problem - if there is one - is the solid state three-phase. Ditch the fucking thing. It's easy to buld a rotary, do it once and never have to think about that square-wave crap again. Electronics suck.

If you turn this into an abortion, then in six months you do another machine, then in a year you get a chance to move to a great place with real three-phase, you have to undo the whole mess. And/or selling it is going to be a project. Bah. The machine was built for decent electricity. Supply same. Big bubbles, no troubles.
 
Easy, 3 things to do: rewire motor(s), change heaters or overloads, rewire control transformer for new input power, you should also verify the wiring can handle the new additional amp load.
I would not use multiple power sources to run any machine. You or someone else will turn off the main power to work on it and get electrocuted by the other power source that by all rights should not be there.
 








 
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