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480v 3ph in the home shop

austin136

Plastic
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Jun 26, 2015
So Im in Winchester va and just bought a 480v 3ph cnc mill assuming i could switch it to 240v got it home and in the shop late last night and discovered its 35A 480v only. i currently have a north american 30hp rotary phase converter that runs all my other equipment. Can i use a transformer between the the rotary phase converter and the cnc machine? and if so what size do i need? or is there a better way to accomplish this?

Thank you all for the help.
 
its a deckel style cnc mill sold by summit machine tool all of the electronics on it are seimens and its a sinumerik 802d control
 
I think a step-up transformer is the best option without modifying the machine, but they typically can be expensive. Size is in voltamps and will depend on the voltage and watts/amps that the machine is using. Google "volt amp calculator" to convert your machines data into what size trans you will need.
 
So Im in Winchester va and just bought a 480v 3ph cnc mill assuming i could switch it to 240v got it home and in the shop late last night and discovered its 35A 480v only. i currently have a north american 30hp rotary phase converter that runs all my other equipment. Can i use a transformer between the the rotary phase converter and the cnc machine? and if so what size do i need? or is there a better way to accomplish this?

Thank you all for the help.

I would recommend a step-up transformer. I have a Deckel mill that is setup for 400V, and am using a 3-phase 230V to 400V step-up transformer, and it is working just fine.
 
Will the RPC have enough amps to provide the 35 @ 480? I think North Am Rotary sizes their units by total hp that can be run assuming an easy start. That would leave you undersized unless the output amperage is in the 70+ range @ 240. I'm often wrong though. Dave
 
X 1.73 for 3 phase so 30 kva That 30 hp rotary converter is a tad small for this but I am no RPC expert..........

Does the mill have that much H.P. ?

And will the OP max it out with every cut ?

Not like this in an air compressor.
 
35 amps times 480 is 17 kva. I would go with at least 20 kva or even 25 kva.

Tom

Standard 3 phase transformer sizes are 20, 25, then 30kVA. I would go with 30kVA to avoid a voltage drop when trying to start it; you typically want your kVA to be 2-2.5x the load for AC motors starting across-the-line. 25kVA might work too if there is no load on it, but I think 20kVA would be too small. The voltage might drop enough to where you lose the control power and it never works.

You only want to buy the transformer once...

Re: VFD; you would STILL need a transformer to step up the 240V to 480V, and it (and the VFD) would need to be bigger to handle the single phase current. He said he already has the RPC.
 
Does the machine have a variable speed spindle motor? (Either AC motor and VFD or DC motor and SCR drive.)
If so, you don't have to worry so much about the inrush from across-the-line starting the spindle. The VFD can give you a soft start.
Could be the biggest motor you'll have to start across-the-line is a coolant pump or something like that. So your RPC should be able to handle it.

Depending on how hard you are going to push the machine you could probably get away with a 20kVA transformer. But a 30kVA is the proper match to the 35A input rating.

I have no clue what that would cost new. HGR surplus in Cleveland OH usually has a good selection of transformers. This $400 one would do you nicely. https://hgrinc.com/productDetail/Electrical/Used-Square-D-Transformer/04201700010/

Of course shipping 375 lbs to Virginia will add a bit to the cost.
 
Im uncertain why the manufacture claims it needs 35 amps i don't see what could draw that much power on this machine but it dose have 3x 35 amp fuses in it as well. by my math the spindle motor is 16A?

i will also say im a little confused about witch of these drives in the picture are for what. and i guess i should also add it also has a 4th axis as a cnc rotary table

IMG_1706.jpgIMG_1708.jpg2182309_11703_19801_0001 - Copy.jpg2182309_11703_19781_0001 - Copy.jpgIMG_1704.jpg
 
Im uncertain why the manufacture claims it needs 35 amps ...
35 amps at 480 ? That's like 70 amps at 240, it does seem a little excessive !

Also, being from Germany, it's probably intended to run at 380v 50hz. It's probably already been modified to run at 480 ... you might want to do a little more looking internally before jumping to the "add another conversion" method.
 
The only transformers i see are real small for accessories. it looks like it would run anywhere from 380 to 480 with the drives in it.
 
......

Also, being from Germany, it's probably intended to run at 380v 50hz. It's probably already been modified to run at 480 ... you might want to do a little more looking internally before jumping to the "add another conversion" method.

Motors shouldn't need any "conversion", 380 at 50 Hz is the same as 460 at 60 Hz, in terms of Volts/Hz.
 
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You have a Sinamics S120 16kW SLM on the front of your servo system - and your largest motor load is 13A 3-phase (spindle) and your axis motors (assuming they are all the same) are 4.5A continuous . . . assuming that you are pulling continuous current from all of them simultaneously you have 13A + 4x4.5A = 31Amps (I see what looks like 4 motor leads going to the pair of double motor modules).

Looking at your line up you have a 16kW Smart Line Module (SLM) on the left - this is a bi-directional power supply that you feed with 3-phase and it develops DC power for all of the drives. The DC bus passes from left to right under the light blue covers running along the top.

Next module to the right is your spindle drive . . . a SMM (Single Motor Module)
Next module to the right after the spindle is a DMM (Double Motor Module) which could be X and Y
Next module to the right after the DMM which likely is Z + a rotary axis?

The Smart Line Module (SLM) is line regenerative, i.e. if you are stopping your spindle and all your axes simultaneously, all of the braking energy from decelerating the motors pumps up the DC bus . . . when the DC bus gets sufficiently high the drive front end is an inverter that pumps that energy back onto the line and feeds power back to the utility. Thus, this system does not require braking resistors.

Realistically, you can likely get away with 25 Amps for the drive system. I don't know what else you have for loads (coolant pump? control power transformer?).

I wouldn't attempt to run this with a VFD unless you like smoke and fireworks.

FWIW, I have run that model of 16kW Smart Line Module from 240V three phase with no difficulties - but that will limit how much power you can pull off the DC bus and your maximum speeds on your servo motors will be limited as well. Typically your system would also have a SITOP 24V power supply that may also tolerate operation at 240V, you should double check this . . . so if you can live with less than rated power, then run it at 240V. You "may" need to adjust a low voltage threshold on your controller . . . the voltage thresholds are adjustable with the Sinumerik controller. But you will need to know the password which is well known if left at the standard Siemens default but who knows if the OEM has altered it.

If it truly is a 3-Axis system + spindle you would likely be fine at 20Amps @ 480V using a 240:480 transformer. If you can find a transformer with adjustable taps, this would help with balancing the voltages which would make the regenerative front end on your drive system much happier.
 
What was the final on this? I'm looking at having to do something like this - I need 480V for a Autometric Model B I'm installing in my "home" shop. It's 480V and has about 3 pairs of contactors so it looks like rewiring the motors and replacing the contactors is likely to be the same cost as building a 480V supply through a RPC and step-up transformer.
 








 
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