Roatary Phase converter ??

[newbury]

Another reason for a VFD! Takes up hardly any room, and can be mounted on the wall or the machine.

Also with a VFD you won't be as tempted to buy more inexpensive 3 phase equipment.

 

[muddstopper]

Muddstopper, what are the three motors you need to drive on your mill? Obviously you have your spindle motor and probably a coolant motor, but the 3rd one is maybe a table drive? Reason I'm asking is you might want to look into a VFD. I use them on both my lathes but I only drive the spindle motor and don't use the coolant motors (removed them). For what I use them for, I can just manually apply coolant. I know a lot of hobbyists use the TECO brand VFD's because of the price and they are very happy with them.

I have never used and dont know anything about how a VFD works so I did the google thing to find out a little more about it. Just reading and with no experience with a VFD at all, here is what I have sort of learned. First off, they are one machine specific. Meaning if in the future I wish to add another 3phase machine in my shop, I would have to buy another VFD to power it. Second, for any motor over 3-5 hp, the motor must be derated or the VFD upsized by a factor of 1.73 -2 times the size of the motor wishing to run. Third thing I have learned is that VFD's are not cheap, to run my 5hp 3phase mill, I would need a 10hp VFD and it cost over $900. Yea there are a lot cheaper VFD's, but they are for smaller 3phase motors. The mill has three motors on it, pump, spindle and table, Does that mean I need a VFD to power each individual motor???? Not sure how that works. and I am not even sure every motor is three phase, could be pulling 110v off one leg of the 3phase for all I know. I am already thinking about buying another lathe, doing so would mean another VFD and depending on the size of the lathe another $900. A few minutes worth of searching doesnt make me and expert on VFD's, so someone will have to clue me in to what I am missing.

Edited to add, after a little more searching I have found 10hp VFD's for around $360, which makes large ones a little more affordable, but if I still have to spend that kind of money eveytime I add a piece of equipment, is it really going to be cheaper than just building a RPC

 

[BukitCase]

Agvg - "But do they not build 3 phase in new areas? must give a very heavy load on that singel phase that feeds an area? "

Transmission to local areas uses 3 phase, then individual transformers at each house (up to 2 or 3 houses) - these transformers use ONE of the three phases and ground for primary windings, which are properly ratioed (wound) so their secondary windings provide 2 outputs - those outputs are each 120 volts relative to earth ground, but are 180 deg. out of phase with each other -

That way either output to ground gives 120 volts rms but using BOTH legs of that feed gives 240 volts rms.

Neutral (needed for return in 120 VAC circuits) is achieved using a SEPARATE line that ties to earth ground - this lets 120 VAC outlets have a separate earth SAFETY ground which draws ZERO current during normal use, and the "neutral" leg, which (in normal operation) has the same current flowing as the "hot" wire, in order to complete the circuit.

For 240 volt use, older circuits did NOT use a "neutral" but only two 120 VAC "hot" wires (240 VAC across them because they're 180 deg. out of phase) and a SAFETY ground, which shouldn't draw ANY current -

Newer devices that need 240 volts often have electronics that want 120 VAC - these get a 4-wire plug. This plug has both 120 VAC "phases" to get 240 VAC, the SAFETY ground, AND a NEUTRAL - that NEUTRAL wire is used for a RETURN line for any 120 VAC circuits in the device being powered, and will have the same current flowing as whichever "leg" of the connection is supplying the 120 VAC portion of the device, PLUS the current that is being drawn for the 240 VAC portion of the device -

Typically this results in one leg of a 240 VAC circuit (clothes dryer, water heater, cooking stove, etc)drawing maybe 1 or 2 amps more than the other leg.

Typical semi-local transmission comes in on 3-phase, 10,000 volt lines, and overall load is balanced by using a different phase of that 10KVAC for each successive "customer" - individual transformers then step their SINGLE phase down to 240 VAC - That secondary winding is center-tapped, the center tap is GROUNDED, so you get two "out of phase" 120 volt feeds.

So YES, 3-phase is available in pretty much ALL areas - but power companies don't do anything for free, and transformers and wire aren't free either - so it's rare and expensive to find 3-phase power (to an end-user) anywhere but a farm or industrial site here.

Clear as mud??!? ... Steve

 

[kennyd]

I have never used and dont know anything about how a VFD works so I did the google thing to find out a little more about it. Just reading and with no experience with a VFD at all, here is what I have sort of learned. First off, they are one machine specific. Meaning if in the future I wish to add another 3phase machine in my shop, I would have to buy another VFD to power it. Second, for any motor over 3-5 hp, the motor must be derated or the VFD upsized by a factor of 1.73 -2 times the size of the motor wishing to run. Third thing I have learned is that VFD's are not cheap, to run my 5hp 3phase mill, I would need a 10hp VFD and it cost over $900. Yea there are a lot cheaper VFD's, but they are for smaller 3phase motors. The mill has three motors on it, pump, spindle and table, Does that mean I need a VFD to power each individual motor???? Not sure how that works. and I am not even sure every motor is three phase, could be pulling 110v off one leg of the 3phase for all I know. I am already thinking about buying another lathe, doing so would mean another VFD and depending on the size of the lathe another $900. A few minutes worth of searching doesnt make me and expert on VFD's, so someone will have to clue me in to what I am missing.

Edited to add, after a little more searching I have found 10hp VFD's for around $360, which makes large ones a little more affordable, but if I still have to spend that kind of money eveytime I add a piece of equipment, is it really going to be cheaper than just building a RPC

You are correct, once you get over 3HP a VFD becomes less cost-effective, I apologize-I missed that fact in your first posting. Are you sure the table drive and coolant pump is 3-phase though? Often they are not even if the motor is.

I do agree with others on the coolant though, I have it on my mill and never use it, just too messy and some can go rancid from sitting. I just brush some cutting oil on when needed, much rather replace a cutter a little more often than have to deal with the mess of flooded coolant.

 

[Agvg]

Thanks for the info, always interesting to learn something new.

 

[Tractor Seabee]

But do they not build 3 phase in new areas? must give a very heavy load on that singel phase that feeds an area?

AG, its all about first cost vs the demand. Residential areas do not normally have any 3 phase loads. Here, they run one phase conductor on the pole line and connect from that to ground for the primary side of the transformer.

Ron

 

[LD1]

Double check your table and coolant pump. They are 110v more often than 3ph

 

[Tractor Seabee]

Not an expert on phase converters; so, question if they can provide a derived neutral to provide the 120V for small motors? An open delta transformer solution does provide the neutral; Caution though one phase will be the "wild" with about 190V to neutral. There are motor/generator sets for this application. Single phase motor drives a 3 phase alternator. Simple on the PCs is a small 240-120V transformer.

Ron

 

[Mysfyt]

Agvg - "But do they not build 3 phase in new areas? must give a very heavy load on that singel phase that feeds an area? "

Transmission to local areas uses 3 phase, then individual transformers at each house (up to 2 or 3 houses) - these transformers use ONE of the three phases and ground for primary windings, which are properly ratioed (wound) so their secondary windings provide 2 outputs - those outputs are each 120 volts relative to earth ground, but are 180 deg. out of phase with each other -

That way either output to ground gives 120 volts rms but using BOTH legs of that feed gives 240 volts rms.

Neutral (needed for return in 120 VAC circuits) is achieved using a SEPARATE line that ties to earth
ground - this lets 120 VAC outlets have a separate earth SAFETY ground which draws ZERO current
during normal use, and the "neutral" leg, which (in normal operation) has the same current flowing as
the "hot" wire, in order to complete the circuit.

For 240 volt use, older circuits did NOT use a "neutral" but only two 120 VAC "hot" wires (240 VAC across them because they're
180 deg. out of phase) and a SAFETY ground, which shouldn't draw ANY
current -

Newer devices that need 240 volts often have electronics that want 120 VAC - these get a 4-wire plug. This plug has both 120
VAC "phases" to get 240 VAC, the SAFETY ground, AND a NEUTRAL - that
NEUTRAL wire is used for a RETURN line for any 120 VAC circuits in the device being powered, and will
have the same current flowing as whichever "leg" of the connection is supplying the 120 VAC portion of
the device, PLUS the current that is being drawn for the 240 VAC portion of the device -


Typically this results in one leg of a 240 VAC circuit (clothes dryer, water heater, cooking stove,etc)drawing maybe 1 or 2 amps more than the other leg.

Typical semi-local transmission comes in on 3-phase, 10,000 volt lines, and overall load is balanced by
using a different phase of that 10KVAC for each successive "customer" - individual transformers then
step their SINGLE phase down to 240 VAC - That secondary winding is center-tapped, the center tap is
GROUNDED, so you get two "out of phase" 120 volt feeds.

So YES, 3-phase is available in pretty much ALL areas - but power companies don't do anything for free, and transformers and wire aren't free either - so it's rare and expensive to find 3-phase power (to an
end-user) anywhere but a farm or industrial site here.

Clear as mud??!? ... Steve

Thanks for beating me to the explanation, BuckitCase! You explained it WAY better than I could!

 

[muddstopper]

Double check your table and coolant pump. They are 110v more often than 3ph

I suspect you are right about the table and coolant pump not being 3phase, which makes me wonder how those motors will react if I hook the machine up to a rotary converter. I am now thinking that there might be more wireing needed done to the switches on the machine. My son is a commercial electrician, I might have to pull him in to do the wireing.