Rewiring BOSS for single phase
I am wanting to convert my machine to single phase, to eliminate the phase converter. Spindle will use a vfd, that should be the only thing that requires 3 phase. The power supply for the steppers seems to be kind of odd though. Each leg of the 3 phase incoming power goes into a seperate coil, making 3 seperate (50 or 60v I think) power supplies. Can I make this work on single phase?
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If you try to make everything idiot proof, someone will just breed a better idiot!
Hello Jderou
Do you have a wiring diagram for your machine. If you do, study it. I was able to get a R2E4 Boss 9 to run on single phase. Just by disconecting a wire and adding a jumper wire. I only had to run the phase converter to run the spindle. I ran the machine like that for about 4 years. I have done the same to my Boss 10 but the phase converter also runs the coolant pump.
Richard
You are comparing apples and oranges. The BOSS 9 had a single phase axis power supply. They just tried to spread the load from the machine over the 3 input phases.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
So in order to run on single phase, can I just run L1 and L2 to each coil?
If you try to make everything idiot proof, someone will just breed a better idiot!
It sounds like your machine has a 3 phase axis power supply. So you can't do what I did. I have an apple, you have an orange.
Richard
You need someone with a degree to say for certain. PROBABLY, the original design was such as to spread the load over 3 phases since they were available. You will be getting triple the load on one phase plus the 110 V transformer. Plus the logic supply and the 54V supply. I have not seen this done.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
The use of 3 phase AC to feed a DC power supply is common. Many elevator motors are DC motors that use 3-phase AC rectified to DC. Three phase rectified power has no points where the resultant DC voltage is zero, unlike single phase. Use of rectified three-phase power therefore can avoid the need for large capacitors to even out the DC voltage under load.
DC supplies are and can be made from single phase, but it would generally require larger (or additional) capacitance that may not be present on the three-phase supply.
This effect is more important than the evening out of power draw over the three phases.
The rest here applies to the three-phase spindle motor and power conversion.
With the addition of appropriate run capacitors (which must be listed as "run" capacitors, use of electrolytics results in explosive failure of the capacitor), as well as start capacitors which can be electrolytics (both of which a good static phase converter matched to the motor will have), you can run the 3-phase motor on two phase power. The designs for rotary phase converters are, minus the motor, essentially designs for static phase converters with, in this case, the spindle motor in place of the rotary motor.
Dynamic power-factor boxes are more sophisticated with respect to "static" conversion, switch in capacitance as needed, and can be used with multiple motors. These boxes are generally advertised for the purpose of power-factor management in commercial settings and are used even where there is a 3-phase supply; by switching in banks of capacitors they effectively provide all inductive loads (i.e. motors) with run capacitance dynamically matched to the conditions. If a motor is turned off then the power-factor box will switch out capacitance accordingly to keep the current to a minimum, given the new inductive load. This is exactly what is accomplished by run capacitors in a rotary phase converter, but with the additional benefit of dynamic adjustment.
While some will tell you that power factor management is only important in a commercial setting (due to the power factor charges that are made on commercial accounts), it nevertheless affects motor power, smoothness, and the difference can be heard. One need only do the experiment of running with and without them to experience the difference.
I performed that experiment. Some argue that with a sufficiently powerful 3-phase supply, like the power company or an outsized rotary converter, run capacitors are unimportant or negligibly so to operation of the motors. However, we are talking about single-phase base power. So my experience is that the run capacitors matter. If you build your own rotary phase converter, use them. I built mine, and can hear the difference in the motors including the idler with no load.
I do not use dynamic power factor adjustment, but I have only one 3-phase motor in my garage. When I add the next one (I need a bigger compressor), I will add run capacitance to that motor as needed, so it will switch in with the motor. If I were to have several 3-phase motors, I would get a dynamic power-factor box and have no need to alter anything on the motors.
The other reason for smoother DC on three phase F.W. is not only less ripple amplitude but the ripple frequency is 6x the supply freq. as opposed to single phase FW being 2x the supply freq.Originally Posted by karlden
However I suspect in the posters machine, that although a 3 phase transformer was used, it fed three single phase transformers for 3 independant supplies?
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Using a static phase converter sounds like a pretty good idea. The third phase will still be weak, but it will be there.
In general, with a machine this size the VFD for the spindle can run from single phase with proper derating.
Man I'm getting confused, so should I pursue it or just leave well enough alone. It sounds like it may be a bad idea, but then I know some cnc machines run on single phase so what is the difference?
If you try to make everything idiot proof, someone will just breed a better idiot!
If you had a schematic you could post of how it is wired right now, then you could probabally get a definitive answer, if the present supplies are single phase, but three ph transformer fed than it should be no problem to convert to 1ph.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
I converted mine to single phase. Don't know if yours is the same though. L1 and L2 fed one transformer and L2 and L3 fed the other. All 3 legs went to the reversing starter for the motor. I ran L1 and L2 to both transformers that fed everything else in the panel except the motor. I added a single phase in 3 phase out vfd for the spindle. I have some minor things with spindle control I don't like that I may or may not be able to tweak out. IE spindle starts slower, reversing when tapping, slowing spindle speed sometimes causes a drive fault, etc.
I've been running mine this way for 18 months but I don't know if it will work for you.
Roger
Roger, what model boss do you have?
Thanks,
Joe
If you try to make everything idiot proof, someone will just breed a better idiot!
I've got a V2XT. I'm guessing a mid to late 80's vintage. Here is the schematic for my machine. Sorry, it's upside down.
At first glance that does appear to be the same as mine. I'll have a closer look at my schematic tonight and verify.
If you try to make everything idiot proof, someone will just breed a better idiot!
Finally getting back to this. Moved into a new house, so I am starting new with machine wiring. What I have is a typical 3-phase transformer with 3 primary and 3 secondary windings made onto the same core. It came from the factory wired for each phase to power a separate winding. I rewired it so that the coils are in parallel, powered by single phase.
This is my big question. I know when it was running off a phase converter, it would pull around 20 amps at the breaker box with the spindle running (single phase breaker). So at the machine it was seeing around 7 amps per phase (or less). Now that I have the machine wired in single phase the main fuses should be seeing the total amp draw of around 20 amps. The fuses are rated at 20 amps. It sounds like I am going to be blowing fuses. Would it be safe to replace the wires from the fuse block to transformer with heavier gauge, and step up to 30amp fuses? Obviously I would be going with heavier wiring all the way back to the breaker box.
If you try to make everything idiot proof, someone will just breed a better idiot!
I was anxious to try mine after converting to single phase with a vfd. I left the two fuses as they were. Pulled some 12 ga wire and tied it to a 15 amp breaker in my shop panel. Have never had an issue. So, I haven't changed it. Haven't checked the actual amp draw. Not saying it's right or yours will work.
rfdoyle
properly wired, can anyone tell me about how much current each leg of the transformer should draw? Right now I have the output of the transformer disconnected, so I can verify its output voltage before frying anything else down the line. Surely, if wired correctly, the total current would be less than 20 amps.
If you try to make everything idiot proof, someone will just breed a better idiot!
With the secondary windings disconnected, the transformer will not draw much current since there is no load on it. Even if you hook up the secondaries, but do not turn on the drive enable button (limit override button), you should not be drawing much current. Once you push the limit override button, your drive amplifiers will begin to draw current and put a bigger load on the transformer.
Just keep the secondaries unhooked and verify the voltages of each winding pair. There should be multiple secondary taps for various voltages....60V, 70V, 80V....or something like that. These all depend on your input voltages.
I was wondering why their are several wires coming off the secondaries that aren't tapped, thanks eric.
If you try to make everything idiot proof, someone will just breed a better idiot!
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