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Cnarter Oak RF45 Mill conversion

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native34

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Hello I'm getting ready to convert my Charter Oak mill to CNC. I have converted a couple of machines in the past, but they were stepper based controls. I would like to convert this with Servo control. I am having problems figuring out the electronics that I would need to complete this. would anybody have a diagram of the conversion process I could use as a rod map. I am looing to use CNC4PC C32 Multifunction breakout board, Dugong DGS-16035 Drivers, 3 KL34-180-72 (NEMA 34) Dual Shaft 1125 oz.-in Peak 72V/40A, VFD for spindle control, Proximity switches for Limits and homing. One of the biggest problems I'm having right now is trying to figure out the right size power supply to power the system. I will be using 24V and 5V for the low power stuff, but I'm not sure how to calculate for the right power supply to power the servo motors themselves (i.e. correct voltage and Amperage) suitable for all drives. Can I use one power supply for this or will I need to use multiple power supplies?

Rod


Complete motor specs:

KL34-180-72 (NEMA 34) Dual Shaft, Front Shaft 1/2" Rear shaft 1/4":1125 oz-in Peak 72V/40AGreen is Ground, Red is +, Black is Common)Constant Torque: 226 oz-inPeak Torque: 1125 oz-inNo load Speed: 4000 R.P.MTerminal Voltage : 72 VDCContinuous Current: 7.8 APeak Current: 40 AWeight : 4.25 KgSkewed Rotor Design
 

native34

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#2
Also could someone explain this to me?

According to the people over at Gecko drive the formula below is what is used to calculate correct Voltage for power supply. When I plug in the values from the motor specs from CNC4PC Servo motor mentioned above. I get a power supply voltage of 50.596V. I am not understanding how this is possible if the Servo motor terminal voltage is 72VDC. Could someone explain this to me. I am very good with the mechanical stuff when it comes to building but as you can see by my questions I am not so good with the electrical and electronics. It seems the more I try to understand it the less I feel I know.

What should my drive supply voltage be?

A.) You should find out your motors inductance and use it in the following formula:

32 * √mH Inductance on the motor = Drive Supply Voltage

The answer is going to be your motors maximum running voltage. Anything above this is going to potentially damage your motor.
 

JimDawson

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#3
Are you sure Gecko is not talking about stepper motor inductance? I think you will be pretty safe using the name plate voltage on the motor. 70 volt supplies are quite common. And the odds of ever actually hitting that voltage is pretty slim. Running at 100 IPM my servos are running at about 35 volts at the motor terminals if I remember correctly. I am using one 70 volt, 5 amp supply to run both of my servos, and one stepper.
 

native34

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I'm not sure about the stepper thing as it was in an FAQ for their sub form on cnczone. I thought the name plate voltage would be what I use but then I seen that formula and got confused. I remember when I did my stepper systems I had to use that formula to figure out voltages. How do I figure out how many amps I need in my power supply? If a motor is rated at 7.8A continuos and 40A peak what number should I used to determine power supply requirements. The other part of this question is, about total amperage. For power supply. Let's say my motor requires 7.8A cont and this is the number we use for determining power supply amps. Would I need to multiply the number of amps required by the number of motors being used, let's say 4 motors at 7.8A = 31.2A. So would I then need a power supply that is rated for my motors nameplate voltage and total Ampere's needed (I.e. 72V 31.2A power supply)? If that's the case where do I find a supply that size, as all the power supplies I have found in the 72v range do not carry 30 or more amps. When I look at pics of other peoples controls for the 45 size mill I only see one power supply for the drives. So how are they accomplishing this? Sorry for the long winded post just trying to make sure I completely explain what it is that is really confusing me about choosing correct power supply.
 

JimDawson

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#5
As I said above I'm using a 70V, 5 amp rated supply to run my mill. The supply will actually output close to 80V unloaded, but drops of to it's rated voltage with a bit of load. This is not a problem. The drives in my case are rated for 80 and 100 volts respectively. Your Dugong drives are also rated at 80 volt.

I am running one 6.3 amp stepper, with a 10 amp drive, and two 140 volt, 5.8 amp (30 amp peak) DC servo motors. So if you add all the amps up, you get 17.9 amps, all running off of a 5 amp continuous rated supply, that will probably output 20 amps for short periods of time. I have never experienced any performance problems. Keep in mind that my mill is a 10x50, 3 HP machine, quite a bit larger than your RF45.

Originally my mill had a 100 volt servo power supply, but I checked the voltages to the servos, at the motor terminals, and found that the maximum voltage a was about 35 volts at 100 IPM. I checked this to determine if I could run the servo motors on the 70 volt stepper supply so I didn't have to run two separate power supplies unless I really needed to.

Unless you plan on running your all of your axis motors at maximum speed and torque simultaneously, I think you will be fine with a power supply rated far under the combined amps. Just use proper fusing on the supply to protect the system in case the controller goes crazy and tries to run everything at maximum speed.

In mine I have software protection set up to fault out the controller on an encoder fail that could cause a runaway. If the lag error becomes too great, the controller faults and kills the motor power.

If you want to build a 30 amp power supply, here is what I did for one application. It was built this way because I expected that the axis drives might all be used at maximum power.

PS.gif

[TABLE="width: 570"]
[TR]
[TD]80VDC POWER SUPPLY[/TD]
[TD]P/N[/TD]
[TD]Vendor[/TD]
[/TR]
[TR]
[TD]70HF40 - STANDARD DIODE, 70A, 400V, DO-5[/TD]
[TD]08R0232[/TD]
[TD]www.newark.com[/TD]
[/TR]
[TR]
[TD]Capacitor, Al; 6900uF Screw; 200VDC[/TD]
[TD]59K0162[/TD]
[TD]www.newark.com[/TD]
[/TR]
[TR]
[TD]Clamp, Mounting; For Capacitor[/TD]
[TD]14F413[/TD]
[TD]www.newark.com[/TD]
[/TR]
[TR]
[TD]Bleeder Resistor, WIREWOUND, 5K OHM, 10W, 5%[/TD]
[TD]64K8006[/TD]
[TD]www.newark.com[/TD]
[/TR]
[TR]
[TD]TRANSFORMER ENCAP 5KVA 480x240VAC TO 240VACx120VAC[/TD]
[TD]C1F005LES[/TD]
[TD]www.automationdirect.com[/TD]
[/TR]
[TR]
[TD]CIRCUIT BREAKER, 2P, 40A, D CURVE, DIN RAIL MOUNT[/TD]
[TD]WMZT2D40[/TD]
[TD]www.automationdirect.com[/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[/TABLE]

IMG_1995.gif

The black rectangle in the center of the panel is the heatsink (not in the parts list) for the diodes. The transformer is not shown, it hangs on the side of the enclosure. Note: The heatsink is electrically hot, so it must be isolated with insulating stand-offs.

PS.gif IMG_1995.gif
 

native34

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#6
When determining power supply amperages. Do you take the sum of the amps of the motors or just one motor?
 

dave2176

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#7
You could look for a power supply rated at 1.5 times the requirements of one motor. This would be sufficient since one motor is ramping down when another is ramping up. While it appears that servos and steppers are running simultaneously they are in fact run one at a time and the pulses are coming so fast it appears simultaneous.
Dave
 

JimDawson

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#8
I just use an educated guess based on the projected use. Theoretically, you should add all of the motor amperage's together to derive the required output. But I look at the application. On a small mill, you could not run all of the servo motors at maximum power simultaneously, you would break something. Most of their life will be spent running at less than 10% power. In most cases only one motor is running at a time, or when cutting a ball you may have all three running, at varying rates where in general one or two will be almost stopped.

If I were building a big machine for heavy manufacturing use, then I would add the motor amperage's together to determine the power requirement. But I would be using drives that have their own internal power supply, and I would just supply the appropriate 480 volt, 3 phase supply to the drives. The last big machine I worked on had eight 15KW servo drives on it.
 

native34

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#9
My plan is to run a 72V 20A unregulated toroidial power supply. Does anyone think I will have a problem running the charter oaks, previously the industrial hobbies Z45 mill with a power supply of this size? From the sounds of everyone's response I shouldn't. Also I'd like to thank everyone for their info and patients on this subject of power requirements. I'm sure I will have more questions with the electronic side of things as I go, like I said this the only area I am unsure of but am very Willing to learn so I can be more self reliant with these things.

Rod
 

JimDawson

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I think that the 72V 20A will work just fine.
 
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