Printable View
I need help deciding how to power my servos. I have a Bridgeport V2E3 which I am rebuilding the control and wiring. The servos came with the machine and are 100vdc 11a, the best I can tell. I believe I need a power supply which will convert 240vac to 100vdc at about55-60a for 4 servos. I have tested the with a 100vdc 10a power supply running 3 servos, but the power supply faults out.I don't believe there is a power supply with all the amps i need, so what do i do?
What motors and drives do you have?
Do you not have the original transformer/power supply for the servos?
No, I junked it. Hind sight 20/20.Quote:
Originally Posted by Jim Dawson
Quote:
Originally Posted by Gunmachinist
OOPS!
What motors and drives do you have? There should be some part numbers and data tags somewhere.
I don't know any information on the servo motors, there is no markings, they have been warn off. The drives im running are AMC 25A20. I have been running them with a 110vdc 10a power supply, (2) 48vdc increased to 55vdc 10a wired in series, but they fault out when attempting to run a third servo. I would like to be able to run up to 4 servos in the future.Quote:
Originally Posted by Jim Dawson
We can make some assumptions here. Since your original power supply was 100V output, we can guess that the motors are 90V to 140V, most likely rated on the higher end. The 25A20 drives are rated at 40 to 190V, 20A peak, 10A continuous. Your motors are most likely in the 750W range, around 35 in/lb torque, maybe 3500 RPM max, common on that size machine. In this case torque = current, and voltage = RPM in almost a direct relationship.
What I find interesting is that your 100V, 10A power supply would not run the motors. I have a similar setup on my machine and run it with a 75V, 5A power supply with no problems at all. The original power supply was was around 100VDC and 20A as I recall.
What kind of power supply did you attempt to use? Switching power supplies do not work well in this type of application, you need an unregulated transformer type linear power supply.
I would think this one should work fine unless you really need 400 ipm rapids. https://www.automationtechnologiesin...0vac-or-230vac
An alternative would be to use a 240/480 - 120/240, 3 KVA or so transformer. Somethinglike this one https://www.ebay.com/itm/30415066281...oAAOSwE2FhRMzP
Wire the primary for 480V, wire the secondary for 120V, and apply 240V to the primary. This will give you 60VAC output. Then feed that to a 50A bridge rectifier and a couple of properly rated large caps, and you will have an instant 30 amp, 82VDC power supply.
Ok, Its probably the power supply I have which is a Mean Well din rail power supply. I'll try one of these you suggest.Quote:
Originally Posted by Jim Dawson
Replaced the power supply with one you suggested and now i have a working machine.Quote:
Originally Posted by Jim Dawson
Quote:
Originally Posted by Gunmachinist
Awesome! :banana:
What kind of power supply did you attempt to use? Switching power supplies do not work well in this type of application, you need an unregulated transformer type linear power supply.
I tried that with a brushed DC spindle motor (180 VDC/4A). It was truly awful. It rattled in a very noisy manner.
The caps were not enough (they never are at mains frequency) to stop a DC spindle motor from seeing huge amounts of AC. I am not going to do that to my spindle.
The current spindle drive is a KBWT-26 SMPS unit, but it has died. The +15 VDC supply inside it now gives ~60 mV. I have emailed KB, but they have not been very helpful. I guess that a single overseas customer is not very high priority. Support matters however.
I have ordered a similar SMPS supply from China, but delivery may not be until mid-January. Aargh. Air freight delays.
So I may have to build my own SMPS unit from scratch, for 180 VDC @ 4 A. I have the gear and the knowledge to do this, but I would really prefer to be running the machine. If anyone knows of some good references to MYOG units of that capacity, I would be grateful.
Cheers
Roger
Sydney, Australia
Quote:
Originally Posted by Gunmachinist
Din rail supply?.
That's even worse than having a usual silver switched one.
There was something else going on there, DC motor have been ran on Triac and SCR bridge controllers with no smoothing whatsoever with no ill effects or signs, T.M. controllers for one.Quote:
Originally Posted by RCaffin
I have also done this in many applications.
I would never used a SMPS with any kind of large DC motor. Mains transformers cost a little more, but if the motor is 90vdc or 190vdc and above, the controller can be ran direct from rectified and smoothed 120vac/240vac.
Again, as is done in T.M.'s where smoothness is a needed criteria
DC motor have been ran on Triac and SCR bridge controllers with no smoothing whatsoever with no ill effects or signs,
Yes, I have done this, but the motors were noisy, due to the large amount of mains AC superimposed on the DC. That is not good for the bearings, or the stator.
Then I switched to an SMPS (0-200 VDC @ 0-5 A) and the motor ran very quietly and far more smoothly. I would not go back to a transformer version.
I think one has to try both to see the difference. Yes, it did surprise me a bit too.
Part of the problem may be the huge cost of the filter capacitors. Once you get over a few millifarads at several hundred volts, the costs really rocket. And right now they are not on the shelves either!
A trick one has to be aware of with an SMPS: the output from a commercial one is rarely well filtered. Do not try to stick a large capacitor there: the smoothing may upset the feedback system. Instead put a large filter inductor into the circuit: a balanced dual-winding E-core works well. Cuts down the RFI too.
Cheers
Roger
Odd that major servo drive manuf such as A-M-C, Copley Controls, Applied Motion use a simple bridge and around a ~1200uf cap in their drives that use a built in P.S., you cannot hear these systems operate at all. Smooth a silk, you cannot afford less on a CNC machine.
I have used the DC 2.5hp/3hp T.M. motors for spindles, using the MC1200 PWM controllers that come with them.
These also have a 1000uf electrolytic for smoothing, you cannot hear these operate either.
Odd that major servo drive manuf such as A-M-C, Copley Controls, Applied Motion
I have used Copley in the past.
But it might be worth noting that their designs are often 50+ years old, pre modern semiconductors.
It may well be possibly to go this route IF you put a very large smoothing inductance in the path. It would need to be a gapped design of course.
Hum . . . I wonder . . . Rats around in the cupboard.
Cheers
Roger