Power supply for Servo DC Question

[GEORGETOUBALIS]

First of all sorry for my bad English.

Hello
I want your opinion about a power Supply that I have to build (not me)!
Here Is the Facts

-I have a 5 axis Servo controller.!
5 Axis Large Mill / Router (Package Deal 026)
http://www.lowcostcncretrofits.com/2...rvosystem.html[/

My motors are
http://www.motioncontrolgroup.com/pr...formance-specs
Voltage rating up to 90 Vdc
Rated Speed: 4000 RPM
Rated Power: 245 watts (0.33 HP)
Current at Cont. Stall Torque, o-peak A dc 5.56 Amp
Current at Peak Torque, o-peak A dc 38.93 Amp
Resistance, L-L R 1.33 ohms

I need 4 Axis.!


There is a label on my controller that says "Max Input voltage 80V DC"

The Question:
What power supply I have to order for this configuration.???
I asked a friend of mine and says that a 75V DC 30A is fine.... (cost about 500 US$
Can you please tell me your opinion?
Thanks..!
George

[NC Cams]

You have 2 voltage ratings to worry about:

Voltage required by motor to achieve design power and torque.

Voltage rating of controller - to make it capable of switching the power that goes to motor.

Too much voltage applied (over rating) applied to controller will usually/probably cause it to fail.

Slightly too high voltage applied to motor will cause overheating and overspeeding. The amount of overheat/overspeed is roughly proportional to the % of overvoltage.

It is best to have your parts all matched for voltage - IE 90v motor uses 90V P/S.

You can use a 80V P/S with 90v motor - speed/power will be reduced about 11% however.

Use of 100v P/S with 80v controller however may result in smoke emissions from controller.

For you motor, assuming the use of 4 axis at peak possible load, roughly a 90v power supply would give you 100% design speed potential from the motors. Current wise, figure 100% of 4 x 5.56 would give you a 100% duty cycle for current at "normal" useage.

For stall conditions, 4 x 38.93 x 60% should be your absolute "peak" current capability used with all 4 rotors locked (improbably) to look for from a P/S.

75V / 30 amp should work.

[GEORGETOUBALIS]

Thanks A lot...!
I will order it...

[Al_The_Man]

Over heating of a servo can be caused by allowing too high a current.
Continuous too high a voltage will cause excessive rpm, in itself will not cause overheating. It just exceeds the safe recommended manuf. rpm.
Most drive manufacturers will suggest voltage supply to be anywhere from 110% to 150% of the max motor rated voltage, provided the drive can handle the voltage.
With modern PWM drives, the max current can be controlled by the drive, and the higher voltage, in and off itself, will not damage a motor, providing the rpm is kept within specs.
Although this high voltage is applied to the motor, it is not continuous, as would be a direct connection to the PS, the same applies to the control of current.
Using a PS/drive with a high current rating, but lower voltage rating than the motor, will allow a high torque to be obtained, but the max motor voltage (max rpm) will not be achieved.
Al.

[GEORGETOUBALIS]

"Most drive manufacturers will suggest voltage supply to be anywhere from 110% to 150% of the max motor rated voltage, provided the drive can handle the voltage."

Do you think that I m going to have a problem...?

[Al_The_Man]

You might if you want to achieve the max motor rpm.
Al.

[NC Cams]

Define what you mean by "problem"????

For DEFINITE answer on "drive problems", your best source is the tech dept of the drive maker. They should be able to tell you what drive wlll tolerate in overvoltage and/or current limits.

Use of message boards is OK for basic information - but to base high dollar buy decision on "message board experise" NO MATTER HOW GOOD the expert - can result in good, bad or indifferent results - it all depends on applicability of infoirmation to ACTUAL design capabilty of the drive.

Good advice from noted expert with non-robust drive put in overvoltage results in "problems".

Simple review of label specs will not tell you EVERYTHING you need/want to know - the tech dept of drive maker should be able to give better EXPERT/EXACT advice, however...

[GEORGETOUBALIS]

The ametek motors that comes with the controller was very slow for me (about 1200rpm).
I told the seller about it (www.lowcostcncretrofits.com) and he suggested that i should buy the MGC motors.
I also bought the power supply (big mistake) which is 55v DC and about 15A.
When i tested the motors with a MACH3 I had a lot of Errors. Suddenly the motors stopped and the leds of the drives was on.
I connected 3 motors of them and when I tried to tune them with a low speed, the number of Errors were reduced.
One guy (his job is to build machines for factorys for 30 years) said that the problem was the power (low Volts & low Ambers).
I am really confused.
I have uploaded some photos for you, hoping that you can get a better idea with the situation.






Also a label on the controller say that "NEVER EXCEED 20A per Axis.
If I tune the motors to 3000 prm MAX I think I ellimimate the Errors
What do you think.?

[NC Cams]

Servo's MUST be matched to and with their power supplies if you want them to achieve the designed performance.

A 100 volt motor run on 80 volts will only achieve 8% of the speed it is capable of making. If you run an 80 volt motor on 100 volts, it will run at about 125% of rated speed - it is simply a proportion of votage

The amount of torque the motor will put out will be determined by how much current it draws from the P/S. If the motor asks for more current than the P/S can put out, the motor will not put out torque or perhaps slow down due to voltage "sag" by the P/S. If the P/S can put out more current than the motor needs, this is usually not a problem outside of cost - you paid for current capacity that you are not using.

Hodge podge, mixed bag surplus buys can be good deals. However, if the parts are mismatched (voltage/current/size/etc), slow speed, wierd performance and generally unsatisfactory performance can be expeted.

Casually, it looks as if you need to do a better job of "matching" and then selecting parts for your CNC retrofit - a bit more study into the engineering involved may also be of help. Some of the CNC stuff does bolt together but the interfacing of the componentes simply doesn't allow the stuff to "fall" together.

[GEORGETOUBALIS]

The servo Controller Cost me A lot of Money As the motor do!
I think that ...I give it a try with 75V DC 30Amb.
If I have problems I will change the system with another.
The sure is that I can't burn the motors or the controller with this power supply.

[Al_The_Man]

Unfortunately you may have gone the wrong route in your selection process.
Generally the first thing is deciding on the mechanics of the machine, or purchase the basic machine, then the motors can be sized according to the demands placed on them by the mechanical structure and the performance required of them.
Once the motors are selected, then the appropriate rated drives and power supply can be selected.
The components you now have should work, although the PS voltage is probabally lower than will allow maximum speed, and current can usually be easily set for limit/fold back to avoid damage to the motor or supply.
IOW you may not get the maximum performance they are capable off.
Fortunately, DC brushed motors are usually easiest to mix and match as far as drives are concerned.
The drives I use mainly are A-M-C or Copley, AMC does not supply motors so it is always mix and match with their product.
I usually prefer to initially tune the drives themselves, independant of the controller, this either requires a ±10v analogue battery box or a step/dir generator.
Good luck with the machine.
Al.

[cjmerlincnc]

You should also check your encoders as the problem with limited speed and faulting drives may stem from the encoders being mismatched.

Mach3 has a limit on how many pulses it can put out. If you have high count encoders then your motor speed is going to be slow no matter what the power supply is.

From your first post using those motors and a power supply of 75v at 30 amps you should have a half decent setup.

To get any kind of speed and resolution out of Mach3 from the printer port setup, you'll need a max of 2000 pulses per 1mm travel.

More pulses per mm = less speed

John