Am I sending enough amps to the motors?

[watsonstudios]

After testing the motors (un-mounted to the machine) they all jog correctly.
But, when they were mounted to the axis' on the machine, I would jog the axis then a few seconds later it would stop with a loud whining sound. Does this mean the motor has reached it's torque limit and stalled?

Since I only have a 4.5 amp power supply, I assigned only 1.2 amps per motor - thinking i need to share all the amps - is this correct? with 4 motors, can I set them all to 3 amps or do I need to share the 4.5 amp supply?

I did order a second power supply to run the two X axis motors.

Will more amps per motor give me more torque? I have 495oz steppers.

[Torchhead]

Torque comes from amps, speed from volts. You can probabaly run two motors rated at 3A (and set at 3A) off a 4.5A unregulated supply. 3 might be a push but reducing the chopper current on the motors to below the rated value will cause the torque/rpm curve to move in towards lower numbers.

Load whining is lost steps.

tomCAUDLE
www.CandCNC.com
BOB's
Digital THCs
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[watsonstudios]

I have the second supply wired up now so I have 2 motors on each power supply. I set each driver for X and A(slave) to 2.1 amps since they are always running together - the next step up would be 2.4amps each - This would pull 4.8 from the supply - is that recommended? or should I be safe and keep at 2.1a?

Should I set Y and Z at 3amps each since they are not always running together, or should I bump it down a bit?

I think the motors are rated at 3 amps.

[nh_eng]

Can we have more specifics on the power supply? Is is unregulated? What is the rated voltage? The torque of a motor will drop off significantly with lowered input current. You should always run the motor at full current if you need the torque. You can't just add up the currents in both motors to get to 4.5A, its not what simple, because once the motor has the selected current, the (Bipolar?) chopper drive will recirculate that current without additional load on the power supply.

[watsonstudios]

It's 24v regulated

[nh_eng]

Regulated power supplies are not recommended for driving stepper motors for several reasons. Firstly, stepper motor chopper drivers switch the current to the power causing current spikes; a regulated supply will cutout when its max current is reached - not good - as you will experience motor stall when that happens. Secondly, a regulated supply cannot "average" your load, whereas an unregulated supply will simply reduce the voltage as you attempt to draw surges in excess of the rated current. For example, if you have two motors drivers with current settings of 3.0A, and a 4.5A unregulated supply, consider when both drivers demand 3.0A - the supply will need to e able to deliver 6.0A for a short time. An unregulated supply will not care since it is typically thermal limited. It will put out the 6.0A , but at a reduced voltage. It will not "overload" unless the average current exceeds 4.5A. Since stepper drivers only drive pulses, you can typically use an unregulated supply for steppers at about 1.5 times its rated output. So if you have two 3.0A step drivers, you need a supply 2 * 3.0 /1.5 = 4A. This is a rule of thumb and generally works well.

[watsonstudios]

Sorry, my bad! - I guess it is a "switching" power supply - not a regulated one. I don't know exactly what that means, but they are power supplies that are meant to be used with steppers. They come with the CNC kit from Keling Technologies.

With that in mind, can I go ahead and set my drivers at 3.0amps each? The supplies do have overload protection.

[Torchhead]

Switching power supplies (regulated) work fine for smaller steppers. If you are worried about surge currents or motor current spikes (limited by motor impedence) driving the supply into current limit, then the addition of a 2000 to 4700 MFD cap at 35VDC across the PS outputs would help to smooth out the current spikes and flatten out the loop gain characteristics.

They do offer short circuit protection and will fold back if motor Back emf starts to raise the buss voltage.

The primary reason regulated supplies are not used in commercial applications for motor drive is that they cost a lot more to buy.

Seldom if ever do the steppers draw their rated current in chopper mode. If you look at the average watts dissipated with a 3V 3A motor (even with 24VDC supply volts) given IR losses and switching losses the total power is probabaly 18 to 25 W.

The 60% rule (add all of the nameplate currents and take 60%) is conservative and assumes all motors moving at the same time under load. Actual measurements of working equipment show that the average current (RMS current) is about 40 to 50% of the nameplate values.

I have a small table top router/engraver with 3 260oz-in motors with a 24VDC switcher supply running a xylotex card. It runs for hours at a time and it has never lost a step with a 5A power supply and the current limits set to 2.8A each motor.

tomCAUDLE
www.CandCNC.com
BOB's
Digital THCs
DXFTool Software
Complete Electronic Packages
Stepper & Servo Systems
Hand Controllers

[The Blight]

I also have these motors, and I use a 36V 600W power supply (16A unregulated) for 3 steppers with the option of a 4th and 5th. No lost steps and high speed (480rpm). I run them at 3A.