Power supply effects

[wendtmk]

Couple of quick questions on power supplies - if I increase the voltage, what effect does this have on the stepper, and if I increase the amperage, what effect does this have on the stepper?

Thanks,
Mark

[tdpomodoro]

Hi Mark,

From my readings:

- Increasing voltage, decreases step time as the inductance of the motor is able to be overcome more quickly. Result is it can step faster

- Increasing current, increases the holding torque of the shaft.

With increased current comes more heat and risk of coil burnout so increase current with caution.

Hope this helps.

Regards,
tdpomodoro

[wendtmk]

Thanks. More voltage is definitely a good thing then, to a point? Since it moves the stepper faster, does it give the stepper more turning power (or torque)?

My reason for asking this, I've got a relatively heavy Z axis on my gantry machine. In order to keep from stalling or losing steps, I have to run the stepper slower than I'd originally intended to. I wanted to try a higher voltage transformer to see if I could help the Z axis out a bit, since the higher voltage transformer is a relatively inexpensive upgrade.

Mark

[diecutter]

I run my power supply at 20 times the voltage on the stepper nameplate which is what has been recommended by various articles as a reasonable max figure to use. The steppers seem to work great at this voltage.

Make sure the new voltage does not exceed the maximum voltage spec of the control board. Also keep in mind that the ac voltage level off the transformer will change after it goes through the rectifier.

[jschmitt]

DC voltage will be about 1.4 times the AC voltage.

Another max voltage formula for stepper motors is 32 times the square root of the motor's inductance according to Maris of Gecko drives.
As cautioned check your stepper drives max voltage.

[Matt Adams]

A picture is worth a thousand words...

[wendtmk]

Matt,

Perfect! That's exactly what I was looking for. I'm somewhat limited to 40 VDC by the drivers (Keling 4030's). The power supply that came with the kit is a 24 volt 8.3A (KL-201-24) and I was thinking up upping that to the KL-350-36, a 36 VDC 9.7A power supply. The steppers have a 4.17V rating in bipolar, so I was hoping to give it a bit of a boost.

mark

[RomanLini]

Just be aware that you will get increased resonance and vibration with higher motor voltages when the motors are moving slowly!

I recently "upgraded" my PSU from 25v to 40.5v and I'm getting some significant vibrations, and on cutting hard materials a worse surface finish, and on cutting soft materials it is more likely to gum and melt. A lot of people here seem to be gung-ho about getting super rapids speeds, but for me it's not worth sacrificing significant cutting performance just to get 20% faster rapids on the rare times I want faster rapids.

I'm just about to mod my new power supply to drop it back to about 33v for testing. Hopefully that will be a nice medium.

[cnczoner]

Be careful about back-EMF too though. The stepper-motor coils are inductors, and will generate a voltage back into the drivers (called "Back-EMF"). You can notice this if you connect a voltmeter to any coil of a stepper motor (not connected to anything else) and rotating the stepper shaft. When added to the power-supply voltage, this total must not exceed the driver voltage rating (though there are exceptions to this rule). Calculating how much back-EMF will be generated is somewhat of a black art, and depends on the specific motors, the speeds you're running it at, and whether or not it's a full moon.

The exception I mentioned is that some drivers will claim a voltage spec, but can handle a temporary higher voltage for those back-EMFs. IIRC Gecko's do this. You can also add a small circuit to shunt the back-EMF and prevent it from going into the drivers.

EDIT: Found the shunt circuit...
http://pminmo.com/PMinMOwiki/index.p...le=Power_shunt

FWIW, I got my CNC mill used with very nice IM805 drives but a crappy 24V switching PS. I upped that to a 68V linear PS and pick up loads of performance.

Cheers,
-Neil.

[cnczoner]

RomanLini -- have you considered a vibration damper, such as this... http://www.cnczone.com/forums/showthread.php?t=32284

[RomanLini]

Thanks for the suggestion. I've already got vibration damping linear bearings and vibration damping leadnuts.

I was just making a point that going from a 25v PSU to a 40v PSU gave significantly worse performance. If high rapids speed is the only type of performance you are concerned with then by all means bump your PSU volts right up there...

[wendtmk]

I like the vibration dampener solution that uses hockey pucks...

mark