G540 - 4 motor connection problem

[dachopper]

Hi guys,

I have just purchased and installed this G540 4 axis kit.

All of the motors, in any combination, seem to work correctly by themselves, or two or three of them plugged into the G540, but as soon as all 4 of them are connected at the same time, I get a fault anywhere from 5 seconds to 30 seconds later.

The motors are 3.5 Amp per phase,
Power supply is 48 Volt 12.5 Amp,
All of the motors have 3.48K resistors installed on their DB9 connectors.

I'm at a loss, but the issue seems to have something to do with power supply, or the resistor setting, as it only ever occurs when 4 motors are connected, sometimes even without moving them.

I've read other threads, which all mention power supply, but then ppl point out 7 Amps should be fine, and I'm not even moving the motors sometimes. I have 18 Gau wire between the power supply and the gecko.

Any thoughts?

Nick

[Neale]

Those resistors should set a motor current of approx 3.5A per motor. Stepper motors draw current even when not moving (to hold position). That's 14A. You are using a switch-mode PSU that probably hard-limits at its rated current - 12.5A. I see a problem here...

[dachopper]

well, I was hoping not, as it was a kit bundled together, and that was the largest power supply they had for those motors.....

Why would a retailer bundle kits that don't work together - all of them have less power than required?

the fault seemed to occur at slow speeds, and not high speeds, and when coasting or reversing direction ( I have the acceleration set very low at the moment )

Rapid Speeds around 5000 - 8000 mm/min on a 10 pitch screw
5000 on the 5 pitch

[Clive S]

Why would a retailer bundle kits that don't work together - all of them have less power than required?

This is exactly the reason that we generally always inform new members never to buy any kits of parts as they are rarely matched

[m_c]

That size power supply should be fine. As these are modern chopper style drives, they won't actually draw the full 3.5A from the power supply unless you are really pushing all the motors hard at speed, which is quite unlikely.

It could however be a problem with the power supply. Ideally I'd connect an oscilloscope over the power supply, and see what is happening with all the motors connected.
You may be able to catch any dip in voltage with a voltmeter, as the dip would likely have to last for a second or two for the drive voltage to drop low enough to cause problems.
Does the power supply have any kind of voltage OK output? it may be worth connecting up a lamp to see if the power supply is shutting down when the problem happens.

[Neale]

As Clive says, the kits are often put together using less than ideal choices of components. In this case, I would guess that the kit uses a switch-mode power supply because these are smaller, lighter, and in particular cheaper than a linear supply, which is the preferred option from a purely technical viewpoint. The linear supply can cope with peak overload without breaking into a sweat where the SMPS can trip internal overload protection. I'm a bit surprised as well that there is a problem, though, but seeing that it appears to be load-related, and is a bit variable suggesting that perhaps it is when all motors are trying to deliver pulses simultaneously which won't happen all the time, maybe it is the PSU. Does seem on the face of it to be the most likely issue. My own machine uses small, cheap SMPS boxes for control circuitry where the load is smaller and well-defined (very cost-effective here) but I use a linear supply for the stepper drivers.

[Clive S]

If I am not mistaken depending on the how the drives are set the motors will draw more current when stationary

[m_c]

I would expect the internal filtering capacitors of the Gecko drives to minimise any harmonics that could cause high instantaneous current use.

However, what I'm wondering is what is the actual fault being caused?

[komatias]

With the 3.5A tuning and your power supply the gecko should work 100% fine. I suspect there is something tripping the chargepump.

What are you using to drive the Gecko? parallel port? Is that conking out and causing the chargepump to go low?

[dachopper]

This is my power supply http://www.automationtechnologiesinc...upply/48v12-5a

I have the G540, connected with the DSUB ribbon to UC400ETH controller, then that goes Cat5 cable to a switch, and cat5 to my laptop.

When the fault occurs, the connection between the UC400ETH and Laptop and UCCNC program looks normal ( the G540 disables the servo's from moving, and the UCCNC software shows that the motors are still being told to move without any limit switch activation.
)

I noticed aswell, a little noise from the servo's when they are stationary and they are all connected, but less when there are 1 or 2 or 3 motors connected is this normal?

I've checked the resistors and they are 100% correctly installed, and re-wired the power supply to G5540 + and - with other 14G braded wire last night