Issues with stepper motors losing power

[Steven W]

Hi Guys

I have an issue that has left me tearing out my hair out...well what's left of it.

To give a bit of background. Bought a Chinese cnc router about 10 years ago. The cnc controller connects to a Dell 5150 Inspiron pc (running Windows XP) which has a Moschip MCS9835CV PCI Parallel Port Card. The cnc router has worked very well with regular use - no issues, until I left my Dell 5150 pc out in the workshop over winter - the pc no longer works.

I have a spare pc (Dell Optiplex 780) that runs on Win XP, which I hooked up and fitted the PCI card and driver to. Here is the issue:

Switch on the pc and the controller. The pc starts to boot up. Fan comes on the controller and you can hear the stepper motors getting power to them and they lock rather than being able to move by hand. This is what I would expect to happen. As soon as the Windows XP window appears on the monitor the power to the stepper motors goes off although the controller is still switched on and the fan is still running. I don't know why. As soon as the pc starts booting down the stepper motors come alive again. I can't get to the bottom of it. I've tried taking the power pack from the Dell 5150 (which I know works) and fitted it to the Dell 780 as I read that since the controller takes power from the pc the Dell 780 has a less powerful battery than the 5150 and maybe not be able to supply enough power to the controller. The issue is still the same with the 5150 power pack

I also have another old Dell pc that runs Win 7 but again the issue is still the same

Has anyone else experienced anything like this or can point me in the direction that will fix this and help my sanity

cheers Steve

[JAZZCNC]

This could something like a Charge pump issue but without knowing more about the controller and software then it's hard to say.

If you don't know what a charge pump is, It's a feature on the controller or breakout board that watches for a signal from the PC software which it monitors 1000's times per second and if it doesn't see this then it will shut down all it's outputs because it thinks the PC as gone AWOL.

However, it usually works in reverse to what you are seeing, it shouldn't allow the steppers to power up without the PC and its control software running. So it could be that the polarity of the new parallel port is different and the output needs inverting in the software.? What software is it. ?

Another feature that could stop the motors from turning is the enable signal on the drives, if this is connected then it would shut down the drives' motor outputs, however, it wouldn't power them down only stop them from spinning.

My first place to look would be going into the control software and look in the outputs for the charge pump signal, then change the active state to the opposite to whatever it's set to know ie: if set to HIGH set it LOW or vise versa.

Other than this can't think of anything else which would cause it to do what you are experiencing without knowing more about the software and controller etc.

[dazp1976]

iWhen you say they go off, do you mean the main power to the drivers or that they disable?.
If just disable.... Do you have the enable pins wired up to the drivers?.
Worth a check. Might just be working backwards (low/high) enabled when idle/disabled when wanted. Or on wrong output.

[JAZZCNC]

iWhen you say they go off, do you mean the main power to the drivers or that they disable?.
If just disable.... Do you have the enable pins wired up to the drivers?.
Worth a check. Might just be working backwards (low/high) enabled when idle/disabled when wanted. Or on wrong output.

The enable won't drop the holding torque, it will only disable the drive outputs so they don't spin, they will still be locked and he says they drop holding torque and spin when the controller starts up so won't be the enable pins.

[ZASto]

Many drives (read TBxxxx and similar), when Enable is asserted, switch off their output stage and motors are unlocked, i.e. you can spin them by hand - no holding torque.
It is quite common that motors act "weird" while PC is booting, unless charge pump is enabled in Mach3.
Many years ago I made an interface between Mach3 and RZNC breakout board and added charge pump circuitry to be sure that machine will not play silly while booting.

[dazp1976]

he says they drop holding torque and spin when the controller starts up .

Where does he say that?.
The op has no mention of getting any movement at all. Only controller fan. All he gets is power to them and motor locking, then power going off when booted.

[A_Camera]

The enable won't drop the holding torque, it will only disable the drive outputs so they don't spin, they will still be locked and he says they drop holding torque and spin when the controller starts up so won't be the enable pins.

That is not the way my CNC works. When the driver is enabled there is a holding torque. When it is disabled the holding torque is lost and I can rotate the motors with my hand. This is the way I want it to work.

[JAZZCNC]

Where does he say that?.
The op has no mention of getting any movement at all. Only controller fan. All he gets is power to them and motor locking, then power going off when booted.

Slip of the keyboard, it should have read " he says they drop holding torque and WON'T spin when the controller starts up" I wasn't quoting him either.!

That is not the way my CNC works. When the driver is enabled there is a holding torque. When it is disabled the holding torque is lost and I can rotate the motors with my hand. This is the way I want it to work.

Depends on the drives, some do, some don't, some can be configured via software to work either way.
The most common config is the opposite of yours where the motors instantly powered up when power is applied to the drives and drop the holding torque when the enable pin is set. Again this can be inverted on the drive or thru software depending on the drive. This is why the enable pin can be left unwired on most drives.

[A_Camera]

Depends on the drives, some do, some don't, some can be configured via software to work either way.
The most common config is the opposite of yours where the motors instantly powered up when power is applied to the drives and drop the holding torque when the enable pin is set. Again this can be inverted on the drive or thru software depending on the drive. This is why the enable pin can be left unwired on most drives.

I am not sure what you mean by "The most common config is the opposite of yours"... My system works just like are describing. Perhaps you misunderstood what I wrote. Disable = no holding torque Enable = Holding torque the way I see it. The signal can be active low or active high, depending on some other things, but that's a different thing.

You were saying earlier: "The enable won't drop the holding torque, it will only disable the drive outputs so they don't spin, they will still be locked"

The Enable signal controls the holding torque. If the Enable changes state (goes from low to high or high to low) it will enable or disable the driver which will apply or drop the holding torque. On most drivers, if the Enable is not connected (floating) the holding torque is applied and the driver is enabled. The motor is locked only when there is a holding torque (driver enabled). If the driver is disabled and there is no holding torque, the motor can't spin, not even if you apply step pulses. When the driver is enabled the motor is on holding torque but starts spinning as soon as step pulses are applied.

[dazp1976]

I am not sure what you mean by "The most common config is the opposite of yours"... My system works just like are describing. Perhaps you misunderstood what I wrote. Disable = no holding torque Enable = Holding torque the way I see it. The signal can be active low or active high, depending on some other things, but that's a different thing.

You were saying earlier: "The enable won't drop the holding torque, it will only disable the drive outputs so they don't spin, they will still be locked"

The Enable signal controls the holding torque. If the Enable changes state (goes from low to high or high to low) it will enable or disable the driver which will apply or drop the holding torque. On most drivers, if the Enable is not connected (floating) the holding torque is applied and the driver is enabled. The motor is locked only when there is a holding torque (driver enabled). If the driver is disabled and there is no holding torque, the motor can't spin, not even if you apply step pulses. When the driver is enabled the motor is on holding torque but starts spinning as soon as step pulses are applied.

This is why I suggested to check he didn't have settings or the wiring backwards - high/low (if actually wired in that is).
Enabling during pc booting, disabling when it comes to life.