Dynomotion

Group: DynoMotion Message: 9338 From: Hugh Sontag Date: 3/21/2014
Subject: Snap Amp faulting
Hi Tom,

I am having difficulty with our CNC machine. 

This is a CNC router with 4 stepper motors - two (X0 and X1) for the gantry, one for the Y axis and one for the Z axis. Axis X1 is slaved to X0.

When I power it up and initialize it, the Y and Z axes, which are connected to Snap Amp 1, work normally. They can be moved with the arrows in KMotion CNC, and they seem to be functioning as expected.

Snap Amp 0 is connected to the X0 and X1 stepper motors. Snap Amp 0, even when the X0 and X1 axes are not enabled, seems to start faulting without cause.

For example, from power-on, and after initialization, SnapAmp 0 starts making the clack-clack-clack characteristic of an ongoing fault, even though the X0 and X1 axes were never enabled.

I get > 10 M ohm from each stepper motor wire to power supply ground, and > 10 M ohm from each stepper motor wire to its shield.

I've attached screen shots of the Analog Status for SnapAmp 0 and SnapAmp 1, to show what I'm seeing.

The initialization program has been operating previously without a problem. I've attached a copy of that as well. Since this problem surfaced, I commented out the enable of the axes, and I have been doing that manually.

Could you suggest some things I can do to narrow the problem down? I suspect that it's related to SnapAmp 0, but perhaps you can suggest other possible causes.

Hugh

   @@attachment@@
Group: DynoMotion Message: 9340 From: Tom Kerekes Date: 3/21/2014
Subject: Re: Snap Amp faulting [3 Attachments]
Hi Hugh,

I see one problem.  It looks like you have a 75V supply but are telling SnapAmp to clamp the voltage at 60V.  This can draw huge currents and may damage SnapAmp.  With a 75V supply you should clamp at 80V.

You should check your Steppers that there is no short between the coils.  And that the coil resistance is reasonable.

But otherwise you may have a bad SnapAmp.

You might disconnect the motors and see if it still draws big currents.

Or try swapping the SnapAmps (But you should check the motors and wiring beforehand)
If you want to send us the board we can test it.

Regards
TK


Group: DynoMotion Message: 9341 From: Hugh Sontag Date: 3/21/2014
Subject: Re: Snap Amp faulting
Thanks, Tom. I'll correct the clamp voltage tomorrow and retest.

I have measured the resistance of each coil (plus the wire that goes to it) at the SnapAmp connector, with the connector pulled out of the SnapAmp. In each case, the resistance is 0.6 to 0.8 ohms, which is what I expect.

Hugh


On Fri, Mar 21, 2014 at 8:19 PM, Tom Kerekes <tk@...> wrote:
 

Hi Hugh,

I see one problem.  It looks like you have a 75V supply but are telling SnapAmp to clamp the voltage at 60V.  This can draw huge currents and may damage SnapAmp.  With a 75V supply you should clamp at 80V.

You should check your Steppers that there is no short between the coils.  And that the coil resistance is reasonable.

But otherwise you may have a bad SnapAmp.

You might disconnect the motors and see if it still draws big currents.

Or try swapping the SnapAmps (But you should check the motors and wiring beforehand)
If you want to send us the board we can test it.

Regards
TK


Group: DynoMotion Message: 9342 From: Tom Kerekes Date: 3/21/2014
Subject: Re: Snap Amp faulting
Hi Hugh,

Also don't forget to check for a short between coils.  They should be completely isolated.

Regards
TK

Group: DynoMotion Message: 9345 From: Hugh Sontag Date: 3/22/2014
Subject: Re: Snap Amp faulting
Hi Tom,

I double-checked that the resistance between windings on the stepper motors are > 10 M ohm, as they should be. 

Changing the clamp voltage to 80 volts didn't change any of the symptoms.

The X stepper motors (I call them X0 and X1, they are for the gantry) are on SNAP0. The Y and Z stepper motors are on SNAP1.

I've disengaged the rack and pinion on the X motors for testing.

Just enabling one of the X axes causes SNAP0 to fault. The ADC's in the Analog Status show -19 A on #8 and #9, and -18.8 A on #10 and #11. If I turn off the 74-volt power for the motors, which is connected to the power input on the Snap Amps, the A/D values stay the same. They're not constant, but they are consistently right around the values I mention. 

The only thing that resets the A/D values on SnapAmp 0 is turning off the +5V power to KFLOP and turning it back on again.

Also, just running the Z axis motor causes Snap Amp 0 to start faulting, even though the X0 and X1 axes are not enabled. I can hear the clack-clack-clack coming from the X0 motor.

I'm ready to send our KFLOP and both Snap Amps to you for testing. Is that OK with you?

Thanks,
Hugh


On Fri, Mar 21, 2014 at 10:03 PM, Tom Kerekes <tk@...> wrote:
 

Hi Hugh,

Also don't forget to check for a short between coils.  They should be completely isolated.

Regards
TK

Group: DynoMotion Message: 9346 From: Tom Kerekes Date: 3/22/2014
Subject: Re: Snap Amp faulting
Hi Hugh,

Sounds like a bad SnapAmp.  Email Support for an RMA # and we will test them for you.

Regards
TK