[Stigoe]

Hi all.

I have a problem with the CNC conversion of my mill and I could use some help figuring out my problem.

My mill is the same as a G0704 (BF25) with steppers (KL-5056/KL-8070 drivers), KFLOP, Konnect and homemade breakout board. Konnect is connected to JP6, while the BOB is connected to JP4, JP5 and JP7. The KFLOP is Rev 1.2 and it is powered externally. The power distribution and a picture (with the BOB disconnected from KFLOP) of my control cabinet are attached to this post.

DC Gnd is common between 5V and 24V, but 48V Gnd is isolated and is only used for the stepper drivers.

What happens is that when I turn on the power for the 48V, after a few seconds, I get a message in Kmotion about "Read failed - Auto Disconnect" and I have to reconnect the USB cable to get it back (after turning off the 48V). I tried to disconnect the BOB from KFLOP and the Z-axis (only axis connected) started to move by itself when I enable the 48V. I still get the auto disconnect message. I have used a ferrite core on the USB cable right where it is connected to the KFLOP.

Anyone have any ideas as to what can cause this and what I can do to fix the problem?

TIA,

Stig

[TomKerekes]

Hi Stig,

Can you tell if KFLOP is being reset and re-booting (LEDs blink and configuration resets to default).

If so it may be picking up noise in the reset wires in your cables. KFLOP Rev 1.2 and earlier are somewhat sensitive to this. Adding a ceramic 1000pF cap on KFLOP's reset input close to KFLOP should eliminate this.


Please see this post on our Yahoo Group.
https://groups.yahoo.com/neo/groups/.../messages/9011

Regards

[Stigoe]

Hi, Tom.

The LEDs flashed a couple of times after I enabled the 48V so I added a 1nF cap between Reset and Gnd. Now the LEDs don't flash, but I still get the error message after about 5 seconds.

Even if nothing is connected to the KFLOP, but powered externally, it still disconnects. I tried to power it by USB without anything connected, and this time it stayed connected. In addition, this time the Z-axis didn't move either. I think it is probably time to break out the scope and take a look at the 5V power...

Stig

[Stigoe]

It took some time, but I finally managed to do some more investigations.

First my scope didn't pick up any spikes on any of the power rails (5V, 24V or 48V), but that was probably that I hadn't set up triggering correctly. I don't know if it is normal to connect DC Gnd and Earth, but I noticed that the DC Gnd on the power plug and the USB shield on the KFLOP is tied together and also tied to the mounting holes, so DC Gnd and Earth are connected together through the KFLOP. I also tried to connect DC Gnd and Earth together with a separate wire, but it was still disconnecting after enabling 48V. I have also connected 48V Gnd to 5V and 24V Gnds.

I found that if I disconnected power in to the stepper drivers, KFLOP didn't disconnect when 48V was enabled. I also tried to re-wire the 48V supply so that the Emergency Stop Relay disconnected the secondary instead of the primary, but no change. I tried to remove the wires going from the BOB to the stepper drivers and powered up KFLOP from USB power (with Konnect and BOB connected) and it was still disconnecting.

Later, I managed to set up the scope trigger properly and when connecting to the "power test points" by the JR1 connector, I see that when I enable 48V I get a drop in voltage to about 3.8V on the 5V supply (*10.46.59.jpg), but the ringing is gone after 3uS (*10.48.34.jpg). I don't know if this could be the reason for the disconnects. I also checked with power disconnected to the stepper drives and I got some much shorter pulses both when enabling and disabling 48V (disabling - *11.01.54.jpg).

Edit: I also checked the settings on the card after it disconnected and I had reconnected, and the settings are the same, both before and after.

[TomKerekes]

Hi Stig,

Here are some thoughts:

That scope trace looks pretty bad but since the USB Disconnect happens a few seconds after 48V is applied I think you should be looking for noise after 48V is turned on not when it is turned on.

The USB Shield is connected to KFLOP DC GND at KFLOP. But the mounting holes are isolated on KFLOP. There is one GND Lug hole marked "GND". Are you using that for mounting?

I think the ferrite ring should be at both ends of the USB cable or more importantly at the PC end.

Unplug the USB cable from both ends (KFLOP and the PC) and check that the shield continuity from end to end is less than 1 ohm. Also check that the shield is completely isolated from Earth GND (and all GNDs) when unplugged (It looks like you have a panel connector. Is the shield connected to the panel at that point?)

It seems your 48V was originally isolated from KFLOP. I think it should remain isolated. Why is the 24V not also isolated?

Regards

[Stigoe]

The USB Shield is connected to KFLOP DC GND at KFLOP. But the mounting holes are isolated on KFLOP. There is one GND Lug hole marked "GND". Are you using that for mounting?

No, I'm using top left, top right, second bottom left and bottom right mounting holes. See attachment.

I think the ferrite ring should be at both ends of the USB cable or more importantly at the PC end.

I can try that as well.

Unplug the USB cable from both ends (KFLOP and the PC) and check that the shield continuity from end to end is less than 1 ohm. Also check that the shield is completely isolated from Earth GND (and all GNDs) when unplugged (It looks like you have a panel connector. Is the shield connected to the panel at that point?)

I tested the connectivity of the shield from PC end to KFLOP and the shield connectivity was broken. I have two short cables in series inside the cabinet and the shield was broken on the one connecting to the KFLOP. The other also measures varying high resistance (~10-100 ohm). Two other cables show the same. The normal USB cable had a connectivity of just under 1 ohm. I connected this straight into the KFLOP and now it stays connected, so it looks like it was the missing shield being the problem.

It seems your 48V was originally isolated from KFLOP. I think it should remain isolated. Why is the 24V not also isolated?

It just made wiring easier. I'll try to disconnect the link between the 48V and 5V/24V.

Thanks for the help. Much appreciated. Now I just have to make the configs and, eventually, all the other programs for the planned options.

Br,
Stig