[rogerfries]

I have another issue with my new plasma table. My setup is new so something could be wired wrong. I have an intermittent fault on power up. Sometimes it faults most times it doesn't. If it faults I just power cycle it and it probably will work next time. It does not seem to fault while it's running, just on power up. Any Ideas?

Thanks!

[rogerfries]

This problem seems to be worse in the cold. When the motors are cold it may take 3 or 4 restarts until it starts. Once it starts (goes ready with no fault) it's good and does not fault while running. It seems like the big inrush current of starting these motors causes the fault. I have an Antek toroidal Transformer 29.3 VAC tests at 31.6 no load
Driver power 41.6 VDC @ No Load. Power conditioning board PMDX-136-5010.

Any ideas? Thanks!

[morestuff]

Where are you switching the power on and off?

This should be done on the primary side of the transformer.

Switching the DC going into the G540 is not recommended
by Geckodrive.

Regards,
Steve Stallings
www.PMDX.com

[rogerfries]

Steve,

Yes, I'm switching the AC main on the primary side of the transformer using a magnetic contactor (PMDX-Contactor18-120). I've seen some posts about adding a capacitor to to solve this. There are of course capacitors on your PMDX-136-5010 board. Is a bigger capacitor worth trying?

One thing that makes this problem particularly annoying is when I power this transformer up or down the interference either hangs or reboots my PC. I put the computer motherboard in the same metal box as the Gecko & power supply. Probably a bad idea. I think I'm going to try to mount the power supply in a separate metal box to see if that helps the interference problem. The power supply and the PC are plugged into separate surge protectors and separate outlets. I also have a MOV across the coil on the contactor as you recommended.

Seems like no CNC workshop this year in Ann Arbor :-( Any chance I'll see you at Cabin Fever in York PA?

Thanks

[morestuff]

Hi Roger,

Extra capacitance across the DC power leads is not likely
to help. As you stated, your supply already has plenty.

Inrush current may well be an issue. There are three
sources of inrush in this system. The first is the magnetizing
current of the toroidal transformer. This is because a
toroidal transformer is more efficient and has a low
input impedance at startup. This inrush should not be
visible to the current limiting circuit in the G540.

The second is the capacitors across the DC motor supply,
both those in the PMDX-136-5010 and inside the G540.
The charging current for the capacitors inside the G540
could trip the circuit IF you were switching the DC side
of the supply, but since you are not, this is not suspected.

The third is the magnetizing current of the stepper motors.
This usually not an issue, but I cannot rule it out. As a
test, you could unplug one or more of the motors as a
test because the over-current sensor in the G540 looks
at the total current used by all 4 drivers.

You could try putting an inrush limiting device in series
with the primary of the transformer. The CL-60 device
from Digikey is one good example:

http://www.digikey.com/product-detai...C006L-ND/19756

This approach would slow down the ramp up in DC supply
voltage and allow more time for the capacitors and motors
to stabilized without excessive current.

Please note that this device limits inrush but does NOT
substitute for a fuse. Also, these devices are based on
thermal action and can be fooled by quickly cycling the
power after they have warmed up.

If you are suffering from electrical noise due to the power
supply turn-on, you could put MOVs across the contacts
of the power contactor in addition to the one you already
have across its coil.

It is sad that there will not be a CNC Workshop in 2013. If
they decide to run it again, I will plan on being there.

PMDX will be at Cabin Fever as usual.

Regards,
Steve Stallings
www.PMDX.com

[rogerfries]

Steve, I tried both the inrush current limiter and the MOV's across the contactor. No Luck. I'm now dealing with the interference problem by using an Ethernet smooth-stepper and relocating the PC a distance from the Plasma machine. As for the power up bug, I can deal with it just power cycle it a few times to wake it up.

I'll see you at Cabin Fever

Thanks