Re: [CAD_CAM_EDM_DRO] Gnds, and more Gnds and Gecko's Questions..........

wanliker@... wrote:

>I am finally making progress on my control panel again, for the EMCO Compact
>5 CNC Lathe I am converting....
>Tim, will be here tonight and want to persuade him to help me set it
>up..............
>
>In the mean time I have questions about grounds,
>
>I am using an early Wonderboard that has two separate 5 volts supplies. One
>is marked (Comp). The other is (Ext). The two +5 volts supplies are
>completely isolated from each other
>
>The first one is a +5 volts (Comp), supply with its ground connected only to
>the computer ground, and the ground for the Opto Isolators on the input side.
>
>Its +5 volts is providing, thru 1 K pull-up resistors, the power for the
>input side of the Opto Isolators only, from the computer.
>It is not a +5 that comes from the computer itself, it is a separate power
>supply, on the Wonderboard.
>
>The second +5 volt (EXT). Supply, is for the external Opto Isolator circuit
>to the drives, it is feeding the output side of the Opto isolators, I will be
>using these signals for the step and direction to the drives.
>
>Questions:
>1. When using the Opto Isolated circuit, do I still connect the computer
>ground to the main power supply ground????????
>

This is done through the parallel port cable.

> This would tie the controller
>to the electrically isolated Computer/Parallel port if I do......It is
>isolated now, with its own Opto Isolated circuits and the separate +5 volt
>(Comp). Power supply, on the Wonderboard.
>
>2. Am I correct, that, the +5 (EXT). volt supply that feeds the output side
>of the Opto Isolators, is the same + 5 volts that goes to the Gecko's?????
>This output side is where I am getting the step and dir signals for the Gecko
>320's.
>
>

Yes, I think that is right. But, these optocouplers are wired to pull
high, and have a 1K pulldown
resistor to GNDEXT, which is almost certainly not enough current to
light the optocoupler inputs
of a Gecko wired in common +5 mode. Can this Gecko model be set for
common gnd mode?
It is possible that using a lower value resistor SIP in RP2 would help,
if you can't set your
Gecko for common ground.

>3. Do I do anything with the Ground of that +5 volt (EXT). supply?? This is
>the Ground that is for the output side of the Opto Isolators that are feeding
>the step, dir, and +5 volts to the Gecko's.
>I have it connected to the controller main power supply ground now, is this
>correct??? Or should it be floating??? Or connected some where to the
>Gecko's?????? This is the - of the +5 going to the Gecko's, assuming I am
>correct in question #2.
>
>

Don't connect this ground to the main ground. it should be floating,
but must connect back to the
wonderboard's GNDEXT terminals, pins 2,4,6,8 of ST1, and pin2 of ST2,
and pin 9 of J1.

>Gecko 320 questions:
>EStop
>5. I am using relays to select the power on and off to the Gecko's, for
>driver selection. The cabinet has X, Y, Z, and A drives. For the lathe I
>will only be using X and Z, later the same cabinet will be controlling a
>Mill, and using X, Y, Z, and sometimes A.
>
>The relays drop out under an EStop or Fault, I have 470 MFD caps mounted
>right at the Gecko's G-320 terminals.
>
>6. When dropping the relays with an EStop or Fault, will this cause any
>problems for the Gecko 320's?? Can I drop/isolate both the Power Supply +
>and - with the relays or will dropping both cause a problem for the
>Gecko's??? This would happen in an E stop or Fault situation only, or if the
>drives were not selected for operation.
>
>7. I have some 1000 MFD capacitors, that I could mount at the output side of
>the relays, would this be good for the G-320's in an EStop Stop condition or
>Fault to allow them to have more capacitance during shutdown????? Assuming
>breaking both the + and the - at the same time.
>
>

This will likely cause big problems - not on estop, but on coming OUT of
estop. You have the
main DC supply charged up, and then close the relay, connecting the caps
in the power supply
to the caps in, on and around the Gecko drives. The huge current surge,
perhaps 1000+ amps,
will either weld the relay contacts on the first closure, or degrade
them badly so they won't
work after a few cycles. I have a pretty complicated circuit I have
used in a couple situations
like this, and specifically on my own servo amps. See the 2nd schematic
on this page :
http://jelinux.pico-systems.com/EMC.html
The idea here is that the small 3-pole relay connects a charging
resistor to the amps/drives with
the big capacitors first, charges the capacitors gently (about 1 amp for
the drawing) and then
closes a high current contactor after a delay. It then enables the
drives after a slight delay.
(My drives require a 12 V enable signal). It also provides a drain path
to discharge the amps
and brake the motors after an E-stop.

There's no need to break both + and - at the same time.

Jon