RE: [CAD_CAM_EDM_DRO] Re: E-stop relay welds contacts for load dump resistor

Don:



I have done industrial CNC equipment for some 25+ years, basically retired
now. In ALL cases, the E-Stop is exactly that and Emergence Stop and is
designed to interrupt the incoming AC power. In most cases, there is a
smaller relay which in turn controls a much larger contactor designed to
handle the full load current for the machine. In some smaller machines we
simply interrupted the 110VAC "control" circuit. Of course once that
circuit was interrupted everything stops, including the power to the servo
drives. I missed your earlier posts but get the idea you are trying to stop
just the drives with your circuit. That is actually dangerous and, as you
seem to be finding out, doesn't work very well. Again, not having seen your
earlier posts, I am not completely certain of what you are attempting to do.
Contact me at cnc002@... <mailto:randyabernathy@...> if
you think I might be able to help. A copy of your machine schematic would
help.



Randy Abernathy
CNC and Industrial Machinery
service, repair, installation and
design

4626 Old Stilesboro Rd NW
Acworth, GA 30101
Fax: 770-974-5295
Phone: 678-982-0235
E-mail: cnc002@...

_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of David G. LeVine
Sent: Sunday, January 30, 2011 8:06 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: E-stop relay welds contacts for load dump
resistor

On 01/30/2011 02:48 PM, kzf817 wrote:
> + Terminal on power supply Cap---> 7 ohm resistor--->

I did not see where there was an interlock on the power supply to
protect the resistor against the power supply against the ESTOP
crowbarring the output. You need one or the 7 ohm resistor must be
better than 1/2 KW!

Consider a DPDT relay. When energized (I.E. no ESTOP), it allows AC to
flow into the supply and is open in the resistor path. When deenergized
(i.e. ESTOP or power failure), it opens the AC input to the supply and
shorts the 7 Ohm resistor to ground.

WARNING ACSII ART!

AC in ------- |
^------| Power supply Contact #1 Normally Open
| AC input
AC return ---------|

|
+ out |-------------> To load
| |____[resistor]___
Power supply DC output | ________________V Contact #2, Normally Closed
| |
return|------------> To load
|

If this is confusing, I will make a better drawing, but it is pretty
easy to understand. If the relay is powered on, AC flows into the power
supply and runs the load (motors, etc.) If the relay is powered off,
the AC turns off and the dump load goes across the power supply output,
pulling it to zero. Until the relay is repowered, the supply will not
deliver power.

Without Contact #1, the dump resistor will draw 1/2 KW + until the relay
is released, or something fails.

Dave 8{)





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