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{)