Hi John,
I'm using a dump circuit but, not for decceleration/back EMF issues. The dump
circuit is to bleed off the current in the large capacitors on the power
supply. The reason for this: When the E-stop is pushed, unlatching that
circuit, through a DPDT relay, the resistor in the dump circuit will rapidly
bleed off the current stored in the caps and bring the machine to an abrupt
stop rather than slowly coming to a stop as the motors eventually bleed the
caps. Its a safety issue. In regards to back EMF, most CNC PC based softwares
like Mach2 allow the user to configure the acceleration/decceleration and
velocity. Known as servo ramping. As far as I know, the controlled
decceleration prevents high rates of back EMF. Unless one is planning on rapids
of some astronomical rate and very abrupt stops and starts, back EMF generally
isn't an issue.
Ron
John Meissner <[EMAIL PROTECTED]> wrote:
Hi Ron,
I'm just wondering if you are using a "dump" circuit to drain off
the back voltage when slowing the motors rapidly? I'll be using a
75VDC supply and after what you say about the 118VDC breakup point,
would a dump be absolutely necessary?
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