View Full Version : Moving Servos with power off

01-26-2010, 12:57 PM
I've read somewhere that if you push your gantry around with power off that it can back feed voltage to the control box and damage it. Any truth to this in the case of DynaTorch machines?

And a dumb question about grounding. I've grounded everything to it's own rod right under the machine per the manual with one exception: It shows grounding the moniter also, how in the heck do you attach a ground wire to a unit with no exterior metal parts?

01-26-2010, 04:26 PM
Can't speak for Dynatorch, but a motor also regenerates when decelerating, if the energy can be possibly be to high, drives are fitted with regen braking resistors or circuitry to absorb this.
Unless it has a really large reduction, the regen voltage should not be excessively large when physically back feeding the motor.

01-26-2010, 05:29 PM
It depends on the components of the circuitry, TTL components are less common in CNC machines because any voltage over +/-5V will most likely toast them. CMOS components are heartier (+/-12V) and as previously stated, electrical induction by way of moving the gantry (which moves the magnets in the motor coil) is probably not going to fry the integrated circuitry. You'd need to analyze the circuit diagram and get spec data on the components in "the line of fire" to figure out just how susceptible the circuit is to such feedback.

as for the monitor, i think it's a safe bet that it's already grounded through the relevant circuitry.

01-26-2010, 05:36 PM
The motor, stepper, AC, BLDC is going to be fed from high voltage switching components, this is where the BEMF will be directed, so I don't think any TTL components would be affected, also, as mentioned, when normally decelerating fast, this same back EMF is also generated at this time in normal operation.