Re: [CAD_CAM_EDM_DRO] Servo heat-sensors or paranoia? servo protection questions

Jon Elson <elson@...> wrote:

A fuse before the drive should blow before the motor fries.

>

This is not likely to work, until the drive burns out! Due to the
switching action, and the fact that a stalled
motor develops no back EMF, the voltage across the stalled motor is near
zero, therefore the power consumed
is small (voltage x current). While the motor may be getting 20 amps
(at a few volts), the drive will be drawing
just a few amps at the DC supply voltage, so that power in is close to
power out. So, the fuse will have little
current through it, and will NOT blow. (For instance, I test my PWM
servo amps at 20 A into a nearly dead short,
an ammeter shunt. With 30 V in and 20 A out, the amp only draws about 5
A from the power supply.)

Jon

/////Hi Jon, I see, the current between the drive and servo is isolated from the DC supply side of the circuit. So, a fuse there is moot? Then what type of protection is possible in the event of a stalled servo using a Gecko? Would it be effective to fuse between the drive and the servo instead?

Also, what is actually happening with an encoder when a servo is at idle? There is 5v, ground, A channel and B channel. Is there a constant A or B signal back to the drive or is it simply a fast pulse and the drive waits for another to move, correct, etc.? Seems there could be some type of device that monitors and in the event of lost encoder activity which would unlatch the E-stop circuit.

Ron

(still laughing)



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