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Relay timing - MAHO MH400E - gearbox control

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RotarySMP:
I am working with a friend who is a professional programmer to create a LinuxCNC comp to control the 18 speed gearbox of my MAHO 400E CNC mill:

I have a question about the timing of motor relays (please refer to the attached schematic), and I would like your opinions:
Sometimes I need to power a relay to reverse the direction of travel of a 24VDC motor, and power the motor relay it at the same time. We could implement a delay in the software, but it would be added complexity.

Is it okay to set 11K7 "reverse direction" and also 11K4 to power the motor at the same time (1ms) ? Or would it be better to give some delay for the reverse relay to close and settle before putting on the power. If both relays are are powered similtaneously and if the motor relay closes faster, then the motor circuit will start to energise in one direction, and then the reverse relay will have to break that rising EMI of this inductive load, before reversing it, causing possible sparking of the contacts? Or is this not an a valid consideration with only 24VDC?

If anyone is interested in the larger project, the retrofit is documented in the LinuxCNC forum:
https://forum.linuxcnc.org/12-milling/33035-retrofitting-a-1986-maho-mh400e?start=450

While the gearbox control software project is in github:
https://github.com/jin-eld/mh400e-linuxcnc/wiki
Mark

awemawson:
It is usual to have a contact on the 'forward' relay that disables 'reverse' and a contact on the 'reverse' relay that disables 'forward' to ensure that they CANNOT both be energised.

RotarySMP:
Thanks for looking at this Andrew.

These is not separate forward and reverse relays, but a "reverse direction" and a "motor on" relay. Motor on always powers the motor, CW if 1K7 is de-energised, CCW if 1K7 is energised.

At the start of a gear change both are de-engerised. If I need to turn CW, no big deal, only the "motor on" relay is energised.

The questions is the case I need to turn CCW. So I command "reverse direction" and "motor on". Does it matter if I energise both at the same time, with the risk that the "Motor On" is a little quicker, and starts building EMF in the forward dierection, before 1K7 closes, and reverses it?

PK:
I guess it depends on how far you want to go. Andrews approach of going from ON+DIRECTION to FWD+REV is sensible and reflects his experience with motor control hardware.
Staying in that space, you can have FWD+REV+BRAKE where the brake relay kicks in when the other two aren't on using simple relay logic. The brake relay just connects a resistor across the motor and pulls some energy out of the mechanism before the next relay engages.

As a software guy I say put a prox tach on the motor and, for a few lines of code control the motor in every situation.  Now you could do this in electronics, but it's nowhere near as easy as doing it in software.

Just my 2c worth.
PK

RotarySMP:
Thanks PK.

THe relays are in the mahcine and work, I am not changing them, just activating them with LinuxCNC instead of the original Phillips controller.

My question is limited to whether delay is needed between switching with 24VDC relays.

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