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Author Topic: Stepper motor driver  (Read 428 times)

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Offline drinuTopic starter

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Stepper motor driver
« on: March 24, 2014, 12:16:40 PM »
Hi all,

Can I use one DM556 to drive two stepper motors (not at the same time)? I was planning to use relays for selecting the motor to drive. When I contacted the seller he told me that I cannot do this. Below is the reply I received:

"It is not recommended that you switch one drive to two motors.
There is no protection for an open circuit."

Is this true? Do I have to buy a driver with 2 channels?

Thanks in advance.
« Last Edit: March 24, 2014, 12:18:49 PM by drinu »

Offline jwatte

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Re: Stepper motor driver
« Reply #1 on: March 24, 2014, 02:50:57 PM »
I assume that you would use two DPDT relays to switch the output of the driver to the coils of one of two motors. This can be made to "work" and can be cheaper than using two drivers.
Note that energizing and de-energizing coils while the driver is on may generate inductive spikes. You should make sure those spikes are not higher than the rated voltage of the driver (50V in this case.)

Note that the switching with the relays will not be entirely synchronized, because relays are mechanical parts.
Also note that the un-driven motor will not "hold its position" -- it will be free rolling. If the motors are driving threaded rod type mechanisms, or other mechanisms that don't back-drive, this may be acceptable.

If it were my project, I'd buy two drivers and be happy that it's robust :-)

Offline drinuTopic starter

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Re: Stepper motor driver
« Reply #2 on: March 24, 2014, 06:46:39 PM »
Thanks a lot for the reply. He said that "There is no protection for an open circuit"? Will the driver trigger a fault while the relays are changing position (at the time that no motor is connected, hence to load is detected)?

Offline jwatte

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Re: Stepper motor driver
« Reply #3 on: March 25, 2014, 10:26:31 AM »
It's quite possible that the driver might trigger a fault. Or it's possible that he was referring to the inductive spikes of switching an active circuit.

It sounds to me like you're trying to save the $90 or whatever of buying a second controller, by instead dropping in $20 of relays and relay control circuitry. So, your current project plan will be:
- $90 first controller
- $20 relays
- total: $110

What will very likely happen, is that the project doesn't work like you intend it. Let's say that the problem is inductive spiking, and you fry the controller. You then learn that the intended design doesn't work, and you have to buy two controllers to make your project work. The end budget of your project is then:
- $90 first controller (dead)
- $20 relays (not used)
- $180 two more controllers (working)
- sum $290

An alternative is that the project doesn't work because of open circuit detection, and the first controller doesn't die. In that case, the sum of the project is:
- $90 first controller
- $20 relays (not used)
- $90 second controller
- sum $200

If you want to aim for the $110, knowing that it may very well not work, and you may end up paying $290 to get to the end goal in the end, then that's probably a fine learning experience.
If you just want your project to work, I'd highly recommend this option:
- $180 two controllers (works)

Also, if this will control equipment with spinning tools or heavy construction, where people are nearby, the safety factors are important. If someone ends up with a blind eye or crushed hand, $70 in savings isn't really worth it. If this project doesn't get close to people or is very light duty, then that's perhaps less of a concern.

Offline drinuTopic starter

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Re: Stepper motor driver
« Reply #4 on: March 26, 2014, 01:36:12 PM »
Thanks for the reply. This will be a school project and the reason that I was planning to use a single driver is because I am limited with space and also have a limited budget  :-\ If before switching the relay I disable the driver from the ENA connector, will the driver still see inrush current? The stepper motors will be connected to a horizontal ballscrew so disabling the motor will not make any difference.

Offline jwatte

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Re: Stepper motor driver
« Reply #5 on: March 26, 2014, 02:59:28 PM »
If you disable the driver, then switch with a relay, then enable the driver, it might work.
I haven't worked with that particular driver, nor those motors, so I have no idea whether it will ACTUALLY work.
But, given those usage requirements you're suggesting, it may be worth a try. The worst that can happen is that you fail, but hopefully in that case, you'd learn something from it :-)
(Often, failures actually are better learning opportunities than successes.)


 


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