I’m working on a project that has 8 step motors #1476 with 8 controllers #3134 being powered from a 240W 24V 10A Meanwell power supply.
The motors are only spinning aluminium disks (art project) 400mm x 3mm.
Everything works well if the motors are decelerated nicely, however if the motor is accidentally halted (click on the wrong button in the TIC driver software) then things go crazy with the rail voltage raises to 40V or more and the Meanwell power supply shuts down for several minutes.
I can put a suitably rated diode from each controller to stop the back feed into the rail but can the TIC controller be damaged? Does it have any internal mechanism to deal with such a high voltage?
UPDATE: maybe I’m worrying for nothing, the supply rail does indeed go to ~32V as read by the TIC software and about the same with an analog meter. However this only happens when the “De-energize” button is clicked and not the “Halt motor” button. The motors will be driven via UART commands so as long as we don’t issue the equivalent De-energize command it should all be OK. We were worried that the same thing would happen if the power suddenly was lost but that’s not the case.
Halting a stepper motor and de-energizing it are very different. When the motor is halted it stops, but continues to hold position and draw current. When the motor is de-energized it stops because the driver stops supplying it with current. If your motors are drawing significant current and then are commanded to de-energize abruptly there will be a lot of energy that needs to get dissipated and that can result in the voltage spike you are seeing and current going back into your power supply.
Adding a diode inline with the supply like you suggested is a good precaution, but yes, you would also want to protect the Tic by adding some kind of zener or TVS diode near its power input. We are actually very close to releasing a shunt regulator board that should be useful in protecting against issues like yours. I expect it to be for sale later this week. If you are interested, keep an eye on our new product category or blog.
Thanks for the reply Claire, we were thinking along the same lines for the protection of the driver, maybe with a small series resistor with the zener, the controller is rated at 35V max.
As far as the new contoller is concerned one of the panel with 8 motors is already built and the other 8 motors and drivers were shipped out yesterday from your place, we’ll keep it in mind for future projects.
Someone else is writing some code to talk to all 8 motors, once we have them all running at the same time we may try to see what happens, maybe blow up 8 controllers at the same time but I think that if the shutdown sequence is well controlled, ie halting the motor and then de-energize, the problem is not going to occur.
The shunt regulator board I mentioned would not take the place of the Tic. It would get added separately across VIN and GND in your system (similarly to how you would add a zener or TVS diode).
Good luck with the project; we would love to see it when it is all put together!
Another option you can consider is connecting a battery with the same voltage in parallel with the power supply, which will help absorb the back-emf generated by accidentally halting the motor/rapid de-acceleration.
Not sure how the new shunt regulator would work here, I have 8 motors that could stop at the same time. I also see that the series diode is not part of the board making things a bit messy.
My understanding was that the diode was mounted on the board to prevent the back EMF getting back into the power rail and the MOV?? clamping the voltage to the local driver board. (8 off)
The blog seem to indicate just one BIG diode in series with the power rail and one shunt board? I know it makes the board smaller having SMD resistors but I would have preferred big 5W or even 10W concrete block resistors and a huge FET.
The series diode is often not necessary, and it needs to be big enough to support your load current, so that is something that should get selected to match your application and budget, including power and heat dissipation budgets, since that could waste quite a bit of power. That is why it’s not on the board, and if you want to use one, you would need to add it externally.
How to arrange your regulators depends on the details of your system. One board might be completely sufficient. If you have long wires to the motor controllers, you might want to put a separate regulator at each motor controller, or one for every few controllers. However, please note that putting more than one shunt regulator right next to each other is not effective since they won’t be exactly matched, so just one of them would end up taking all the power, anyway.
but I think that if the shutdown sequence is well controlled, ie halting the motor and then de-energize, the problem is not going to occur.