Driving stepper motor - ok to keep it energised? - Page 1
Forum section: electronics / projects

author: deephaven
author_rank: Frequent Contributor
timestamp: April 18, 2012, 07:45:02 am
content: If I'm driving a hybrid stepper motor but need to have a strong braking action (over and above the detent torque), are there any issues with keeping it energised for a long period of time whilst it is stationary?

author: Psi
author_rank: Super Contributor
timestamp: April 18, 2012, 07:47:58 am
content: I imagine this will depend on the stepper motor in question.Do you have the datasheet?There might be issues if the stepper has a fan inside to keep itself cool, as this wont be spinning.But i've not seen inside many steppers so i dunno how common internal shaft fans are.

author: deephaven
author_rank: Frequent Contributor
timestamp: April 18, 2012, 08:11:46 am
content: Data sheet pdf:http://www.geeplus.biz/FTPROOT/stepper_motor_size23.pdfIt's a DSM5776H-18100

author: Rerouter
author_rank: Super Contributor
timestamp: April 18, 2012, 08:39:25 am
content: with stepper motors, its generally ok to do so, but it shall get very hot it for a large number of minutes,what i have seen done before (very odd odometer design) was a reversable catch, where you have a toothed gear, and a solenoid that normally rests pressing out, so normally it locks the gear in place, and while the stepper motor is in motion, the solenoid is pulled back,perhaps specify your braking force required?

author: amyk
author_rank: Super Contributor
timestamp: April 18, 2012, 10:55:47 am
content: The datasheet doesn't mention maximum power dissipation (nor maximumoperating temperature) but you can calculate how much power it's dissipating as it's essentially a resistor when supplied with steady current. Forced cooling may be required.

author: G7PSK
author_rank: Super Contributor
timestamp: April 18, 2012, 08:11:37 pm
content: Why not use a motor with electric brake, something like this.http://www.mclennan.co.uk/datasheets/european/stepper/steppermotorbrakes.pdf

author: deephaven
author_rank: Frequent Contributor
timestamp: April 18, 2012, 08:19:35 pm
content: Quote from: G7PSK on April 18, 2012, 08:11:37 pmThat could work and would be a good solution as the brake is on when it is de-energised thus lowering the standby power requirement. Thanks for pointing that one out.

author: jerry507
author_rank: Regular Contributor
timestamp: April 19, 2012, 01:40:42 am
content: There is a reason they give RMS current in the data sheet. Stepper motors are typically driven with a current chopper circuit. Essentially the current in the coil is compared to a reference current. For a stepper that is stepping in full steps, this reference current is the max current for the motor (given in the datasheet). Different current ratios for the different coils allows microstepping.The chopper is simply a comparator driven with the voltage representing the reference current and the voltage across a sense resistor. When the sense voltage is greater than the reference, the stepper driver outputs are turned off. This allows the stepper to hover around the max torque (giving you holding torque) while not dissipating too much heat in the motor.So the short answer is no, there is no problem with that. In fact that is generally how they are used and how most every stepper driver IC is set up to work.

author: Kremmen
author_rank: Super Contributor
timestamp: April 19, 2012, 07:21:21 am
content: That is basically correct. Additionally to that, i have seen drivers that have a control input to modify the current limit based on the driving state of the motor. The intention is that when accelerating or pulling a heavy load you can increase the limit beyond nominal to achieve maximum torque and when the motor is just holding position, you can lower it to whatever is sufficient to reliably prevent movement.The smart current limit requires an external connection to the current limit comparator reference pin so it works only for certain types of drivers and controllers.

author: deephaven
author_rank: Frequent Contributor
timestamp: April 19, 2012, 09:23:16 am
content: Thanks guys, all useful information. Looking at data sheets for modern stepper motor drivers, they come in alarmingly small packages for power drivers.

author: Kremmen
author_rank: Super Contributor
timestamp: April 19, 2012, 02:09:51 pm
content: So did you plan to design the driver yourself or buy an off the shelf box to do the job? In the former case the vanilla L297 / L298 parts seem to be a good match for the motor. They would be cheap(ish) and dead simple to apply. If you planned to buy ready made kit the something like the Gecko products could be the ticket. I know those have been pretty popular here in Finland. But of course there are any number of products to choose from.

author: deephaven
author_rank: Frequent Contributor
timestamp: April 19, 2012, 02:29:10 pm
content: Quote from: Kremmen on April 19, 2012, 02:09:51 pmI plan on doing my own driver. My existing driver board I designed more around 25 years ago and uses the L297 and L298. I decided it was time to use a more modern chip with all the useful features it offers including micro-stepping.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: April 19, 2012, 02:39:56 pm
content: Quote from: deephaven on April 19, 2012, 02:29:10 pmIt's normal to keep your stepper energised when stationary to prevent movement etc as stated. A nice drive board by a Uk designer I have used is herehttp://www.diycnc.co.uk/

author: jerry507
author_rank: Regular Contributor
timestamp: April 20, 2012, 06:48:52 am
content: The funny thing about steppers is that people see the 1.8 deg/step figure, and then see all these microstepping drivers and assume they can easily step at 1.8/16 deg/step really easily. "Stepper motors are so easy!" Sadly your mechanics and your load properties largely determine the step size you can accurately hit, so don't go overboard with the microstepping. Unless you've got some nice critically damped mechanics, you will probably be best off only 1/2 or 1/4 stepping, depending on what your driver uses.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: April 20, 2012, 06:55:21 am
content: Quote from: jerry507 on April 20, 2012, 06:48:52 amUnless you spend BIG bucks on the motor/driver card andare very careful with the setup

author: deephaven
author_rank: Frequent Contributor
timestamp: April 20, 2012, 08:18:59 am
content: Quote from: jerry507 on April 20, 2012, 06:48:52 amMy application isn't very critical on positional accuracy, but it is critical on the acoustic noise level. I am hoping that by using micro-stepping I can reduce the noise level and also keep away from the motor's resonant frequency.