Stepper motor 28BYJ-48 and A4988 - Page 1
Forum section: electronics / beginners

author: NHSA
author_rank: Regular Contributor
timestamp: December 21, 2021, 06:38:33 pm
content: Hi,I want to drive a 28BYJ 5V stepper motor with a A4988 driver and use 12 V. Motor will be converted into bipolar by taking away the common wire and separating the copper connection on the motor PCB.I assume this is possible if I adjust the current limit to the calculated 240mA which I get by dividing 12V / 50 Ohm per phase.Is it that simple or why do they have 5V and 12V versions of this motors.Thanks Rainer

author: Doctorandus_P
author_rank: Super Contributor
timestamp: December 21, 2021, 06:53:41 pm
content: There are several different manufacturers for this motor.It is a very common motor, originally designed to control the air flaps in air conditioning systems.There are lots of subtle differences between these motors:* Different gear ratio's* Different voltages.* Some (most / all?) have build in overload protection that slips if the output axle is hold still.Voltage ratings for stepper motors do not mean much, as any decent motor driver controlls the motor current directly.Because there are so many variants of this motor, it's difficult to get exact or verifyable specifications.Therefore the best option is to measure it yourself. Start with a moderate current, and then increase the current until the motor gets hot. If it gets too hot, then reduce the current again.If you want the motor to run quickly, then buy the low voltage variants, because these have lower self inductance.

author: NHSA
author_rank: Regular Contributor
timestamp: December 21, 2021, 06:57:59 pm
content: Thanks Doctorandus_PWill do as suggested.I still do not have the motor but wanted to be ready when I get them.Thanks Rainer

author: NHSA
author_rank: Regular Contributor
timestamp: December 22, 2021, 08:01:58 pm
content: Hi,Just got the 28BYJ-48 5V stepper motors and measured the coils after removing the red wire and converting it into a Bipolar motor. Not yet tested with the Arduino and CNC shield with A4988 driver.The coils have both exactly 44.24and so I need to adjust the Vref of the A4988 to about 12V / 44= 272 mA and the Vref is .272 x 8 x 0.1 0.7 = 0.152 V ~ 0.15 VRainer

author: lscw
author_rank: Contributor
timestamp: December 23, 2021, 10:26:05 pm
content: I'm driving a 5V aliexpress-ish 28BYJ with 9V for additional torque at approximately 20RPM, for 30 second bursts of operation to raise or lower a window blind. It gets a little too warm at that voltage with repeated/extended use so I made sure to disable the stepper during inactivity but for the low duty cycle it works well.

author: MarkLiu
author_rank: Newbie
timestamp: December 24, 2021, 02:40:24 am
content: 5V is the rated voltage. Nowadays, constant current drivers are generally used, and the recommended range of drive voltage is 12-24 V. Generally speaking, the higher the voltage, the higher the torque, but the higher the heat, so it is not recommended to use too high a voltage. In addition, a good 12V switching power supply is indispensable, the power supply will last a long time, and it is not worth it to damage the equipment. This Meanwell power supply is I found the price-performance is quite good.https://www.omc-stepperonline.com/power-supply/

author: Refrigerator
author_rank: Super Contributor
timestamp: December 24, 2021, 08:21:50 am
content: I've used these motors with these drivers in a homemade 3D printer and you can adjust the curent to make them work.I pushed mine prety hard and had to glue heatsinks on to keep them operational.But if you don't push them too hard it's ok.

author: lscw
author_rank: Contributor
timestamp: December 24, 2021, 09:03:36 pm
content: The A4988 doesn't appear to be a constant current driver. The only mention of current regulation in the datasheet is a 2A over-current cut-out. Whenever I've seen one of these motors for sale bundled with a driver it's been a ULN200x darlington array.

author: wizard69
author_rank: Super Contributor
timestamp: December 24, 2021, 10:35:13 pm
content: People have already mentioned that steppers are controlled by current not voltage. If you look (you have done this right) at the A4988 datasheet you will find this equation: ITripMAX = VREF / ( 8 × RS) and frankly a bunch of others that will help you set the operating point. If you want more info on steppers and stepper technology try:https://www.geckodrive.com/support.html.Generally operating voltage is much higher than the "rated" operating voltage for the stepper, as this allows the driver to quickly saturate the windings at the correct operating current. When using single chip drivers though you need to be careful about the driver chip's rating.A couple of other things to consider:People often set motor current based on how hot the motor feels, this can be a mistake. The case of a stepper can be extremely hot, to human touch and still be operating within specs. Generally you want to set operating current for a specific motor correctly and see what you get. The only way to know if it is too hot is to measure temperature and compare to data sheet specs for that motor. Now a lot of the low end motors from China, have little in reliable specs and may not perform well compared to name brand, documented steppers so use some common sense here. In a nut shell proper current is the only way to realize the rated torque from a motor. By the way the reason steppers feel hot is that the windings are right next to the case surface, in some cases the case is the metal laminations for the stator.The windings of a stepper have an inductive component which impacts the utility of measuring DC resistance. This goes back to why modern stepper drives operate at a much higher voltage than a motors rating. It can be useful to know a motors DC resistance but not really for getting the stepper to operate correctly with modern drive tech. With a modern driver you really want to set operating current, voltage impacts speed and can also have an impact on heat. A good elementary explanation of voltage in relation to steppers can be had here:https://www.e-jpc.com/stepper-motor-voltage-explained/.Here is another approach to how you set a steppers operating voltage:http://www.piclist.com/techref/io/stepper/inductance.htmNote the last couple of lines: "Where does the 32V or 64V come from?Max supply voltage is 32 times the square-root of inductance in mH. It's an equation we derived for NEMA-23 motors without a heatsink where the motor temperature rise will be 85C above ambient.That's a nasty-hot motor.". In this case the attempt is absolute max performance which might not be what everyone wants. It should be noted that on commercial machinery it is very common for manufactures to put warning labels on steppers or near them because they get extremely hot. In other words take care.Lastly some of these Chinese steppers where never really designed for precise motion control work. They are often ran well under even the mystery manufactures specs to aid in long life in non precision applications. That can mean crappy mechanical tolerances that don't respond well to high operating temperatures or bearings with cheap low temp lube. A cheap motor can be frustrating, so it doesn't hurt to have a few on hand possibly from different sources.Quote from: NHSA on December 22, 2021, 08:01:58 pm

author: lscw
author_rank: Contributor
timestamp: December 24, 2021, 11:21:46 pm
content: Quote from: wizard69 on December 24, 2021, 10:35:13 pmThanks for pointing that out, I missed that.As far as the OP is concerned, Texas instruments yt channel has some good motor control seminars. One such series is calledTeaching Old Motors New Tricks