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I am a newbie electrical engineering hobbyist who is trying to get four 28BYJ-48 stepper motors to turn for a split flap display project. I managed to get each motor working perfectly well individually but when I tried all four together the motors did not have enough torque to turn the flaps. I do not have a multimeter available to me so I require some intelligence in figuring out the problem.

My question is: why are my motors not receiving enough power? Each motor requires 12V to run, I don't know the amperage required and it seems this info is hard to get. Rough estimations online seem to suggest about 250 mA is required per motor but nobody seems sure

Here is the schematic below, I'm using an arduino&ULN203 Driver board to run the steppers I apologize if it is terrible but please know that I am trying my hardest:

If an addition knowledge is needed please do not hesitate to ask for it. Many thanks -KWC

schematic

simulate this circuit – Schematic created using CircuitLab

Slightly tidied up schematic by @Transistor.

Links: Wallwart 12V Motor+UL2003 Driver [pics][3] pics2

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    \$\begingroup\$ Exactly which 'Wallwart 3A 12V' power supply do you have, and which ULN2003 driver board? "I do not have a multimeter..." - time to get one! Please show us a photo of your setup, including all wiring. \$\endgroup\$ Jun 1, 2021 at 21:48
  • \$\begingroup\$ I don't see a +12 connection to your stepper motor but maybe it's in the motor connector. Note how we're able to eliminate a lot of wiring by using GND symbols which instantly show all the ground-referenced points as well as removing a lot of clutter. PSUs are oriented + at top by convention. \$\endgroup\$
    – Transistor
    Jun 1, 2021 at 21:50
  • \$\begingroup\$ @BruceAbbott Will do give me a minute, to collect the stuff. Although I'm confused on how to answer the which wallwart question, I'll get you the link \$\endgroup\$ Jun 1, 2021 at 21:50
  • \$\begingroup\$ @Transistor yes the its the motor connecter. Oh! Thank you the reason for the GND triangles always mystified me. \$\endgroup\$ Jun 1, 2021 at 21:51
  • \$\begingroup\$ Links to products are up, adding the picture now, there are a lot of wires though and I'm not sure it will be helpful :l \$\endgroup\$ Jun 1, 2021 at 21:58

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If the motors are turning individually (or under no load) then it is most likely a power\load problem. This results from resistance\inductance in the wires, large loads cause the voltage to drop in the cable especially in switching applications. This voltage drop leads to a loss in power.

  1. Get a better power supply (like a bench supply with current and voltage display so you know how much power your design is using).

  2. Don't step all the motors at the same time, stagger the stepping so the load on the power supply is distributed.

  3. Use a [power bypass capacitor][1] (or several one for each ULN2003 placed next to the inputs of the ULN2003 on the 12V line and ground.

  4. Use better wires, smaller gauge wires have a lot of resistance and jumper wire may not have that great of contact resistance. It may be that some of the connections may have more than 100mΩ resistance (or the total resistance from the supply to the motor might exceed 100mΩ with the setup above). 100mΩ will cause a 0.12V drop, 1Ω will be a 1.2V drop which would be a significant loss in power.
    [1]: https://www.electronicshub.org/bypass-capacitor-tutorial/#:~:text=A%20Bypass%20Capacitor%20is%20usually%20applied%20between%20the,bypasses%20the%20high%20frequency%20components%20of%20power%20supply.

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  • \$\begingroup\$ Thanks, but I'm confused I why I don't have enough power? I think that I have all the things I need to make this work but haven't put them together right. Buying more stuff seems like a waste of money \$\endgroup\$ Jun 1, 2021 at 22:23
  • \$\begingroup\$ @KidWithComputer: Until you get a meter to measure the current drawn by the motors and the voltages at various points with motors running (or trying to run) you won't know whether or not you have enough power, or where you are losing power. \$\endgroup\$ Jun 1, 2021 at 23:29
  • \$\begingroup\$ @PeterBennett I've had a lot of people tell me that and your probably right, but I'd rather debug for 2 hours then fork over $40 \$\endgroup\$ Jun 1, 2021 at 23:56
  • \$\begingroup\$ @KidWithComputer If you're seriously strapped for cash, you can get a cheap piece of junk multimeter for like $5 at a home improvement store. I strongly advise against this if you have any way of remotely affording a good $50~$100 meter (Extech's EX505 is a good budget one), but a piece of junk meter is better than no meter. Just don't go sticking a $5 multimeter into a power outlet to measure your mains voltage... And especially don't go sticking it in to measure your mains current! (common mistake beginners make that results in blown fuses on good meters and exploded meters on bad ones) \$\endgroup\$
    – Hearth
    Jun 2, 2021 at 0:51
  • \$\begingroup\$ Even the 'junk' $5 meters are fine for low voltage use, and most are remarkably accurate for the price. The extra features you get on expensive meters (auto-ranging, true-rms etc.) usually aren't needed or even wanted. Just don't use the supplied leads for measuring high current, as they often have quite high resistance. \$\endgroup\$ Jun 2, 2021 at 4:33

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