Maintaining power to motors [SOLVED]

Other Hardware Motors, Mechanics, Power and CNC
1

Hi,

I've tried reading posts on this, but couldn't find a complete answer (or maybe I just couldn't wrap my head around it), so apologies if this has been covered before.

I have a circuit which has 12V input, going through a LM2596 DC-DC regulator to step down to 5V. The 5V power line, then goes on to power the arduino (along with other 5V components) and some stepper motors (28BYJ-48 5V).

When the motors are active, the power line (after the LM2596) drops to 3.3V close to where the ULN2003 driver board is connected causing the motors to be underpowered. Closer to the LM2596, the voltage is closer to 5V but does still drop a bit.

How could I stablise the power line so it is 5V consistently even with the motors running?

Whilst I can turn up the LM2596 output (i.e. to 6V which means the motors run closer to 5V when active), the problem then is that this would be too high for the Arduino and other 5V components attached.

For the moment I have it connected through Vin pin instead of the 5V pin on the Arduino (so it goes through the regulator), which solves the Arduino power if I do have the LM2596 set to be higher than 5V, but the other 5V components connected to the breadboard then are at risk unless I add another linear regulator along the way.

Could I maybe add a capacitor instead of setting the LM2596 to a higher voltage to maintain 5V to the motors?

If that is viable, how would you work out the capacitor value to maintain 5V to the motors?

I've included a quick png of the basic hookup at the moment. I haven't included all the 5V components but they would be connected to the breadboard power rails.

Appreciate any advice or input
Thanks

Power drain issue_bb.png
Power drain issue_bb.png3237×1740 456 KB

2

Image from Original Post so we don't have to download it. See this Simple Image Guide

1410e276859ae83456b2ad5ae9195c52dd319cb1.png
1410e276859ae83456b2ad5ae9195c52dd319cb1.png3237×1740 456 KB

...R

3

Psychobob:
When the motors are active, the power line (after the LM2596) drops to 3.3V close to where the ULN2003 driver board is connected causing the motors to be underpowered. Closer to the LM2596, the voltage is closer to 5V but does still drop a bit.

That suggests there is resistance in the line between the power unit and the motor.

Solderless breadboards are not intended for high currents. Try connecting the wires together without the breadboard.

Also, many of those long breadboards have breaks in the side longitudinal connections at the centre of the board.

...R

4

Thanks for the tip about embedding images.

Robin2:
That suggests there is resistance in the line between the power unit and the motor.

Solderless breadboards are not intended for high currents. Try connecting the wires together without the breadboard.

Also, many of those long breadboards have breaks in the side longitudinal connections at the centre of the board.

...R

I was doing this on a solderless breadboard just because I am still working out much of the circuit, but it's good to be aware of what you've told me as it does make sense.

When connecting some wires directly, the voltage still drops, though not as much; now it's more like 4.5V. With one stepper motor it drops 0.5V, I have another 3x to connect (so 4x total), with that I imagine this will drop 2V which puts me back to that first place where the voltage line drops.

Eventually I will make this a permanent circuit with stripboard (or PCB as it doesn't seem too costly to get one made these days), but is there nothing I can add to maintain the voltage level during development?

Ideally I was hoping it was the case of adding some caps to offset the drop, but if that is still not correct, what if I add a second DC-DC converter?

I'm thinking I run the 12V input to two DC-DC coverters, one is for the motors, and the other for the arduino + 5V components (shiftregisters, leds, a few switches etc...).

Thanks

5

IS your circuit for the LM2596 just like shown in the data sheet example?

Paul

6

Paul_KD7HB:
IS your circuit for the LM2596 just like shown in the data sheet example?

Paul

Aside from trying to now connect the ULN2003 driver board to the LM2596 with wire instead of via the solderless breadboard, it is the same as the fritzing diagram.

7

What's the wire current rating? Typical hookup wires are completely unsuitable for high current, you need something with enough copper in it.

8

Thank you all for the advice.

As this is still a WIP circuit, I wanted to avoid soldering anything permanently, but based on your advice I soldered some female header pins to a bit of stripboard, connected the LM2596 to that (which has male header pins soldered). I then added some male header pins to the stripboard and used some female jumper cables to them connect from the stepper driver boards to the stripboard.

I also connect the arduino and 5V components solderless breadboard (for the moment), to the stripboard header pins and those are much better also.

Now if I measure again:-

  • The output of the LM2596, it's 5.1V (I turned it up a tiny amount)
  • The stepper driver input power pins is 5.05V (so a lot better now and only dropping 0.05V)
  • The solderless breadboard for arduino and 5V components is 4.9V (a bit under, but this will go through proper wires later which should bring it back up and for now I think things will still run fine with the small drop)

So seems to be a lot better now!

Thanks again for the help, I'll mark this as solved for now (well, in 5 mins when the forum lets me that is :P)