Using computer PSU as source for project

Using Arduino Project Guidance
1

Hey gang-

Circling back on a project, that is using a computer PSU as my power source... and have some questions/looking for guidance. :slight_smile:

My project is using stepper motor, servo, relays, solenoid vales.. (will eventually also power a RPi and a touch screen).

I figured a computer PSU would be great solution as it have +12v, +5v (and +3.3v) outputs, which covers all my components needs/requirements as far as voltage.

I'm not sure what happened. but things were mostly working fine during testing stages..etc... but the servo started to 'randomly' work.. and then now, not at all. (I can hear it trying.. and when I actually use my hands to move it where it is 'trying to'.. it moves.. and then moves back (with my aided help).. but alone it only make a 'noise' now when attempting to move.

My 'arduino' is a RoboRed (which has a different voltage regulator, and was advertised as supposed to be able to power a servo directly off the I/O pins broken (I/O, +V, GND rows)..

I have tried to use those pins to power the servo (which originally worked during initial project stages).. and also the PSU +5v/GND pins... and for some reason it will no longer 'move' on it own.

I took the servo out of the project, to see if it was servo related issues.... grabbed a different Arduino, and used my benchtop PSU set @ +5v.. the simple servo test worked and things moved.

I threw it back into my project, and the same as above. (a noise/hum) each move attempt.

I checked the wires going to the servo, and it was a +5v (actually I think it was +5.2 or something.. which should not matter for the servo since +4.8-+6.8v is the range). Its a 25g high torque servo.. when the benchtop PSU was used.. I saw it was maxing at roughly 400mA or so.. so should be a problem for the computer PSU to power.

Q: Is my PSU going bad or something?

Q: I read online some people mentioning all GND wires in the PSU should be connected together? (other places to do not mention this?)

Working on this project all day, only to have the servo stuff crap out on me after assembly..etc. I'm all burnt out now hehe, not sure what direction to go here? or what things to trouble shoot?

Clarification:
The steppers, solenoids..etc.. all work fine. (seems to be just the servo?)

Thanks!

2

Hi,
Use your DMM on AC range and measure the DC rails, see if you have significant ripple.
Do you have fuses in the output terminals, the 5V supply can have quite high current capabilities, so if it encounters a short, you can destroy your project.

Power the servo directly from the 5v on the PSU, not through the RoboRed.

Yes, so they all have a common gnd reference, join in star config so the currents in each gnd wire do not cause any interference with each other.

Tom... :smiley: :+1: :coffee: :australia:

3

At a guess, your code may be doing that.

4

Code hasnt changed, and was working fine before? (on the same PSU)

5

As you say, for " testing but then failed".
Try a clean power supply (batteries).

6

Thanks @TomGeorge

My DMM has: DCV, ACV (only 750 & 200 options), DCA.. are you suggesting a capacitor need (by 'ripple')? :slight_smile:

  • I have no fuses, outside of anything in the Arduino/PSU..etc..

  • I am running the servo directly of +5v from PSU (II have also had it on the RoboRed before, when it was working , and stopped, so I tried the PSU +5v rail)..

    As far as the GDN wires.. if they are all connected into eventually in the PSU, why would I need to connect them all together? (online said this gives you more current?).. but I also read that they are all connected together in the PSU.. but broken out because certain outs can pull a lot of current and the wires are only broken out so the gauge of the wires can handle it together/distributed more or less)

I only have a normal/cheapie DMM, how can I check the current output?

Thanks!

7

"I took the servo out of the project, to see if it was servo related issues.... grabbed a different Arduino, and used my benchtop PSU set @ +5v.. the simple servo test worked and things moved.

I threw it back into my project, and the same as above. (a noise/hum) each move attempt."

That's why and it's a guess.

A computer PSU usually needs a minimum load just to run stable, or they used to.

8

I dont have a battery pack that has multiple (+12v & +5v) outputs..

I would have to connect the servo back to the RoboRed. (which I was under the impression that if powered by an outside +12v source allowed it provide enough current for servos to be directly connected anyways??? because of its alternate voltage regular compared to an UNO.) but maybe I'm wrong?

9

I sorta feel it is the PSU as well..

but if it if powering the:

  • Arduino/RoboRed
  • 8 x solenoids
  • 8-channel relay board
  • Nema17 stepper
  • stepper driver board
  • servo

would it not be under some sort of 'load'??

Maybe there are (affordable) computer PSU's that are are already modified for DIY usage (instead of pc's)..? (hmmm)

10

Well, you are going to have to start somewhere and a battery supply would, to me at least, seem like a good place given you need to get back to basics to cure this thing.

11

Is something moving all the time?

You can buy an OEM PSU with 6V output and get a buck converter to power just the board at 5V while the motors run on 6V. A 60W brick now might cost over $10.

12

Yes, your ground wires should all be connected together.
Power your servo from an Arduino clone at your own risk. With a PSU available, there's no reason to risk your board.
Are you powering your Arduino with a PC USB and everything else from a PSU? If so, be sure to ground the Arduino from a gnd pin to the PSU ground also. I

1 Like
13

I am getting a wild voltage on this +5v line from the PUS.. jumping from around +4.9v-+5.2v on my cheapie DMM

What does this mean then?

@bluejets

I will take my benchtop PSU and power things using +12v.

I will then connect the servo to the RoboRed +5v/GND rails, which should negate needing a multi-output power source.

14

Also, did you correctly modify the PSU ahead of time?
https://www.electronics-tutorials.ws/blog/convert-atx-psu-to-bench-supply.html

1 Like
15

Hi,

Try it on the 200Vac range, it will tell you if you have some major ripple.
Computer PSUs are SMPS and they place a great amount of high frequency ripple current on their output capacitors, hence ESR failures.

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An extreme cap failure.

Tom.... :smiley: :+1: :coffee: :australia:

16

@hallowed31

I believe so.. the led is working, resistor in place to have a consistent pull, power switch all working.
, I'll go through the tutorial again to make sure.

@TomGeorge

OK.. ACV/200 settings on the +5v/GND lines going to my servo. (I'll check it out)..

Assuming ripple.. what is the fix here? (and why was it working previously?, but not now?)

update:

ACV/200 setting: anywhere from 9.3-10.0 (at one point I saw a 8.8 when I was first connecting.)

17

Hi,

What readings are they?

Tom... :smiley: :+1: :coffee: :australia:

18

Sorry, I dont understand?

The values displayed on the DMM were jumping from: 9.3-10.0

19

No.. only when the Arduino gets some serial input data, with it parse it and move the steppers/servo and/or also enable a solenoid.

@hallowed31

ok.. so all external GND wires should be connected as 'one' line that feeds the project?
I am only using 1 x 12v connector/line and 1 x +5v connector/line from the PSU.. the others are all tucked away/not used

The 'clone' is a RoboRed (again) supposed to be able to power +5v (higher current) devices like servos directly from the board.

I am powering the Arduino from the +12v power source from the PSU, not the the USB. If you power the RoboRed with the +12v source.. it will regulate @ +5v with higher current to power devices directly... but either way I have tried to directly power from the +5v line from the PSU directly.. but it seems to jump around and not be a steady +5v.

I still need to remove the PSU from the equation, power things @ +12v from my benchtop power supply, and connect the servo back to the RoboRed to see if the benchtop PSU works. :frowning: (fingers crossed)..

Thanks everyone! any more ideas are appreciated! :slight_smile:

20

Please explain clearer, what units and where.

Is that volts and on what voltage line?
If 12V then there is your problem.

Can you please post an image of your project and a schematic?

It sounds like your PSU is the very old type that didn't regulate all the supplies, just the 5V one, the others were extra secondaries that produce an approximate respective output.

Open your PSU and post an image of it, possibly you have some swollen electrolytic capacitors.

Thanks.. Tom... :smiley: :+1: :coffee: :australia: