Powering Arduino off 24VAC & Interference

[goettldesign]

Let me preface by saying this is my first time working with arduino, and I am a mechanical engineer not EE, so while I have a good understanding of the basics, some of the advanced topics still evade me. 

Short version: I am trying to run a DC stepper motor with an EasyDriver and Arduino off of 24VAC power supply. 

I've attached a schematic (please excuse the drawing if I have used the wrong symbol etc. I tried my best not having made many in the past) but here is the verbal write-up:

There are three enclosures to the system - Enclosure 1 which houses the stepper motor, Enclosure 2 which houses the arduino, EasyDriver, AC-DC Conversion (buck converter, bridge rectifier, capacitor), and two SPDT toggle switches , Enclosure 3 which houses a 24VAC actuator. Enclosure 2 and Enclosure 3 are mounted together

The 24VAC actuator is an off-the shelf product and is just a 24VAC motor, capacitor, two limit switches and DPDT switch. One of the toggle switches in enclosure 2 controls the components in Enclosure 3. In one position, the AC motor spins until it hits a limit switch. Then when the toggle switches to the other position it reverses direction until it hits another limit switch. 

The second SPDT toggle switch controls the stepper motor. In one position, the stepper motor rotates 180 degrees, then in the other position it rotates the other direction 180 degrees. 

24VAC power is converted to DC using a bridge rectifier, capacitor, and a buck converter. 

The DC toggle controls the DC half of the circuit pretty well (minus some coding issues). The AC toggle controls the AC half of the circuit perfectly. The issue I am having is that operation of the AC circuit also causes the stepper motor on the DC circuit to activate even when not called. There is some major interference occurring because I have deconstructed-reconstructed the wiring and everything multiple times. We have attempted a few solutions namely moving components around and the issue still stands: 

1. Mount the arduino, buck converter, easydriver in Enclosure 1 leaving just a toggler and AC-DC conversion in Enclosure 2 - problem still exists (Enclosure 1 & Enclosure 2 are 15+ft away).
2. Use two separate power supplies. Not an option for us unfortunately. 
3. Add some snubber circuits/diodes into the assembly to help reduce the noise. This is a leading option, but I am just not knowledgeable to spec all those myself. 

Really just looking for some guidance and advice. I've learned a lot so far, but I've reached my limit on personal experience and research to make educated attempts at a solution from here. 
 

[gilshultz]

I am just taking a quick guess but I think your power supply is collapsing when the motor operates. 47uF at 60Hz is not enough capacitance.  Depending on the tolerance of the capacitor (some have a max of a -80% tolerance rating) Try something in the 1000uF range or larger, depending on the stepper current requirements.  A ruel we used was 1000 uF per amp. Any arduino pins that leave the enclosure are antennas and will cause you similar problems to what you are seeing. If you have a scope monitor the 24 volts DC and see where it goes, use the lowest point on the pseudo sine wave you will see.  A DC voltmeter may show part of the drop but they are not fast. First thing I would try is adding capacitance and see where that takes you, I have a feeling it will make a noticable difference.

[Grumpy_Mike]

Your schematic seems to show a transformer being fed with a DC voltage to power your stepping motor driver is that what you have? If so that will not work and the driver is getting its power some other way like parasitic powering through the signal leads. This will lead to problems and possible damage to your parts.

On the other hand that might not be a second transformer, if so what is it?

If you attach a jpeg or png image rather than a pdf it will be displayed automatically in the post.

[TomGeorge]

Hi,
Welcome to the forum.

When attaching diagrams and images, please put them in jpg form, some platforms will not give an image to pdf images.

Do you have a DMM?
OPs circuit.




Thanks.. Tom..

[MarkT]

I think that transformer symbol is supposed to represent a DC-DC converter - don't draw it like that,
its a source of enormous confusion.  A simple box with "DC/DC conv" legend is fine.

47µF is way way too low for mains frequency rectification, think 2200µF per amp or so.

[goettldesign]

I think that transformer symbol is supposed to represent a DC-DC converter - don't draw it like that,
its a source of enormous confusion.  A simple box with "DC/DC conv" legend is fine.

47µF is way way too low for mains frequency rectification, think 2200µF per amp or so.

Yes the second transformer is just a DC-DC converter. Its a buck converter that I can control the drop-down in voltage. Seems like the consensus is to try a larger capacitor there.