Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations GregLocock on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Relay EMI is triggering sensors on custom Arduino PCB 2

Status
Not open for further replies.
SolarTrap

SolarTrap

Computer
May 5, 2014
89
Hi All,

I have a problem with the relay on a custom PCB I designed. On my breadboard prototype the parts where somehow spaced out enough to not show the problem.
The relay I am using is a DPDT 120VAC (Mouser: 653-LY2-DC24). In 50% of the switching operation, a button is triggered as a side-affect. It is 'Push_button1' or 'Push_button2' that get triggered - luckily it does not also trigger the reset-button. I found some resources talking about arc suppression at relays that are RC elements. But I dont know how to use that with a DPDT relay. I use the relay to switch a load between 2 power sources.

Any suggestions?

Markus
buttons-pcb.png

bare-bone-shield.jpg

back-side-annot.jpg
 
Replies continue below

Recommended for you

Sort by date Sort by votes
The common way to do it is to connect an RC combination parallel to the load(s). Either buy complete RC combinations or build your own. There are a few things to Think about, so I recommend to buy the snubbers from a reliable source. You will most likely be fine with a 100 nF/100 ohm combination.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
Upvote 0 Downvote
Markus; It's not clear to me that the relay problem is caused by the load it's switching or by it's own coil impulses. Does your phantom switching occur only when switching a load or has it ever occurred with no load involved.

Is there a flyback diode associated with the relay's coil?

Keith Cress
kcress -
 
Upvote 0 Downvote
Keith, I have a flyback diode, see below circuit.

>Does your phantom switching occur only when switching a load or has it ever occurred with no load involved.

That is not 100% clear at the moment, I would have to construct an test program to do lots of switching and measure.

So in case its the arc, between which pins 1-6 do the RC elements go?
(5+6 are load and 1/3 and 2/4 are the 120VAC source)


relay-part.png
 
Upvote 0 Downvote
Across the load. That would be between JT1 and JT3 for one load and between JT6 and JT3 for the other load.

The R in the RC combination can be reduced down to around 10 ohms, if necessary. A 10 A Contact can easily handle that.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
Upvote 0 Downvote
Gunnar, the relay is switching both poles of the same load, so JT1 and JT3 belong to the same single phase AC plug. Also what I need to add is that this is basically the core of a UPS. That means one source (pins 1/3) are coming from an DC-to-AC inverter where the load is not against neutral. The other pair (2/4) is from mains power.
 
Upvote 0 Downvote
OK, then connect between JT1 and JT6 - i.e. across the load.



Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
Upvote 0 Downvote
I found this link here for a formula to design the circuit: Link

That would mean in my case: 120VAC, 10A --> R = 50-100 Ohm (1/2 Watt) and C = 5-10uF

Is this correct?
 
Upvote 0 Downvote
Upvote 0 Downvote
Gunnar, I am in the USA so 125VAC applies to me. I looked at manufacturer catalogs and I found this component: Link
Since UL/CSA Recognition is important to me there is only one item: 104MACQRL150 - 150 Ohms (1/2 watts), 0.1uF
The ohms are far away from your suggestions so I am not sure what to do.
 
Upvote 0 Downvote
The resistor is there to protect the relay contacts, mostly. It has a certain damping effect also, but that is not important in your application. The main problem with too high a resistance is that the inductive part of the load current can create too high a voltage across the resistor - which may initiate some arcing when the contacts open.

If your inductive load is "humble" (low) you can try out the part you found. It will probably work, but I feel more at ease with a lower R. Some experimentation is in order. Use a scope (and a differential probe) to observe the contact voltage.

A MOV can, of course, also be used. But RC snubbers are more reliable in the long run.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
Upvote 0 Downvote
It is hard to predict the load - the snubber should ideally be able to deal with all kinds.
But in my particular case it should work well with compressors in refrigerators. Do you see a problem there?
 
Upvote 0 Downvote
No probs with that kind of load if you keep R low. Except for the heavy start. All relays cannot handle the temporary high current. But that is more a question of thermal capacity with the relay's contact.

Also, make sure that ALL the PCB tracks that carry load current are wide enough so they don't "curl up" when current gets too high momentarily. Match fuse to trace width.

I hope you are testing this worst case Before starting production.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
Upvote 0 Downvote
Aside from reducing the transients from the arcs, can you improve the noise rejection of the button inputs? Different caps, external (stronger) pull-ups, software debouncing?
 
Upvote 0 Downvote
@Gunnar: The peak load on compressor start-up is 1600W but only for 0.5 sec. I have picked 2oz copper for the PCB and I have a 10A slowblo fuse inline.

@BrianE22: I do debouncing in software but that does not do the trick.
 
Upvote 0 Downvote
What is the basis for assuming that it's specifically the relay? The relay closure initiates other things that could also screw things up, like the fact that you are now dumping 50A into the same ground circuit that the Arduino sits on.

TTFN
faq731-376
7ofakss

Need help writing a question or understanding a reply? forum1529
 
Upvote 0 Downvote
2oz at that thickness - not worried! [viking2] Thor - thunder God.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
Upvote 0 Downvote
Depends on how good the layout is, and where exactly the grounds are tied together.

TTFN
faq731-376
7ofakss

Need help writing a question or understanding a reply? forum1529
 
Upvote 0 Downvote
IR, wasn't answer to you. It was about current carrying capacity of the traces. 2 oz Cu is OK.

BTW, do you really think that Power is tied to Arduino GND? I don't tink it is.

Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

A
  • Question
Best Sensors for Detecting Freshness of Meat and Fish?
Replies
5
Views
2K
IRstuff
IRstuff
M
  • Question
What kind of control is this
Replies
2
Views
2K
iop95
iop95
Sparweb
  • Locked
  • Question
Sources for custom PCB 2
Replies
4
Views
115
bidrohini
bidrohini
durablack2
  • Locked
  • Question
two proximity sensors, One LED light for system status 1
Replies
2
Views
1K
IRstuff
IRstuff
jmacion
  • Locked
  • Question
relay wont close consistently with open collector input
Replies
16
Views
676
hacksaw
hacksaw

Part and Inventory Search

Sponsor

Back
Top Bottom