Need a Snubber Circuit for Project?

Hello Everyone,

I'm a little in over my head right now. I'm almost finished with the recirculating heater I'm working on but I'm having trouble with the 12v relays causing blanking of the small character LCD when they open. I've read this is a common issue with the LCDs and that I need snubber circuits across the relay coils. I've try different combinations and a .1uf capacitor and 47ohm resistor seem to have made a small differance but the issue is still definitely there.

How can I calculate the correct resistor and capacitor combination? If I can't get this right is there another way around this? Could solid state relays be a solution?

Thanks

Please show us a schematic of your circuit.

You need diodes across the relay coils (not snubbers) and better decoupling of the power supply. The LCD is responding to power supply instability.

Yes, a schematic would be very helpful. Does the issue go away if you disconnect the recirculating heater? What AC voltage is the heater? If you are using a relay module, please provide a link. Otherwise, include part numbers for the components. Thanks in advance.

I’ve attached a basic schematic. Sorry for the lack of detail.

I started with diodes but they didn’t seem to have any affect.

Here are the relays I’m using:

The heating element in 120v. The issue does go away when there is no load on the relays. Right now I’ve disconnected everything but one solenoid and I’m still having the issue. I even tried a separate power supply for the relays so that the arduino and LCD are on their own. still nothing.

Thank you so much for the help!

Basic Heated Wash.doc (47.5 KB)

Thanks for the information but the circuit isn't a proper schematic. Need more details and proper schematic in order to help. What is the product being controlled? Are you repairing this product or designing a new control circuit for it?

Note that these relays draw 90mA each just to energize the coil and the Arduino's 5V supply cannot handle this with 4 relays. The maximum current the outputs can deliver (without degrading reliability and life) is 20mA. Also, the relay coils require a diode connected across the coil.

The issue does go away when there is no load on the relays.

This signifies contact arc/EMI interference problems ... no point in trying to resolve this until we get more information on your circuit and product.

Hi, Sorry the diagram is not detailed enough, how are you connecting the relay coils to the arduino, do you have back-emf diodes across the coils. We need to see how it is powered and relays are driven by the arduino, please. The arduino outputs cannot provide the current needed to directly power the relay coils.

Can you please post a copy of your circuit, in CAD or a picture of a [u]hand drawn[/u] circuit in jpg, png?

Tom.... :)

Sorry, I am no good at all when it comes to these diagrams. Hopefully this is enough. I've attached a diagram of how the relays are wired to the arduino. the 5 volts to energize the coils are provided by a separate 5v 2amp power supply, but the arduino and the separate 5 volt supply share a ground.

I removed the diodes when I added the snubbers. Should I have both diodes and snubber circuits across the coils?

I removed the diodes when I added the snubbers. Should I have both diodes and snubber circuits across the coils?

At this time, your attachment doesn't show up.

The diodes should remain across the relay coils (see reply#2). Snubbers are usually designed for the AC load and connect across the load to help protect the relay contacts when they open (break). MOVs are also popular for this but they also need to be sized correctly.

the 5 volts to energize the coils are provided by a separate 5v 2amp power supply, but the arduino and the separate 5 volt supply share a ground.

You could try a ferrite core on the Arduino's 5V wire and common ground to dampen/eliminate any spikes. However, opto-isolation is a common solution here.

EDIT: You may also want to consider using zero-cross switching SSRs instead of relays ... easier to control and no EMI.

Haha, whoops! :slight_smile:

Here it is

schemeit-project (1).png

Too much wrong with that ... consider something like this (replace the base resistor with 270Ω-470Ω):

Again, I’m sorry for the poor diagramming. Attached is a more accurate diagram. I have 1kΩ resistor on the base now. I can replace it with a low resistance one as you mentioned. Will that help?

schemeit-project (3).png

Will that help?

Probably, because you're only driving it with 3.3V logic. Are you following the example circuit provided? Do you have the diode installed?

EDIT: If you use 270Ω, the base current will be (3.3-0.7)/270 = 9.6mA. Now the transistor's collector should easily control (sink) 90mA from the relay coil.

I am using the example circuit provided.

I did not have a 270Ω resistor so I used a 220Ω. I replaced the 1kΩ on the base with the 220Ω. I tried this with a diode across the coil and with a snubber circuit consisting of a .1uf capacitor and 47ohm across the coil. Neither made a difference. Should I use a snubber circuit and diode together?

Should I use a snubber circuit and diode together?

NO. Post a properly drawn circuit diagram. Use pencil and paper and post a photo.

How’s this?

That circuit should be fine, if the +5 V [u]does not[/u] come from the Arduino.

I would add a .1uf capacitor across the contact and one across the valve. Make sure the 12v common is "not" connected to the Arduino GND. Keep 12 wiring away from Arduino wiring. .

I tried adding a .1uf cap to the coil and valve but the issue still exists.

The 5v is not coming from the arduino. Its a sepate supply but the grounds are tied together So that the 3.3v back a complete circuit back to the arduino? The 12v Is completely separate.

The original snubbed seems to have made the most difference so far.

Can you take a picture of the wiring and show it to us?

Also try a diode across the valve:

2016-03-02_14-24-02.png
.