mcp23017 resets and relays stop working!

The fan may be a much more difficult load than the lights - but if switching the relay makes it go wrong only if it's the fan that is switched then it is probably something to do with the characteristics of the fan/regulator combination.

I should mention that you need to be very very careful using the Sainsmart board to switch mains voltages - you must be very careful with your wiring and make sure things are in a box and firmly screwed down. You could try putting  a transient suppressor across the relay contacts for the fan - something like this:

   

 

Manufacturer: EPCOS

TAKE CARE WITH MAINS !!

MK

Good idea since the Fan is an  inductive load and as Michael says make sure that all the equipment especially the mains equipment is bolted down to some board to keep it neat and safe.

Out of interest does this problem occur if you use a normal light bulb (incandescent not florescent) if it's ok then most likely the inductive nature of the fan is most likely your problem.

As a tip an old style incandescent light bulb makes for a very useful, cheap and simple to understand load for any mains project like this!

I'm not seeing a pullup resistor between the SCL and SDA lines to 3v3 (which is what the Pi GPIO is).

If there is no 4k7 resistor the lines will be floating and very susceptible to any spikes.

The capacitors across the supply lines are very worthwhile, but spikes are best dealt with by adding a 0.1uF (100nF) capacitor in parallel to the 100uF capacitor.

The mains inrush/switching should not be enough to do any resetting.

The relays can be controlled with the Pi, but you may need to reduce the series resistor (usually 1000 ohms) in series with the opto and run it from 3v3 while powering the relays from 5v.  It means you don't need the MCP23017.

Mark

It won't be the mains inrush current that is the problem (that would be worse with incandescent lights) but more likely the inductive spike when the relay controlling the fan is opened. I did mean to suggest that Nilay should try to find out if the errors are triggered by turning the fan on or off.

MK

Sometimes when i change speed from regulator the ic is reset and relays stop working.

This was mentioned at the start, and could be triggering the SCL and SDA lines, which makes the MCP23017 reset the relay.

First thing is add the pull-ups and the capacitors and then see.

Mark

I would like to inform you all that a capacitor across vdd and vss has helped .. slight voltage spike upto 2-3v is observed but its not resetting the mcp anyways. thanks to everyone who contributed ,specially John Wiltrout sir as you suggested the capacitor.

further i would like to ask is there any effect of the voltage spike on relays in future?. I read it somewhere that this spike eventually damage the relay .

No sir this problem was not occurring while turning the bulb on /off .only with fan or its regulator. yes i do use the bulbs initially but i wanted to experiment with all the home appliances. between do these relays support heavy current loads like ac or geyser?  

Are solid state relays better to deal with ac loads than these electromagnetic ones?

Hi Nilay, Every time that a relay opens and closes under load there is some wear to the contacts. This is particularly true of large loads and inductive loads. Micael Kellert suggested a good part to put accross the relay contacts that will minimize the wear. The other thing that is important is to make sure the contacts are rated for the voltage and current that is demanded by your load. Solid state relays do have a softer contact and release but they have their own set of side effects. If you want to power heavier loads with the small relays just use the small relay to power a larger relay. The other thing that can damage a relay quickly is if it is chattering (turning on and off rapidly) under load. For this reason make sure you are incorporating hysteresis into your design.
John

Sir, mov is not making any differnece to the cirkuit (i.e. the spikes still reset the ic).i have connected it across the relay contacts .i have used v14k 275v mov since my mains is 250v.is it the right value? i also tried 1 across the load (fan) still no use. please help.!