Hi all,

I have designed a little circuit to turn on a 230V dosing pump through an SMS controller (part of bigger project)

I am worried about the relay's sticking as if this happens it will be a disaster..The end relays im using are here of which energise the 230V pump

http://www.maplin.co.uk/6-and-12v-6a-miniaturerelays-2525

The 12V side of the above relay is triggered by one of these

http://www.hunters-wholesalers.co.uk/12v24v-secsmins-timer-8amp-doublepole-relayis-p-2621.html

of which is initially triggered by a 1 second pulse from the sms controller this way I can set exactly how many seconds/minutes the pumps stay on for and as of my calculations the dosing pump delivers 33ml per minute

If the dosing pump some how decides to keep running due to the end relay sticking or whatever I will be screwed...I am wondering if theres a way of adding another relay that works with the end relay so that if one becomes faulty and stays on the circuit will be broken?

Thanks

 

If I were worried about a sticking relay, I think I would just install two relays - coils in parallel, so they both activate together, but run the contacts for the load in series. Then if one relay sticks, the other turns the load off.

 

...I think I might of just worked this out

the 12V from http://www.hunters-wholesalers.co.uk...is-p-2621.html powers 2 x of these http://www.maplin.co.uk/6-and-12v-6a...urerelays-2525 in parallel this will then energise 2 x relays 12V coils...I could then join one pin of the relays 230V sides together with one wire and put the 230V live pump wire between the other terminal of one relay and the other terminal of the other relay..this im hoping would mean if one sticks and the other functions normally the circuit will break..the chances of both of them sticking are very slim..does this make sense?