bishbosh Posted June 11, 2009 Share Posted June 11, 2009 I am looking for a thingy wotsit . What I want is some kind of relay that closes the second circuit when the first (coil?) circuit is closed, but the second circuit stays closed when the first is subsequently broken. When power is cut to the second circuit it then reverts to open. To explain a bit clearer, what I want to do is interrupt an ignition fed 12v feed with this device and use it to complete the circuit when a button is momentarily pressed. When the ignition is turned off, the circuit reverts to open. Ignition back on, still open. Press the button and the circuit closes until the ignition is turned off again. Make any sense...? You may have guessed that I am not the most advanced electrickery person so go easy on the technobable in your replies please!! Quote Link to comment Share on other sites More sharing options...
Bull Bar Cowboy Posted June 11, 2009 Share Posted June 11, 2009 Yes it does exist .............. You require a latching relay ............. they used to be very common in the telecoms industry but that was a few years ago ............ here you go ........ http://uk.rs-online.com/web/search/searchB...t&R=2130787 Ian Quote Link to comment Share on other sites More sharing options...
cipx2 Posted June 11, 2009 Share Posted June 11, 2009 A simple relay with an extra normally open contact will do the job. It's called a relay in a an auto maintaing configuration (or something like that). > feed the relay coil to ground and +12V after ignition ON but cut one of the wires and insert the push button (normally open contacts) - what you get is a circuit that will energize the relay as long as ignition is ON and the button is kept pushed > you need to make relay stay energized without keeping your finger on the button > have the extra relay contact do this for you - wire this extra contact (which will get closed when the realy is energized) in paralel with the push button > use the other contact to feed whatever you need (the contacts should be able to withstand the current of the circuit) > voila! Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted June 11, 2009 Share Posted June 11, 2009 Yeah, what cipx said. Get a sprung relay and use the current to hold it closed. Quote Link to comment Share on other sites More sharing options...
bishbosh Posted June 11, 2009 Author Share Posted June 11, 2009 Ian, So the latching relay will keep the circuit closed without the button being pressed but needs another "pulse" to open the circuit again? IS the right? If so where do I get the "pulse" from? Cipx, Err, diagram required please!! how many pins on the relay? Four? Five? If the "extra contact" is in parallel with the push button wont the circuit energise as soon as the ignition is on? Confused......... Quote Link to comment Share on other sites More sharing options...
Mark90 Posted June 11, 2009 Share Posted June 11, 2009 Think this should do what you want using a standard relay... 30 to ignition switched 12V 85 to earth 86 to ignition switched 12V via mom switch 87 to curling tongs jumper wire across 86 to 87 to keep coil energised while relay is closed and mom switch has been released. One potential draw back is the load pulling current through the mom switch while it is closed. Could be a problem depending on what you're planning on powering. If it's a high load you could use 87 to trigger another relay. Just sent you a text with a pic of my back of envelope (literally) circuit diagram. Quote Link to comment Share on other sites More sharing options...
cipx2 Posted June 11, 2009 Share Posted June 11, 2009 This is the circuit I suggested (separate contacts in order to have separate circuits - easier to troubleshoot, separate fuses etc) This is the circuit Mark90 suggested (the push button needs to withstand the current for the driven circuit, you need to be careful at the fuse rating you take feed from). +12V in the diagrams = +12V after ignition ON Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 11, 2009 Share Posted June 11, 2009 Yep, what cipx2 says, diagram #1 is the better of the two What are you powering Bish? Quote Link to comment Share on other sites More sharing options...
Mark90 Posted June 11, 2009 Share Posted June 11, 2009 I agree that using a DPST relay as in option one would be better, particularly in high load situation, and better than my suggestion of a second relay for high loads. But in low current applications where the single 12V supply and mom switch are up to the limited load then my/option two is sufficient and uses more readily available standard 4 pin relay. I know how much Bish hates putting his hand in his pocket Quote Link to comment Share on other sites More sharing options...
landmannnn Posted June 11, 2009 Share Posted June 11, 2009 The circuit could be used for a fuel solenoid, one that only allows fuel through when energised. Turn the ignition on, press a very small hidden push button, fuel is available until you turn the ignition off. It would be better than a on/off switch which would probably be left in the on position negating the security potential. Quote Link to comment Share on other sites More sharing options...
bishbosh Posted June 12, 2009 Author Share Posted June 12, 2009 What are you powering Bish? The circuit could be used for a fuel solenoid Close, but no cigar..... ;) Thanks all for the help. Off to dig around in my collection of salvaged electrikery tat for a suitable relay....... Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 12, 2009 Share Posted June 12, 2009 Just don't forget to tell SWMBO about it! Quote Link to comment Share on other sites More sharing options...
bishbosh Posted June 12, 2009 Author Share Posted June 12, 2009 OK, so I have had a root around and come up with four different relays from my stash. The yellow one is obviously the standard 4 pin that Mark is talking about. Even I can work that one out! But are any of the other three any good for the other circuit option? Quote Link to comment Share on other sites More sharing options...
Dave W Posted June 12, 2009 Share Posted June 12, 2009 If you want to move away from electromechanical stuff... a Triac will do exactly as you describe and will automatically turn off without an additional "pulse" when the power is removed from it. They are available in a huge variety of voltage and current ratings. Essentially it's a solid state switch that turns itself off when the current through it's contacts stops. So you can hook your ignition supply to one side of it and the load to the other. You connect the extra switch to the "gate" of the Triac. It won't conduct anything until you momentarily apply power to the gate. After that the only way you can stop it operating is by turning the power off to it, effectively dropping the current below it's threshold level or hold current. If you know the load current and voltage (12V ?) I can suggest a suitable part if you want to go that way. Quote Link to comment Share on other sites More sharing options...
landmannnn Posted June 12, 2009 Share Posted June 12, 2009 Orange one for cipx2's first circuit diagram. Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted June 12, 2009 Share Posted June 12, 2009 None will give the perfect (two switch) answer, but if you're not drawing big currents then the yellow, black (ignoring the S terminal, "no idea what that bit does so ignore it" - Electronics 101), and green ones will do what you want. The orangey one gives a nice extra contact for the jumper wire too... Quote Link to comment Share on other sites More sharing options...
bishbosh Posted June 13, 2009 Author Share Posted June 13, 2009 Dave W - yes please! 12V application. Everyone else - so the "orange" (actually brown!) one is "close" to diagram 1? How close? How do the pin outs fit to Cipx's diagram? Quote Link to comment Share on other sites More sharing options...
Mark90 Posted June 13, 2009 Share Posted June 13, 2009 Everyone else - so the "orange" (actually brown!) one is "close" to diagram 1? How close? How do the pin outs fit to Cipx's diagram? Nope. Orange one is will give essentially the same circuit as option 2/my suggestion of using a 4 pin relay (there's a subtle difference, but it's basically the same as option 2 not 1). The two outputs 87 and 87b become connected togther when the relay is closed, so not seperate circuits. For option 1 you need a true double pole single throw relay, which will have two fully seperate sets of contact, ie two 30's and two 87's. Even given the advantages of option 1, I would use option 2 for your application. Simpler wiring, one into the circuit and one out, so easy to fit into an existing wire, no need for additional fused supplies, suitable mom switch could take the load no problem (the 'load' is really only a switching current anyway). Quote Link to comment Share on other sites More sharing options...
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