Electrical Relays - HELP!!!!!
Discussion
Thanks Guys.
The online catalogue doesn't carry anything like what I'm after.
I've also tried the 2 relays in the circuit but unfortunately only 1 will ever seem to trigger. Can't understand it as my school boy physics logic says that both should. One of my relays appears to have a little diode in which must be allow some current through allowing the other relay to trip, but not the other.
Confused!
Mark
Anyone any other ideas???
The online catalogue doesn't carry anything like what I'm after.
I've also tried the 2 relays in the circuit but unfortunately only 1 will ever seem to trigger. Can't understand it as my school boy physics logic says that both should. One of my relays appears to have a little diode in which must be allow some current through allowing the other relay to trip, but not the other.
Confused!
Mark
Anyone any other ideas???
Is it for a 12v system?
Do you need the two switched circuits to be completely isolated from each other? If you can get away with one common pole then you can use a standard automotive twin pole relay. Otherwise your easiest option would be two separate single pole relays with a common control. The control circuits need to be wired in parallel, but this is all very straight forward.
Maybe there's some other factor you haven't told us about which prevents you from using multiple relays. In which case you can get multi-pole relays, I was working on a projet a couple of years ago which required very close synchronisation on the two circuits so I used a 4-pole relay, standard component cost be a couple of quid from Maplins.
Don't know what you're trying to do but from what you've said so far there's nothing difficult about it.
Do you need the two switched circuits to be completely isolated from each other? If you can get away with one common pole then you can use a standard automotive twin pole relay. Otherwise your easiest option would be two separate single pole relays with a common control. The control circuits need to be wired in parallel, but this is all very straight forward.
Maybe there's some other factor you haven't told us about which prevents you from using multiple relays. In which case you can get multi-pole relays, I was working on a projet a couple of years ago which required very close synchronisation on the two circuits so I used a 4-pole relay, standard component cost be a couple of quid from Maplins.
Don't know what you're trying to do but from what you've said so far there's nothing difficult about it.
The diode is in there in case the relay is switched by a transisitor. Trannies get a bit hot and bothered by the spikes resulting when the current flowing in a relay coil is suddenly turned off (it's analogous to the points in a car ignition system switching the coil low tension on and off and causing a 'pulse'), so the diode conducts and takes the spike to the 'earth' side of the circuit, for want of a simplified explanation 
A couple of possibles as to why your circuit doesn't work: you are using the correct coil type, aren't you? That is to say, relays designed to work from AC won't work from DC, and vicky vercky.
Secondly: the coils are wired in parallel, not in series? It is sometimes possible for series coils to allow one to switch, although in theory neither should...
A couple of possibles as to why your circuit doesn't work: you are using the correct coil type, aren't you? That is to say, relays designed to work from AC won't work from DC, and vicky vercky.
Secondly: the coils are wired in parallel, not in series? It is sometimes possible for series coils to allow one to switch, although in theory neither should...
Guys,
Thanks for all your advice. Please bear with me as I am still learning a lot about auto electics.
Yes it is a 12v system, yes I do need to have 2 INDEPENDANT circuits switched either by 1 relay or 2.
I have tried 2 relays (they both work ok independantly)but wont work together when linked in series in the same circuit. Which is why I was thinking about the feasability of a 'double switch' relay.
To expalin matters more it is for a Nitrous kit bottle heater circuit.
The circuit comes live when a switch is thrown in the car. The switch also illuminates. There is also an automatic pressure switch in the switch circuit so when the heater gets the gas to the correct pressure the pressure switch cuts the current and switches the relay for the blanket off.
This is ok so far but the problem is I'm in the cockpit with the heater switch on and still illuminated so I don't know if the gas is at pressure. (can't butcher the dash for a gauge).
I though the simple solution was for the pressure switch circuit to trip the heater relay AND another relay taking the eath from the switch light.
I though Bingo! Switch on illuminated = heating not at pressure......... Switch on, light goes out = pressure achieved, heat off light off, therefore GO!
There must be a simple way of achieving this, but so far this numpty is still rolling a square wheel!
Mark
Thanks for all your advice. Please bear with me as I am still learning a lot about auto electics.
Yes it is a 12v system, yes I do need to have 2 INDEPENDANT circuits switched either by 1 relay or 2.
I have tried 2 relays (they both work ok independantly)but wont work together when linked in series in the same circuit. Which is why I was thinking about the feasability of a 'double switch' relay.
To expalin matters more it is for a Nitrous kit bottle heater circuit.
The circuit comes live when a switch is thrown in the car. The switch also illuminates. There is also an automatic pressure switch in the switch circuit so when the heater gets the gas to the correct pressure the pressure switch cuts the current and switches the relay for the blanket off.
This is ok so far but the problem is I'm in the cockpit with the heater switch on and still illuminated so I don't know if the gas is at pressure. (can't butcher the dash for a gauge).
I though the simple solution was for the pressure switch circuit to trip the heater relay AND another relay taking the eath from the switch light.
I though Bingo! Switch on illuminated = heating not at pressure......... Switch on, light goes out = pressure achieved, heat off light off, therefore GO!
There must be a simple way of achieving this, but so far this numpty is still rolling a square wheel!
Mark
Hi Mark,
what you want to do is definitely possible using two ordinary 12v relays. Just make sure that you wire the control circuits for the relays in parallel (if you wire them in series you will only get half the voltage across each coil and it is pot luck whether either of them work).
You haven't described the circuit in sufficient detail to tell whether you actually do need two separate circuits - I have a suspicion that by careful circuit design you can achieve what you want with a single relay. But two relays is easier to understand which is probably the main thing at this point!
what you want to do is definitely possible using two ordinary 12v relays. Just make sure that you wire the control circuits for the relays in parallel (if you wire them in series you will only get half the voltage across each coil and it is pot luck whether either of them work).
You haven't described the circuit in sufficient detail to tell whether you actually do need two separate circuits - I have a suspicion that by careful circuit design you can achieve what you want with a single relay. But two relays is easier to understand which is probably the main thing at this point!
Whereabouts in the circuit is the thermal switch that disconnects the blanket?
You could simply connect the warning lamps ground wire to the connection between the heater and the thermal switch. Depending on the order the heater and thermal switch appear in the circuit, this will either cause the warning lamp to extinguish when the bottle gets hot enough (thermal switch on ground side of heater), or the lamp to illuminate when the bottle is hot enough (thermal switch on "hot" side of heater).
You could simply connect the warning lamps ground wire to the connection between the heater and the thermal switch. Depending on the order the heater and thermal switch appear in the circuit, this will either cause the warning lamp to extinguish when the bottle gets hot enough (thermal switch on ground side of heater), or the lamp to illuminate when the bottle is hot enough (thermal switch on "hot" side of heater).
I feel I'm getting closer to my Nirvana! 
ok a circuit in words (if possible).
3 amp feed to illuminated switch, out to pressure switch, out to relay (which would switch 25Amp heater circuit on/off depending on pressure switch position) and out to earth. This circuit works ok so far.
Illuminated switch has an earth. Bulb stays lit whether the heater relay is on or off. My thought was to put another relay in the bulb earth circuit to also be triggered by the the on/off current from the pressure switch.
For some reason when doing the additional relay to the first circuit only 1 of the relays will fire, usually the one on the bulb circuit? This confused no end.
My simple thought was therefore to get 1 double pole relay to be triggered by the pressure switch and then activate the higher amp heater circuit, and the low amp bulb earth.
There must be a simpler way of achieving this.
One thing I have thought of is that the 2 relays I was trying with were both 30amp, but from different manufacturers. One definately has a diode in and is usually the relay that wont throw when in a twin situation. Would this be an issue?
Thanks again
Mark
ok a circuit in words (if possible).
3 amp feed to illuminated switch, out to pressure switch, out to relay (which would switch 25Amp heater circuit on/off depending on pressure switch position) and out to earth. This circuit works ok so far.
Illuminated switch has an earth. Bulb stays lit whether the heater relay is on or off. My thought was to put another relay in the bulb earth circuit to also be triggered by the the on/off current from the pressure switch.
For some reason when doing the additional relay to the first circuit only 1 of the relays will fire, usually the one on the bulb circuit? This confused no end.
My simple thought was therefore to get 1 double pole relay to be triggered by the pressure switch and then activate the higher amp heater circuit, and the low amp bulb earth.
There must be a simpler way of achieving this.
One thing I have thought of is that the 2 relays I was trying with were both 30amp, but from different manufacturers. One definately has a diode in and is usually the relay that wont throw when in a twin situation. Would this be an issue?
Thanks again
Mark
Right think I've got it!
1 way would be to put the pressure switch in the circuit first. Pressure on = all circuit off, including the bulb. Only down side is total dead circuit I would not know if pressure ok, or one of many fuses has gone. Will dwell on this
Other way would be to put switch first, then pressure switch then relay for the heater, then to ground. I could interupt the 25Amp heater circuit after the first relay, and install the second. I could actually use the higher amp circuit to switch the lowere amp bulb earth.
One thought (reference the circuit live or not scenario) would be to put a 2 position relay for the bulb earth. For example, while heater on, relay switches bulb relay to earth for 'red' not ready setting,...
... then when the pressure switch activatesoff it triggers the heater relay which switches the red bulb from earth and back through a green bulb (ie for 'go').
This (I hope) when the main arming switch is on a red bulb for heating, and green for correct pressure and heat off. If switch on but no bulbs then I know I have a fault.
Phew.
What do you think???
Thanks again
Mark
1 way would be to put the pressure switch in the circuit first. Pressure on = all circuit off, including the bulb. Only down side is total dead circuit I would not know if pressure ok, or one of many fuses has gone. Will dwell on this
Other way would be to put switch first, then pressure switch then relay for the heater, then to ground. I could interupt the 25Amp heater circuit after the first relay, and install the second. I could actually use the higher amp circuit to switch the lowere amp bulb earth.
One thought (reference the circuit live or not scenario) would be to put a 2 position relay for the bulb earth. For example, while heater on, relay switches bulb relay to earth for 'red' not ready setting,...
... then when the pressure switch activatesoff it triggers the heater relay which switches the red bulb from earth and back through a green bulb (ie for 'go').
This (I hope) when the main arming switch is on a red bulb for heating, and green for correct pressure and heat off. If switch on but no bulbs then I know I have a fault.
Phew.
What do you think???
Thanks again
Mark
wedg1e said:
This any help?
Wedg1e,
Thanks mate. Will be giving it a go. The right hand 'heat' lamp looks as though it will only come on when the heat is on, I need it to go off, or illuminate in the off position.
Think I will fit a switching relay and have the bulb (green) to come on when the relay switches away from the heat. This will give me confirmation that the circuit is working (illuminated) but heat is off/pressure correct as relay switches over to the bulb.
Confusng but I think I understand it.
Thanks all for your help.
Mark
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