Spdt Relay advice

[The Bishop]

Ok, I was trying to get cleaver but got stuck!

I have installed a red flashing LED to mimic an alarm. It works fine with a switch but that is dependent upon me turning it on each time. I thought it would be good to use a realy so that when the ignition is turned off it turns on the flashing red light (I'll keep the switch to override it for ocassions when you don't want it flashing for example while sleeping in the van).

So I think I need a SPDT relay and bought : http://www.maplin.co.uk/40a-spno-and-30 ... elay-37526" onclick="window.open(this.href);return false;

All installed and it flashes when the ignition is on but not when the ignition is off. i.e. the opposite to what I want. Am I right in thinking I have an NO relay and I need a NC relay? or am I just wiring it the wrong way round?

Anyone got any ideas where to buy them?

Thanks,

[Footprint]

How many terminals does your relay have? If five as I suspect you'll need to have the trigger on 85 and 86, the supply on 30, and the alarm LED on 87a.

[Oldiebut goodie]

Just get a 5 pin then you will have a NC terminal.

[Oldiebut goodie]

How many terminals does your relay have? If five as I suspect you'll need to have the trigger on 85 and 86, the supply on 30, and the alarm LED on 87a.

http://www.maplin.co.uk/40a-spno" onclick="window.open(this.href);return false; - normally open = 4pin usually.

[bigherb]

You don't need a relay. Just connect the positive of the LED to a permanently positive supply and the the negative of the LED to an ignition switched supply.

[The Bishop]

Thanks for the responses I was in the garage and sorted it out. Thanks all. Intrresting to see your solutions.

What else can we do with these relays?

[MidLifeCrisis]

You don't need a relay. Just connect the positive of the LED to a permanently positive supply and the the negative of the LED to an ignition switched supply.

This method makes me nervous.
I know it's (one of the solutions) posted on the Wiki for wiring a headlight reminder circuit but .......

Correct me if I'm wrong but doesn't this mean that when the ignition is switched off, the ignition switched circuit will then draw its 12v supply through the LED you just fitted so anything on that circuit will now be getting 12v even though you have turned off the ignition.
(BTW - I think its less of an issue for the headlight reminder buzzer because in theory this would only be active for a few seconds, until you turn off the headlights - but for the 'fake alarm' LED it would be active for hours!!)

[Footprint]

normally open = 4pin usually.

Both are listed on that page and the one pictured is five pin which is changeover, that is NO and NC, also OP stated SPDT, which is five pin NO/NC - 30 wiper, 87 NO and 87a NC.

[Oldiebut goodie]

I just read the link in the post - spno.

[The Bishop]

OK so that worked a treat.

Thinking forward, I could make an imobilisor so that in NO mode the ignition is cut off and in NC mode the ignition mode the ignition is connected and free to start. I could power the coil from a switch hidden somewhere but it would be nice to power it from a remote control bleeper. But as this would just give a pulse of powerhow would I make the circuit stay open/closed?

Where could I buy such a remote from ?

Do you clever people think this would work? It seems I might be able to install a imobilisor for less than a tenner.

[California Dreamin]

Hiya mate,
The idea has been around for years, commonly called an imobiliser, just happpens that most are designed with an alarm function as well.

Martin

[The Bishop]

Hiya mate,
The idea has been around for years, commonly called an imobiliser, just happpens that most are designed with an alarm function as well.

Martin

Smart a***! Yes but my little dabble in electronics has got me interested in how I can do these things. Not necessarily that I will do it. More problem solving and curiosity.

Didn't you use relays in conjunction with your light switches to improve the current to the lights? This is on my list to understand and do.

[tonytech]

You don't need a relay. Just connect the positive of the LED to a permanently positive supply and the the negative of the LED to an ignition switched supply.

This method makes me nervous.
I know it's (one of the solutions) posted on the Wiki for wiring a headlight reminder circuit but .......

Correct me if I'm wrong but doesn't this mean that when the ignition is switched off, the ignition switched circuit will then draw its 12v supply through the LED you just fitted so anything on that circuit will now be getting 12v even though you have turned off the ignition.
(BTW - I think its less of an issue for the headlight reminder buzzer because in theory this would only be active for a few seconds, until you turn off the headlights - but for the 'fake alarm' LED it would be active for hours!!)

If you fit a 12v LED (or standard LED and current limiting resistor) as described then only a few milliamps can flow.
No more than fitting an LED with relay. Much less than digital / analogue clock etc.
The main current path would probably be through the fuel gauge / temp gauge, fuel. pump relay etc, but much too little to register or activate them.
T