14 replies to this topic

[Stimpy]

I've installed an 'emergency fuel cutoff' switch - next to a start button

 

I also have a flashing LED (white) next to the switch.

 

When I flick the emergency switch (and the fuel pump audibly stops) The LED flashes as a kind of 'warning' light due to an emergency situation.

 

Somehow I wired it up and it worked exactly right. I don't know how!

 

Anyway I had to do some rewiring and part of this involved the flashing LED.

 

The flash in LED is quite simple as a unit - provide it with 12v and earth the other terminal and off it goes.

 

However I want it to flash when I flick the emergency switch (which cuts the circuit for the fuel pump)

How on earth do I supply power to the flashing LED light when another circuit is switched off?

 

Confused!

 

If anyone can think of a way I'd be very appreciative 

 

Cheers

 

Steve

[Tamworthbay]

Relay, there are two ways to wire through standard type, normally open or normally closed. Just wire it so when it's not energised the circuit you want is closed.

[gazza82]

You need to include a relay that will allow the current to flow to one pole when the power is cut.

[One step at a time]

A normally closed relay will as its called "close" when it looses power and therefor power the lashing led.

[KernowCooper]

Normally open relay where the pump feed is on terminal 86 and earth on 85, 30 is the 12v feed ignition switched if you need it to go out when switched off , 87 is the feed to one side of the led and other to earth. Under normal conditions when the fuel pump is on it opens the relay contacts = no led, cut the fuel pump supply =no feed the the relay the contacts close which makes the circuit on a normally closed relay =led on, switch ignition off =led off. relay type here http://www.ebay.co.u...C-/140894204593

[Stimpy]

I see 'relay' as a popular word up there.  I'll do some (safe) experimenting but thanks a lot for coming up with solutions.

 

I would still like to know how the hell I managed to do it - without a relay - by accident - last time.

I was thinking that I might have 'accidentally' wired it up in the same way as the IGN light goes on/off due to certain conditions.

 

Mentioning 'relay' has made me come up with another idea - I have one of those 10 seconds 'on' relay - perhaps I can use that to power the flash LED.  Seems a good idea for it to stop after 10 seconds

 

Thanks again folks - VERY appreciated - and so quick too

 

Steve

Edited by Stimpy, 28 January 2015 - 11:38 PM.

[Dan]

Use a changeover switch instead of an on/off switch. Switch in position 1, power to pump. Switch in position 2, power to LED. Simple.

Safety switches are far better being automatic though, its not much help if you are unconscious. It is no safer than the regular ignition switch.

[Spider]

An even easier way using the switch you have.

 

Wire the LED across the Switch so that the Anode of the LED (or +ve) is to the 12V supply, which is also on the 'Incoming' side of the Power Switch.

 

Next, Wire the Cathode (or -ve) side of the LED to the Pump feed side of the switch along with the Pump.

 

Earth the earth side of the Pump as Normal.

 

Hope that all makes sence, even if it appears unconventional.

 

Because the LED draws only ~20 mA, it will Earth via the Pump (which is fairly low resistance) when the Switch is Open, The 20 mA isn't enough to allow the Pump to run.

 

When the switch is closed, the volts across the LED Terminals will be the same (or near enough), so the LED will go out, but the Pump will run.

 

Easy Peazy, Japaneasy

Edited by Moke Spider, 29 January 2015 - 07:57 AM.

[Dan]

Yes, but you should add a blocking diode if you do that or it won't be fail safe. Depending what pump it is (probably worse with a cube pump I would think) the back EMF coming off the coil the first time you shut it off could well be enough to blow the LED, and then the pump will start running again and you won't be able to stop it!

[Spider]

Yes, but you should add a blocking diode if you do that or it won't be fail safe. Depending what pump it is (probably worse with a cube pump I would think) the back EMF coming off the coil the first time you shut it off could well be enough to blow the LED, and then the pump will start running again and you won't be able to stop it!

 

If it makes one feel better then yes (I've not bothered). With the LED may short - briefly - the current drawn by the pump with blow it open.

 

Obtain a stock Rectifer type Diode (say an 1N4001), connect the Cathode to the Incoming 12 V +ve and the Anode to the Pump side of the Switch.

 

now, back to that package, was it the Red wire or the Blue wire,,,,,,,,,

Edited by Moke Spider, 29 January 2015 - 08:46 AM.

[Stimpy]

Thanks for all the alternative methods - that certainly should make the task easier.

 

​FYI the swift is like this:

 

http://www.ebay.co.u...T-/281445158333

 

 

The extra contact is for the LED at the top of the switch

[Spider]

Thanks for all the alternative methods - that certainly should make the task easier.

 

​FYI the swift is like this:

 

http://www.ebay.co.u...T-/281445158333

 

 

The extra contact is for the LED at the top of the switch

 

 

OK, to connect that up as I've suggested, connect the LED Earth Terminal to the 'Load' Terminal of the Switch. Job done. Those being for Automotive applications won't need any addition Diode that Dan was on about, they already have one fitted.

[Stimpy]

Thanks everyone!

[Stimpy]

So rude! I never really got back to e everyone on this topic.

 

It's been an education!  I never knew that a relay could do the opposite in relation to supplying power with some relays having two 'to circuit' terminals

 

So I wired up a 'reverse' type relay and I get precisely what I needed.

 

Using IGN as the power source rather than live meant that the circuit was dead when everything was switched off.

 

So - again - thanks for the info; and when you know it - it seems so simple - however I needed a kick start and this forum provided that, so top marks all round (is that a bit patronising?)   

[Stimpy]

Dare I add another idea to this thread.  Well - ok - I'll go ahead based upon what i have learned here.

 

With the (above) problem sorted I thought I'd pose an additional related Q.

 

I use a durite relay that keeps the internal courtesy lights on for 10 seconds after the door is closed.  Very nice.

 

I was thinking that there must be a way of mixing a relay with the durite relay to do the following:

 

you drive the car

you then stop.

you turn the ignition off and the courtesy lights come on *despite* the door still being closed.  along with the durite 10 second delay.

if you leave the door closed then the light goes off after 10 seconds.

If you open the door then the 'normal' process occurs where the light stays on until the door is closed for 10 seconds.

 

So - let me throw it out there - can this been done?  I've done a few experiments but i just cant clinch it.  with how the relays operate there must be a method in how to do this.

 

Any help comes with the usual appreciation

 

Steve