Relay / wiring question

[l1ttle_d3vil]

Got a random question - if I wanted to kill the power output from a relay (which is otherwise on constantly) using a single aux wire that will switch to ground when required, how should it be wired up?

I can see how it would work if it was a physical inline switch that breaks the connection, or the aux was switched to ground constantly and disconnected when power was to be cut, but is there any way that the above setup could be made to work?

Hope this makes sense, cause its confusing me

Cheers

[matt dunn]

If I understand what you mean,


use a changeover or normally closed relay.

Connect term 30 and 85 to +ve supply,
you will get +ve out of terminal 87a all the time,

until you earth terminal 86
and while it's earthed you will not get any power out of the output/87a.

[Rick]

What if you were to join the aux wire to were the relay would normally be grounded (earth -) then you can switch that aux wire to ground to operate the relay.

[MAGN1T]

You need to run 2 wires to intercept the coil wire via a switch. Otherwise you're likely to get a flat battery if there's constant power on the live side of the relay coil.

Steve

[matt dunn]

You need to run 2 wires to intercept the coil wire via a switch. Otherwise you're likely to get a flat battery if there's constant power on the live side of the relay coil.

Steve

Not always,
depends on what your using it for.

[l1ttle_d3vil]

If I understand what you mean,
use a changeover or normally closed relay.

Aah, such a simple solution Would I need to use diode fuses for this setup?


By "constantly on" I mean while the car is running, not while car is switched off.

Cheers

[sergei]

diode fuse?
You mean clamping diode to dissipate the back-EMF? I would recommend to use them, as relay produce hundreds of volts spike on disconnection.

[l1ttle_d3vil]

No, definitely been told to use diode fuses.

Maybe that's if its getting wired up differently to how I'm doing it...?

[MAGN1T]

No, definitely been told to use diode fuses.

..?

There's no such thing (or maybe there might be but it's not what you want).
You've got more chance with a flux capacitor ar better still an electrostatic coil.

Steve

[l1ttle_d3vil]

Connect term 30 and 85 to +ve supply,
you will get +ve out of terminal 87a all the time,

until you earth terminal 86
and while it's earthed you will not get any power out of the output/87a.

OK everything is 99% set up, 30 and 85 have +ve supply and relay is working exactly as required. only issue is 86 has a +ve supply too, until it is earthed. im guessing this is where the "diode fuse" should be used, to prevent the power making its way back to the aux pin and damaging the unit. sound about right?

steve must be right - there seems to be no such thing as a diode fuse
is it just a standard diode i need for this? dse or repco can't tell me what any of their diodes do, only that they have lots in stock. it will help a huge amount if I know exactly what I'm asking for


and one other thing - can a standard relay be used to switch to an earth, rather than switch to power? seems to work, but any reason why it shouldn't be done?

30 - connected to chassis
85 - connected to chassis
86 - switch - +ve
87 - earth output

so 87 will only be earthed when 86 has power?

cheers
-matt

[matt dunn]

power making its way back to the aux pin and damaging the unit.

cheers
-matt

What unit? If you fit a diode so the power doesnt get to the aux pin, the circuit wont work as the aux pin cant earth the relay?

what are you using the circuit for?

[l1ttle_d3vil]

The aux pin is what provides the earth when required though. I assume if it has a voltage going in to it any other time it could cause some problems.

Isn't the idea of a diode to prevent a signal from going one way, while allowing one to go the opposite? So it should prevent power from going back to the aux pin, but allow the earth signal to go from the aux pin to the relay...

[Lloyd]

86 has power showing at that pin when all the wires are plugged into the relay? Thats what you'd expect as there is power at 85 which will be feeding through the coil and sitting there waiting to be earthed at 86.

If you get a certain relay they will come with a doide in already. Probably easier to just do that

[matt dunn]

If you get a certain relay they will come with a doide in already. Probably easier to just do that

Those diodes are a PITA and means you need to ensure the correct polarity of the relay windings,
I normally try to avoid using them, and use the ones with a resistor instead,
but the will still not stop power being at the aux pin when it is not earthing,

nothing will
as if there is no power at the aux pin when the aux circuit is off,
how the hell is the aux pin going to turn the circuit off?