Reverse relays?

Hi folks.

In various automotive parts shops, I have seen (and occasionally bought)
relays, for fitting extra stuff on bikes and cars.

Those relays use a low power "signal" to switch on a higher powered circuit.

Can one buy a relay that works in reverse, where when the "signal"
circuit has power, the higher powered circuit is off, and when the
"signal" circuit is off, the higher powered circuit is on?

If yes, where?

regards,
CrazyCam

 

A " normal" one is a relay with normally open contacts ( contacts are
open with no power on)

A "reverse" one is a relay with normally closed contacts ( contacts
are closed with power off)

Just try you local auto elec or auto store, ask for a relay with
normally closed contacts

Mh

 

Many relays actually feature both types of contacts...

Pietro

 

Yup, no problem. Most commercial relays have both normally open and
normally closed contacts. Any automotive shop should have a bunch in
12 or 24 volt. Or try Dick Smith even. The Guzzi has a half dozen or
more from the factory.

Theo

 

Thanks to Jordan,MartyH, Sharkey, Pietro, and Theo.

It was the "magic words" of "normally closed" that I didn't know and
needed to know.

Thanks, folks.

regards,
CrazyCam

 

Jaycar dick smith has gone to pot.

 

Forgot comma after Jaycar.

 

Ain't that the truth . . .

 

And that's where things get interesting. There appears to be a
"standard" for Automotive relays and their terminal numbering.

Having worked in the electronics industry for the best part of 20
years, I have no idea what drugs they were on when they come up with 30,
85, 86, 87 and 87a.

No really, WTF is that about? Best I could come up with is it
originated from Bosch or Volkswagon depending on who you listen to.

Either way, rest assured you're going to end up being more confused
than when you started.

 

Good Lord almighty!
This is your basic 12V auto relay.
http://www.the12volt.com/relays/relays.asp

This layout is bog standard. It's not rocket science. You can buy the
damn things anywhere for a few dollars. I probably have a half dozen
in the shed. Cam needs the SPDT version, it has pin 87a.

Theo

 

Ah! Right, now I understand. Thanks Theo.

I think I have one of those fitted to the BMW, for the driving lights,
but now must go and check that pin 87a can't touch anything!

On the Triumph, under the petrol tank, there is a relay which feeds
power to the headlights.

What I want to do is put another relay onto that wire feeding the
lights, which I can then switch on or off, but I'd like to have it
arranged so that, if there is any problem with my switch or wiring, the
set-up will fail to a safe, as in headlight on, situation.

regards,
CrazyCam

 

There are all kinds of relays with all kinds of pinouts. Feel free to
point me to an automotive relay using pins 85, 86, 87, 87a and 30 that
is different internally, or externally, to the layout shown in the url
I provided. It will be the first different one I have seen, but I've
only been working with these since the 1960s.

Theo

 

Cut your existing live wire, connect the live end to pin 30 on your
new relay and jumper it to pin 85, Connect the other end of the wire
you cut to pin 87a. Connect a wire from pin 86 to your switch, connect
the other end of your switch to ground. Done.

When you turn on the switch the relay will activate, turning off your
lights.

Cheers
Theo

 

But that's the good thing about standards, there's so many to choose
from.

 

I concur - but I only had 20 years experience in Auto Electrics...so I
defer to Theo

 

[points] Ha ha ha ha haaaah haaaaah ............
....err
[looks around nervously]

[shuffles out]

 

Shades of that Pat Paulsen quote: "I've upped my standards. Now, up yours!"

 

Jaycar or dicksmith