Help finding suitable relay

[StayGold808]

Hi Guys,

I'd like assistance finding a suitable relay for a new circuit I'm wiring.

The relay should have at least 7 pins:
1) 12V constant
2) Earth A
3) Earth B
4) Earth C
5) Power A
6) Power B
7) Power C

If pin (2) is earthed, pin (5) should output 12V.
If pin (3) is earthed, pin (6) should output 12V.
If pin (4) is earthed, pin (7) should output 12V.

Any help greatly appreciated,
Adam

[Chuck.H]

Why not just use 3 standard relays?

Even if such a relay existed, it sounds expensive and difficult to source when it fails somewhere in west Texas (from what I've heard, Australia has lots of places as or more remote than west Texas!)

Chuck.H
'89 TurboLookTarga, 384k miles

[hcoles]

^ +1 - there might be a relay out there that is 3 in 1 but I haven't seen it. If size is an issue you could look for miniature models. You didn't mention the current draw for the load you want switched. Also, you might consider if you want some sort of added feature to reduce or prevent fly-back current. Using standard parts (relays) help because you can easily get the receptacle/pins/etc. to make everything work nicely.

[DaveMcKenz]

I tend to agree. There are relay sockets for the standard Bosch relay which gang together side by side, and allow a neat, although not particularly small package.
Good luck,
Dave

[Dave Colangelo]

you may find what you need at digikey.com however there are reasons why relays gennerally only control 1 if at that 2 circuits.

1. Cost to replace, in you case lets say you are controlling 3 separate circuits 2 are lower power and one is high draw. The high draw relay may see more arcing when you turn it on and thus wear out faster. You can pay for a costly 3 unit relay every time you replace it (when 2 of the channels have plenty of life left) or you can break that into 3 units and replace them as needed.

2. Arcing and fail over. In this case you really want to keep everything discrete and separate. In a 3 unit relay you could get a case where a short in one channel may cross over and short out other components that are run through the other channels of that relay.

3. Different ratings. Relays are rated to operate at various voltages and cary either AC or DC current at various different amp values and voltage levels. A 3 way unit in some cases may be needed in one spec and other a completely different arrangement so there would be far to many combinations to make. You will most likely find a constant operating voltage and current type/voltage limit unit. Thus its cheaper and easier to make single pin throw units and use a lot of them.

All that in consideration there are multi throw units out there, cars often only have a 1 or 2 throw unit but im sure there are applications for other things out there. If you want to use one unit so that if say one thing fails the other 2 shut off as well, consider using a master relay instead.

Regards
Dave