# Need some help with a circut

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#### alonr

##### New Member
Hi guys,

I nned some help with a circut.

It has:
3 negatives (with no contact between them)
1 positive (12V DC)

I need to be able to connect the positive to the 3 negatives using a simple on/off switch.
I assume the best way to do this is using a relay or a transmiter.

- Am I right?
- What kind/type of relay or transmiter can I use?
- How should the circut look?

Alon

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• circut.png
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##### Well-Known Member
As drawn connecting A to B, C, or D will result in a short. However, if a short is what you want just use a 3PST switch the way you drew it. You make no mention of the application, current or voltage so have at it using a switch. So based on the limited information use a switch, if high current use a really, big, big switch.

Ron

#### carbonzit

##### Active Member
This makes no sense (at least as I see it).

You have, basically, a wired "OR" circuit, where any of three connections (B, C, D) can energize a relay. (I ASS-U-ME that by "relay" in that circuit you mean "relay coil", not relay contacts, right?)

You say you want to "connect the positive to the 3 negatives using a simple on/off switch", the 3 negatives being B, C and D.

So why have B, C and D in the first place if you're only going to be using a simple on/off switch? Just connect the switch between the + and the relay and be done with it. No need for the three branches in the first place.

Instead of this approach, why don't you tell us what you're really trying to do here? Describe your application, not your idea of the circuit needed to implement it. That way, we can come up with a workable solution.

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#### alonr

##### New Member
I'm actually trying to create a 3PST switch like Ron suggested, but all the 3PST switches I found were too big (I need this installed on my bike).
So I thought about using transistors or a relay (coil) to create a small 3PST circut which I can control using a simple tiny on/off rocker switch.
The cuurect is 10-15A, and voltage is 12VDC.

The application is very hard for me to explain, as I don't possess the proper terminology,
but generally speaking I'm trying to short the right and left turn signals + the rear break light in order to create hazard lights for my bike.
I olready have everything wired up and it works with a 3PST switch - but it's just too large to be placed on the dashboard of the bike.

Hope this makes sence

#### carbonzit

##### Active Member
What makes you think you need a 3PST switch? Here's what you need:

As someone here likes to say (one of the Rons?), the diode is your friend. They protect the normal independent operation of each light. When you flip the switch, all 3 lights will be illuminated. (The switch can also be a flasher circuit if you want flashing hazard lights.)

The dashed lines show the existing connection to each light.

By the way, I think the words you are looking for are "brake" and "sense".

=================================================

Whoops, my bad. Do not use 1N4007 diodes! Your house will burn down! Your cat will be electrocuted! Your hair will catch on fire!

Heh, just kidding. But I missed your "10 to 15 amps" up above. (Do your lights really draw this much?) In which case you'll need to use much beefier diodes. I'd suggest something like this diode from Digi-Key. It's a Schottky diode, which you definitely don't need, but no harm, and it's cheaper than some other non-Schottkys ($1.88.ea), and can handle 20A, which should safely work for you. Actually, this diode would be better (a little more expensive,$2.60, but can handle 35V reverse voltage instead of the 15 of the one above).

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##### Well-Known Member
Use the diode scheme but I still find 10 to 15 amps extreme for a bike's lights. Just remember the switch will see the current of the 3 lamps. Wish the lamps were mentioned sooner.

Ron

#### alonr

##### New Member
What makes you think you need a 3PST switch? Here's what you need:

As someone here likes to say (one of the Rons?), the diode is your friend. They protect the normal independent operation of each light. When you flip the switch, all 3 lights will be illuminated. (The switch can also be a flasher circuit if you want flashing hazard lights.)

The dashed lines show the existing connection to each light.

By the way, I think the words you are looking for are "brake" and "sense".

=================================================

Whoops, my bad. Do not use 1N4007 diodes! Your house will burn down! Your cat will be electrocuted! Your hair will catch on fire!

Heh, just kidding. But I missed your "10 to 15 amps" up above. (Do your lights really draw this much?) In which case you'll need to use much beefier diodes. I'd suggest something like this diode from Digi-Key. It's a Schottky diode, which you definitely don't need, but no harm, and it's cheaper than some other non-Schottkys ($1.88.ea), and can handle 20A, which should safely work for you. Actually, this diode would be better (a little more expensive,$2.60, but can handle 35V reverse voltage instead of the 15 of the one above).

This worked like a charm!! thanks pal

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