Relay trigger wire carries both 12v and ground


Old 08-06-14, 04:29 PM
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Relay trigger wire carries both 12v and ground

Regarding a regular 5 post spst relay. My question is, if a relay is wired to receive a negative trigger, what would happen if 12v is sent instead. Like if pin 86 has 12v, what would happen if 85 received 12v? Applying 12v to both sides of a magnetic coil, does it burn it up or anything? What about ground to both sides?

The reason I am asking is I have an ON OFF monetary switch, that sends a 12v when on is pressed, and a ground signal when off is pressed, all through the same wire. Going to wire one relay (relay A) so that when on is pressed, the relay turns on the 12v output which is jumped to keep the relay on. I need a way to turn this relay off. So I was going to have another relay (relay B) where 87a is powering pin 30 on (relay A), when the off button is pressed it sends the ground to (relay B), which cuts off power from 87a to pin 30 on (relay A) just long enough to break the jumper and turn the relay off. The trigger wire of course the same wire, just 12v or ground depending on which button is pressed.

Just want to make sure its not going to do anything bad if 12v is applied to both sides of the coil, and vice versa.

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Old 08-06-14, 07:27 PM
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I think I'd need to see a drawing to figure out exactly what you have planned. But in general, applying the same voltage to both sides of a component (relay coil) is the same as applying 0v. You need a positive and negative to have any voltage pass. Two negatives don't do anything nor would two positives.

This is assuming of course that you're working with a basic 12v system and not something more funky like a +12/-12 volt setup.
Old 08-06-14, 09:23 PM
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You aren't really sending a ground signal. Your sending power or your not.
I've used those "Bosch" type relays by the thousands. At one time I was buying them 100 at a time.

Relay 1 does the main switching. Relay 2 interrupts the ground to relay 1's coil to turn off relay 1 when off is pushed. The diode in relay 1 supplies power to the coil from the load output. It keeps the full load from being connected across from the switch. This circuit assumes your load is a 12v load as that's what the relay coils are.

If you have other needs the circuit is easy to change. You can wire these relays any way your imagination and needs require.

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Old 08-07-14, 08:31 AM
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Ok thanks. I didn't think applying 12v to both sides would do anything but just wanted to make sure.

The picture is the on off switch wiring. When off, the output wire is grounded. When on is pressed, it sends 12v through output wire, then drops to around 7 volts when released. The other buttons change the voltage when pressed but those don't really matter as they won't be pressed.

Basically I need a way to turn a relay on when 12v is applied, and off when ground is applied. Would be easy if 12v was constant, but it's not so I will have to have the relay latched to keep it on with the button not pressed. I think I've got it figured out, just wanted reassurance that the relay wasn't going to die if 12v was applied to both sides of the coil. Thanks
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