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Old 04-15-2009, 09:18 PM   #1
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Relay help required - alternating ground


Guys, help would be much appreciated.

Basically my mirrors for my car are wired upto a switch which allows me to fold them in/fold them out. but im hooking up a relay so they fold out when the ignition is on, and fold in when the ignition is off.

Im using an SPDT relay to do this, but have found out that when the 'mirror in' wire is in use, it uses the 'mirror out' as the ground. and alternatively when the 'mirror out' wire is in use, it uses the 'mirror in' as the ground.

Wondering how id be able to hook up a second relay which switchs the ground wire to the opposite wire in use. Or if you have a completely new solution for how i could make the setup work that would be awesome! cheers, Josh.

here is a drawing of the setup before i knew the earths alternated:

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Old 04-15-2009, 10:32 PM   #2
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Relay help required - alternating ground


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Originally Posted by roleystoner View Post
Guys, help would be much appreciated.

Basically my mirrors for my car are wired upto a switch which allows me to fold them in/fold them out. but im hooking up a relay so they fold out when the ignition is on, and fold in when the ignition is off.

Im using an SPDT relay to do this, but have found out that when the 'mirror in' wire is in use, it uses the 'mirror out' as the ground. and alternatively when the 'mirror out' wire is in use, it uses the 'mirror in' as the ground.

Wondering how id be able to hook up a second relay which switchs the ground wire to the opposite wire in use. Or if you have a completely new solution for how i could make the setup work that would be awesome! cheers, Josh.

here is a drawing of the setup before i knew the earths alternated:
You need a relay that has the same contact arangement as a double pole, double throw switch.
Basically, you are just reversing the current flow through the motor to move the mirror in and out.
One problem that it doesn't appear that you have considered is that the power must not be left on all the time or the motor may be damaged.
This would require a momentary push button switch that would be operated to apply the power!

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Old 04-15-2009, 10:56 PM   #3
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Relay help required - alternating ground


Here's one solution

The delayed off and one shot relays can be eliminated if there are limit switches built into the mirror circuit to cut power to the motor when the mirror is in position.
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Old 04-15-2009, 11:00 PM   #4
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Relay help required - alternating ground


is it possible they are simply reversing polarity? On a DC motor, that would be typical.

and yes, are there limit switches built in or are you doing this full manual now and must release the switch to stop the motor.
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Old 04-16-2009, 03:34 AM   #5
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Relay help required - alternating ground


Cheers guys.

I think there are limit switches built in... as all the current switch did was send a current to the motor, it would fold in/out and then the motor would stop.

Ill give it a go with just the DPDT relay to see if the limit switches are required. thanks for the replies!
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Old 04-16-2009, 11:32 AM   #6
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Relay help required - alternating ground


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Originally Posted by Wildie View Post
You need a relay that has the same contact arangement as a double pole, double throw switch.
Basically, you are just reversing the current flow through the motor to move the mirror in and out.
One problem that it doesn't appear that you have considered is that the power must not be left on all the time or the motor may be damaged.
This would require a momentary push button switch that would be operated to apply the power!
Exactly. You cannot have power to one direction all the time. The constant 12 volt pictured must be connected to a common terminal that is open until you push the button or however you are moving the mirror.
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Old 04-16-2009, 11:34 AM   #7
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Relay help required - alternating ground


Alls good guys!

thankyou for all the help. have just hooked up a DPDT relay and works perfect! will post some pics up if anyone wants.

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