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What do a Use? Relay?

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lee_man_tbu

New Member
Hey everyone,

I have just installed a remote starter in my car and have a small problem. To unlock and lock my doors, I require +12v dc. The problem is, the output from the car starter is a negative output(either 0volts or -12volts).

Does anyone know what i should use or have any schematics that would be usefull ?

Thanks

Lee
 

ljcox

Well-Known Member
Remote starter

I assume that the negative end of the battery is connected to the car's frame. Is this true?

If so you you appear to be saying that the starter switch applies 0 Volt and your door locks need +12 Volt.

If this assumption is true, then you can use a relay or a transistor to switch the locks.

If you need further help, please ask.

Len
 

john1

Active Member
Hi,

Sounds to me that the cars 12v system is positive ground,
and the door-locks want the newer negative ground.

The suggestion to reverse the supply to the door-lock
system is unlikely to work, because the return wire on
almost every system (except some military vehicles) is
the bodywork of the vehicle, in fact a lot of vehicle
parts are made so that their construction is such that
only one wire feeds them, and the fixing becomes the
return wire. To make insulated fixings and provide a
separate return feed would be possible maybe.

I would consider reversing the vehicles polarity, unless
there is a good reason not to do so.

John :)
 

john1

Active Member
note:

I should mention that reversing a vehicles polarity
involves more than just swapping battery connections.

One has to involve the generator also.
It is unlikely to be an alternator, but it might be.
It is most likely a dynamo.
With a dynamo,
the residual field magnetism is reversed by a process
known as 'flashing'
This is best done by someone who knows what they're
doing, as getting it wrong can burn out the regulator.

John :)
 

lee_man_tbu

New Member
Thanks for the help everyone,

ljcox->, yes the remote starter gives 0 volts as a signal to unlock and lock the doors. So yes, i beleive using a relay will work fine thanks

John1-> reversing the polarities would not work either, due too the reasons all ready stated, plus too activate my trunk release, i need too send a ground signal too it.

Thanks everyone for your help, and if any knows a simple method or a simple schematic for connecting a relay or which kind of relay too use that would be great.

Lee
 

ljcox

Well-Known Member
Car door lock

I'm still not sure whether the car has the negative or positive end of the battery connected to the frame. Also, the door lock will be activated by a solenoid, so the polarity should not matter. But if someone is to design a circuit for you, we will need to know the polarity.

And in addition, the lock will need a pulse, not a steady signal. So when you turn on the ignition, a circuit should generate a pulse to lock the doors. Is this what you want?

Len
 

lee_man_tbu

New Member
Len-> The Negative post of the Battery is connected too the frame of the car. I could not locate the solenoid for the door locks, so i tied into the unlock/lock switch(SPDT) in my door. My remote starter generates a pulse for the lock/unlock but it is a negative output. I was thinking on using an 20A automative Coil Relay, Digi-key Part# "2982-ND". I have never used one of these before though and i am unsure of what the package even is or how too connect it.

Any help on this would be great.

Thanks

lee
 

ljcox

Well-Known Member
Car door lock

Try the attachment..

EDIT
Note that I did the attachment in a hurry as we were about to go away for the long weekend.

I read SPDT as DPST. So the relay only needs one contact. So R2 and D3 are not necessary.

Len
 

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