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Need a simple 12 volt latching relay.

jsmith1717

New Member
Hi im need a relay for my mini cooper for the fog a driving lights, both will need the same relay so I can just make to of them but need to know how to make one. This will be for an auto so about 12v give or take and the lights them self are on there own relay just need this to power the relay. I want to do this so that I can use the factory switches which just send a pulse from the switch for on and another from same switch for off. Also can you make this as idiot proof as possible, I get the basic ideas of it but just can't figure it out. thanks very much
 

Joe G

Member
Just call the dealer's parts dept. and ask for the stock relay that comes with the fog light package. most cars have them as a dealer installed accessory when you buy it.
 

jsmith1717

New Member
That won't work for me, mini has to have you buy so many more parts to add it and there relay won't work, its like a standard 4 pin 12v relay.

I did find something on using 3 5pin 12v auto relays and wirng them up to make a latchig relay, will this work?
 

MikeMl

Well-Known Member
Most Helpful Member
A latching relay requires a single relay and two momentary switches; one to set it (usually NO), and another to clear it (usually NC). You want a relay flip-flop, where each push of a single momentary switch toggles the circuit to the other state.

I dont think the posted circuit is going to work as a flip-flop. The left relay will buzz, because as it breaks its no contact, its coil is turned off, so the spring pulls its armature back before it travels far enough to energize the right relay...

Here is a two relay toggle flip-flop.
 
Last edited:

jsmith1717

New Member
ok well those style won't work for me as I don't have my own switch I just have the wire coming out of the switch panel. how about the diagrams below will it work?, also could I use the relay above with these.
 

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MikeMl

Well-Known Member
Most Helpful Member
... I don't have my own switch I just have the wire coming out of the switch panel. ...
Does the panel switch connect to 12V or ground when pushed?
 

MikeMl

Well-Known Member
Most Helpful Member
From what I can read the wire coming from the switch is 12v+
Then use the +12V signal to momentarily pull-in a standard bosch automotive relay. This relay will be on only while the car's switch is pushed. Wire a NO contact from this relay where the pushbutton is shown in the circuit I posted above (the two relay flip-flop). This will make a total of three relays, like the circuit you first posted.
 

jsmith1717

New Member
Then use the +12V signal to momentarily pull-in a standard bosch automotive relay. This relay will be on only while the car's switch is pushed. Wire a NO contact from this relay where the pushbutton is shown in the circuit I posted above (the two relay flip-flop). This will make a total of three relays, like the circuit you first posted.
that should work but how would it be with regular relays, kinda cofuses be with the picture, I get the idea
 

MikeMl

Well-Known Member
Most Helpful Member
that should work but how would it be with regular relays, kinda cofuses be with the picture, I get the idea
NO =Normally-Open
NC =Normally-Closed
Com=Common

d1 is a Double Pole Single Throw (DPST) Relay.
d1.1 is the first set of NO (Normally-Open) contacts inside d1.
d1.2 is the second set of NO contacts inside d1.

d2 is a Double Pole Double Throw (DPDT) Relay.
d2.1 is the first set of NO-Com-NC contacts inside d2.
d2.2 is the second set of NO-Com-NC contacts inside d2.

Replace PB1 with the NO contacts from the third relay.
d1 could be DPDT, just don't use the NC pins.
 

crutschow

Well-Known Member
Most Helpful Member
What about automatically turning the lights off when the car is stopped. Is that needed?
 

eTech

Active Member
Hi im need a relay for my mini cooper for the fog a driving lights, both will need the same relay so I can just make to of them but need to know how to make one. This will be for an auto so about 12v give or take and the lights them self are on there own relay just need this to power the relay. I want to do this so that I can use the factory switches which just send a pulse from the switch for on and another from same switch for off. Also can you make this as idiot proof as possible, I get the basic ideas of it but just can't figure it out. thanks very much
What about using an "alternate action" pushbutton instead of momentary? Push the button to close the circuit, push button again to open the circuit?
Then you could use it with a single, ordinary, non-latching relay.

eT
 

jsmith1717

New Member
Cause I'm using the stock switch that's basically a momentary switch that sends a signal to the bcm that turns on the stock fogs, except I don't have the wiring in my car for
the fogs our the bcm programmed for them
 

crutschow

Well-Known Member
Most Helpful Member
If you could build a small circuit, you could use a toggle FF IC, such as a CD4013 with a transistor buffer, which would alternately turn a single relay on and off in response to the PB signal.
 

MikeMl

Well-Known Member
Most Helpful Member
What about automatically turning the lights off when the car is stopped. Is that needed?
If the feed to the relay logic/fog lamps comes from a fuse in the fuse-block that is switched on/off with the key, then problem solved.
 

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