Hooking up Relay and Switch

[Andy]

I am going to do some work in my car. So everything I talk about
should be ~12 volts. I have some electronics knowledge, but I am no
expert. I plan to use a relay to switch certain things. Here is how I
plan to hook up the relay (coil side):

Battery positive to toggle switch
Toggle switch to relay coil
Relay coil to ground
Ground to battery negative (Of course)

This will not be a short, will it? (Or do I need some sort of resistor
in there?) The relays I plan to use can be seen at
http://www.allelectronics.com/cgi-bin/category.cgi?category=search&item=RLY-412&type=store
The important detail (I think) of the relay is that the coil is 72
ohm.

Also, is it safe to use DIP switches? I don't know if they can handle
the current that will go through the relay coil.

--
Andy
http://dynamicbits.com

 

[Kevin]

Andy, don't forget to fuse both your switch and your supply leads. I
have been in the auto electronics biz for almost 20 yrs and have seen
many cars that got burnt because of careless (unfused) wiring. Good
luck.


"Dana Raymond, a minor God" <draymond@austin.rr.com> wrote in message news:<E4A0b.202385$xg5.113877@twister.austin.rr.com>...

The relay is rated 12Vdc 72R (approx 170mA) so your wiring sounds correct.
The 72R coil limits the current so there is no 'short'.

170mA for a dip switch is high is my opinion. It could handle it if the
switch stayed closed but the life of the switch may be reduced, especially
if it is opened while the relay is energized.

Use an automotive-rated toggle switch instead. The automotive environment is
second only to aerospace in its harshness (voltage spikes, current surges,
temperature extremes, vibration, etc.)

Hope this helps.
Dana Frank Raymond


"Andy" <andycool1@hotmail.com> wrote in message
news:f737ac9d.0308191708.3b43a6cf@posting.google.com...
I am going to do some work in my car. So everything I talk about
should be ~12 volts. I have some electronics knowledge, but I am no
expert. I plan to use a relay to switch certain things. Here is how I
plan to hook up the relay (coil side):

Battery positive to toggle switch
Toggle switch to relay coil
Relay coil to ground
Ground to battery negative (Of course)

This will not be a short, will it? (Or do I need some sort of resistor
in there?) The relays I plan to use can be seen at

http://www.allelectronics.com/cgi-bin/category.cgi?category=search&item=RLY-
412&type=store
The important detail (I think) of the relay is that the coil is 72
ohm.

Also, is it safe to use DIP switches? I don't know if they can handle
the current that will go through the relay coil.

--
Andy
http://dynamicbits.com

 

[Si Ballenger]

I can't speak for today's cars, but in years past the coil was
designed to run on ~9v instead of 12v. The reason for this was
during cranking the system voltage would drop to around ~9v due
to the very heavy starter pull on the battery. In the start
position the battery was fed straight to the coil. When the key
is released back to the run position, the battery was routed
through a ballast resistor to drop the now system 12v down to the
9v for the coil.

On 19 Aug 2003 18:08:48 -0700, andycool1@hotmail.com (Andy)
wrote:

I am going to do some work in my car. So everything I talk about
should be ~12 volts. I have some electronics knowledge, but I am no
expert. I plan to use a relay to switch certain things. Here is how I
plan to hook up the relay (coil side):

Battery positive to toggle switch
Toggle switch to relay coil
Relay coil to ground
Ground to battery negative (Of course)

This will not be a short, will it? (Or do I need some sort of resistor
in there?) The relays I plan to use can be seen at
http://www.allelectronics.com/cgi-bin/category.cgi?category=search&item=RLY-412&type=store
The important detail (I think) of the relay is that the coil is 72
ohm.

Also, is it safe to use DIP switches? I don't know if they can handle
the current that will go through the relay coil.

--
Andy
http://dynamicbits.com