ffastje <ffastje@cox.net> wrote:
> jon@dakota-truck.net wrote:
[...]
>> I hope that helps! If you need any help such as a wiring diagram
>> or something to show how a relay would be used, just let me know.
>>
>>
>>
> Jon us newbies to working on wiring would love to see
> a wiring diagram
> or something to show how a relay would be used.
Ok, its pretty simple, here's a quick doodle, optimistically
referred to as a "diagram" for the remainder of this e-mail:
jon@dakota-truck.net/relay.jpg">http://www.dakota-truck.net/attachments/jon@dakota-truck.net/relay.jpg
Not shown in the diagram for the sake of simplicity is a wire
running from the positive terminal of the battery to the switched
power source, but that's basically implied, and that's not a wire
you'd need to run anyway; the factory already did it. (The switched
power source technically wouldn't *need* to come from the battery, it
could be something like a 9v battery, but in that case, the coil would
not share a ground with the battery as shown in the diagram, terminal
85 would connect to the negative pole of whatever you were using for
your switched power source. In a vehicle though, usually all power
originally comes from the battery, as does the shared ground.)
Its pretty easy, a relay is just a switch; instead of flipping a
switch yourself, the relay does it when you apply power across the
coil terminals. (I believe how it works in most mechanical relays is
the coil is actually a little electromagnet, and it pushes or pulls
a contact into position when it is energized, then when the power is
cut, there's a spring or something to push the switch back to its
"off" position. It only takes a tiny amount of power to energize the
relay's coil, but there can be a lot of current on the wire it is
switching. (There are different sized relays for different current
demands. Off the top of my head, I think most automotive relays you'd
buy in a parts store are rated for somewhere around 25-30 amps.)
I've numbered the terminals in the diagram to correspond with the
numbers on standard automotive relays, and also scribbled a diagram at
the bottom to show which terminals are which. (Usually the numbers
are on the relay itself though.) Terminal 87a isn't present on all
relays. A relay that doesn't have 87a is a SPST relay; the output 87a
is disconnected from the common (30) until the coil (85 and 86) is
energized. A SPDT relay is exactly the same except it will have the
87a terminal, which is normally closed until the coil is energized.
(So, if you had something that you wanted to be on all the time except
for when you supply power to the relay, you'd feed it from pin 87a.
Normally though, you want the load to come on when you apply power to
the relay, so terminal 87 is usually the one that is used.) Its
something to be aware of though; if you're using a SPDT relay, you
need to remember that when the relay is "off", there is +12v (or
whatever you are switching) on that 87a terminal, so block it off if
it isn't being used. A quick note about the coil terminals: in the
diagram, I show the coil being energized with + on 86 and ground on
85, but it normally doesn't matter which terminal you use for which,
as long as one is positive and one negative. (If polarity is
important for the coil terminals, the relay you buy will say so.)
Relays can be fun. When you use a bunch of 'em together, they can
even make simple logic circuits or even be a really, *really* simple
mini-computer. :-) Here's a pic of the redneck "control board"
(literally a board, since its mounted on #2 pine) ;-) for the air horn
system in my '01 Ram:
http://www.jonsteiger.com/WWW/ram3500/airhorns/25.jpg
The four relays on the board are the brains of the system. In that
setup, I actually did make use of the 87a (normally closed) terminal.
The control panel for the air horns allows you to activate or
deactivate the air horns as well as the stock electric horn. (As long
as my air tank is full, I leave the electric horn off and the air
horns on.) By making use of the 87a terminal, I was able to wire the
system in a "fail safe" manner - by running the electric horn wire
through a relay on the board, (in common and out 87a), the electric
horns are only off if I energize the relay by flipping a switch on the
control panel. Otherwise, the electric horn circuit path is
connected. So, if a fuse blows in the air horn system or when the
ignition is off, pressing the horn button will sound the electric
horn.
Hmmm, I seem to have rambled on a bit - sorry about that! I do
enjoy working with relays though. They are such simple devices, but
deceptively so - you can do some fun stuff with them!
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
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