12V switched power source - hookup

[Rogan]

thanks man !!

good stuff

Someone exaplain relays ??? In a very basic way., I have NO IDEA.

Ok, very basic, a relay is nothing more than an electrical 'switch'. Using a standard Single Pole Double Throw (SPDT) relay as an example

a Single Pole Single Throw (SPST) looks like this (same, minus the 87a pin)

The "coil" section is what drives the internal switching. This is an electro-magnetic coil. When this coil is energized, it creates a magnetic field that flips a switch to connect two terminals.

As a standard, pins 85 and 86 are the connections for the coil. I always put ground to 85, and 12v switched power to 86 (it can me the other way, as polarity isn't a factor on the coil.)

Pin 30 is your 'common' point. At 'rest', or with the coil not energized, pin30 and 87a are connected. Once you energize the coil, then pin30 and 87 share the same connection. It takes 12VDC to trigger the coil, but only 250mA, or 1/4 amp, so a very small switch can handle this task.

The rest of the circuit (pins 30, 87, 87a) can handle whatever the relay is rated for (usually 30 or 40A as a standard.)

I used to put my "input" on 30, then whatever I wanted to trigger with the relay on 87. The downside to this is, that if you put 12VDC on 30, and the relay is not energized, then you have 12VDC sitting on 87a, and nothing connected to it, leaving 12VDC sitting on an open, exposed pin. This isn't really a good idea. So, I changed my methods (I'm talking 15+yrs ago) and put my input signal on 87, and use pin30 as my output. This leaved the unused 87a to never see voltage, which is how I prefer it.

Are you still with me? Good.

So, in a practical exercise, we'll wire up something, and show you how to properly use a relay.

Here's a circuit without a relay. As you can see in the top example, the switch carries the full load of the work to drive the lights. Not good.

In the bottom example, we add a SPDT relay (a SPST will work, as well, depending on the load rating.) Now, you see the switch is only triggering the coil with voltage, as the other side of the coil is grounded, allowing the relay to carry the load of the circuit, rather than the switch.

Below is another example of allowing the relay to carry the load, rather than the switch. This time, the switch is supplying a grounded signal, while the other pin of the coil sits at voltage.

So, as you can see, building a circuit properly takes a little more time, and components, but will work better, last longer, and most importantly, BE SAFER.

I bought a 120V 10A switch from home depot - thats the one I am using

http://www.lowes.com/pd_75666-1071-161U_0__?productId=1100285&Ntt=toggle+switch&pl=1&currentURL=%2Fpl__0__s%3FNtt%3Dtoggle%2Bswitch

does that mean I only need a 10A as the switch itself is 10A ? I guess I still need to confirm the 'A' of the fan

That switch is a 10A switch, yes.. But for 120VAC circuitry. Just go to Radio Shack, and pick up a relay (SPST or SPDT), a 12V toggle switch, a fuse holder, and some connectors, and do it up right ;) Return the Lowes switch. Or use it, whichever you prefer. It'll work, but USE A RELAY, additionally.

Any drawback to using a 30A fuse when all you need is a 10 A ?? Guessing something to do with it won't break the circuit early enough if their is an issue and result in the thing your trying to protect breaking ?

YES, there is. To an extent. If you're only operating a 10A load, then I'd probably go no higher than a 15A fuse. Reason being is, that if there's a problem with the device you're operating, there's a much higher chance of causing more damage, if you allow more amperage through the circuit than is required (read: possible electrical fire) Yes, it can/does happen.

Hope this helps you understand relays a little more, and educate you in the benefits of using relays.

note: I snagged pics off the interwebz for illustration, rather than create new ones. Saved time in writing this book LOL

[elshadow001]

Well here is something to share!someone can put it in the download I am not allowed.

ohms law.zip

[Rogan]

Well here is something to share! someone can put it in the download I am not allowed.

You got it up there... twice ;)

[elshadow001]

Sorry I didn't see it.

[JOHNFAK]

Man - cool stuff I only 'just' followed it ... and not the detail - the concept "we add a SPDT relay (a SPST will work, as well, depending on the load rating.) Now, you see the switch is only triggering the coil with voltage, as the other side of the coil is grounded, allowing the relay to carry the load of the circuit, rather than the switch. So, as you can see, building a circuit properly takes a little more time, and components, but will work better, last longer, and most importantly, BE SAFER."

ok ...... so by using a relay do you mean a relay like what we have for some of our existing circuitry - like our horn, lights whatever ? eg buy a xAmp relay and use that in spare slot ? Or do you build the relay from ground up ? Might need isx to show me this one when I see him next

[Rogan]

ok ...... so by using a relay do you mean a relay like what we have for some of our existing circuitry - like our horn, lights whatever ? eg buy a xAmp relay and use that in spare slot ? Or do you build the relay from ground up ? Might need isx to show me this one when I see him next

You can get the relay with harness for < $10, making the job a little easier. It'll look something liek this: http://cgi.ebay.com/ebaymotors/12V-12-VOLT-30-40A-SPDT-RELAY-w-SOCKET-WIRE-HARNESS-_W0QQcmdZViewItemQQhashZitem4a9657e5d9QQitemZ320349922777QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories You'll need to hard-wire the pigtail. You could use an empty slot in the power distribution block, or whatever, but that may be a little above your experience level, just yet. I'm not trying to be condescending by any means, but that type of 'mod' can get a little tricky. But to answer your initial question, you can use the OE-style relays, too, as long as you understand what pin does what. Bottom line, it still functions along the same principle, just may have a different physical interface (pinout) appearance.

[ISX]

I'll show you how it's done John

[JOHNFAK]

yeah thx guys - great info - but starting to sink Sure - I'll drink a beer and watch/listen ISX THAT I CAN DO !!! lmao

[Mopar1973Man]

yeah thx guys - great info - but starting to sink

Sure - I'll drink a beer and watch/listen ISX THAT I CAN DO !!!

lmao

Ummmm... It should be...

Sure - I'll watch/listen ISX and then drink a beer THAT I CAN DO !!!