school me on relays

[mtnbike28]

I need to figure this out: Currently I have a big gauge wire running directly from my battery into a fuse at the battery - through the firewall into the cab to a generic store brand switch - back through the cab and into the bed. I use this for powering my thermal electric (read cheap) fridge - that is the reason for the switch. I am installing a new CB tomorrow and want to use this power wire (before the switch) to power it. I went to the parts store today to ask abut a relay and they gave me a fuel pump relay and explained to jump from this prong to that prong, and on and on - and it seemed to be not what I wanted. Does anyone have a simple (with store bought parts) way to wire this? Hot off the battery, a switch in the cab to turn on the rear outlet and a power lead for the CB?
Thanks

 

[Robthebrit]

I read your question 3 or 4 times but I am not 100% sure what you want to do. What is the relay going to be used for? Do you want to power the CB with the relay, the fridge or the entire circuit?

Do you want the existing switch to control the relay?

Rob

 

[ExploringNH]

Having large gauge wire and current running to a switch not rated for the load is a good way to start a fire. Glad you are changing that out. Im not entirely clear on what you want to do with the CB, but this would be a circuit for the fridge. I would just run a small gauge power wire from the battery to the CB as permanent power and not bother with any relay setup.

The relay you got at the store should have a rating on it, I would assume it is 20A or so. Just make sure that amperage rating is higher than your fridge will draw (Im sure it is). The relay should have 4 posts on it.

Two posts go to the coil of the relay. When power is applied to these two posts, the relay pulls in and closes a contact across the other two posts.


Wiring diagram in text:

+ from battery to one side of switch - small gauge wire.
other side of switch to one side of coil post on relay - small gauge wire.
other coil post on relay to - battery (or close ground).

That completes the control circuit. When you flip the switch, it closes the relay and makes the contact through the other terminals.

The load circuit is:

+ from battery to one side of load posts on relay - heavy gauge wire.
other load post to power wire on fridge.
- wire on fridge to - battery (or ground).

Good luck. If you need more help, I can draw it out in Paint.


Edit: This is a good diagram for the relay part of it. Just replace air horn with fridge and ignore the stock horn part. When the coil gets power, it closes the switch between 87 and 30.-
http://www3.telus.net/desktopsolutions/Miata/AirHorn/PhotographsAH/horn_relay_wiring_diagram.gif

 

[mtnbike28]

Thanks and clarifacation?

Yeah I am sure my question doesn't make sense! I am looking for the best way to wire my set-up. Ryan answered part of the question. Just run a new wire to the battery for the CB. So I want the relay to replace the large wire coming into and out the cab (as Ryan said it's a bad idea) - The relay the parts store gave me was for a fuel pump and looked like it plugged into something. It also had more than 4 prongs. Do you know what I need to ask for? And Ryan, if you are bored, I would love a drawing (I am more visual) but your write was great and I think (big letters think) I understand it.

Thanks again

 

[ExploringNH]

Relays can have more than 4 prongs and still be useful for what you need. The relay you picked up sounds like it is for a certain make and model car, but most use the same setup.

Does it look like these will fit on the prongs of the relay?
http://www.dclinearactuators.com/wp-content/uploads/2007/06/spade-connectors-female.jpg

They come in many sizes. If it is a different style prong, it may be best to just get a new relay.

If you have more than 4 prongs, you want to find the two that go to the coil, and find two that are NO (Normally Open) and wire to those. Ill try to draw up a pretty picture for you tomorrow. It would help to have a pic of the relay you have, or the diagram of it, if it has one.

 

[mtnbike28]

Is this right?

http://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/foglites.htm
http://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/foglite.jpg

If so, would I run a small gauge wire from the battery into the cab for the CB and the switch?

Sorry for the noob questions. I suck at wiring!

 

[ntsqd]

Substitute the "fog/driving lights" for what ever high current device that you want to power and that diagram will work. The fuse or circuit breaker should be rated for the load of the device. Also, the indicator light shown is entirely optional.

Why do you want to turn this circuit on and off from the cab? Normally this sort of thing is handled at the cooler via it's own switch.

I have a wire on my Toyota truck that runs from the battery, through an 80 amp fuse, and back to nearly the rear of the truck. In two spots I have an isolated stud for an easy way to tap into this power wire. One of those taps supplies a Power Point that my fridge plugs into.
Isolated stud:

 

[spencyg]

To delve back into confusing for just a second (great diagram nt), a relay is just a remote switch. I find it easier to apply their services when I think of it that way. They are very simple in principal. Basically inside the "black box" (relay), you've got a set of BIG contacts which can handle high current/high load (30 and 87 in NT's diagram). Then there is a small electromagnet which is mechanically connected to the big contact, basically acting to "throw the big switch". The "click" you hear when you've powered up a relay is that contact being made. The electromagnet circuit (tabs 86, 85) doesn't draw much current, so you can use a smaller wire and switch to activate it. When you throw the switch to turn on your fog lights (for instance) in a relay-type circuit, your switch is actually just powering up the electromagnet. Tab 85 needs power because the electromagnet needs power....you provide this power through your dash switch. Tab 86 is the ground for 85....without a ground you won't make the electromagnet do anything. 30 and 87 are just pass-thru....just like a wall switch in your house.

As I said...probably more confusing, but I usually find that understanding the method behind the madness helps in long-term comprehension.

Good luck.

Spence

 

[ntsqd]

Thanks, but not my diagram. Was linked above, I just made it visible in the thread. I thought it being visible up front might help the discussion.

 

[mtnbike28]

Thanks again

Thanks again, I now understand what I want to do... still debating if I want the switch at all (per ntsqd's question) The reason I wanted it was to allow me to turn on/off whatever I connected to the acc. outlet in the bed from the cab.

Final question, it looks like the Bosch relays are popular but do I need to weather proof the prongs were I connect the spades? I plan to bolt it under the hood somewhere...

 

[mtnbike28]

Next question.

OK I am in the middle of the CB install and went to Radio Shack to buy a $50 SWR Meter... but not the darn cable between the meter and CB (why can't they include that?) I ran power to the CB with RA 58 shield cable directly to the battery (read that tip on the internet). So I spliced together the ends to make a short antenna cable to connect the meter and CB - is this bad, ie messing up my SWR readings? I just want to use it long enough to test SWR. I tested the continuity and it buzzed...

Thanks again