relay and breaker help

i'm not sure what part of the forum this should be in,so mods please move it if it ain't in the right place.

so i want to put this: http://www.autozone.com/autozone/ac...-25gq?itemIdentifier=32322&_requestid=6947829
in my truck wired to the battery,
i can build a mount and run the wires but,
how do i calculate what size relay and breaker do i need?
i want to run the relay so that the power gets turned off when the ignition is off.

right now i only plan on running 2 12v plugs to power a cb and having extra if i need it.

 

making this an "accessory" triggers fuse block is going to be difficult. A single relay only poweres 30-40 amps depending on brand/quality. WIth that in mind, this says 30amp max, but I am assuming they mean 30amp per fuse slot max since the picture only shows 3 out of 6 fuses and it is over 30amps total already. So making this accessory would require you to run 6 relays to power this thing as accessory only, but wiring up 6 relays would completely defeat the purpose of the fuse block itself.

what you need to do is make the fuse block a constant battery source, then if the item you are connecting MUST be accessory, then add a relay between the block and the item. it would go like this: Battery>Block>Relay>Accessory. IMO if your using relays anyways, there is not point in a fuse block.

Now, whatever you decide to do, a breaker is recommended between the battery and this block. The size of the breaker can ONLY be determines once you know exactly what accessories your connecting to it. If you have only 2 simple items each using only 10amps max, then a 20 amp breaker is plenty. However, as soon as you add a third accessory, you need a larger breaker. Since breakers are not cheap, I would recommend a different solution to your problem. Get a larger glass fuse holder like what you would use for an amp power wire like this:




Then once you have your holder in place using at a minimum of 8 gauge wire (id recommend 4g) because assuming you max out the block at 30amps x 6 slots = 180amps and the distance from battery to block is probably a few feet. 180amps at 2160 watts for less than 2ft requires 8g wires, 2-8ft requires 4g and more than 8ft needs 1/0g. So assuming the block is in the engine compartment, id say 8g is ok, but 4 is best. Now you can easily swap out fuses according to how many circuits you are using and how many total amps your drawing. If your only using 1-2 slots right now (for a cb and 1 extra thats no more than about 5-10 amps. So in the slot on your fuse block you put a 10amp for each of the 2 slots your using, and then in your larger fuse holder connected to the power wire, you put a 20-25amp fuse. Once you add more accessories to this fuse block, then increase the size of your glass tube fuse in your main line to equal the total of the small fuses being use plus about 5-10% extra. Its much cheaper to swap fuses than continuously change breakers out.

Now, your setup should be as follows: BATTERY > LARGE GLASS FUSE HOLDER > ADDED FUSE BLOCK > RELAY (only if you want accessory and not constant) > ITEM BEING POWERED.

To wire the relay for accessory power, it would be as follows:
85- Ground
86- Accessory power
30- Aftermarket Fuse block added
87- out to accessory being powered
87a- not used

In all honesty though, the idea of this fuse block is a giant waste of time if your going to make these items accessory power since they will need a relay anyways, you mine as well just connect straight to battery with their own fuse holder per accessory, and then just make a nice fancy mounting shelf for your relays instead of the fuse block. just my opinion though.

Hope this wasnt too confusing for you

 

Most of your questions answered well above.

I run one of these fuse blocks (constant power in my instance). They work pretty well. Main power input pin is pretty small (say 1/4 dia) so keep in mind when choosing connectors. Also, mine at least, did not come with any protective cover over the pin to help with potential arch short if you are working around the box. I used a heavy vinyl vacuum cap to cover it once everything was connected as I have it mounted under dash.

I understand what you'd like to do in your instance and it is perfectly possible, depending on power usage as detailed in above post.

From what I see on a Cobra CB I looked at, the power draw at full is 1.5 amps. The issue you need to look at and plan out is exactly how many circuits you plan to run now and possibly in the future off of this fuse panel. What would the total draw on the system be? Look at the items you are planning to run and they should list power draw in the instructions/manual or perhaps on the item itself. If this can be covered within a relay power range then okay you are set. Just be mindful when installing add on items.

Just me, but I’d wire it to the battery with a fuse within 6 inches of the battery. Run your wire with protective sheath into the cab through a grommet. Wire to your relay and then out from the relay to the fuse block. From there you have a simple wire in connection for ignition switched power by just placing an appropriate fuse in the block at whatever terminal and connecting your wire to the corresponding output spade. Just keep in mind your relay, input wire and fuse capabilities.

Wiring the relay is simple. Buy a quality relay. Some will have 4 prongs, but most will have 5 as standard. If you look at the prongs you will typically see that they are numbered next to each prong. These numbers are standardized. Connect your main fused source power wire to prong 30, connect your output power wire to your fuse block stud to pin 87. Connect a chassis ground wire to pin 85. Pin 86 is going to be your switched wire that you will connect to an ignition switched wire that is hot when you have the key on. Pin 87a on the relay (if you have one) will not be used.

The relay itself takes very little to activate so you can tie into pretty much any switch ignition wire from your harness. Just be sure to keep all wiring protected, wire tied securely, away from moving objects or sharp surfaces and ensure all connections are secure and tight.

 

it wouldnt be cheap but you could do something like a 200 amp continuous duty relay to power that setup.

now if it were me, i would use the fuse box and simple relays after each output. i do not like running multiple wires from the battery so a fuse box is a great idea.

 

I have the Buss 6 terminal fuse block...
use it to power 8ea. 50w rock lights.
4ea. 30a relays are used for the those.
Two terminals remain unused.
The fuse block, as well as the 4 relays
are mounted to a piece of wood...
and then was rtv'd to the sheet metal.
It's held there for 6 years without issue.

I have an inline fuse between battery and fuse block.
Tho' it should be closer to the battery...
I haven't had an issue with it..and chose not to worry about it.

* Since this fuse block is not water proof, nor even water resistant...
I recommend locating it somewhere within the cab.

Mine is located in the cubby hole behind the driver's seat.
I used 8g cable to route from the battery to the fuse block.
It is routed down the driver's side under the door's threshold cover.

note: My cable leading from the primary/Ign. battery to the fuse box
was relocated... and it now leads to an aux. battery instead of the primary.
The cable's fuse is still too far away from the aux. battery...
but I was too lazy and cheap to purchase all new cable for that correction.

pictures just 'cause

Buss fuse block...



primary inline fuse...



rocker switch location (set up for driver/passenger switching)...

 

thanks for the help guys, i'll probably go with the large glass fuse,
and i might mount the fuse box in the cab, i'll look around under the dash and see whats what.

"200 amp continuous duty relay" i'll look into that, thanks.

and i was doing more research on this and it said a solenoid could be used as a relay, can anyone back this up?

 

You might find this of use as well.

http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

You mention wanting to run a couple of power outlets as well. This factory Tacoma setup might help as a guide for you perhaps.

 

thanks for the links when i get a chance i'll look them over.