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Old 09-13-2013, 12:34 PM   #1
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Another wiring question

So, I have a 40AMP Relay powering my 55W HIDs and my 20" LED Bar. I'm not very Learned on Relays but can I add the 50" Bar to this circuit?

Right now there are two Switches on the circuit, one for the HIDs and one for the LED, So I would be running a seperate 20amp Switch to the 50" bar. Or, would I need another seperate Relay for the the 50" Bar?

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Old 09-13-2013, 04:26 PM   #2
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Watts/Volts = Amps

So . . your 55W HIDs draw about 5 amps.

You don't say what 20" LED Bar you have, so let's assume it has 40 3W LEDs. Thats 120 Watts or about 10 amps.

So between the two you are drawing 15 amps through the relay.

You don't say what 50" bar you have, so let's assume that a 50" bar will draw 300 Watts (I went high to be safe.) That's 25 Amps.

Added together, you'd be right at the limit for the relay, which I wouldn't advise. And bear in mind that just because the relay supports 40 Amps doesn't mean that the wiring will. You didn't specify what gauge wire you are using.

But all of this is really academic. Why would you use the same relay for all three lights? Do you really want them all to come on at the same time? Generally, each would be switched separately with it's own relay.

I know your 2nd paragraph talks about having two switches, but you seem to think you only have one relay. That doesn't make sense to me. Switches and relays are installed as a pair. Unless I'm missing something, like you have some weird "dual" relay, only one of your switches is working your relay and only one device is on it.

The bottom line is that if you want separate switches for each light, you'll need separate relays. You might be able to get by without a relay for the small light bar, but I would use a relay nonetheless as it is the best way to go.

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Old 09-13-2013, 04:31 PM   #3
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Quote:
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Watts/Volts = Amps

So . . your 55W HIDs draw about 5 amps.

You don't say what 20" LED Bar you have, so let's assume it has 40 3W LEDs. Thats 120 Watts or about 10 amps.

So between the two you are drawing 15 amps through the relay.

You don't say what 50" bar you have, so let's assume that a 50" bar will draw 300 Watts (I went high to be safe.) That's 25 Amps.

Added together, you'd be right at the limit for the relay, which I wouldn't advise. And bear in mind that just because the relay supports 40 Amps doesn't mean that the wiring will. You didn't specify what gauge wire you are using.

But all of this is really academic. Why would you use the same relay for all three lights? Do you really want them all to come on at the same time? Generally, each would be switched separately with it's own relay.

I know your 2nd paragraph talks about having two switches, but you seem to think you only have one relay. That doesn't make sense to me. Switches and relays are installed as a pair. Unless I'm missing something, like you have some weird "dual" relay, only one of your switches is working your relay and only one device is on it.

The bottom line is that if you want separate switches for each light, you'll need separate relays. You might be able to get by without a relay for the small light bar, but I would use a relay nonetheless as it is the best way to go.
Awesome Thanks. That's what I figured. I'm passing on rewiring everything with a fuse box to get things a little neater too anyway
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Old 09-14-2013, 01:51 AM   #4
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So this is what I was going to rewire to. Does this look right? The yellow ovals are the relays. So I would have everything fused for protection before the switches and relays between the switch and appliance.

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Old 09-14-2013, 07:23 AM   #5
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I don't think you need to run grounds from the fuze box. Just pick up a ground locally to the lights. Fuze boxes that have a negative bus bar are typically for marine applications where everything is fiberglas and you can't get a local ground. It can't hurt to run the ground, though . . . just more work.

The one thing that is missing from your diagram is that the lights need to be powered directly from the battery through the relay. The concept is that turning on the switch powers the relay to make a connection between the battery and the lights. That way, the power to the lights isn't running through the switch. So you'll have a power into the relay from the switch, a power into the relay from the battery, and a power out of the relay for the lights. The 4th connector on the relay is the ground.

Look at the diagram in Atthehop's post in THIS THREAD. The diagram is for fog lights but the concept is the same.
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Old 09-14-2013, 10:46 AM   #6
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I don't think you need to run grounds from the fuze box. Just pick up a ground locally to the lights. Fuze boxes that have a negative bus bar are typically for marine applications where everything is fiberglas and you can't get a local ground. It can't hurt to run the ground, though . . . just more work.

The one thing that is missing from your diagram is that the lights need to be powered directly from the battery through the relay. The concept is that turning on the switch powers the relay to make a connection between the battery and the lights. That way, the power to the lights isn't running through the switch. So you'll have a power into the relay from the switch, a power into the relay from the battery, and a power out of the relay for the lights. The 4th connector on the relay is the ground.

Look at the diagram in Atthehop's post in THIS THREAD. The diagram is for fog lights but the concept is the same.
The only thing from his diagram I don't understand is the fuse box is not in line with the circuit, how would it protect it? Wouldn't the fuse he has between the battery and relay be enough?
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Old 09-14-2013, 03:38 PM   #7
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You'll actually be using two fuses per circuit.

The first fuse is on the battery --> relay --> lights circuit. This fuse should be as close to the battery as possible. It protects the circuit created by the relay when it is energized.

The second fuse is on the some power source --> switch --> relay circuit. This protects against a short in this circuit. In the diagram, this circuit is protected by a fuse in the fuse block. The two circuits are technically independent of each other and thus each need fuse protection.

The fuze block is probably powered from the battery as well, but that isn't shown. The power lead to the fuse block should be protected by a large fuse as well. You don't need to get power to the switch from an independent fuse block as the current (amp) draw is very low. You could use one of those saddle taps on the interior block behind the glove box. (That's were it is in a TJ.)
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Old 09-14-2013, 06:01 PM   #8
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You'll actually be using two fuses per circuit.

The first fuse is on the battery --> relay --> lights circuit. This fuse should be as close to the battery as possible. It protects the circuit created by the relay when it is energized.

The second fuse is on the some power source --> switch --> relay circuit. This protects against a short in this circuit. In the diagram, this circuit is protected by a fuse in the fuse block. The two circuits are technically independent of each other and thus each need fuse protection.

The fuze block is probably powered from the battery as well, but that isn't shown. The power lead to the fuse block should be protected by a large fuse as well. You don't need to get power to the switch from an independent fuse block as the current (amp) draw is very low. You could use one of those saddle taps on the interior block behind the glove box. (That's were it is in a TJ.)
I may still run an independent fuse/power supply for the switches. I'd like to keep any new equipment separate from the existing system. So would something like this work? Or is it overkill? Although, for me, a little overkill Just means safer.

Ps sorry for the crazy photo, lol
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Old 09-14-2013, 10:55 PM   #9
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Yep. That'll get it!
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Old 09-14-2013, 11:47 PM   #10
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Yep. That'll get it!
Awesome, thank you for all your help
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Old 10-14-2013, 07:28 PM   #11
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Where did you run your wires from the light bar to your battery?? I'm putting one up at the moment and I'm wondering if I need to drill or what
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Old 10-14-2013, 09:46 PM   #12
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I ran mine down the window and under the vent
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Old 10-15-2013, 09:27 AM   #13
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Bumper Lights

I was thinking of using this as to wire my new bumper lights. In the future I would like to put some lights on the windsheild. Will I be able to just tie into this relay or would I need to run it the same way? What size relay do I need? Would most auto parts stores have them? The lights are 55w h3 halogen. (Basic Relay Use Diagram page 2)

Thanks
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Old 10-15-2013, 09:33 AM   #14
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that was not supose to be a reply. sorry about that

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