Light Bar Question/s....

[miscott]

Hey All...
  First off, a big Hats Off to "bikerboy1951". Thanks Brad!  You made my year!

  I have a couple question about wiring/circuits.... I know, "search is my friend". It is, and I did. 
 Just wanting to clarify a couple things,
  The Show Chrome Accessory Switch that I went with for my light bar is only rated at 2 Amps.

  How do you control the amount of amps in a circuit?

  From the reading I've done in studying the installation of light bars, I'm unable to find a direct answer to this question...
  Are the amps in a circuit determined by the amount drawn by the device being powered? (this would seem to me to be the obvious conclusion, but I'm no electrical engineer.  )

  I've pretty much figured out the basic wiring for the install, except for how to keep from worrying about frying the circuit board in the switch. Being as it's only rated at 2 amps, I'm just wanting to make sure I understand what I'm doing before I find out the hard way that I didn't understand what I was doing.  Does the switch side of the relay draw less than 2 amps?

  I've got a 6 fuse panel block that I'm going to hook everything up to, and the relay to put in the light circuit, that will be activated by the switch, which will be hooked up to a 2 amp fuse, which will be powered from the blue w/white stripe keyed wire in the bundle under the right side cover. I'm thinking I'll put the relay in the front of the battery box with the fuse panel, all mounted to a panel made out of an old mc license plate frame. ( search was my friend. ) Where would be a good place to ground the relay to?
Can I ground it to the neg. side of the battery?

  I'm thinking that the lights will be powered from the positive battery terminal to the relay, to the fuse block, to the lights. Lights grounded to the bar, bar grounded to the forks. What size wire would be best for this circuit wired up this way? It appears to me that the wire coming out of the lights is only 16 gauge.
  In just re-reading some of the older posts about this on tech board, I'm wondering, why is the relay before the fuse block? I assumed that the fuse block would have been before the relay.
 
  Are the old style cobra lights 35 watts, or 55 watts? Think I read at Rattlebars site that their 35 watt?
I know I need the power feed to the lights going through a 15 amp fuse, just was wondering what the wattage on the lights are, for future upgrading reference.  Should I wire this "power" feed to the lights with the 16 gauge, and it will work with upgraded lights later? Or, do I need to wire this "power" feed with the 14 gauge for when I want to upgrade to the 55watt lights down the road? What would be the fuse rating for 55watt lights? 20amps, 25, 30?

  Got the bars mounted and the turn signals wired up and mounted this evening. Hoping to have the driving lights wired up and finished in the next couple days so that I can get out riding  before the rains start around mid week! Their forecasting 4 days of rain! 

[pancho]

Hey Miscott,,  The amperage is a measure of the current draw. The current draw can be figured by the wattage of the lamps. Wattage is a power measurement fuigured by current times voltage,, so the wattage of the two lamps added together divided by 13.2 (nominal battery voltage) will give you the current requirement. for example, two 45 watt lamps is 90 watts divided by 13.2 battery voltage requires a current draw of of almost seven amps. In that case you would need to power a relay with the two amp switch and let the relay power the lamps. 

The total load that can be safely handled by a two amp switch on a 12 volt vehicle is about 20 watts,,, you always leave a safety margin,,,

[Gryphon Rider]

With all these questions, it's hard to know where to start. First I'll answer an easy one, then move on to others as my late-night energy allows.

First, your 2A switch powered by the blue and white wire servicing the control side if the relay is fine. The current draw of the relay coil is likely less than half an Amp, and certainly less than 1 Amp. Also, to ground any circuit, you can use any screw that screws into the bike's frame, or the negative battery terminal, which is also electrically connected to the frame. Now, for the question of should the relay be before or after the fuse block. Do you want the relay to switch ALL the circuits coming out of the fuse block, or just your lights? If all, put the relay before the fuse block. If only the lights, after the fuse block.

Now for the questions about current, Wattage, and wire size. All circuits, when not switched off, allow electricity to flow from the positive battery terminal to the negative terminal. The rate of flow is measured in Amperes (aka Amps, 1A=1 Coulomb of charge per second). The flow of current (Amps) depends on electromotive force, i.e. voltage (you can think of this as electrical "pressure"), and impedance to this flow, usually considered to be resistance in DC automotive circuits, measured in Ohms (Greek letter omega, which my iphone won't let me type).  Small wires restrict electrical flow, therefore having more resistance per unit length than larger gauge wires. Electrical power is measured in Watts, and is the product of voltage and current, i.e. W = V x A. So assuming your lights are 35W each (and I don't know if they are), and are powered by a 12V supply, 35W x 2 lights = 70W; 70W / 12V = 5.83A. Minimum fuse size is 1.2 x expected current, so 5.83A x 1.2 = 7.0A. The closest common fuse size higher than this is 7.5A. Using the same method, the fuse for two 55W lights should be 11.0A. Since this size isn't common go up to the next common size, 15A.

Okay, now I'm getting tired, so I'll just say 16Ga wire is fine for 2 x 55W lights, but they might look slightly brighter with 14 Ga wire. Google "voltage drop" to learn more.

[tank_post142]

http://www.rattlebars.com/valkfaq/circuits.html

save these pics as one day chet may let this website die.

[miscott]

Thanks for the info!  

  Answered all my question! But, one  2 more, for the road....
    Gonna wire up the power to the lights using 14 gauge wire. For the 2 amp switch, would 18 gauge wire be better than 16 gauge?  Should I fuse that switch with a 2 amp fuse, or 1.5 amp fuse? Do they make a 1.5 amp fuse? I would think by doing that, the fuse would blow before the circuit board in the switch, whereas a 2 amp fuse on a 2 amp switch would risk frying the switch?

    I googled Voltage Drop.......  My brain hurts!

   You were right. I read it tonight somewhere about having the relay before the fuse, now I can't find it! But in digging deeper the last hour or so, every diagram I've come across has the fuse, then the relay!
    
                  

   Now I need to find out how many watts the original cobra lights are. Just re-read chets wiring page and he says " Cobra and other light bars ship with 35 watt lamps".
   Gryphon Rider - According to your calculation, 35 watts means a 7.5 amp fuse. Wiring this up with 14 gauge wire, would it hurt to use a 10 amp fuse, and when I upgrade to 55 watt lights just swap  that one out for a 15 amp fuse?

   Yeah, I think I will stash Chets diagrams, they really helped me to understand what to do, and how to do it!
   Took a few days of readin`, but at least now I understand what I'm looking at when I see a diagram like that! Guess an ol` dog can learn new tricks!  
   Gonna hit the sack before my brain blows a fuse!!  
              

[jimmytee]

Fuses are generally sized 1st  for the protection of the wire, and 2nd the components.  Example of catastrophic failure would be some one who uses a wire too small for the amp load and too large of a fuse or no fuse. The wire then can become basically a heating element, potentially causing a fire.
 As far as your switch, there should be nothing more than a switch and an LED right? You mention a circuit board, unless the Show Chrome switch utilizes transistors/ic chip for switching it is most likely just a switch. If your concerned with burning up your switch, then wire in an inline fuse. You can get glass fuses with less than 2amp ratings and put them in an inline fuse holder.
Myself, I bought a Show chrome Light bar w/55 watt lights. I got the Kury three switch item that mounts to the resevoir. I looked at the Show Chrome switch and debated, but because of the three switches on the Kury and the 10 amp rating I went with the Kury. Even though the 10 amp rating would've been sufficient,  I still used a relay. The Kury switch came with fuses inline to protect the switch. Basically it comes down to this. The protection a fuse offers is primarily after the fuse. If a problem develops after the fuse that causes an amp draw higher than the fuse's rating, then the fuse should blow and cease current flow. The cessation of current flow will protect components preceding the fuse, but the fuse will only react to problems after the fuse. I hope this helps.

[Denny47]

The top rear stud that the right side panel snaps onto is a decent place to ground and is close to the batt compartment.

[Gryphon Rider]

2A fuse is fine as is any wire size 20Ga or physically larger (smaller gauge number, e.g. 18 Ga is bigger wire than 20Ga). The only reason not to use larger wire is physical space for it and harder to hide, neither of which are likely to be issues.

[Brian]

This suggestion maybe an over kill but never hurts since grounding is as common issue when things don't work right. When I installed my National Cycle light bar I ran another ground wire from the headlight bucket to frame bolt that holds the coils on the left side frame. I had the tank off and the headlight out anyway running all the wires to relay under my seat.

[Gryphon Rider]

Good suggestion, Brian, I've done the same thing.

If anyone is wanting a good basic understanding of electricity, read this:
http://www.gtsparkplugs.com/pdf/AutomotiveCircuitTheory.pdf