4 Roof Rack Lights, 100 watts each

[xperienced]

I recently purchased a light bar from 4x4parts for the factory roof rack.  I am planning on installing some offroad lights, but haven't messed with high output lighting before.  I am weary about running the proper wiring, fuse, and switch.

Is 10 gauge wire strong enough to support a 100 watt light? 
Is a 55 amp fues strong enough for two 100 watt lights? 
Can I run four 100 watt lights from one battery and the stock alternator?

My plan is to run the lights through the roof, down the windshield post, and to a fuse.  Then from the fuse to a switch and finally to the battery.

I'm attempting to tackle the job myself, but want to make sure I only do it once.  Any insight would be greatly appreciated.

[Paul]

Normally it's not recommended to run the power thru the switch but rather to activate a relay that passes the power.

I ran two separate circuits so that I could activate each set of lights one at a time. 12-gauge wire is strong enough for my sets of 150w x2 lights and 100w x2 lights. I ran an 8 gauge ground wire because both circuits share that wire.

8-gauge wire can carry 70 amps of power (840 watts)
10-gauge wire can carry 50 amps of power (600 watts)
12-gauge wire can carry 35 amps of power (420 watts)

Based on single conductors in free air at 104 degrees Fahrenheit using 167 degree type cable (common). With temperatures above 104 degrees there's a rating factor which lowers the current carrying ability. I tend to error on the next size up.

4 Roof Rack Lights, 100 watts each

[Paul]

Oh your fuse.

400 watts divided by 12 volts is 33.3 amps. A 40 amp fuse ought to do you for all four lights and a 20 amp fuse for each pair.

I don't know what the first generation Xterra has for an alternator but I think the second is blessed with a nice 90 amp alternator. In use I've driven my 610 watts worth of aux lights and not notice any dimming of the stock 110 watts worth of head lights. That's only 60 amps worth of lights forward, likely another 5 on the sides and back, and another 10-20 to run the truck's radio and othe loads.

[superslidestyle]

You should be fine using 10 awg. wire which is only good for 40 amps. at 90 deg. C. (w/ambient correction).  The diagram above is pretty accurate for everything that you must have gotten when you bought the lights.  If I were you, (again, this is just me) I would run all four lights off one relay, using one switch, and one wire with all four lights tapped into it.  For the ground wire you can also use one wire (10 awg. min.) to tap all four lights also.

The reason you want to run the lights from a relay is that when you turn the switch on, there is a small spark as you complete the circuit and it eats away the contact points over time.  The contact points on a relay are stronger and beefier to handle the extra current draw.  If you only had two 55w lights, you would be ok to run those straight from the switch.  But not for four 100w lights.  It'll be too much for the switch and you would notice it when it's overheating.  Trust me, I know.

[AV Xterra]

1. Paul, nice diagram
2. Always use a relay, even for 55w
 

[ultrapc40]

I ran mine 4 roof light through two 30 amp relay (one per pair).  Both relays are controlled by one switch.

[XterracerX]

This is something I need to work on as well... eventually!

[ultrapc40]

BTW for the light bar, just go to home depot or Lowes and pick up some 2 inch AL angle piece and cut it to size.  I was able to make 2 light bar with the stock I got from Home Depot.

[xperienced]

Wow, thanks for all of the help!  You guys are the best.

I'll let you know how it goes.

Gavin

[Oz]

hey Paul - is it ok to have a small LED on the  Switch side of the Relay ?

                                                                     (Ground)
                                                                           |
                                                                           |
(Ignition Pwr)-------(Switch)-------(LED)-------(Relay)-------(Lights)-------(Ground)
                                                                           |   
                                                                           |
                     (Ground)-----(- Battery +)-------(Fuse box)   

Hope the font spacing renders this ASCII circuit okay !

[xperienced]

I ran over to the nissan dealership and got the specs on gen 1 alternators:

4 cyl (KA24DE) = 70 amps
6 cyl (VG33E and VG33ER) = 80 amps

It looks as though my stock alternator won't have the output amps to power the lights.  Now I have to determine if I want to buy a 180 amp alternator for $350.00 plus the upgraded charge wire for $125.

If I install a high output alternator, does anyone know if I'll blow fuses?

I think I may just run an additional battery to power the lights.  When I drain the battery I can hook up a trickle charger.

[ultrapc40]

Are you planning to run your lights everyday?  If not, don't worry about it.  You will do fine.  I ran a red top with 4 roof lights at 100watt and 2 fog lights at 100 watt with no problem.  Granted I only turn the roof lights on when I am moving.

[Aperion]

I ran over to the nissan dealership and got the specs on gen 1 alternators:

4 cyl (KA24DE) = 70 amps
6 cyl (VG33E and VG33ER) = 80 amps

It looks as though my stock alternator won't have the output amps to power the lights.  Now I have to determine if I want to buy a 180 amp alternator for $350.00 plus the upgraded charge wire for $125.

If I install a high output alternator, does anyone know if I'll blow fuses?

I think I may just run an additional battery to power the lights.  When I drain the battery I can hook up a trickle charger.

You'll only blow fuses if you put too much of a load on the connection, alternator only puts out as much power as is required. I put a 90A alternator in my samurai, it only comes with a 30AM stock alt. and I made no changes to the wiring. although I will need to once I start adding more electronics

[Paul]

hey Paul - is it ok to have a small LED on the  Switch side of the Relay ?

                                                                     (Ground)
                                                                           |
                                                                           |
(Ignition Pwr)-------(Switch)-------(LED)-------(Relay)-------(Lights)-------(Ground)
                                                                           |   
                                                                           |
                     (Ground)-----(- Battery +)-------(Fuse box)   

Hope the font spacing renders this ASCII circuit okay !

You've got the LED in series with the load of the relay which isn't the way it's normally done. Typically the LED connects to the far side of the switch and the other end is grounded though the correct sized dropping resistor. When the switch is closed it energizes both the LED and the relay's coil. You can buy LEDs with pre-matched dropping resistors, you'll see them sold as 12 VDC LEDs.

[Oz]

You've got the LED in series with the load of the relay which isn't the way it's normally done. Typically the LED connects to the far side of the switch and the other end is grounded though the correct sized dropping resistor. When the switch is closed it energizes both the LED and the relay's coil. You can buy LEDs with pre-matched dropping resistors, you'll see them sold as 12 VDC LEDs.

                                                (Ground)      (Ground)
                                                       |                   |
                                                       |                   |
(Ignition Pwr)-------(Switch)-------(LED)-------(Relay)-------(Lights)-------(Ground)
                                                                           |   
                                                                           |
                     (Ground)-----(- Battery +)-------(Fuse box) 

like this Paul?