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Thread: overkill wire size thoughts

  1. #1

    Default overkill wire size thoughts

    i am planning some overhead offroad lights for work lights. the light setup would be 9 halogen 55w farmer lights forward facing (with the plan to add a second row of 9 led forward facing when i can afford the 125 apiece from larsen) plus 10 (4L 4R 2 rear facing) led on a halo (they are 2 rows of 3 so 6 diodes total? in a flood pattern).

    now i have the 9 halogens and the 10 leds. the max amps i would be putting out if i had them all on at one time would be 62 amps (36 amps for the halogens and 27 for the leds. this formula was figured using a watt to amp calculator at 495 watts on a 12v system plus the instructions on the leds say 2.7 per pod).

    the distance from the battery to the lights is about 8 foot give or take a few inches and i want the lights to think the battery is on the roof right next to the lights.

    i have all the necessary accessory equipment for either set of wires, lugs, terminals, circuit breakers, relays, 10 slot fuse boxes, 4 slot fuse boxes, anti ox compound, weather proofing boxes, smaller wiring. when i say everything, i mean the only thing i dont have are capacitors to directly connect to the bulb for balancing continuous voltage with no flickering.

    the question: i have about 20 foot of 4/0 aluminum service wire (the bundle with grey wrap where its 3 wires of insulated 4/0 and 1 wire of bare 2/0, so 60 foot total of useable wire) and i have 80 feet of 4 gauge copper thhn wire. so i have plenty of each type. i feel the 4/0 (single wire not bundled) would be ideal because it would have a .64% volt drop where the 4 gauge would drop about 2.05% according to an online volt drop calculator.

    i know its overkill but what would be better realistically.

  2. #2
    Flashaholic* XeRay's Avatar
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    Default Re: overkill wire size thoughts

    I would only use highly stranded wire, and if you are grounding locally (chasis or body) rather than back on the ground buss then your effective distance (voltage drop) is 8ft, if back to a larger buss is double 16 ft rather than just 8 ft, 2 X 8 ft distances.
    I will let others suggest wire gauge with recent experience etc.

    There are charts online to be found for voltage drops over distances for different currents and voltages, also the warming of the wiring if in a conduit or in bundles or open to the air.
    Last edited by XeRay; 11-23-2020 at 11:23 AM.

  3. #3

    Default Re: overkill wire size thoughts

    XeRay, i googled volt drop calculator and used the first one that popped up which is from calculator . net, it specifically states " *Please use one-way distance to the load. Not round trip distance." so i think it automatically calculates round trip distance into the equation... i think??? but i dont know the page formulas or algorithms.

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    *Flashaholic* Lynx_Arc's Avatar
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    Default Re: overkill wire size thoughts

    A voltage drop of 1/4 of a volt is probably not even noticeable as your eyes can adjust that much and solid wire of any type especially aluminum in a vehicle can over time break if there are vibrations and some movement that affects the wire.
    I lean heavily towards stranded copper 4 Ga wire and save the larger wire for heavier current loads. LED lights probably are regulated such that the voltage would have to be lower than normal to affect their output so larger wire may not help them one bit. You can run about 400A through 20 feet of 4 gauge copper as most good jumper cables start at that gauge and get larger for there. If you were to split your lights into several banks and feed each from separate 4 gauge wires the overall voltage drop would theoretically be less plus it would make it easier to shut off sets of lights with one relay and switch. I'm not sure why a capacitor is needed for incan lights as they will get dimmer and brighter with the engine speed regardless I would think. I had two 55 watt driving lights on a car once and replaced the bulbs with 100 watt bulbs and they did fine on the wiring I used 10 ga wire for them as it was what I had at the time 12 ga probably would have sufficed as you can put over 1500 watts through it or about 25- 55 watt lights. If you have ever run a hairdryer on the same circuit as the light in the bathroom do you really notice the drop in the light output? I don't.
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  5. #5

    Default Re: overkill wire size thoughts

    i just counted them because i could not take a picture and i have 19 strands of aluminum in the wire and 19 strands of copper... are they not stranded?

    i have have parts to split off from the 4/0 to 4g before going to the fuse blocks

  6. #6
    Flashaholic* XeRay's Avatar
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    Default Re: overkill wire size thoughts

    Quote Originally Posted by offroads View Post
    XeRay, i googled volt drop calculator and used the first one that popped up which is from calculator . net, it specifically states " *Please use one-way distance to the load. Not round trip distance." so i think it automatically calculates round trip distance into the equation... i think??? but i dont know the page formulas or algorithms.
    In that case it should say if it is assuming grounding locally or it automatically assumes wire used for round-trip based on the 1 way distance. It should not assume anything without telling you the basis for it.

  7. #7

    Default Re: overkill wire size thoughts

    AC wiring is not my forte, but something keeps bugging me about this -- I can't remember the details, but isn't there a difference in volt drop behavior between AC and DC circuits? Or is that only at kilohertz frequencies?

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    Moderator Alaric Darconville's Avatar
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    Default Re: overkill wire size thoughts

    I'm not a fan of mixing Al with Cu unless with the correct connectors to prevent electromigration and subsequent corrosion of the wiring, introducing resistance and sometimes *fire*. Or at least in house wiring.

  9. #9

    Default Re: overkill wire size thoughts

    xeray: if you poke around the site maybe you would be able to see something i didnt? idk on that.

    virgil: no AC circuits, just the wire.. everything else is DC from the fuse boxes to the relays to the terminals. and i got both sets of wire plus about 80% of my "accessories" free from an old electrician i knew who passed away.

    alaric: i have al to cu connectors and anti oxidant paste in tubes.. a whole box of them.

    i have enough stuff that i would suspect that i could match set up the 4 of you that have replied with the same set up as mine, tear it all apart and redo it with the opposite wire... minus the relays, fuse boxes, and lights... thats part of the 20% that i personally paid for.

  10. #10

    Default Re: overkill wire size thoughts

    My point bringing up AC vs DC is that if there is a difference, make sure you're using the right kind of volt drop calculator/calculations.

  11. #11
    Flashaholic* XeRay's Avatar
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    Default Re: overkill wire size thoughts

    http://www.aeroelectric.com/articles/wiresize.pdf

    here is a good resource, I'm an aviation guy not automotive so much, but it applies the same.

    This is DC only

  12. #12
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    Default Re: overkill wire size thoughts

    I would pull out a reference like Uglyís Electric and look up the ohms per foot (may be given in ohms per 100 foot) then look at load and total feet of wire and do the math. I have a hunch you are over thinking this. But it is good to actually run the numbers. Using standard wiring code rules (20 amp circuit on #12, 30 on #10, etc.) isnít ideal when you are using 12 volts instead of 120 or 240, because home loads donít care about a volt of drop.

    I am a big believer in copper wire with fine strands where there is vibration. Just because a 1980 Oldsmobile had crappy solid aluminum wiring on some of its lights does not mean you want it. That stuff has been known to vanish when exposed to road spray. I finally retired after 45 years in powerhouses and switchyards, may have acquired a few scraps of type SIS ďhingeĒ wire along the way: gray 600v insulation with good temperature rating, but ďhingeĒ is for going from the stationary part of a panel to instruments on a section that swings open. Where standard #14 SIS has 7 strands of tinned copper, #14 hinge has 41, #12 is 60 strand, and I forget the count for #10, but you get the idea. In your place, and given whatís laying around here, Iíd probably drag out the length of #2 welding cable Iíve been saving to make a set of jumpers, and use that. Iíll save the 2/0 welding cable for for running electric winch wiring to both ends of a truck, with 350 amp Anderson connectors on cable and winch.

    Have fun with your project. But as time goes by, LED work lights are getting cheaper. I used to prefer halogen for cost effectiveness and quality of light, believing the expense of HID then LED was only justified where space and/or power was limited, such as motorcycles or small cars. But, given that work lights are not so critical as driving lights when it comes to beam pattern, Iím even thinking about LED for my 60 year old Massey Ferguson.
    There are two kinds of light - the glow that illumines, and the glare that obscures. ~James Thurber

  13. #13

    Default Re: overkill wire size thoughts

    felix: i have no clue about house wiring.. but i got the wiring for free and generally have no use for it else where except the scrap yard. thats one of the reasons the thread title is overkill, using what i have to make it work.. and in a 12v system im ok with having oversized wire than a "itll work, maybe" sized wire any day.

    as per led vs halogen vs hids vs blah blah... im ok with leds but they generally dont have the pattern i was looking for. i chose the halogen farming lights because of the trapezoid pattern of lights. they reach slightly farther than a flood light, while giving a little more side lighting than a spot light.. all the searches i found only produced 1 set of led trapezoid pattern and they are 125 apiece for a 6 diode (bulb) pod from larsen. other than that you have the choice of flood and spot only. the first time a light bar comes out with floods on the outside traps in the middle and spot in the center, they would be on my truck the same day my order was delivered.

  14. #14
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    Default Re: overkill wire size thoughts

    I still have more halogen than anything else. But I am seeing more and more LED on both newer farm equipment and on industrial equipment like log handlers at mills. Still, looking at prices, whether a Northern Tool catalog or a site that specializes in Hella lights, I can see that halogen still makes sense if youíre not rich, and you have the electrical system to power it. Actually, I still see a lot of good in old fashioned sealed beams, when it comes to rigs that donít see constant use and do sit out in western Washington weather.

    Do take care with connectors when using aluminum. It has a different coefficient of expansion than copper. Thatís why some devices are rated only for copper, some for aluminum, and some for copper and aluminum. Also, thereís good reason we no longer see those mobile homes with aluminum wiring.

    I only mentioned house wiring to make the point that more voltage drop is acceptable when you are starting out with ten times the voltage. At least thatís my opinion. Judging by the small wire we see on 100+ amp alternators today, cost obsessed automotive designers donít always see it that way. 🙄
    Last edited by Hamilton Felix; 11-27-2020 at 06:02 AM.
    There are two kinds of light - the glow that illumines, and the glare that obscures. ~James Thurber

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