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LED Light Bar Power Source and Wiring Harness

Discussion in 'Power Electronics' started by twentyeggs, Feb 21, 2020.

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  1. twentyeggs


    Feb 21, 2020
    Hello, I don’t know much about electrical currents.
    I just bought an LED Light bar for my truck and I am just curious about how I should wire it up. There are a few different pieces, and I would like to add maybe another bar later on.
    Here are the specs:
    -Power: 300 Watt
    -Voltage: 10-30V DC
    -Beam Angle: Combo (spot&flood)
    -LED color: White (6000K)
    -Raw Lumens: 27,000 lm
    -Material: Aluminum Alloy Metal Housing, PC Lens
    -Waterproof Level: IP67
    -Life Span: 50,000 hours
    -Dimension: 52x 2.3 x 2.6 inches

    The second is a pair of spot beams/bars:

    • LED type: 5050-SMD (Total 48 LEDs)
    • Color Temperature: 6000K (Pure White)
    • Beam Angle: 30°(spot beam) Long distance illumination
    • Power: 120W (Single unit)
    • Operating Voltage: 9 - 30V DC
    • Luminous flux: 12,000 LM (Single unit)
    • Light Transmission Rate: 98%
    So I would basically have 2-3 separate wiring harnesses for each but of course I’d like it all on the same single switch. I am curious about the power output and requirements from a regular car battery. Would stringing them together dim the lights or is there more than enough power to run them all together. I guess maybe that depends on the gauge of wire? It also says it is suitable for 9-30volt vehicles.
    I am wondering if there some sort of power regulator in there.

    Also, a bonus question. They are still boxed up and Id like to test them out, I have one of those lithium car jump starter things. If I tried connecting the light bar to the cables, would I fry everything/pop a fuse, or would it be just fine?

  2. dave9


    Mar 5, 2017
    These types of lights with the 9V to 30V range have a buck current regulating circuit inside, so there should be no issue hooking it up to your jump starter, except that jump starters are typically not very high Ah capacity so you will have a limited amount of time to run them from it for testing.

    Your total power draw is marginally excessive unless you upgrade your alternator. 540W total / 12V = 45A. The actual total may be a bit lower. Lights like those are often fraudulently rated based on # of LEDs * 3W per LED to arrive at a wattage claim, while the actual drive current is reduced to ease heatsinking so they can make the enclosure at lower expense. This is more clear with the "spot beam/bars" which if they have 48 x 5050 LEDs (which are 300mW each max rating), that is 14.4W, not 120W. Perhaps they are using shady ratings and "forgot" to elaborate that the 120W figure was really an incandescent wattage equivalent. In fact, 14.4W could easily be very near a 120W equivalent using existing LED tech.

    This factor makes a proper calculation quite difficult. You could use an ammeter to measure the current of each light from your vehicle electrical system, "temporarily" connected directly to the battery, though even then it would be nice to have fuse in case something goes wrong.

    Once you have an amp reading, you can calculate total current draw and determine the rating and number of automotive relays to use. You'd ran the battery to the relay contact, the other relay contact to the light bar(s), and use a second run from the battery, to relay coil, then the other relay coil terminal to the switch in the cabin, then the switch to any chassis ground point. The negative from the light bars would go back to the battery negative if they're remotely as high current as specified rather than a chassis ground.

    Once you determine the total current, then you can pick an appropriate wire gauge.

    Personally I would be going over all the light specs again because there's no way that 48 5050 LEDs are going to produce 12K lumens, and if the other light has false specifications as well, you may have overpaid or at least are supporting fraud. If this does not bother you then you still should determine the true power consumption for the purpose of not overspending for more relays and wire gauge than needed to get the job done plus a conservative margin above that.

    However it is not much more expensive to get a higher current relay so you might just get 2 x 30A relays and run the so-called 300W light bar from one and the pair of spot beams from the other. The two relays would simply be wired in parallel except of course for each output going to the respective lights they're powering, and being automotive relays you'd expect and should make sure they have 12V rated coils.

    Previously I suggested powering these from your vehicle electrical system because it, with engine running, should have a more stable voltage than whatever the jump starter is producing, and then you'll have roughly 14V to the lights but should take the current measurement and then factor for 12V if you wish to run these without the engine running, except that this is quite a power draw to have for a typical starter battery without the engine running so it would be best not to use them with the engine off.

    As far as what your existing alternator is capable of, "IF" they do truly draw 45A, your alternator will not be able to keep up unless your engine RPM is above some threshold higher than idle speed. There are too many variables for me to determine the exact speed and it may not be worth bothering if the lights aren't even rated accurately and end up drawing a lot less current than the specs suggest.

    You might check with the seller to see whether they also sell a wiring kit. It may be made of garbage quality components but at least you could ask what is in the kit as far as wire gauge or relay ratings. If they can save a dollar building the kit for the true need rather than the questionable ratings they might do so and so you would see what they're thinking is enough current capacity.
  3. twentyeggs


    Feb 21, 2020
    Dang! Thank you... the perfect response. I also have a voltmeter coming tomorrow. I’m probably going to spend hours on YouTube learning how to use it but maybe I’ll be able to get a better picture of what I’m dealing with once I start probing around.
    The reviews from the people who bought these products are pretty impressive. I’m sure the numbers are buffed, most “budget” item advertisements are seeing as the “real” light bars you see on professional racers cost $1,200-5,000. But a few thousand people collectively gave it a rating of 4.7 stars and here as a few pictures from two reviewers. Based on these images, they are adequate for what I need for now.

    Of course I’m the kind of person that would thoroughly enjoy laughing maniacally as I switch on a portion of the sun and defeat all darkness 10 football fields in any direction, but I’ll have to save that day for when I can build my own monster light. This light bar I just got is basically my introduction into this world of electronics. I fully intend to learn and understand the math and knowledge behind it all, and hopefully soon. Skill wise I am a pretty accomplished wood worker/metal fabricator, soldering, wrenching, basic and some advanced mechanics, basically I can do most anything except electricity; even though I am heavily into building drones and other RC aircraft/vehicles, and tinkering around with gadgets. Even discharged the capacitor behind a tube style TV once in a ridiculous project. I guess you can do a lot of stuff without understanding the knowledge behind it. It’s the one thing I avoided getting into and I think it’s time to turn my attention to it.

    If it’s possible to use a multimeter to measure what the lights are pulling from the power source, where would I be probing to get that reading? My end goal here is just to set it up to run reliably and at an optimal performance.





    [MOD NOTE: resized huge images and removed too many examples .... we get it ;) ]
    Last edited by a moderator: Feb 22, 2020
  4. twentyeggs


    Feb 21, 2020
    Oh and the jump starter I was curious about using to test out the lights

    Starting current aka the leads with the clamps: 1500A Peak, 200-350A cranking amps, 29.6Wh.
    The cranking amps sound safe, it’s just that peak amp number that had me worried about hooking them up.
  5. twentyeggs


    Feb 21, 2020
    Ok I just opened the box and the wiring harness relay is rated for 12v. 40A. 14VDC.
    Seems like a well built harness and the 40A relay and 30A fuse indicate it really is pulling quite a bit of power. Does this change any of the information you gave me? The other two 7in light bars did not come with a harness. I wonder how I’m going to splice them into the one harness I have.




    [MOD NOTE: resized huge images]
    Last edited by a moderator: Feb 22, 2020
  6. twentyeggs


    Feb 21, 2020
    Ok so I took everything out and laid them down.

    There are the two red/black wires that come from each light. 2 from the 52” bar 4 from both 7 inch bars. The harness is fully built. The only thing it looks like I’ll need is extra wire to connect the two 7” bars to the 52”. I am planning to hook all the red wires and black wires from all the lights directly into the wire that goes to the relay. Instead of connecting them in a series. Hopefully that is the right decision. I don’t know why but I feel like that is the better option? And then the switch they gave me I don’t like it. It’s made to stick on to something but I want something installed into my dash. The switch provided has a very healthy click and spring inside so I know the internals are beefy. I’ll just have to wing it and guess whether the switch I buy is good enough and won’t weld itself open.

    I’ve been watching some YouTube videos and I see people connecting the wiring harness into the fuse box as a power source; which is what Dave suggested. But the harness is really not set up to do it the way I see in the videos where there is a switch on the same line, is it possible to just connect the red power source wire directly into the fuse box instead of the battery? There is an inline 30A fuse before it goes into the relay.

    I am still wondering if harness/relay/fuse is able to handle adding the two 7 inch light bars. I don’t want to hurt anything and I also don’t want to lose any performance. Since I have zero experience in this, I’ll just have to take the word of someone who is willing to comment on here. Dave said it would be fine but I think he’s coming from the point of view that these light bars are way over rated. But they seem to be pretty legit.


    [MOD NOTE: Resize huge image and place inline]
    Last edited by a moderator: Feb 22, 2020
  7. dave9


    Mar 5, 2017
    The switch "should" only be handling the relay coil current, which from looking up the part #, appears to be a bit under 200mA @ 14V, so doesn't need to be of much current handling at all, just durable enough to survive an automotive environment.

    Similar might be true of the wiring harness, to use thicker, lower gauge wires to better survive that, but the thing to do is measure the current so you have real data.

    I do not recommend hooking it into the fuse box. It should be wired direct to the battery with a fuse you (or they, since you mentioned it has a fuse) add in series, at (very near) the battery, unless through measurements you can determine it has sufficiently low current that there is some fuse box circuit with enough current margin to handle this extra load.

    The included relay and wiring harness were only meant to handle the light bar they were included with unless the instructions state otherwise, but again data is needed to determine how much current all lights together need.

    If you don't want to or can't measure the current then use a 2nd relay and wire (built up the same as the existing harness except you only need one wire run to the switch input and then a 2nd wire added to switch output to each relay coil, in parallel with the existing one to power the other two lights, and those two lights could be in parallel with each other from this 2nd relay. The same switch could activate both relays if you don't wish to have independent control over them.

    I see a picture of a lit roadway. Remember these lights may not be legal for public road use.
    Last edited: Feb 22, 2020
    davenn likes this.
  8. davenn

    davenn Moderator

    Sep 5, 2009

    ^^ THIS ! ^^

    Maybe OK if incorporated into the existing dipswitch so they turn off when lights are dipped
  9. Kiwi


    Jan 28, 2013
    Hope this helps you wire up the lights.
    Top drawing shows the switch connected to battery positive on terminal 30 of the relay. This looks like how the loom is wired in your photos. The lights will work independently from your headlights, so you will also have to switch them off in traffic.
    The bottom drawing shows the switch connected to the existing high beam headlight circuit. The lights will only work with the high beam headlights, so they will also go out when you dip the headlights for traffic.

    LED Spots.jpg
    davenn likes this.
  10. twentyeggs


    Feb 21, 2020
    Oh yes, these are strictly for off road/empty back roads only. I can’t imagine being dazzled by these while driving.

    Ok I decided to get a separate wiring harness for the two 7 in bars, exactly like the one in the picture. I am don’t need them to work independently so I am going to do what Dave said and use one switch to operate both relays. The switch I am looking at is rated at 20Amp 12V/DC and 10Amp 24V/DC.
    The only problem I have now is the current wiring harness I have, uses a 2 pin switch, but the switch I want is a 5 pin switch (the second harness I am looking at is set up to connect to a 5 pin) so I am confused as to how I will make that work. The switch has a light inside that stays on when connected to power.
    I’ll leave a picture of what it shows on the amazon page.


    Is there a way to connect a the two wires from a 2 pin switch into this?[/QUOTE]
    davenn likes this.
  11. dave9


    Mar 5, 2017
    You'd wire it exactly as shown except pin 3 "To Light" going to both relays' coil pin 86 to have one switch operate both, and then switch pin #7 & #8 "To Ground" going to any ground, either chassis metal near the switch or wherever you joined the other grounds together like shown on Kiwi's diagram of relays' contact #85.
  12. twentyeggs


    Feb 21, 2020
    I’m sorry, I don’t understand what you said. You’re going to have to speak stupid for me.
    “Pin 3 goes to relay.” From the wiring diagram it looks like the entire current is going through the switch. That is ok to put into the relay?
    “Coil pin 86” what does this mean?
    “Switch pin 7&8” switch it? With what/how?

    Maybe I can make this easier.
    The second wiring harness is built to plug and play right into this switch. So I won’t have any problem hooking up the two smaller bars. I am just wondering how to hook up the big light bar since the wiring harness that it comes with only has two wires that come from the relay. So if it works, I’m wondering which pins do these two wires go to?

    I’m thinking, wire the the switch and harness exactly like the picture shows for the two smaller bars. Then for the large bar with only 2 wires, out the black wire on pin 7 and the red wire on pin 3? Or can you not use a 5 pin switch with the way my harness (2 wires to relay) is built without changing things?

    So frustrating... I’m sure this seems so simple for you guys but it’s like speaking a different language for me. I’m almost to the point of just buying two of the same harness so I don’t have this problem.
  13. dave9


    Mar 5, 2017
    The picture of the switch shows that pin 3 on it goes to the light. The thing you do differently is take that to the relay coil like shown on the diagram Kiwi posted. Coil pin 86 also refers to the diagram Kiwi posted, the relay pin #s on that are a very popular arrangement. If your relays don't have this pin numbering then you just consider the relay coil's pins to be pins 85 & 86.

    I can't really assume what the wiring harness really "is" opposed to how it ought to be. The combination of my post, Kiwi's post including the diagram, and your post of the switch should be enough to get this done.

    If it is not then I recommend finding someone local to help because this should be done right to have it in automotive wiring, including having potentially dozens of amps current handling and potential fire risks.
    Martaine2005 likes this.
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