LED light bar mod

Bimmber · 2018-12-21T14:57:22.000Z

Gentlemen,

As my first ever led DIY project I would like to upgrade cheap and crap 24v (for a truck) Chinese light bar with better chips like Cree XHP70.2. But I`m stuck on few questions.

They quote following on their listing: Power: 360w (90 chips * 4W)

How are they wired?

If in series (voltage gets added, current stays same), then, if 4w chip has forward voltage of 3.5v for example, that would be 315v. So, they are not wired in series, but in parallel.

If in parallel (voltage stays same, current gets added), then 3.5v and for example 700mA would be 63 amps, which is massive. Truck has about 120 amps available. For 60 amps, cable would be as thick as broom stick!

Voltage is limited to 24v, so must be wired in parallel? But 24v would blow chips with 3.5 fv when wired in parallel.

But what about thermal runaway risks when wired in parallel?

They also state this:
Operating Voltage: DC 9-32V (Fit 12V/24V vehicle).

They cannot predict it will be used in 12 or 24v system, so how do they know how to wire them in factory? If they pre wire them for max 32v combined forward voltage, then using it in 12v system would mean it would not be that bright? 12v is nearly 3 times less than 32v.

If I`m looking to replace them with xhp 70.2 (unless there is better option?), how do I calculate max I can drive them at, so that light bars case is able to handle the temps?

I noticed, the harder you drive chips, less efficient they get. But I can imagine for light bar which has sole purpose to throw light as far as it can to illuminate road and roadsides ahead, there is no option to have efficiency, because driven at something like 700ma, they would be super efficient, but quite dim? From my understanding - to have max long throw of light, chip needs to be driven as hard as possible (which xhp70.2 can be).

Why do led bars have 90 x 4w chips, but not 3 x CXB3590 driven at high current? So that they can spread heat across whole length of the bar?

Sorry for noob questions, I`m learning.

Thank you

DavidEF · 2018-12-21T15:40:21.000Z

Is that the picture of the actual light you bought? If so, it looks like the “lens” in front is mainly just for decoration and to keep dust/mud out. In really nice light bars, each emitter gets a reflector. In the picture above, there are no reflectors, so it would be assumed that they used “lenses” to collimate the light. That isn’t exactly the case, though. There are only 24 “lenses” in that lens, but you say there are 90 LEDs. So, there is really no collimation. So, you can make the light much more impressive and useful just by fixing that.

The voltage range means that they used a driver that changes the voltage somehow. I would expect a simple boost driver with 9V - 32V input. Alternatively, a cheap buck driver. Buck drivers with input from a few volts up to 32 or 35 volts input are common and cheap. The input has to be a little bit higher than the output. So, if it is one of those, it would indicate the output to the emitter bank is less than 9V. The emitter bank doesn’t have to be wired in series only or in parallel only. It is probably wired in some combination, perhaps 3x series by 30x parallel.

If you really want to maximize the potential of this light bar, you should remove all the emitters from the large PCB they’re soldered to, but leave the PCB itself as a back plate. Install new emitters, on MCPCB’s, on top of the back plate. You could use individual emitter MCPCB’s or triples or quads. Add new optics for the LEDs so that each emitter has an optic associated with it. Change the front lens to smooth glass or Plexiglas or Acrylic.

The driver can probably be adjusted to output the right voltage for your new arrangement. Show a picture of the driver here, along with a confirmation of how the emitters are wired, and how your new emitters are to be powered, and someone will be able to tell you what needs to be changed to make it work.

Bimmber · 2018-12-21T15:45:28.000Z

Thank you. Picture I posted is random one, just as sample what I meant with “light bar”.

I was thinking to use these:

DavidEF · 2018-12-21T15:45:20.000Z

Okay, if you want really useful help, it will be better if you post relevant information. Every build will be different, and the recommended changes will be based on what you’re starting with. Do you have a picture of the actual light bar you bought? Also, some pictures of the internal workings would help. The more accurate information we have, the more helpful the advice can be.

Bimmber · 2018-12-21T15:48:58.000Z

Haven`t bought one yet as I want to be sure 100% my idea is even possible. My brother and wife`s dad have bought them for their trucks, but they won`t let me crack them open as they are sealed for waterproofing reasons.

If you are saying my mod idea is 100% possible, then I`ll go ahead and buy one.

DavidEF · 2018-12-21T15:51:05.000Z

Here are some old threads you can look at to see where you want to go with the mod.

DIY Offroad LED Light Bar LED Spotlights

I dub thee: El Jefe. It is the boss is because it starts out cold at 270 watts (about 34,000 raw lumens), then when it warms up, it stays at 270 watts. Indefinitely. The power level was defined by the amount of heat that could be shed operating at 100% continuous duty under worst case conditions - which would be parked, idling, on a hot desert night, so no airflow in an ambient temperature of 100°F / 37.8°C. Commercially available light bars cannot do this, their heat sinks are much too small …

Custom High power LED light bar Flashlight Modding and DIY Parts

Hey guys, I just wanted to post a quick pic of the preliminary light bar design. First and foremost, the optics are TIR lenses by Gaggione, the two large ones are the 67mm LLC56N, 12 degree spot with a XHP-70, or 9 degrees with a XHP-50. The 4 smaller ones are an elliptical 45mm LLC49E, 40 degree wide beam and only 14 degrees vertical beam, it’s a wide flat flood, which is what you want in an automotive light. The floods HAVE to be the XHP-50 as the 70’s are too big for them. But the spots can …

Also, look at MTN LITEbar for what is truly possible. The owner of that site is a long time respected member here, and also owner of Mountain Electronics, where we can buy flashlights and components in the USA.

Bimmber · 2018-12-21T15:53:21.000Z

Will check those threads. Thanks.

Omg!!! That MTN light bar! I did check it out few days ago and nearly got led-orgasm from it Just amazing, I take my hat off for that guy.

DavidEF · 2018-12-21T16:04:34.000Z

Well, let us know when you do buy a light bar, and take pictures of:

The emitters (and PCB layout if possible)
The optic(s) and/or reflectors if any exist
The driver circuit
The internal wiring

…and we can go from there!

D03Boy · 2020-07-10T09:15:04.000Z

Hello! You have a really interesting idea for your first DIY related LED lamp. I want to immediately warn you that it will not be easy and you will encounter a whole mountain of difficulties! When I decided at one time to hang my car with LED lamps, I ran into a whole bunch of problems, so be careful.
By the way, it will be useful for you to read How to install LED shop lights
Let me know how things are going with your DIY)

alpg88 · 2022-09-08T23:58:53.000Z

Leds may be wired in series and parallel, there most likely several drivers with leds wired in clusters. optics is an individual TIR lens for each led, in theory it should be working fine, but how it is in reality we do not know, whether quality\design and alignment of the lenses is correct, and you have some useful beam, or just a flood wall blinding everyone.

Xhp70 are very powerful leds, they will definitely create more heat than stock leds, much more, i would not bet that cooling capacity of the housing is sufficient even for the leds installed, let alone leds of 10 times the power. You got another issue how to drive those new leds, stock driver\s certainly wont do. you'll have to supply much more power. Then you got optics, stock ones are not designed for xhp70, they most likely will just give you a wall of flood. In all, spending so much on leds, proper drivers, and be limited by inferior design housing/optics........idk seems like a waste to me. Might as well build one from scratch, definitely be easier with much more useful outcome. imo