Suggestion for Led driver: monster spotlight!

RC cars get away with that for a few reasons, first the wires are very short, there is not a lot of voltage drop. In a light bar the wiring could easily be well over 10 feet depending on where it is mounted. At 150A with a 10awg wire that is a voltage drop of 3V giving a usable voltage of only 9V and a loss of 450W worth of heat in the wires. Upping total wattage from ~1000w to around 1500W to account for that loss, along with the fire risk.

The battery life is such that by the time the wires overheat you are out of battery anyways and swap them out. I also have had some minor RC cars that used 10AWG wires and the wires got burning hot by the time the batteries were dead. NOT ok in a situation that could run for extended periods but ok for a few minutes at a time.

The much better comparison is car audio, it uses high currents with the same basic requirements we have here. For amp setups pulling a true 150A+, you are looking at ~2 gauge wire, so slightly smaller then the top of my head estimate said it would be. according to this:

http://knowledge.sonicelectronix.com/car-audio-and-video/car-amplifiers/what-gauge-wire-do-i-need-for-my-amp/

Although I still say the best idea is to use the mtnlitebar power supply if he can get it, that is proven and we know it does what it is supposed to.

Boost drivers are really not that inefficient if properly designed. Generally getting ~85-90% efficiency is not that hard. Which is only slightly behind a buck driver. The latest flashlight boost drivers are getting over 90% in 17mm form factors.

  1. you’re right, they are short, and even going from a car battery to a light bar that should be only a few feet. No big deal, just calculate the AWG for a bit of voltage loss, which should not be a aproblem since the driver accepts a range of input voltage.

2) 10AWG wires should not get hot at all in an RC car, unless they were getting hot because they were attached to your motor and that was overheating.

3) Car amp wires are severely overestimated for what you actually need. Maybe because of the huge amount of cheap wires out there that have overrated spec.

4) The brand name power supplies sold from mouser and digikey are also proven and do exactly what they are rated for, you just need to know what specs to buy.

5) your boost drivers are not inefficient because you’re only talking about super low current flashlight drivers that do 10 amps or less.

1: If the light bar is mounted in the normal location above the windshield, that is easily 10 feet of wires depending on where the control box is mounted. It is at least 5 feet from the battery in most cars to the top of the windshield, usually more when you factor in that most cars need a lot of extra distance to rout the wire through existing wire gourmets. 5+ feet each way = 10 feet+ total length.

The calculator clearly shows that 10awg will loose about 3V at 150A which is 450W of heat being dumped into the wire, that is not even remotely ok for something running more then a few minutes.

Even if you up it to 8AWG that is still a loss of 1.9V and 285W of wasted heat in the wire, still FAR from acceptable. At 2AWG it is down to a .5V loss and about 75W of heat in the wires. Still more then the wire is rated for. You need 1AWG in order to even be close to the current ratings for the wire at the highest temperatures: http://www.cerrowire.com/ampacity-charts

2: If you are dumping any kind of high current through 10AWG they will get hot, this can be calculated. So either you are not putting nearly as much power through them as you think or the wire is much thicker. Even the batteries in high performance RC cars get hot at those currents. 10AWG at 500A would have to dissipate about 40W of heat. Or the equivalent of an L6 in those tiny wires. Your telling me that an xhp70 could cool itself if I simply ran a few inches of 10awg wire to the LED instead of the big L6 head? The math doesn’t work.

3: Car amp wires are if anything undersized. The ratings on the amps themselves on the other hand are generally overrated. Amps that are rated at 1000W with only a 30A fuse are lying but true 1000W amps need every bit of 2AWG wire to get max performance. Even small losses in voltage has large effects on the amps effectiveness.

4: I am sure they do, I never said that they don’t? I said that it would be expensive, bulky and heavy for it to regulate 150A.

5: The output of the driver has very little effect on the efficiency percentage if it is properly designed. For larger power you need larger components. With said larger components you can reach much the same efficiencies assuming the same level of development in components (aka, 18650 vs 18350 cell tech development). The inherent inefficiency of a boost driver is not all that bad though, only a little behind a buck driver of equal specs.

450W? That seems like complete BS to me, but whatever, you can think what you want.

The power supplies on mouser and digikey are about the same size as the MTN light bar one, except probably bigger if OP wants to run all those XHP70s at 5A.

If he wants to put them in series and use a higher voltage instead of higher current then pretty much all power supplies will take AC110 or 220 input, so he would need to use a DC-AC inverter, lose some efficiency there, and then the driver to go from AC back to DC, and lose more efficiency there.

Use the link above, it clearly shows that it is indeed 450W of loss. It drops 3V at 150A.

3v x 150a = 450W

You would not have to convert to AC to use a boost driver, in fact DC-DC boost drivers are more efficiency (same for buck) since they can use higher switching frequency. That said like was said above I doubt there is an off the shelf option to do this without using multiple drivers.

Most boost supplies work on DC, just search ebay, I already posted one for $5 that would handle 4 LED’s at a time. There are larger versions available for more money naturally. Running the LED’s in 3S or 4S would cut the current sent down the wires by 3-4x. Thus drastically reducing the losses in the wires by the same and allowing for thinner wires to be used.

If he wants to use 2awg wire though, well that is an option as well.

As far as the mtnlitebar power supply, I have never seen one, no idea what is inside it. I just know it works. Do you have any details on it?

It actually says converter module, not driver, so I would assume there is a regular flashlight driver for groups of LEDs inside the bar.

That would be the simple way of doing stuff.

Possible it is running several drivers together but it makes more sense to build a larger unit that can handle all of them or at least most of them at once. for 40A I could see them splitting it into 2 separate drivers but not a lot of reason to go smaller then that, there would be nothing to be gained in either cost, size or specs. Although I bet things would still prefer a single larger unit.

It is for sure either a buck or boost driver, no argument there at all. An FET driver would not work well in this situation. I would not be surprised at all if it is a boost driver.

Electrical system failure is the second most leading cause of car fire. This includes car audio with insufficient power wires. I have seen it my self a number of times. I was shocked the first time I saw an entire length of wire start smoking and turning black just cause I cranked some bass tracks through my pieced together teenage engineered audio system. I don’t know the science, but TA knows his stuff and has given good advice with good reference. Whatever is decided I wouldn’t skimp on the wiring.

And I wouldn’t skimp by buying some cheap chinese power supply from ebay like TA said to do.

The one I posted was simply the first one that came up in a search that would work for what he wanted at a cheap price point. There are oblivious better options available for more money. I never said he should use that cheap driver, I simply said that something like it would do the job.

The only power supply like this that I know that uses automotive grade parts (well I am sure it does, I doubt RMM would skimp on that) is the mtnlitebar power supply. Which is why I recommend that.

Automotive grade parts are a certification level above your standard components and generally costs a bit more. You generally only find it in automotive or high end items. It increases the heat and vibration tolerance to survive in a car.

Technically you could run them direct drive if they are on DTP mcpcb’s and well cooled but in the real world that would be a bad idea. Car voltage may be rated at 12V but is usually closer to 13.5-14.5V when running, sometimes higher depending on the car.

The voltage will also vary depending on the engine RPM and alternator, leading to the lights noticeably dimming and getting brighter.

Now you could use an FET driver with pwm to control the current, with first gen xhp70’s the Vf should allow this to work assuming that voltage doesn’t sag too much. This would not be optimal from an efficiency standpoint though and would still be hard to control. It would be possible in theory though.

I would be worried about the heat output in such a case, it could easily overdrive the LED’s to the point of cooking even with massive heat sinks. It would also need some cutom firmware to control the current.

So FET control is possible but not idea for a setup like this where long term heat is a big issue.

Those 4 5200ma cells at 16.6V starting voltage would easily sag to around 14V or less under 15A of load, possibly much less. Then you have the tiny wires we use in lights that would sag some more to keep things working. A car would not have this problem and the only sag would be in the wires, which needs to be kept to a minimum in order to prevent fires.

direct drive at 13.5V could easily end up at over 10A+ to each LED if the wires are properly sized. So it would need some regulation for sure. The LED’s would survive at 10A but the heat would be insane along with the power draw. 30 LED’s at 10A each would be about 1800w worth of power. Keeping that cool would be a dream when not driving. Not to mention an immense load on the cars electrical system.

Although keep in mind I have seen cars with normal voltage of 15v+ and many many cars that will spike into the 14-15V range. Most automotive stuff has to be rated to 18V to account for such spikes, even cheap stuff is generally rated to at least 16.xV.

On top of this that kind of current being PWM will cause massive noise int he cars electrical system. This could, or could not play havoc with the cars ECU.

Better to have it regulated to a known safe current.

An FET with PWM would technically work but you would lose efficiency over a buck or boost driver, although it would technically work. It would need custom firmware and driver setup and at least 5-10 FET’s to spread the load out but it could be made to work. Although for that kind of time and effort I think I would have to just go with a buck or boost driver myself.

Which brings us back to the mtnlitebar driver. It is the only thing on the market designed for this type of use that I know of. I would not trust any of the other light bar drivers I have seen to actually support these kinds of outputs.

We get away with TONS of things in flashlights that you just can’t get away with in other uses. For example in a flashlight running LED’s in parallel is not an issue, thermal runaway is almost impossible due to the batteries limiting max possible current to any one LED and the LED’s are so close together that it keeps the temps balanced between them.

Thermal runaway is a big issue with something like a lightbar where the temps are not even between the LED’s. This is why you want to run the LED’s in series as much as possible. A separate driver for each string of LED’s would be ideal in this case to keep things balanced.

any pics of this… Phoebus?

You could wire them like 2P35S for direct drive.

vice versa, 2S35P

No matter which driver you use if it has PWM in any way you need a big supercap with a few F to protect your car

An LED has most of it’s heat directed backwards into the mcpcb, only a fairly small amount of the heat is sent towards the front (around 30% depending on many factors). So the heat sent forwards is not really worth thinking about, it travels with the light photons and is projected on whatever you shine the light on. Many of my lights can project noticeable heat 5-10 feet away.

The heat we are worried about is what goes backwards through the mcpcb. This is why we want DTP copper mcpcb’s and good cooling paths with lots of surface area to dissipate the heat.

The maglight doesn’t have very good heat shedding so be careful going too crazy with it. I just built an M6 with more mass then a maglight running 4 triples and making ~13k lumens. It gets scary hot in about 90 seconds, I say this with my EDC light getting to around 140f in 90 seconds or so.

…and if you decide to experiment with multiple drivers kaidomain has a number of beefy bad boys…given you figure out the power aspects.

Thermal mass is good for flashlights since it gives us a longer runtime before it gets too hot to hold but besides that it doesn’t do anything. Surface area is what matters for dissipating the heat to the air.

A lot of guys get hung up on copper vs aluminum. I personally don’t really care in most cases.

The one thing that I do want to see in copper is the DTP mcpcb. This is well worth the minor cost increase for the benefits. The flashlight itself I don’t really care what it is made out of.

I like copper spacers in EDC triple builds simply due to the higher thermal mass adding a few extra seconds before thermal step down kicks in. In larger lights I prefer aluminum as it is lighter and usually leads to a more balanced light.

That’s what I wanted to say :slight_smile:

Come on, i want to see the photos