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.
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.
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.
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.
