Hi there,
I’ve built a monster light bar. I’ve got 30 Cree xhp70’s mounted to a heatsink with optics. Now I need a driver. 12v input with ~70v output at a constant current of 5A. The power supply can draw as much amperage as it needs (diesel truck w 200A alternator and dual batteries. I’ve got the lens wired 10 per in series (3 circuits - will need 3 drivers)
Sounds exciting. I don’t have any suggestions at this point, but I’m sure you will get some good ones. Would love to see some pictures. 
Off-the-rack, I doubt it. Probably need to build your own. Goggle “12v flyback driver” for ideas.
Output voltage will be open-ended, really high with no load.
Sense current through the LEDs through a resistor that’d have ~1.2V at 5A, ie, 0.24Ω. (Oh, and a good 25W with heatsink to shed that heat. Power resistors can’t be overcooked like LEDs. They change value and go pouf.)
An optocoupler is used to send feedback to the controller and isolate the high voltage from the low voltage.
Output will be 350W, so it’s gonna be big and hot.
+1 on everything 
70v output from 12v input will be almost impossible to find off the shelf as said above. This is largely due to the fact that voltages above 50v get much much more dangerous from an electrocution standpoint. Most power supplies stop around 48v for this reason (although 48v can still easily kill you if you are not careful).
Depending on what your setup is like, changing to a 6s5p setup would bring the voltage down to ~36v which is much easier to handle and you should be able to find off the shelf power supplies on ebay that would work for cheap prices as well. Although they may not put out as much power as you want.
In which case you could run multiple power supplies to each string of 6 LED’s if needed.
The end result is that 70v with high current will be very difficult to do as most components are not rated for both high DC voltage and high current.
You will have some real problems driving the LED’s to the full ~1000W they are capable of without some expensive custom power supply(s). You could try contacting mtnlitebar.com and see if you could buy some of their power supplies. I think each one pulls 40A and thus is capable of about 500W. 2 of them should power your setup, although I don’t know what kind of voltage range they have or how they work.
Hi there,
I have to admit that your " monster " is very impressive but hard to make it alive !...
For the 70V /5A output that you need , the 12V input will take more than 30A (!!!). The problem is not the car battery ( they can do more than this current...) , but the boost converter able to handle this kind of value.., even the 1200W converters from the market are rated to max 20A , input !
So , you have 2 solutions :
To build your own converter (that is not an easy task , time consuming , suitable components ,laborious tests...) , or to divide the string of 10 Leds in 2 , each with 5 leds in series , and both in parallel .., finally , you'll have 6 strings of 5 series leds, driven by 6 boost converters ! In this way you can use the boost converters of 1200W , because the input current will be under the maximum of 20A ( somewhere between 15 and 18 A , depending of the efficiency of the converter)
Like this is doable , but the price will be 
...,( about 20$ a piece...)
I wouldn’t mind rewiring them if I knew of a driver that would work. The spec sheet says 4.8amps at 6v for these leds. But if I recall I was nearing 70v on my bench power supply to get a string of 10 to 5A.i would like something reliable and robust enough to mount under my hood. Suggestions there?
http://m.ebay.com/itm/LED-driver-LDRADJ29-4-8A-4-8A-12V-DC-10V-28V-Multi-Mode-for-CREE-XHP70-6V-/112453876907?nav=SEARCH
One driver for each led.
What is your budget? This will not be cheap unless you have a lot of time to throw at building your own and even then it would still be pricey.
The best option I see is to see if you can talk mtnlitebar into selling you some of their power supplies. I assume they would work but no idea what kind of power supply they are or if they would sell them separately. At least these are rated and designed for automotive use and already setup for driving a light bar. Although honestly just buying one of the mtnlitebars would have most likely been the best idea.
Such a conversion is almost impossible, that goes beyond the laws of physics
When you convert your car to 24V it might be feasible, but still generates a sh@tload of heat.
Rewiring the setup will be the easiest solution
First, you want to put them in parallel so that you can drive them at low voltage and high current.
Next, you want to go to mouser or digikey and find a constant current power supply or LED driver that has a voltage output range that includes about 6-8v (which is what the XHP70s will use) and has a current of whatever you want to drive your LEDs at.
The driver will need ~12v input.
You can sort by different columns to find what you want, or filter in the top boxes.
You might be able to find a boost driver that can do over 12v with only 12v input, but those are rare for high currents.
First, you want to put them in parallel so that you can drive them at low voltage and high current.
Next, you want to go to mouser or digikey and find a constant current power supply or LED driver that has a voltage output range that includes about 6-8v (which is what the XHP70s will use) and has a current of whatever you want to drive your LEDs at.
The driver will need ~12v input.
You can sort by different columns to find what you want, or filter in the top boxes.
You might be able to find a boost driver that can do over 12v with only 12v input, but those are rare for high currents.
He would need a power supply capable of providing over 150A of current if they were wired in parallel. Just the wires to deliver such power would be something like 0 or 00 gauge wire like that used in high end car amps. The power supply itself is highly unlikely to exist off the shelf, it would be very expensive and large and heavy if so.
A boost driver actually does make the most sense in this case, it also helps reduce thermal runaway.
Some cheap power supplies like this would work: DC DC boost converter Constant Current Mobile Power supply 250W 10A LED Driver | eBay
But they would only handle 3-4 LED’s at ~5A each, so you would need to use 8-10 of them. There are other options on ebay as well but it really comes down to budget and desired options. There are some larger units I saw that could handle ~5 LED’s in a string if you mount them to a heat sink of some sort.
- 12 or 10awg wire can handle 100-200 amps at 12-24v, it is used in RC cars literally everywhere. 1000A peak is also no problem.
I use 8AWG when going near 3-500A continuous.
2) It doesn’t matter if he is using high voltage low current or low voltage high current. Either way it is the same mount of power.
Except, when using a boost converter there is a lot of inefficiency.
3) I would not use some random cheap chinese power supply from ebay or aliexpress for something that uses this much power.
I prefer having less fires and more reliability.
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:
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.
- 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.