Correct, but in general for other reasons. The losses in the system outside the LED are general in proportion to the current squared (I^2 x R), so at 12 volts you have half the current, and that 1/4 the losses that you would get at 6 volts. Also you haven’t specified how many 18650’s and how they are connected. Using a 3s or 4s type pack with a driver will get you much better driver efficiency as a bonus. In general the less you have to change the voltage in the driver, the more efficient the driver will be, and the lower the current in the driver, the smaller the I^2 x R losses in it will be. At the end of the day, power is power, and each 18650 is likely to be something around 11 watt hours. So no matter what voltage you run the XHP-70 at, you only have about 11 watt hours per 18650 cell. Ultimately the run time is a function of battery capacity, not the voltage you elect run the LED at. More cells and higher voltage means more total energy available, as well as lower losses in the driver and wiring. If you figure something on the order of 110 lumens per watt, single 18650’s to drive an XHP-70 at 4000 lumens or more are going to require IMR type cells, because you are looking over 10 amps (hence the suggestion that you use a 3s or 4s configuration). I^2 when I is 10 amps is a big number, if you use a 3s or 4s configuration, you are looking are looking at 3-4 amps, and I^2 when I is 3 or 4 is a lot smaller than I^2 when I is 10 or more. So with a 3s or 4s configuration you get significantly better efficiency in the driver, substantially lower I^2 x R losses, and substantially more total energy because you now have the energy stored in 3 or 4 cells instead of just 1. The Nitecore TM03 using a single 18650 in Turbo will run down the IMR cells used in about 10 minutes (and that is nominally 2800 lumens).
If you limit the current demand to 3 amps or so, even using ICR cells, heating of the batteries is not going to be much of an issue. Obviously at 10+amps it is an issue even for a good IMR cell.
if you connect xhp 70 directly to the 12v car battery then it will be safe for the led …
but you won’t get that 4000lm,because led is getting only 12v and around 0.50 amp while car engine is off and 1.2amp max when car engine is on
lol…………
if any one have any driver that can give me magic number (12v ,2.4amp) plzzzzzzzz tell me
because i have used lot of drivers (40watt to 150 watt) but none have worked….
XHP70 draws at 12V 1A and produces almost 2000 Lumens, but then your battery is almost dead
when the car battery rested a couple hours it has 12.8V so 3000 lumens maximal possible
for 12V the XHP70.2 with about 0.5V less should be the better choice
when the engine is on the car battery voltage should be charged with around 13.8-14.8V, here it gets interesting without driver and massive leads you will burn likely the emitter in DD
>12,8 V voll geladen (100%)
ca. 12,6 V normal geladen (70 %)
ca. 12,4 V schwach geladen (50 %)
ca. 12 V normal entladen (20 %)
<11,8 V ent- und tiefentladen (0 %
Thnx for the reply
Now I have got new problem .at 1st i was using thin wires and got 12v 0.50amp while engine is off and 12.7v 0.80 amp at engine running. Then i changed the wiring to thick one (1mm),now i am getting 12v 1.8amp at engine off and 14.7v 4amp(increasing more but i disconnecting at 4amp so it won’t go higher)at engine on.
Does wire thickness play any role??
What will happen if current go higher??
Plz help me out i am confused
From reading I understand that if you use a 12v mcpcb and heat sink it like hell and use a small gauge wire like 22 you will probably be able to make it work on DD.
Risky business without a driver. Doable tho.
A led emitter requires tight voltage regulation or things can go wrong fast. Relatively small variations on a led's Vf can lead to very noticeable differences in power and flowing current, at least for as long as the power supply can cope with it which, in the case of a car's battery with alternator running, it will.
In a module with current control the key is to adjust the current potentiometer for the desired current output, and the module does whatever voltage compensation required (voltage output needs to be set to at least the minimum possible maximum value, or just “all the way up” once current is set).
yeah in a light project I modded such a Buck driver that was just smaller to drive an LED
customized with a external big potentiometer to control the current, I put a 2. small potentiometer with fixed value on its upper position so the current does not get too high
basically PWM less CC regulation
Hooking an LED that gets warm up to constant voltage is always bad. With rising temperature the Vf of the LED goes down. This causes it get more current which increases power and causes more heat. This thermal runaway will kill it eventually.
So as I understand it there is no easy way to run a 12 V LED on a car? Just 6 V LEDs with cheap DC-DC buck drivers?
The losses in each die of the LED would be the same so just some more on the way.
That is not necessarily so, The_Driver. With beefy heatsinking and a stable output voltage power supply, the key is to tune the voltage low enough for current to raise just up to desired value once the emitter temperature gets “in the zone”. Of course this approach requires a knowledgeable operator's fine tuning which, from an industry standpoint is undesirable (constant current drivers/power supplies are cheap as chips anyways).
Yes, you can do it reliably one time. As soon as outside conditions (air temperature etc.) change, it’s doesn’t necessarily work anymore. Voltage regulation of LEDs is generally not a great idea.