That’s not really a resistor… but rather a “zero ohm” jumper. No, I think you are just lucky that the XHP70 needs more voltage as the current increases… if the voltage can’t keep up this limits the current which is what saved that LED. Whatever you do, don’t try that with a 6V or 3V LED!
Ok, so what do I need to connect this properly to a car battery?
That resistor is actually a 0 ohm resistor. It acts as a bridge between the solderpads.
A fully charged car battery has a voltage of around 13.6-14.8 Volt. And it will drop slightly after some time.
I believe you’ll need to drive the XHP70 around 4.5A for 4000 lumen. So look for a 12 Volt led driver that can supply 4.5A.
But, what battery are you going to use? Most drivers needs to have a higher voltage than the LEDs forward voltage (basically 12V)
That little resistor is Agent 000, got it? 
It’s purpose is to select the inter-die arrangement: 4S1P (12V configuration) with it, 2S2P (6V configuration) without.
LEDs should be current controlled with precise real-time voltage adjustment: the role of a driver. This is because led Vf (the voltage it drops) usually varies proportionally little which regards to a given change in current flow. What this means: a little bump in voltage translates to a much more drastical shift in the current flow.
Now, connect that led again to your car’s battery, while the engine’s running… NO, DON’T DO IT! :person_facepalming: LOL!
Also, led Vf diminishes as its temperature increases, and that is probably the main reason behind the use of a proper driver.
Cheers :partying_face:
Ok, I’ll look for a LED driver with that specs and then I’ll post here to read your opinions.
BTW
I always did it with engine running.
Best regards
Typical autmotive voltage regulator cuts-out around 14.6v (if I recall correctly). Chart below (source linked in pic) by Djozz shows about 11.5 amps at around 7.3ish volts (emitter wired 2S2P). So your emitter could have been producing over 4K lumens if it was properly heat sinked.
I think I found something near perfect.
What do you think of this:
Can it handle a car battery or just a lipo 3s?
How does the LVP works?
Best regards
What size wire did you use for connections? If the wire is too small it will add resistance, limiting amps to the LED, which in your case would be a good thing, keeping you from frying the LED.
Just as an fyi,
I have been driving a 6v xhp70 via 3x14500 3s1p unprotected cells DD, i think budgeting voltage drop and voltage head room we have been too consertitive as a rule. I but i can run the mtg2 the same way.
First they are crap fire cells plus i have not optimized the springs yet. But all in all pretty easy to swap the emitter and the bypass the driver. The host i used is the saik 305.
Will see if with better cells and better springs if it turns angrey blue but so far no issue.
Sounds like a big canned firecracker, my reckless bloke. Three of those low quality CrapFires in series may have above 1Ω of combined internal resistance so, as current flow times the resistance is the dropped voltage, no wonder the led survives. However, due to the undue stress on the batteries, I’d advise you to stop playing Russian Roulette. :person_facepalming:
Cheers :partying_face:
Automotive charging system regulation tends to have very loose and rough specs and it will vary considerable with different cars. I’ve measured as much as 16V with some that had weak batteries just after cranking. Voltage spikes are commonplace too- it’s not something to be trusted for consistency.
Devices meant to be used in cars take that into account when designed. Even when slightly under-driven I’d expect a D-D LED wouldn’t last too long in a car. Using a LED driver gives the consistent regulation needed to get maximum performance from the emitter. It’s either that or to seriously under-drive the emitter directly or through a resistor thus losing a lot of performance.
Phil
Whats better to use if using 18650 batteries, the XHP-70 on 6volts or 12 volts?
I would say 12 volts so the current per cell is lower and therefore the battery will have a long use life and less heat generated on each cell. Is that correct?
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….
I guess this one should work, but you will have to use a 6V mcpcb with the XHP70 LED…
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
But Would it work with 12v car battery??
It will work with some sort of max. current limitation, and on without running the engine likely not at 4000 Lumens
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.