Hello,
I have some LED from Cree model XHP70 that are able to hit 4022lm but I don’t know what I need to do to reach this.
I already tested the LED’s in contact with a cooler and connected a 12V battery directly.
My question is: Am I getting 4000lm of light or do I need to do something else?
Best regards
Welcome to BLF!
LEDs are current controlled, that means that you need to control the current that you feed the led. With a higher current the led will make more lumens (along with heat)
That’s why you need led drivers to drive these LEDs properly.
As I understand you connected the battery directly to the led? Without a led driver? It can work but it all depends on the type of battery. It’s definitely not advised and you might not get the full potential out of the led. (or kill the led…)
Also you’ve mentioned that you hooked it up to a 12V battery. You sure that you have mounted the led on a 12V led board?
…. And heatsink the living s**t out of it.
Don’t think voltage, think current. And it must be regulated. To get those 4022 lumens you need the proper amount of current. A 12v battery is not enough voltage to do it. I know they call it a 12V emitter, but that is just a category. I know I made the same mistake, thinking 12v would be enough. You need more volts AND a current driver
Welcome to BLF!
And helped you are already I see, what nice community!
Thank you all for your answers.
Yes, I connected directly to the LED without a LED driver. It was my car battery.
I bought this XHP with the sinkPAD and connected directly to the battery and it works fine.
What LED driver should I get? I need a small thing.
A car battery can easy deliver 300-600 amps! I think you are very lucky that XHP-70 didn’t evaporate in an instant. Probably what saved you was the XHP-70 voltage requirements being just a bit higher than a car battery which is 12.6V when fully charged, IIRC.
I bought the following item:
Maybe the little resistor saved me?
PS: you have to select “sinkpad 12v 20mm cooper”
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?